recycling of demolished b

Recycling of Demolished Concrete and Masonry

Other RILEM Reports available from Spon Press

1 Soiling and Cleaning of Building Façades Report of Technical Committee 62-SCF

Edited by L.G.W.Verhoef

2 Corrosion of Steel in Concrete Report of Technical Committee 60-CSC

Edited by P.Schiessl

3 Fracture Mechanics of Concrete Structures: From Theory to Applications

Report of Technical Committee 90-FMA Edited by L.Elfgren

4 Geomembranes—Identification and Performance Testing Report of Technical Committee 103-MGH

Edited by A.Rollin and J.M.Rigo

5 Fracture Mechanics Test Methods for Concrete Report of Technical Committee 89-FMT

Edited by S.P.Shah and A.Carpinteri

6 Recycling of Demolished Concrete and Masonry Report of Technical Committee 37-DRC

Edited by T.C.Hansen

7 Fly Ash in Concrete: Properties and Performance Report of Technical Committee 67-FAB

Edited by K.Wesche

Publisher’s Note This RILEM Report has been produced from the typed chapters provided by the membersof RILEM Technical Committee 37-DRC, whose cooperation is gratefullyacknowledged. This has facilitated rapid publication of the Report.

Recycling of Demolished Concrete and Masonry

Report of Technical Committee 37-DRC Demolition and Reuse of Concrete

RILEM (The International Union of Testing and Research Laboratories for Materials and

Structures) Edited by

T.C.Hansen

London

First edition 1992 by E &F N Spon

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Contents

List of reports issued by RILEM Technical Committee 37-DRC vii Preface viii PART ONE RECYCLED AGGREGATES AND RECYCLED AGGREGATE CONCRETE. Third State-of-the-art Report 1945–1989 Torben C.Hansen Building Materials Laboratory, Technical University of Denmark

1

PART TWO RECYCLING OF MASONRY RUBBLE Dr R.R.Schulz Institute for Building Materials Testing, Waldkirch, Germany Dr Ch.F.Hendricks Road Engineering Division, Rijkswaterstaat, Delft, The Netherlands

139

PART THREE BLASTING OF CONCRETE: LOCALIZED CUTTING IN AND PARTIAL DEMOLITION OF CONCRETE STRUCTURES C.Molin Trimex, Sweden (formerly Swedish National Testing Institute) E.K.Lauritzen Demex, Consulting Engineers Ltd, Denmark

240

Index 284

List of reports issued by RILEM Technical Committee 37-DRC

1 Nixon, P.J. (1978) Recycled concrete as an aggregate for concrete—a review. Materials and Structures, 11 (65) September-October, pp. 371–8.

2 Task Force 1—RILEM Technical Committee 37-DRC (1985) Demolition Techniques. European Demolition Association, Wassenaarseweg 80, 2596 CZ Den Haag, The Netherlands, Special Technical Publication, May, 1985.

3 EDA-RILEM (1985) Demolition Techniques. Proc. First International EDA-RILEM Conference on Demolition and Reuse of Concrete, Rotterdam, 1–3 June, 1985, 1, European Demolition Association, Wasenaarseweg 80, 2596 CZ Den Haag, The Netherlands.

4 EDA-RILEM (1985) Reuse of Concrete and Brick Materials. Proc. First International EDA-RILEM Conference on Demolition and Reuse of Concrete, Rotterdam, 1–3 June, 1985, 2, European Demolition Association, Wassenaarseweg 80, 2596 CZ Den Haag, The Netherlands.

5 Demolition and Reuse of Concrete and Masonry. Proceedings of the Second International Symposium on Demolition and Reuse of Concrete and Masonry, Tokyo, Japan, 7–11 November, 1988. Two Volume Set. Edited by Y.Kasai. Volume 1. Demolition Methods and Practice, 520 pages. Volume 2. Reuse of Demolition Waste, 296 pages. Hardback (0 412 32110 6 set). Chapman & Hall, 1988.

Preface

It is becoming increasingly difficult and expensive for demolition contractors to disposeof building waste and demolition rubble. For environmental reasons, public authoritiesare looking for ways of reusing these materials. The purpose of this book is to make theconstruction industry and public authorities aware of the technical possibilities forrecycling of demolished concrete and masonry. It also shows how localized cutting andpartial demolition of concrete structures can be carried out.

Recycling of Demolished Concrete and Masonry consists of three state-of-the-art Reports which have been prepared by members of an international RILEM Committee:

• Recycled aggregates and recycled aggregate concrete • Recycled masonry as aggregate for concrete • Blasting of concrete: localized cutting in and partial demolition of concrete structures.

The three Reports review a very wide range of research and practical experience on thesubjects, much of which has not been easily accessible before. They are intended for useby building industry professionals involved in design and construction at all levels. It isthe authors’ hope that they will be of particular use to demolition and recyclingcontractors, and to concrete technologists and ready mixed concrete producers.

The three reports are the final result of work which was carried out over many years by RILEM Technical Committee 37-DRC on Demolition and Reuse of Concrete. TheCommittee was formed in 1976 and held its first meeting at the Building ResearchStation in Garston (UK) in June of 1977 under the chairmanship of Dr L.H.Everett. In1978 the first RILEM TC-37-DRC state-of-the-art report was published on recycledconcrete as an aggregate for concrete [1].

After the Committee was reorganized in 1981 and the author of this preface becamechairman, a second Committee meeting was held in Copenhagen in December 1982.Since then the Committee has held meetings in the Netherlands, England, Belgium,France and Japan.

The following general terms of reference of the Committee were agreed on at the meeting in Copenhagen in 1982.

1. To study the demolition techniques used for plain, reinforced, and prestressed concrete and to consider developments in techniques.

2. To study technical aspects associated with reuse of concrete and to consider economical, social and environmental aspects of demolition techniques and reuse of concrete.

Three task forces were formed, each with its own specific terms of reference. Task Force 1 surveyed, on the basis of the existing literature, methods of demolition

and fragmentation including economic, social and environmental aspects. It published its

findings in a general state-of-the-art report on demolition techniques [2] and a more specialized report on localized cutting in and partial demolition of concrete structures,which appears as Part 3 of this Volume.

Task Force 2 collected and surveyed codes and regulations concerning demolition in various countries. It did not issue a separate state-of-the-art report. Instead its findings were included in Part 1 and 2 of this volume.

Task Force 3 studied technical aspects associated with reuse of concrete and considered economic, social and environmental factors. It is the findings of Task Force 2and 3 which are published as Part 1 and 2 of this Volume.

The Committee arranged the first international symposium on demolition and recycling of concrete in Rotterdam in 1985 in co-operation with the European DemolitionAssociation (EDA). The symposium proceedings were published in [3] and [4]. Thesymposium gave valuable input to the work of the Committee from an industrial point ofview. Developments were fast, and it was soon decided to hold a second internationalRILEM symposium on demolition and reuse of concrete already in 1988 in Tokyo inorder to make it possible for persons from science and practice from all over the world tocommunicate and exchange experience before the Committee was dissolved at a finalmeeting in Tokyo in 1988. The Proceedings of the Symposium were published in [5].

As chairman of RILEM TC–37–DRC 1 wish to thank the following persons who haveserved as members and corresponding members of the Committee over the years.Members: Mr R.C.Basart (NL), Dr Ch.F. Hendriks (NL), Professor P.Lindsell (GB),Professor Y.Kasai (Japan), Dr K. Kleiser (D), Dr R.R. Schulz (D), Professor Y.Malier(F), Mr R. Hartland (GB), Mr T.R.Mills (GB), Mr P. Mohr (DK), Dr C.Molin (S), MrG.Ray (USA), Mr C. de Pauw (B), Mr E. Rousseau (B), Mr E.K. Lauritzen (DK),Secretary from 1982–1985, and Dr M.Mulheron (GB), Secretary from 1985–1988. Corresponding members: Mr F.D.Beresford (AUS), Mr M. Whelan (AUS), Mr A.D.Buck(USA), Dr S.FrondistouYannas (USA), Mr J.M.Loizeaux (USA), Mr J.F. Lamond(USA). Our very special thanks go to the European Demolition Association for its loyalco-operation in the work of the committee.

The work of RILEM TC-37-DRC is being continued in a new RILEM TechnicalCommittee 121-DRG on Guidance for Demolition and Reuse of Concrete and Masonry.RILEM TC-121-DRG will prepare Technical Recommendations leading to guidelines for production of concrete from recycled concrete and masonry, and guidelines fordemolition and processing of demolition rubble with respect to the reuse of concrete andmasonry. In addition the Committee will prepare a State-of-the-art Report on site clearing and demolition of damaged concrete structures with respect to the reuse of concrete and protection of the remaining structure. Special emphasis will be placed on earthquake andwar damaged structures. TC-121-DRG is supporting the 1st International Conference onConcrete Blasting in Copenhagen in June 1992.

Torben C.Hansen

PART ONE RECYCLED AGGREGATES

AND RECYCLED AGGREGATE CONCRETE Third state-of-the-art report 1945–1989

TORBEN C.HANSEN

Building Materials Laboratory, Technical University of Denmark

The extensive, but fragmented research on recycled concrete aggregates and recycledaggregate concrete, which has been carried out in various parts of the world from 1945 to1989, has been collated to form a comprehensive state-of-the-art document.

A thorough analysis of the data has been made, leading to guidelines for the productionand evaluation of recycled concrete aggregates as well as the design, production, and useof recycled aggregate concrete.

1. Introduction

It has been estimated that approximately 50 million tons of concrete are currentlydemolished each year in the European Economic Communities (1). Lindsell and Mulheron (87) have estimated that 11 million tons of demolished concrete are dumped at landfill sites each year in the United Kingdom. Equivalent figures are 60 million tons inthe United States (2, 3), and in Japan (12) the total quantity of concrete debris available for recycling on some scale is about 10 to 12 million tons. Karaa (93) has estimated that approximately 13 million tons of concrete is demolished in France every year. Very littledemolished concrete is currently recycled or reused anywhere in the world. The smallquantity which is recovered is mainly reused as nonstabilized base or sub-base in highway construction. The rest is dumped or disposed of as fill.

For environmental and other reasons the number of readily accessible disposal sites around major cities in the world have decreased in recent years. Both disposal volumeand maximum sizes of wastes have been restricted. In Japan disposal charges from 3 to10 US dollars per ton were not uncommon in 1985. Moreover, distances betweendemolition sites and disposal areas have become larger and transportation costs higher.

At the same time critical shortages of good natural aggregate are developing in manyurban areas, and distances between deposits of natural material and sites of newconstruction have grown larger, and transportation costs have become correspondinglyhigher.

It is estimated that between now and the year 2000, three times more demolished concrete will be generated each year than today. For these reasons it can be foreseen thatdemolition contractors will come under considerable economic and other pressure toprocess demolished concrete for reuse as unscreened gravel, base and sub-base materials, aggregates for production of new concrete or for other useful purposes.

Large-scale recycling of demolished concrete will contribute not only to the solution ofa growing waste disposal problem. It will also help to conserve natural resources of sandand gravel and to secure future supply of reasonably priced aggregates for building androad construction purposes within large urban areas.

It is the purpose of this report to examine the current state-of-the-art for what concerns recycled aggregate and recycled aggregate concrete and to point out areas where researchis needed in order to promote safe and economical use of such concrete.

Recycled aggregates and recycled aggregate concrete 3

Two literature searches were carried out in June 1987 in order to check whether the author of this state-of-the-art report had missed any major publications in the field. Onesearch was carried out on a data base in the English language (COMPENDEX) and theother on a data base in the French language (PASCAL). Neither of the two searches gavesatisfactory results. Keywords used in the two data bases were CONCRETE,RECYCLING and REUSE for COMPENDEX, and BÉTON RECYCLAGE for PASCAL. Neither of the two data bases covered the recycling of concrete in acomprehensive manner, and very little new literature was found, which had notpreviously been known to the author.

2. First state-of-the-art report 1945–1977

On behalf of RILEM Technical Committee 37-DRC, Nixon (5) prepared a state-of-the-art report on recycled concrete as an aggregate for concrete, covering the period 1945–1977. A list of literature reviewed by Nixon is presented in Appendix A.

In 1977 Nixon concluded that a number of workers have examined the basic properties of concrete in which the aggregate is the product of crushing another concrete. Most haveconcentrated on uncontaminated material, often old laboratory test specimens. There isgood agreement on most aspects of the behaviour of such recycled concrete.

The most marked difference in the physical properties of the recycled concrete aggregate is higher water absorption, and it seems likely that this is due to absorption bycement paste adhering to the old aggregate particles. There is general agreement that thecompressive strength (and judging from limited evidence, the flexural strength) issomewhat lower (up to about 20% lower in some cases, but usually less) compared withcontrol mixes, but there does not seem to be any correlation between the loss in strengthand the water-cement ratio of the final concrete. There is only limited evidence (andsome disagreement) on the effect of the strength of the original concrete on the strengthof the new concrete made with it as aggregate, but it seems probable, that when theconcrete fails, it is the adhering mortar on the crushed concrete aggregate that is theweakest link. The use of crushed concrete fines does not seem to have any great effect onthe compressive strength of the concrete, but it does seem to reduce the workabilitysignificantly. When only crushed concrete coarse aggregate is used, the workability islittle different from control mixes. Again, when using recycled coarse aggregate, there islittle difference in the modulus of elasticity; there is no information on the effect of fines on this property.

The durability of the recycled concrete has been examined mostly with respect to the freeze/thaw resistance of the concrete, and the results suggest that with uncontaminatedconcrete there is no problem. In fact with concrete containing a highly porous frostsusceptible aggregate there may actually be an improvement probably because thecement paste blocks up the pores. Drying shrinkage has been found to be somewhat

Recycling of demolished concrete and masonry 4

greater in the recycled concrete. There is no information on creep, wetting expansion orresistance to aggressive solutions such as sulfates of recycled concrete.

Less work has been carried out on the effect of impurities in the crushed concrete on the properties of the final concrete. Most of that which has been done has been devoted tosulfate impurities, presumably originating from gypsum plaster. This would certainly be amajor problem with the recycling of mixed demolition rubble. The results publishedsuggest that for concrete placed in a position where it is likely to be wet for much of thetime, a limit on the total soluble sulfate content of the aggregate of between 0.5 and 1% isadvisable if ordinary Portland cement is used. Most workers have used finely powderedgypsum in their experiments. What little evidence there is on the effect of particle sizehas suggested that larger-sized pieces of gypsum cause less expansion. There is some conflict of evidence on the effect of pozzolanic cements including fly ash, and more workis needed.

In 1977 Nixon concluded: There seems to be a reasonable knowledge of the basic engineering properties of the recycled concrete, and the main penalty in its use is aslightly lower compressive strength compared with a control mix made with the sameoriginal aggregate. A more thorough investigation of the effect of the strength of theoriginal concrete would seem to be needed, however, and also a fundamentalinvestigation of the mode of failure of the recycled concrete which may enable the reasonfor the lowered strength to be understood and counteracted. The main field in which moreinformation on the behaviour of the recycled concrete is required is its durability. Creep,wetting expansion, and porosity all need to be examined as does the effect of aggressivesolutions.’

The above remarks apply to uncontaminated concrete from a known source. If, however, recycled concrete aggregate is to be used on any scale, then the rubble fromgeneral building demolition would have to be exploited. Here there is a basic lack ofknowledge of what might be expected to occur in the output from a particular method ofprocessing the rubble. Possible methods of controlling impurities, e.g. magneticseparation of metal reinforcement and means of reducing the amount of gypsum, need tobe explored and the effect of the remaining contaminants examined. Once identified,there is some knowledge of the behaviour of common contaminants, but muchinvestigation will be needed in order to deal with all the possibilities, for example theeffects of mixtures of cement other than Portland cement in the crushed concrete.


3. Second and third state-of-the-art reports 1978–

1989

A second state-of-the-art report on recycled aggregates and recycled aggregate concrete was prepared by Hansen and published in Materials and Structures Vol. 19, No 111, May-June 1986, pp. 201–246, covering developments between 1978 and 1985. The current third state-of-the-art report is an updated version of the second state-of-the-art report including developments in the period 1985–1989. More than 80 new publications have been reviewed.

In its scope this report is limited to review developments to 1989 concerning the use of crushed concrete as recycled aggregates for production of new, plain and reinforced,normal-weight concrete in building and road construction.

By crushed concrete is meant concrete made with Portland cements, Portland-pozzolan cements or blast furnace slag cements, and with natural or manufactured sand or acombination thereof and with aggregates consisting of natural gravel, crushed gravel,crushed stone, air-cooled blast furnace slag or combinations thereof. Crushed concretes made with high-alumina cements or with lightweight aggregate, brick-waste aggregate, or aggregates made from other waste products are not dealt with in this review. Crushedconcretes which contain more than 5% of other substances than concrete are alsoexcluded from this review.

4. Terminology

Partially based on a Japanese Proposed Standard on ‘Recycled aggregate and recycled aggregate concrete’ which was prepared by the Building Contractors Society of Japan in 1977, B.C.S.J. (6), the following terminology is suggested:

Waste concrete Concrete debris from demolished structures as well as fresh and hardened concrete whichhas been rejected by ready-mixed or site-mixed concrete producers or by concreteproduct manufacturers.

Conventional concrete Concrete produced with natural sand as fine aggregate and gravel or crushed rock as


coarse aggregate.

Original concrete Concrete from reinforced concrete structures, plain concrete structures or precastconcrete units which can be used as raw material for production of recycled aggregates(or for other useful purposes). Original concrete is occasionally referred to as oldconcrete, demolished concrete or conventional concrete.

Recycled aggregate concrete Concrete produced using recycled aggregates or combinations of recycled aggregates andother aggregates. Recycled aggregate concrete is sometimes referred to as new concrete.

Original mortar Hardened mixture of cement, water, and conventional fine aggregate less than 4–5 mm in original concrete. Some original mortar is always attached to particles of originalaggregate in recycled aggregates. Original mortar is occasionally referred to as oldmortar, or conventional mortar.

Original aggregates Conventional aggregates from which original concrete is produced. Original aggregatesare natural or manufactured, coarse or fine aggregates commonly used for production ofconventional concrete. When no misunderstanding is possible, original aggregates mayalso be referred to as virgin or conventional aggregates. It is suggested to use the notationNs for natural sand, Ng for natural gravel, Ncs, for sand produced by the crushing ofnatural materials, and Ncc for natural crushed aggregate. N stands for natural, g stands for ‘gravel’ while cs stands for ‘crushed sand’ and cc for ‘crushed coarse aggregate’.

Recycled concrete aggregates Aggregates produced by the crushing of original concrete; such aggregates can be fine orcoarse recycled aggregates. Fine recycled aggregate is sometimes referred to as crushedconcrete fines. When no misunderstanding is possible, recycled concrete aggregates maybe referred to as recycled aggregates. This is the case in the present state-of-the-art report. It is suggested to use the notation Rs for recycled fine aggregate and Rc for recycledcoarse aggregate. R stands for ‘recycled’ and s stands for ‘sand’, while c stands for ‘coarse aggregate’.


5. Original concrete

Demolition methods for plain and reinforced concrete are dealt with in another part ofthis book, and in a separate state-of-the-art report (78) published by RILEM TC-37DRC.

Demolished concrete may be mixed with soil or other wasted building materials, or itmay be contaminated by impurities. However, by observing a few simple precautionsduring the demolition process, the potential for recycling demolished concrete can beimproved and the value of the debris increased.

5.1 Separation of different qualities of original concrete

Records of composition, quality, and history of the original concrete are valuabledocuments in determining the recycling potential of any concrete structure. Even whensuch records are not available, but it can be shown that mix proportions and strengths oforiginal concretes are different, such concretes should not be treated as equal duringdemolition.

5.2 Demolition of original concrete and removal of reinforcing steel

Concrete in structures to be demolished may have various types of finishes, claddingmaterials, lumber, dirt, steel, and hardwares attached to them. It is an advantage if suchconcrete, which is to be used for production of recycled aggregates, is made free fromforeign matter before demolition.

Early concern that steel reinforcement in waste concrete would ball up and jam crushers has apparently been somewhat exaggerated. It has proved to be fairly easy toseparate steel reinforcement from concrete, at least for what concerns lightly reinforcedconcrete pavement slabs. This is best demonstrated by describing a set of operations usedin the successful break-up, removal, processing, and rehabilitation of the concretepavement of Edens Expressway in the midst of the metropolitan area of Chicago, Illinois,(Dierkes (7a) and Krueger (7b)).

The 25 cm mesh reinforced pavement was broken by two large mobile diesel hammers. This equipment fractured the old slab into pieces about 60 cm maximum size at a rate ofbetween 460 m and 600 m of 11 m wide pavements during a twelve-hour work shift. Each diesel hammer had an enclosed bounce cylinder and a 1750 kg piston to yield amaximum impact on the breaking shoe. The hammer cycled at over 100 strokes perminute and broke the mesh effectively in one pass. The diesel hammers were towed at


about 15 m/min so as to strike the pavement at 15 cm intervals. The next operation used a rubber tyred hydraulic excavator with a large curved,

pointed hard-steel picker tooth (a so-called ‘rhino-horn’) mounted where the bucket usually is. The excavator was positioned along the side of the pavement. By reaching tothe opposite side of the pavement with the hoe arm, the tooth could be pulled transverselyup and through the shattered concrete. This pulled the concrete pieces towards the centreline and separated most of the reinforcement. The operation was repeated at givenintervals from both sides of the old pavement. (Other contractors load trucks withbackhoes directly off the grade without the rhino-horn. They are likely to pick up more ofthe base material and incorporate it in the recycled aggregate, which is undesirable.)

Workers followed this operation along with hydraulic shears, cutting and pulling outloose reinforcing steel and putting it on the shoulder for pick-up and salvage. The hydraulic shears were also used to cut the reinforcing, once on the shoulder, into shorterlength for easier handling and better salvage value. 90–95% of the reinforcing was removed this way. The remainder was still embedded in the concrete and had to beremoved by crushing.

When the reinforcing in the old pavement was mesh rather than bars, it was somewhatmore difficult to handle. More cutting was required to separate the concrete pieces afterthe tooth had gone through, than was necessary for bar reinforcing. However, nearly thesame percentage of reinforcing could be removed on grade.

The broken pavement was then loaded on to trucks for hauling to a crusher and screening plant which was set up at a clover-leaf type interchange. If the concrete was properly sized when it was shattered, it was put in a stockpile. When an inordinatenumber of large pieces of broken concrete came from the grade, a wrecking ball was usedto break these into a size that the crusher could accommodate.

Concrete was then fed into a primary jaw crusher. 30–40 cm pieces were reduced to 64–76 mm top size. A smaller jaw crusher plus a hammer mill was used for secondary crushing which reduced the top size to 19–25 mm and produced an aggregate which metspecifications, with less than 2% passing the ASTM No. 200 sieve.

Remaining reinforcement and dowel bars presented no problems to the primarycrusher. A large self-cleaning electromagnet was placed over the belt coming from theprimary crusher to collect any reinforcing that had remained embedded in the concrete.About two semi-loads of wire per shift were removed from the broken concrete. It isreported that the proceeds from the sale of salvaged steel from a pavement recycling jobusually more than pays for recovery and for loading and hauling it away.

Several other projects where steel reinforcement has successfully been removed from recycled pavement concrete are reported in (7) and by Chase and Lane (59), McCarthy and MacCreery (67), and Strand (68).

The main concern when removing broken concrete is not to pick up material which is not wanted in the concrete mix. If the construction site is on clay soils, the loading,hauling and stockpiling operation can incorporate clay into the salvaged concrete pile;and the reclaiming operation from the salvage pile to feed the crusher can pick up stillmore. Once clay balls are incorporated there is no reasonable way to get them back out.Extreme care should be taken if the pavement being salvaged or the stockpile, crusher orplant site rests on a clay subgrade (108).


While most projects in the US employ conventional pavement breakers such as dieselhammers or wrecking balls, the Europeans have tried other types of equipment. TheWirtgen machine, made in Germany, was used for two major recycling projects onmotorways near Paris, France. More recently a Wirtgen CB 7000 guillotine concreteshattering machine was used when recycling Detroit’s Lodge Freeway, (109) and (110). These pavement beakers use a 6.3 ton, 170 cm wide guillotine-type drop weight which can generate more than 160 000 Joules of energy, and can be controlled to provide aslittle as 16 000 Joules of energy. The crack spacing and amount of breakage are varied bycontrolling the machine’s speed and the drop height of the weight.

The newest machine to show considerable promise as a recycling tool is the Resonant Pavement Breaker. This self-propelled 50-ton machine employs a 12-feet beam that vibrates approximately 1 1/2 inches 44 times a second. This huge ‘tuning fork’ is equipped with a special knife-like tool that shatters the concrete without transmittingvibrations to the subgrade, underground utilities, or adjacent slabs. One of the moreinteresting uses for this new machine was in the reconstruction of the San Francisco cablecar tracks where it shattered the concrete around the tracks and cableway. In NorthDakota the same machine was used to recycle 12 miles of two-lane pavement on Interstate-94 (20). The Resonant Pavement Breaker creates much less earth vibration than the drop hammer. It also operates at lower production rates and breaks the pavement intosmaller pieces.

Strand (68) concluded that machines which are used to break up concrete pavements are either impact or resonant breakers. Hironaka et al. (117) presents an extensive table of pavement breakers which were available on the commercial market in 1987.

Impact breakers consist of diesel hammers, mechanically, pneumatically or hydraulically activated falling weights, or leaf spring whiparm hammer breakers. Eachtype has unique characteristics. Diesel hammers impact the greatest energy and are thefastest; their disadvantage lies in the depressing of the broken pavement into a yieldingbase. The mechanically, pneumatically or hydraulically activated falling weights seem tobe slower, but the braking patterns are finer, resulting in easier removal of reinforcingsteel.

The resonant breaker is the slowest in production although its use has resulted in more efficient and effective removal of reinforcing steel and less base disturbance. Theresonant breaker is probably most effective where the sub-base is deteriorated and no longer provides good support. The diesel hammer appears to perform best on pavementwhere the sub-base is still firm. However, Hironaka et al. (117) concludes that the effectiveness of pavement breaking equipment depends on factors, that could vary fromsite to site. Therefore, to determine the best systems it is necessary to conduct acontrolled experiment of those systems that appear to have the best production rates todetermine, on a given pavement, the actual rates, percentage of separated reinforcingsteel, maximum size of broken fragments, and amount of fines generated.

Pavement breaking is likely to generate complaints from local house owners if the houses are near the pavement that is being removed. Complaints sometime occur whenmaximum earth vibrations exceed 0.03 inch per second and are likely when vibrations are0.06 inch per second or more. Vibrations caused by 18 000 foot pound hammers getdown below this probable complaint level at roughly 140 feet from the source. The 30


000 foot pound hammer reaches the 0.06 level at about 200 feet. But it is many hundredsof feet from the guillotine-type drop hammer before that low a level is attained (108).

Although the presence of steel reinforcement in concrete does not represent a majorproblem in the recycling of pavements, it does slow down operations. When attemptingto recycle heavily reinforced structural concrete, the problem is more severe, asreinforcement bars and mesh tend to ball up and jam crushers. The problem wasovercome on pavement projects in Michigan and Iowa (59, 67) where reinforcement was effectively separated from concrete by means of an impact crusher hammer and self-cleaning magnets.

Practical experience has shown that very large jaw crushers (8), and even better impact crushers (9) are capable of handling heavily reinforced chunks of concrete without excessive difficulties, provided each chunk can be accommodated by the respectivecrusher. After primary crushing most steel can be removed from the product on its way tothe secondary crusher by means of self-cleaning electromagnets which are placed over the conveyor belt.

De Pauw (10) reported that 0.30 x 0.30 x 0.90 m heavily reinforced chunks of concretewere fractionated by means of explosives. Steel was cleanly separated from concrete andthe resulting recycled aggregates had a particle size distribution which is suitable forconcrete production. Although this process is still at the experimental stage, it couldbecome a desirable alternative to mechanical crushing of concrete.

De Pauw (11) also reported that up to 1.2×1.2×2 m reinforced concrete blocks can besuccessfully fractionated using a type of equipment which is commonly used to crushdiscarded aircraft engines and other large machinery.

Hafemeister (54) reports on an impact roll crusher, produced by Klöckner-Becorit in West Germany, which is capable of processing 300–500 t/hr of 1100 mm maximum size reinforced concrete debris, see also (61).

Zagurskij and Zhadanovskij (83) report that a crushing device has been developed by SKTB Glavmospromstroymaterials and is currently being used in 18 recycling plants inthe USSR. The device is capable of crushing the concrete and sorting out thereinforcement from up to 24 m long, 3.5 m wide and 0.6 m thick precast concrete units.The units to be demolished are placed on a stationary bar-type grizzly by a lifting device, and a hydraulic press which is equipped with a lever knife is moved along the grizzly.Periodically the knife is lowered and crushes the concrete unit. Crushed concrete isdischarged through the bar grate of the grizzly on to a belt conveyor which takes it to aprimary jaw crusher. The clean reinforcement cage is lifted from the grizzly by means ofa magnet and reused as scrap for the production of new reinforcing steel.

Ridout (119) reports on a machine capable of safely demolishing pre-tensioned and post-tensioned structures.


6. Production of recycled aggregate

6.1 Layout of production plants

Plants for production of recycled aggregates are not much different from plants forproduction of crushed aggregate from other sources. They incorporate various types ofcrushers, screens, transfer equipment, and devices for removal of foreign matter. Thebasic method of recycling is one of crushing the debris to produce a granular product of agiven particle size. The degree of reprocessing carried out after this is determined by thelevel of contamination of the initial debris and the application for which the recycledmaterial will be used such as: (1) General bulk fill; (2) Base or fill in drainage projects;(3) Sub-base or surface material in road construction or (4) New concrete manufacture.

Boesman (62) has discussed problems associated with the design of recycling plantsfor demolition waste. Drees (95) has published a comprehensive review of the lay-out of recycling plants for demolished concrete, their equipment, treatment of raw materials andeconomy. Hironaka, Cline and Shoemaker (117) studied different aspects of the recycling process of pavement including breakup and removal, steel reinforcement removal,crushing, screening, stockpiling, mix design, testing, placing, finishing and performance.They conclude that recycling of portland cement concrete require some specializedequipment such as pavement breakers and electromagnets for steel removal; however, allother equipment and procedures are those commonly used in the construction industry.

A number of different processes are possible for the crushing and sieving of demolitionwaste which mainly consists of concrete, such as would be the case for example on apavement rehabilitation project.

Some of these possibilities are illustrated in the block diagrams which are shown in Figures 6.1a and 6.1b, from (62). Installations working according to the principles of oneof these schemes are regarded as first generation processing plants. They arecharacterized by the fact that there are no facilities for removing contaminants, with thepossible exception of a magnet for the separation of reinforcement and other ferrousmaterial. Such plants are frequently used on pavement rehabilitation and recyclingprojects.

Figure 6.1a illustrates the closed system which is generally recommended. The open system of Figure 6.1b is advantageous in one way only, because the capacity is greaterthan that of the closed system, even though the same basic equipment is used. However,the maximum particle size is less well defined when an open than when a closed systemis used, and this can lead to larger variations in the size of the end product, particularlywhen the input flow varies.


Fig. 6.1 a Flow chart of typical plant for production of recycled aggregate from concrete debris which is free from foreign matter, from Ref. (62). Closed system.

Fig. 6.1 b Flow chart of typical plant for reproduction or recycled aggregate from concrete debris which is free from foreign matter, from Ref. (62). Open system.

However, clean concrete cannot always be supplied from the demolition site.Demolished concrete often contains foreign matter in the form of metals, wood,hardboard, plastics, cladding, and roof coverings of various kinds. On the basis of firstgeneration plants, the process scheme can be adapted for small amounts of contaminantsby removing larger pieces of foreign matter mechanically or manually before crushing,and by cleaning the crushed product by means of dry or wet classification. Installationsworking according to such principles are regarded as second generation processingplants. Incidentally, a pilot project which was carried out in Denmark (79) showed that,


when properly organized, manual sorting of demolition rubble on the site and sale ofreusable items can be done as economically as plain dumping of demolition rubble.

All second generation plants are similar in basic design, as shown in principle in Figure 6.2. Large pieces of debris arriving from demolition sites are typically reduced to 0.4–0.7 m maximum size, for example by means of a wrecking ball and hydraulic shears to cutreinforcement. Large pieces of steel, wood, plastics, and paper are removed by hand.Incoming material is then crushed in a primary crusher which is usually of the jaw orimpact type.

Products from the primary crusher are screened on a deck typically consisting of a 10 mm scalping screen. Minus 10 mm material is wasted in order to eliminate finecontaminants such as dirt and gypsum. Plus 40 mm material is passed through asecondary jaw, cone, hammer or impact crusher in order to reduce all products to 40 mmmaximum size. 40–100 mm material from the primary crusher bypasses the secondary crusher. All material is then washed or air-sifted in order to remove remaining lightweight matter such as wood, paper, and plastics, and the clean product is screenedinto various size fractions according to customer specifications. All iron and steel isremoved by self-cleaning magnets which are placed at one or more critical locationsabove conveyor belts.

Recycled and processed aggregates which are made from mixed building rubble willusually contain less than 1 percent of impurities, which may be good enough for roadconstruction purposes, but not necessarily acceptable for concrete aggregates. However,when recycled aggregates are made from raw materials which contain more than 95% ofold concrete, the end product will usually be clean enough to meet specifications forconcrete aggregates without being washed.

In ideal future third generation plants all demolished material should be supplied to the installation, processed and sold without there being any need to transport large quantitiesof residual matter to city dumps either from the demolition site or from the processinginstallation. This would be an ideal situation both from an environmental and aneconomic point of view. The first third generation recycling plant in the world whereboth rubble and wood wastes are processed is already operating in Rotterdam, theNetherlands (81).

Bauchard (135–1) reports that two types of recycling plants operate in France, those that produce aggregates by primary crushing only, and those that employ both primaryand secondary crushing.

Products from plants that produce aggregates by primary crushing only, depend to a large extent on the quality of the demolition material. From an analysis of the products ofthe four plants which were in operation in France in 1987 it may be concluded that thedemolition materials in fact are carefully selected. Only plain and reinforced concrete isaccepted. This ensures that the quality of the aggregates is adequate for the purposesintended. All four plants utilize impact crushers but from different manufacturers.(Bergeaud, Blaw-Knox and Hazemag).


Fig. 6.2 Processing procedure for building and demolition waste.

Two plants are in operation in France, which produce aggregates by primary and secondary crushing. These are more permanent installations which are designed for theprocessing of demolition debris of varied origins. However, only one plant makes use ofthis possibility. It crushes only reinforced and unreinforced concrete. In their overalldesigns these plants are not much different from the Dutch plants, earlier described.

According to Schulz (135d) there are more than 100 recycling plants in West Germany. Most of these are small with only installations for crushing and screening ofpreselected rubble. Compared with the USA more impact crushers are used in Germany


without secondary crushing. These simple plants are not capable of removingcontaminants, with the exception of iron and steel by self-cleaning magnets and rubble fines by screening. Only a few larger plants in more populated areas apply washing or airsifting procedures for removal of lightweight particles such as dirt, clay lumps, wood,paper, plastics and textiles, so that frost resistant subgrade material or base coursematerial can be produced which may justify higher prices. Schulz (135d) discusses howhomogeneous higher grade materials might be produced in the future.

Trevorrow et al. (135r) report that a typical site set-up in the UK to produce crusher run material consists of the following items of plant:

1. 360° tracked, hydraulic backactor. 2. Jaw crusher, single or double toggle. 3. Straight or swing conveyor with screen. 4. Tracked or rubber wheeled loader.

Kabayashi and Kawano (135r) report that the Keihan Concrete Company in Kyoto,Japan, has developed a crusher which will remove much of the mortar which remainbonded to crushed concrete aggregate, thus refining the material. No details are given forwhat concerns the machine. The papers shows that a higher degree of refining for therecycled aggregate can produce higher quality concrete, but that this requires higher manufacturing costs and lower economical efficiency.

6.2 Crushers

A number of different crushers such as jaw crushers, such as impact crushers, hammermills and cone crushers, were studied in a Dutch investigation (11) in order to determine how well they performed when crushing old concrete. The results can be summarized asfollows:

Jaw crushers provide the best grain-size distribution of recycled aggregate for concreteproduction. The cone crusher is suitable for use as a secondary crusher with 200 mmmaximum feed size. Swing hammer mills are seldom used. Impact crushers providebetter grain-size distribution of aggregate for road construction purposes, and they areless sensitive to material which cannot be crushed, such as reinforcing bars. The first useof an impact crusher on a pavement rehabilitation project in the US was in Michigan in1984 (59). Reinforcement mesh was effectively removed from concrete by means of two revolving magnetized drums after the crusher.

When it comes to other properties of recycled concrete aggregate than grain-size distribution, jaw crushers perform better than impact crushers because jaw crusherswhich are set at 1.2–1.5 times the maximum size of original aggregate will crush only a small proportion of the original aggregate particles in the old concrete. Impact crushers,on the other hand, will crush old mortar and original aggregate particles alike and thusproduce a coarse aggregate of lower quality. Another disadvantage of impact crushers ishigh wear and tear and therefore relatively high maintenance costs.

All crushers investigated produced approximately the same percentage of cubical


particles in recycled aggregates and it appears that the properties of recycled concreteaggregates always are improved by secondary crushing, (135m), (135s), (135v) and 135x).

A large proportion of the end product less than 40 mm from a crushing and sievingplant comes directly from the primary crusher. This can cause problems if the primarycrusher supplies a product which does not satisfy the requirements laid down by thecustomer. Therefore, it should be possible to adjust the primary crusher so that the ratiobetween coarse and fine products can be reduced in the end product. This implies that thesecondary crusher should have a relatively large capacity.

Economy of coarse aggregate production can be maximized by balancing the crushers. The primary crusher should be set to reduce material to the largest size that will fit thesecondary crusher without requiring tertiary crushing.

A similar investigation of crusher efficiencies was carried out by B.C.S.J. (12). Table 6.1 shows that, except for grain-size distribution, the physical properties of recycled aggregates

such as specific gravity, water absorption, sulfate soundness, and Los Angeles abrasionloss percentage were not significantly affected by different types of crushers and crushersettings. The results of this investigation is described in detail by Kakizaki et al. (135s). Svensson (101) has dealt with the theory of action of jaw crushers.

Schroeder (114) has analysed removal and reprocessing technologies as they apply to reconstruction of rural highways and airports.

Table 6.1 Physical properties of recycled aggregates produced by various kinds of crushers, from Ref. (12).

Type of Crusher

Type of Concrete

Grain Size of Crusher

Product

Specific Density in

SSD Condition

kg/m3

Water Absorption

Percent

Sulphate Soundness

Loss Percent by

Weight

L.A. Abrasion

Loss Percent

by Weight

max. size, mm

minus 5 mm

fine agg.

coarse agg.

fine agg.

coarse agg.

fine agg.

coarse agg.

coarse agg.

Jaw Crusher

w/c=0.45 w/c=0.55 w/c-0.68

25 25 25

19.2 18.2 20.8

2100 2100 2100

2350 2350 2330

11.0 11.3 11.1

5.8 6.2 6.4

15.5 20.8 18.8

58.9 48.4 60.8

30.5 31.0 31.2

Horizontal Shredder

unknown 30 33.1 2040 2260 10.5 5.3 12.3 40.9 unknown

Continuous Mill

unknown 25 41.7 2130 2340 8.7 4.6 9.9 29.9 unknown


Results from different countries are difficult to compare because differentinvestigations have been made with different types of original concretes. However, itappears that there is a large difference in percentage of sands produced by differentcrushers. For the same maximum size of coarse recycled concrete aggregate (25 mm),shredders produced twice as much or 40% of undesirable crusher fines below 4.8 mm,compared with 20% for jaw crushers. This is important.

It appears that jaw crushers should be used for the processing of plain or lightly reinforced concrete, while heavy impact crushers of various designs appear to be the bestchoice for normal or heavily reinforced concrete.

If demolition waste is to be recycled, methods of demolition should be used which will reduce individual pieces of debris on the site to a size which will be accepted by theprimary crusher in the recycling plant. This is 1200 mm at most for large stationary plantsand not more than 400–700 mm for mobile plants. Thus the recycling of demolitionwaste requires careful planning on the part of all parties involved in such an enterprise.

For those readers who are particularly interested in new developments within the field of concrete crushers a number of access numbers to patents registered in the World PatentIndex are given in Ref. (118). In February 1988 the author of this state-of-the art report conducted a literature search in the following databases: Compendex, NTIS, WorldPatent Index and ESA. Keywords used were: ‘Crushers’ and ‘Concrete’. However, the papers turned out to be too specialized to merit a detailed discussion in this report.

6.3 Sorting devices and screens

In line with specifications for natural aggregate and crushed stone, recycled aggregate isrequired to be free from dirt, clay lumps, gypsum (from plaster), asphalt, wood, paper,plastics, paint, textiles, lightweight concrete, and other impurities.

The first stage at which demolition debris can be sorted is during the demolition process itself. Thus, if given the incentive the demolition contractor can, by the use ofselective demolition methods, recover much of the material from a site in a relativelyclean and uncontaminated form. In most cases, such orderly demolition procedures arenot viable given the confines of an urban demolition site and the realities of time-penalty clauses. As a result, selective demolition is only carried out where both conditions andtime allow and the operation has clear financial advantages. It is significant thatdemolition contracts involving the dismantling of structures consisting of only one typeof material, such as a concrete runway, are highly sought after, since they provide anexcellent source of clean debris requiring the minimum amount of processing.

Once demolition has been completed and the debris taken to the recycling plantopportunities for sorting the debris are confined to selective stockpiling and primaryscreening.

Selective stockpiling is simply the storing of incoming material in separate stockpiles according to its type and degree of contamination. This gives the plant operator theopportunity of dealing with oversize and undersize material separately. In addition, bybuilding up a sufficient stockpile of a single clean material it becomes viable to optimize


the crusher set-up for that material and crush it in a single run. Such stockpiling is only practical on sites with sufficient space. A desirable minimum area is 1 hectare (87).

In most recycling plants larger objects such as pieces of metal sheeting, wooden boards and beams, pieces of asphalt, loose reinforcing bars, and sheets of paper, cloth, andplastics are removed by hand before primary crushing of the debris. After primarycrushing, dirt, gypsum, plaster, and other fine impurities are eliminated by passing thecrushed materials over a set of scalping screens and wasting all material below 10 mm.Self-cleaning magnets which are positioned in various patterns of strategic locations over conveyor belts effectively separate bits of reinforcing bars and other pieces of iron andsteel from the stream of crushed aggregate.

Simple dry sieving only separates on differences in size and form. It can only be used succesfully to separate material crushed with a jaw crusher, because an impact crusherwill crush in a non-selective manner. According to a Japanese study (12), coarse materials are separated more effectively by inclined screens vibrating at low frequencesand large amplitudes, whilst horizontal screens vibrating at high frequencies and smallamplitudes are more effective in separating fine material. Dutch results (62) indicate that for separating lightweight material, adapted flat sieves are the best, giving little loss ofthe stony material whilst removing some 80% of the wood.

Nix (55) reports that most lightweight matter can be removed from crushed buildingdebris and the aggregate brought to specifications by wet classification. Heimsoth (56) claims that the same can be achieved by dry processing when impurities are heavier thanwater.

In principle, fine-grained and lightweight contaminants can be removed from rubble by air classification processes. The most frequently used of these techniques is dry-sifting, a process which can be carried out both vertically and horizontally. An important conditionfor obtaining a sufficient degree of separation is that the crushed product must be dividedinto fractions. This implies that when the product is of a size between 0 and 40 mm, fouror five sieved fractions must be obtained; each of which is sifted separately, thenremixed. It is a distinct disadvantage that dry-sifting produces an excess of dust which must be controlled.

Alternatively, lightweight contaminants can be separated from heavier bulk material bythe use of directly applied water jets in combination with a float-sink technique. The so-called ‘Aquamator’ is based on this principle. It is produced by UBA/BMFT in WestGermany, and it is briefly described by Pietrzeniuk (72) and Drees (95).

By the application of wet classification techniques, wood, hardboard, plastics, straw,and roofing felt as well as suspended sulfates and asbestos fibres can be effectivelyremoved from the size range of 10–40 mm. Sieving on a 10 mm screen prior to washing is recommended, because the 0–10 mm fraction produces large quantities of undesirable sludge in the washing water.

Drees (95) has provided an excellent review of the various methods available forsorting of crushed demolition debris. Efficiency of various types of screens was studiedby B.C.S.J. (12).

It has been suggested by BCSJ (6) and (12) that it should be possible to separate most brick rubble and other deleterious particles from recycled aggregate in a heavy mediumof 1950 kg/m3. In principle, such a technique would allow the processing of highly


contaminated and mixed demolition debris to produce clean, graded aggregates.

6.4 Environmental problems in the recycling of concrete

Recycling of Portland cement concrete presents both environmental advantages anddisadvantages. The advantages are that substances are reused which would otherwise beclassed as waste; reduction of fuel use, reduction of trucking, and reduction of the use ofnon-renewable resources. The disadvantages include the intrusion of trucking intolocations where this is undesirable; aesthetic concerns, and potential noise and dustcontrol problems.

Operation of a crushing and screening plant is always accompanied by the generationof noise, vibrations and dust. Therefore, in the selection of plant location, environmentalconditions of the vicinity and legal requirements must be carefully studied and necessarycounter-measures taken. However, the early concern about noise and dust problems when crushing concrete in mobile plants in urban areas has apparently been exaggerated.

Dierkes (7a) reports on a mobile plant which was set up near a local commercial and residential area in Chicago, Illinois. The only complaints received concerned night-time operations, the banging of tailgates to clean trucks, and the noise from back-up alarms on mobile equipment. Such practices were stopped, and stockpiles and earth berms werebuilt around the perimeter to reduce the noise. The hoppers of the primary crushers werelined with rubber pads to reduce the impact noise, diesel generator engines were equippedwith quieter mufflers, and sound absorbing panels were placed around the generatortrailers.

Copple (7c) reports on a crusher which was set up on a busy urban street in a suburb of Grand Rapids, Michigan, where no complaints were received about either dust or noisefrom the plant.

Environmental concerns in recycling of concrete are discussed in detail by Munro (7d) who concludes:

1.A single purpose job site installation, for example for the purpose of recycling a pavement, is easier to locate than a permanent commercial type installation, but a permanent site has the advantage of being able to recycle slabs and footings from building demolition as well as pavement.

2.To recycle the aggregates into concrete, the best location of a permanent plant is adjacent to a ready-mixed concrete batch plant in an area of heavy industrial zoning. The recycling plant should be located on a road which is already used for heavy commercial or industrial trucking. Once located, there must be sufficient control exercised over the trucks to ensure that they are always using acceptable heavy duty roads.

3.Emission of dust should be limited to Number 1 Ringlemen (which is about 20% opacity) for a period not exceeding three minutes in any one hour. Any discharge less than this is essentially not visible and can be measured only with sophisticated devices.

The easiest control is water. Roads around the site should be continuously watered


as should be stockpiles of broken concrete. Fine mist water should be used at the crusher feed and screens. This spray must be very fine or the material will be too wet and the fine screens will blind. A wetting agent added to the water will give better dust control with less water. Also watering the material at the head pulley of the stockpiling conveyor is helpful in controlling dust as the product is loaded into trucks.

4.The plant should be screened from view. A combination of grade difference and mature scrubs can almost totally shield the view of a plant and its stockpiles.

5.Personnel noise exposure should be limited to 90 decibels for an 8-hour day. In the case of front-end loaders, bulldozers and the like, this can be done by installing noise attenuated cabs. Plant operators can likewise have well-located enclosed operating positions. Personnel which must be around the plant during operation must be protected either by administrative or engineering controls.

Administrative controls involve rotation of personnel during the working day from noisy to quiet environments. Engineering control involves enclosing the crushers and screens. Ear muffs should be used only as a last resort.

6.Community noise, i.e. noise at the receiving property, should be limited to no more than 55 decibels for daytime hours or 50 decibels during the evening. This limit should be exceeded for no more than one minute by no more than 15 decibels.

The simplest way of controlling noise is distance. Noise impact will be reduced by 6decibels for each doubling of the distance, but distance is not a very practical means ofnoise control in urban areas, considering the noise level of a typical crushing andscreening plant which is serviced by front-end loaders. It may be necessary to enclose themachines or to shield the receiving property from the machines by means of noiseattenuating walls.

Controlling the exterior noise from bulldozers and front-end loaders is extremelydifficult until manufacturers of such equipment realize that their equipment must meet thenoise standards, and act accordingly. Until then, the most effective system is to restrict theoperating time to reasonably convenient daytime hours.

Kakizaki M., Harada M. and Motoyasu (135s) have studied the noise levels of differentcrushing machines. They conclude that in city areas the noise levels ought to be loweredbelow those regulated by current noise control-regulations by means of acoustic barriersof various kinds, or complaints are certain to be received.

While demolition wastes earlier could be used without problems as fill or built intoacoustic barrier walls or used for foundations or erosion protection, this is no longerpossible under many environmental laws (95). At earlier times demolition wastes wereconsidered non-toxic wastes which could be disposed of at any city dump because theyconsisted almost entirely of mineral products. This is no longer true. Many buildingmaterials now contain components which are considered toxic from environmental pointsof view, such as chlorinated carbon-hydrogens, phenoles and heavy metals.

Because noise, vibrations and air protection are of primary concern during demolitionand processing of demolition wastes, the operator of a recycling plant must now convinceauthorities that there is no danger of pollution of ground water before he can safely sellthe reprocessed materials. However, in order to keep things in perspective it should beremembered that roads have long been built with asphalt as a surfacing material without


this having given rise to any problems at all. It is difficult to visualise why a smallcontamination of demolished concrete with asphalt should give rise to concern. The fearseems somewhat exaggerated.

Dohmann (130) studied the chemical oxygen requirement and the concentration of phenols before and after treatment of demolition wastes in two different recycling plants.One plant removed contaminants by dry-sifting and one by wet processing in anAquamator. Unfortunately for the recycling industry the investigation showed nosignificant difference between the contents of dangerous chemicals before and afterprocessing of waste in the two plants.

It may be concluded that the only way an operator of a recycling plant can be certain that his products will be free from dangerous contaminants is to make sure that thecontaminants do not get in there in the first place. Such certainty can only be obtained byrefusing any demolition debris which is contaminated with (impregnated) wood, paper,plastics, textiles, cable, non-iron metals, steel (except for small amounts of reinforcing steel), soil and clay, domestic or industrial waste, gypsum and other deleterious mineralproducts, oil, grease, rubber or components which in any way are contaminated bychemicals. This poses a responsibility on the individual operator, and it forces thedemolition contractor to carry out selective demolition at least to a certain extent.Moreover, it increases the cost of processed demolition waste, thus severely restrictingthe quantities that can be recycled. Therefore, authorities should make certain that theirrequirements are justified, which is not always the case.

6.5 Grading of crusher products

Table 6.2 shows a typical grading of the total output of recycled aggregate from alaboratory jaw crusher which was set at an opening of 25 mm with the jaws in a closedposition (13).

The crusher was fed three original concretes of different qualities in the form of old 15×30 cm test cylinders which had been split in halves. For all practical purposes theoverall gradings of the crusher products are independent of the concrete quality in theentire range of water-cement ratios from 0.40 to 1.20.

It is generally assumed that natural rock when fed to a crusher will break according to a’straight-line distribution’ (14) where 15% of the crusher product will be of a size above the crusher setting as shown in Figure 6.3.

Table 6.2 Overall grading of crusher products from Ref. (13).

Size Fraction in

mm

Measured Weight Percent of Total Crusher Product

Estimated Weight Percent of Total Crushed Product According to Figure 6.4 11

w/c=0.40 M

w/c=0.70 L

w/c=1.20


Fig. 6.3 Correlation between crusher setting and particle size distribution of crusher products, from Ref. (14).

> 30 3.0 4.2 3.2 0

30–20 27.4 31.9 27.6 32

20–10 35.9 33.2 33.5 34

10- 5 14.7 13.4 13.2 17

< 5 19.1 17.3 22.5 17

Table 6.3 Overall grading of crusher products, experimental data, from Ref. (7e).

Size Fraction in

mm

Measured Weight Percent of Total Crusher Products

Estimated Weight Percent of Total Crusher Product According to

Figure 6.3

> 38 3 3

38 29 34

25 15 15


It will be seen from Table 6.2 that the actual particle size distributions of crushed concretes are in reasonably good agreement with the predictions that can be made on thebasis of Figure 6.3. Similar results have been obtained by Fergus (7e) as shown in Table 6.3. Usually grain-size distributions of crusher outputs approximate Fuller curves. Thus, it may be concluded that the crushing characteristics of hardened concrete are similar tothose of natural rocks and not significantly affected by the grade of original concrete.

Japanese studies which have been reported by B.C.S.J. (12) confirm that approximately 20% by weight of fine recycled aggregate below 5 mm is produced when old concrete iscrushed in a jaw crusher with an opening of 33 mm, also independent of concrete quality(see Table 6.1). With jaw openings of 60, 80, and 120 mm, corresponding percentages of fine recycled aggregate produced were 14.1%, 10.6%, and 7.0%. With a jaw opening of20 mm Ravindrarajah and Tam (65) found the quantities of fine material below 5 mm tobe 23.1, 25.7, and 26.5% by weight for 37 MPa, 30 MPa, and 22 MPa concretes,respectively.

In order to be cohesive and workable, fresh concrete requires between 25 and 40% of fine aggregate by weight of total aggregate, depending on the type of sand and itsfineness, concrete consistency, water-cement ratio, and maximum size of coarse aggregate. Thus, it may be concluded that by the crushing of old concrete in one passthrough a jaw crusher there is not generated enough fine recycled aggregate to producenew concrete of good quality when the maximum size of crusher output is between 32and 38 mm.

The normal procedure in current American practice is to proportion fresh recycled aggregate concrete mixes so that coarse and fine recycled aggregate may be consumed inthe same ratio that they are produced. However, due to the fact that insufficient quantitiesfine recycled aggregate is produced by the jaw crusher in order to make new concrete ofgood workability, it is necessary to add a certain amount of conventional fine aggregate.As will be seen later, this may also be necessary for other reasons.

At a recycling project in Iowa (7f) it was found that optimum finishing properties and workability of fresh recycled aggregate concrete was obtained when 25% of natural sandwas mixed with 75% of fine recycled aggregate in a standard pavement mixture whichcontained a 50–50 mixture of fine and coarse aggregate of 38 mm (11/2 inches)maximum size.

It is interesting that the recycling of an existing pavement will produce a total of about 50% more recycled aggregate than is needed to produce the quantity of new concretewhich is required to replace the same section with a pavement of equal thickness (7a). However, it will be seen later in this state-of-the-art report that, for reasons of durability, it may not be advisable to use fine recycled aggregate less than 2–3 mm for production of new concrete. However, even if all fine recycled aggregate below 5mm is rejected it is

19 19 19

12.5 8 6

9.6 13 12

4.8 13 11


likely that more than enough coarse recycled aggregate will be produced to replace thesame section with a pavement of equal thickness.

Dutch investigators have developed a concept which they call ‘Crusher Characteristics’ as a useful tool for control of the crushing and sieving processes of old concrete. CrusherCharacteristics are graphic representations of the relations between a so-called reduction factor, R, and the sieve residues of the crusher output on various size sieves. Thereduction factor, R, is defined as the ratio between the particle size of crusher input andcrusher output for the same weight percentage of residue on a given size sieve. Differenttypes of crushers yield different crusher characteristics. If for a specific plant the crushercharacteristic is known, the grading of the crusher output can be forecast when thegrading of the crusher input is known. The use of crusher characteristics can best beshown by means of a numerical example as follows:

In order to determine the crusher characteristic for a given impact crusher, the particle distributions of crusher input and crusher output must be determined. For thefragmentation of concrete demolition waste in a specific impact crusher, these are plottedin one and the same graph as shown in Figure 6.4.

In our example the reduction factor, R, for a sieve residue of 35% equals 59.5 mm grain size of the crusher input, divided by 9.9 mm grain size of the crusher output, or

By calculating the reduction factor R for a number of sieve residues and plotting them inanother graph with the reduction factor along the ordinate and sieve residue along the abscissa, the crusher characteristic (labelled 3) is obtained as shown in Figure 6.5 for the impact crusher which was used in our numerical example. For purposes of comparison,typical examples of crusher characteristics are also shown in Figure 6.5 for a jaw crusher, labelled 1, a cone crusher, labelled 2, and a swing-hammer mill, labelled 4. It will be seen from Figure 6.5 that impact crushers and swing-hammer mills which both affect crushingby means of different kinds of impact, have greater reduction factors than jaw- or conecrushers, which affect crushing by the application of pressure only.


Fig. 6.4 Grain size distribution of crusher input and output for determination of crusher characteristic of impact crusher (example).


6.6 Storage and handling of recycled aggregates

The Japanese Proposed Standard for the ‘Use of recycled aggregate and recycledaggregate concrete’ (6) includes the following recommendations for storage and handlingof recycled aggregates:

1. Recycled aggregates produced from original concretes of distinctly different quality, and recycled aggregates produced by means of different production methods shall be stored separately.

2. Recycled coarse aggregate and recycled fine aggregate shall be stored separately. 3. Recycled aggregate shall be stored and transported in a manner to prevent breakage

and segregation or otherwise cause change in quality of the recycled aggregate concerned.

4. Water absorption ratio of recycled coarse aggregates is large; therefore, such aggregates should normally be used in a saturated and surface dry condition. For this reason recycled aggregate storage yards should be provided with water sprinkling facilities so that recycled coarse aggregates can be maintained at the required moist condition. However, some unhydrated Portland cement and hydrated lime is present in fine recycled aggregates, and there is danger that such fine aggregates in time shall become caked. Therefore, fine recycled aggregates should not be kept in storage for any longer period of time. It is left to the ready mixed concrete manufacturers to solve this problem. We recognize that this, as well as the provision of extra sil capacities are important production problems, but they are beyond the commissorium of this committee to deal with.

5. Recycled aggregates shall be stored separate from other types of aggregates.

6. It is recommended that if different types and qualities of recycled aggregate are produced, the plant should not process coloured material such as brick rubble together with concrete rubble because of the extra cost which is involved in the cleaning of processing units when changing from brick to concrete rubble.


Fig. 6.5 Crusher characteristics (example).


7. Quality of recycled aggregates

Simply producing a clean, crushed and well-graded material is not sufficient to ensure effective recycling. The recycled material produced must be suitable for specificapplications and it should comply with certain grading limits, contain minimal levels ofcontaminants and meet other requirements of stability and durability. Once the concretehas been crushed, sieved and if necessary decontaminated, it can find applications as 1)general bulk fill, 2) fill in drainage projects, 3) sub-base or base material in road construction or 4) aggregate for new concrete. In this section we shall primarily discussrecycled aggregate for production of new concrete. Aggregate for other purposes arebriefly dealt with in sections 7.9, 8.9, 12 and 13.

7.1 Grading, particle shape, and surface texture of recycled aggregates

After screening on an ASTM No. 4 (5 mm) sieve, the grading of an average crusherproducts is compared with ASTM C-33 grading requirements for a 25 mm (1 in)maximum size aggregate shown in Figure 7.1. Data are from Danish (13) and Japanese (15) investigations. Both of the coarse aggregates were produced by the crushing of original concrete in a jaw crusher.

It is evident that both aggregates could have been brought within ASTM grading requirements by slight adjustments of the opening of the crusher. Apparently it is easy toproduce reasonably well-graded coarse recycled aggregate by means of a jaw crusher.

The grading of fine crusher products below 5 mm from three different investigations (13, 15, and 7e) are compared in Figure 7.2. All gradings fall within the shaded area of the sieve diagram in Figure 7.2. All were produced by the crushing of old concretes in ajaw crusher. It will be seen that all gradings are somewhat coarser than the lower limit ofASTM grading requirements. Some are even lower than the lowest permissible gradinglimit of zone 1 sand in British Standard 882, 1201, which is considered to be the coarsestgrading of sand from which concrete of reasonable quality can be produced.

It may be concluded that fine recycled aggregates, as they come from the crusher, are somewhat coarser and more angular than desirable for production of good concretemixes.


Fig. 7.1 Range of gradings of 25 mm coarse recycled aggregates produced by jaw crusher in one pass (from literature reviewed).


Fig. 7.2 Range of gradings of crusher fines < 4 mm (fine aggregate) obtained when 25–30 mm max. size coarse recycled aggregates are produced by jaw crusher in one pass.

As fine recycled aggregates also consist of angular particles, it is not surprising thatconcretes which are produced exclusively with coarse and fine recycled aggregates tendto be harsh and unworkable (7f). However, by adding a certain amount of a finer naturalblending sand it is possible to bring fine recycled aggregates within the grading limits ofASTM C 33. At the same time, concrete workability is greatly improved (7f).

Gerardu and Hendriks (70) report that the best recycled aggregate for concreteproduction is obtained when it is graded within the limits specified in the GermanStandard DIN 4163 for the recycling of rubble (71) which was in force in the 1950s, butwhich has now been withdrawn.

Fergus (7e) found that the quantity of material finer than 75 micron in 38 mm (1½ in)


maximum size coarse recycled aggregates ranged from 0.3% to 0.5%. In fine recycledaggregate below the ASTM No. 4 sieve; material finer than 75 micron ranged from 4.1%to 6.6% depending on concrete quality. In one particular case where original concreteconsisted essentially of cement mortar, the corresponding value was 9.1%.

Hasaba et al. (16) found that 25 mm maximum size coarse recycled aggregate to contain between 1.3% and 1.7% particles finer than 88 micron, depending on the qualityof concrete.

Hansen and Narud (13) found that material finer than 75 micron in fine recycled aggregates below 4 mm ranged from 0.8% to 3.5%, depending on concrete quality.

Considering that ASTM C 33 allows 1.5% dust of fracture in coarse aggregate 5% dustin fine aggregate in concrete which is subject to abrasion, and 7% in all other concrete, itmay be concluded that recycled aggregates in most cases can be used for production ofconcrete without being washed.

In the main these results are confirmed by Karaa (93). Schulz (135d) concluded that recycled concrete aggregates will be adequate for

production of new concrete only if particle sizes below 2 mm are screened out. Morlion(135t) presented grading curves of recycled concrete aggregates used for production ofnew concrete at a large recycling project in Belgium. In this large scale practical project itwas also decided to use coarse recycled aggregate and natural sand, because recycledsand gave poor strength results.

7.2 Attached mortar and cement paste

When old concrete is crushed, a certain amount of mortar from the original concreteremains attached to stone particles in the recycled aggregates. Table 7.1 shows the volume percentage of old mortar which remained attached to original gravel particles inrecycled aggregate, as reported by Hansen and Narud (13) on the basis of the results of an investigation by Hedegaard (17).

A representative sample of various grades and size fractions of recycled aggregate wasmixed with red-coloured cement and cast into cubes. After hardening, the cubes were cut into slices and the slices polished. Mortar attached to natural gravel particles in recycledaggregates could be clearly distinguished both from the original gravel particles and fromthe red cement matrix.

The volume percentage of old mortar, which was attached to gravel particles in each grade and size fraction of recycled aggregate, was determined on a representative numberof samples by means of a linear traverse method, similar in principle to the method whichis described in ASTM C 457–71, ‘Standard recommended practice for microscopicaldetermination of air-void content and parameters of the air-void system in hardened concrete’.

Hansen and Narud (13) found the volume percentage of mortar attached to natural gravel particles to be between 25% and 35% for 16–32 mm coarse recycled aggregates, around 40% for 8–16 mm coarse recycled aggregates, and around 60% for 4–8 mm coarse recycled aggregates (see Table 7.1). However, it appears that for the same cement


and original aggregate the volume percentage of old mortar attached to recycled concreteaggregates does not vary much even for widely different water-cement ratios of original concrete.

Hasaba et al. (16) found 35.5% of old mortar attached to natural gravel particles in 25–5 mm coarse recycled aggregate produced by the crushing of original concrete having acompressive strength of 24 MPa. Corresponding figures were 36.7% mortar for 41 MPaconcrete and 38.4% for 51 MPa concrete.

Figure 7.3 shows the results of a Japanese investigation reported by B.C.S.J. (12) where the hydrated cement paste adhering to recycled aggregates was determined byimmersing the particles in a dilute solution of hydrochloric acid at 20° C. It will be seen that the amount of cement paste attached to sand or stone particles, as determined fromthe weight loss due to dissolution of cement during the test, increases with decreasingparticle size of aggregate. Approximately 20% of cement paste is attached to 20–30 mm of aggregate, while the 0–0.3 mm filler fraction of recycled fine aggregate contains 45–65% of old cement paste. Old cement paste and mortar in many cases unfavourably affectthe quality of recycled concretes, and it should be avoided to use the finer fractions below2 mm. Perhaps it should be avoided to use any fine recycled aggregate at all, for anumber of reasons which will be apparent later in the report.

Table 7.1 Properties of natural gravel and recycled aggregates according to Ref. (13).

Type of Aggregate

Size Fraction in mm

Specific Gravity

SSD cond.

water Absorption in percent

Los Angeles Abrasion

Loss Percentage

Los Angeles

Uniformity Number

L100/L500 Ratio

B.S. Aggregate Crushing

Value percent

Volumepercent

of mortar

attachedto

naturalgravel

particle

Original natural gravel

4–8 8–16

16–32

2500 2620 2610

3.7 1.8 0.8

25.9 22.7 18.8

0.28 0.22 0.20

21.8 18.5 14.5

000

Recycled aggregate (H) (w/c=0.40)

4–8 8–16

16–32

2340 2450 2490

8.5 5.0 3.8

30.1 26.7 22.4

0.30 0.25 0.24

25.6 23.6 20.4

583835

Recycled aggregate (M) (w/c—0.70)

4–8 8–16

16–32

2350 2440 2480

8.7 5.4 4.0

32.6 29.2 25.4

0.31 0.28 0.25

27.3 25.6 23.2

643928

Recycled 4–8 2340 8.7 41.4 0.38 28.2 6


Fig. 7.3 Weight percentage of cement paste adhering to original aggregate particles in recycled aggregate produced from original concretes with different water: cement ratios.

aggregate (L) (w/c—1.20)

8–16 16–32

2420 2490

5.7 3.7

37.0 31.5

0.39 0.38

29.6 27.4

3925

Recycled aggregate (M) (w/c—0.70)

< 5 2280 9.8 – – – –


7.3 Density

Hansen and Narud (13) found densities of coarse recycled aggregates in saturated and surface dry condition ranging from 2340 kg/m3 (for 4–8 mm material) to 2490 kg/m3 (for 16–32 mm material), independent of the quality of original concrete, see Table 7.1. Corresponding s.s.d. densities of original coarse aggregates ranged from 2500 to 2610kg/m3. Narud (18) found an s.s.d. density of 2279 kg/m3 for fine recycled aggregates produced from a particular original concrete which was made with a water-cement ratio of 0.70.

Table 7.2 shows densities of old mortars in original concretes which were used toproduce coarse recycled aggregates, the properties of which are shown in Table 7.1. It will be seen that densities around 2000 kg/m3 are obtained for such mortars. This is much lower than the densities of corresponding hardened concretes which ranged from 2380 to2401 kg/m3.

Hasaba et al. (16) found the s.s.d. density of 25–5 mm coarse recycled aggregate to be around 2430 kg/m3, independent of the quality of original concrete, see Table 7.3. The density of corresponding fine recycled aggregates below 5 mm was 2310 kg/m3. The density of corresponding original coarse aggregate was 2700 kg/m3 and 2590 kg/m3 for original fine aggregate.

In another Japanese investigation reported by B.C.S.J. (12) dry densities of coarse recycled aggregates varied between 2120 kg/m3 and 2430 kg/m3, corresponding to s.s.d. densities between 2290 kg/m3 and 2510 kg/m for recycled aggregates from a wide rangeof original concretes. Dry densities of corresponding fine recycled aggregates rangedfrom 1970 kg/m3 to 2140 kg/m3, and s.s.d. densities ranged from 2190 kg/m3 to 2320

Table 7.2 SSD-densities and water absorptions of original mortars referring to recycled aggregates in Table 7.1 (with additional information, not reported in Ref. 13).

Water/Cement Size of Fraction in mm

Density in kg/m3

Water Absorption in Percent

0.40 4–8 8–16

16–32

2036 2060 2148

17.0 17.0 15.6

0.70 4- 8 8–16

16–32

2041 2060 2091

17.0 16.2 15.8

1.20 4–8 8–16

16–32

2070 2068 2081

16.5 16.6 16.5


kg/m3. Similar results were found by Ravindrarajah and Tam (65). It may be concluded that the density of recycled aggregate is somewhat lower than the

density of original aggregate due to a relatively low density of the old mortar which isattached to original aggregate particles. However, for the same cement and originalaggregate the density of recycled concrete aggregate does not vary much even for widelydifferent water-cement ratios of original concrete. S.s.d. densities of recycled aggregate must

be determined in the laboratory before any mix design of recycled aggregate concrete canbe attempted. For what concerns coarse recycled aggregates this can be done according toASTM designation C 127, ‘Standard test method for specific gravity and absorption of coarse aggregate’. For what concerns fine recycled aggregate such determination by means of the corresponding ASTM designation C 128 is very difficult because it is

Table 7.3 Properties of natural gravel and recycled aggregates, from Ref. (16).

Type of Aggregate

Density (SSD) kg/m3

Water Absorption

B.S. Crushing Value in percent

B.S.

10% Fineness

Sulphate Soundness

% Loss

Content of Old motar vol %

15 mm max. size natural gravel

2700 1.14 – – – –

25 mm max. size recycled w/c=0.42

2430 6.76 23.0 133 23.9 38.4


2430 6.93 23.1 130 23.1 36.7


2430 7.02 24.6 113 28.6 35.5

Unspec. fine recycled aggregate < 5 mm

2310 10.9 – – – –


difficult to determine when fine recycled aggregate is in s.s.d condition. It must also bekept in mind that any subsequent variation in density of recycled aggregate duringconcrete production will give rise to variations, not only in mix proportions and thereforeconcrete properties, but also in yield of concrete produced.

Karaa (93) found that the density in loosely packed condition of a certain type of recycled concrete aggregates was 1350 kg/m3 compared to 1440 kg/m3 for natural gravel in the same condition.

Schulz (135d) has presented diagrams which show general relationships between onone hand particle density and water absorption of recycled demolition debris, and on theother hand density of such materials in loosely packed condition. Such relationshipscould be useful for primitive mix design of concrete by volume.

7.4 Water absorption

In an earlier review paper, Nixon (5) concluded that the most marked difference in physical properties of recycled concrete aggregates compared with conventionalaggregates is higher water absorption.

Hansen and Narud (13) found water absorptions of coarse recycled aggregates ranging from 8.7% for 4–8 mm material to 3.7% for 16–32 mm material, regardless of the quality of original concrete, see Table 7.1. Corresponding water absorptions of originalaggregates ranged from 3.7 to 0.8%. In Table 7.2 are shown the water absorptions of oldmortars in original concretes, which were used to produce recycled concrete aggregates,the properties of which are shown in Table 7.1. It will be seen that water absorptionsaround 17% are obtained for such mortars, which is much higher than overall waterabsorptions for recycled aggregates. Narud (18) found a water absorption of 9.8% for afine recycled aggregate produced from an original concrete with a water-cement ratio of 0.70 corresponding to designation M in Table 7.1.

Hasaba et al. (16) found water absorptions around 7% for 25–5 mm coarse recycled aggregates, independent of the quality of original concretes. Corresponding waterabsorptions for fine recycled aggregates below 5 mm were around 11%, see Table 7.3. Both values are in good agreement with results obtained by Hansen and Narud which arepresented in Table 7.1. In another investigation reported by B.C.S.J. (12) water absorptions of recycled coarse aggregates between 3.6% and 8.0% were found for coarserecycled aggregates, and absorptions between 8.3% and 12.1% were found for finerecycled aggregates.

Similar results were found by Ravindrarajah and Tam (65) and by Karaa (93). It may be concluded that the water absorption of coarse recycled aggregates is much

higher than the water absorption of original aggregates. This is due to the higher waterabsorption of old mortar attached to original aggregate particles.

According to the Japanese Proposed Standard for the ‘Use of recycled aggregate and recycled aggregate concrete’ (6), recycled aggregates should not be used for concreteproduction when water absorption is more than 7% for coarse aggregate and more than13% for fine aggregate. It would appear from what is said above that most recycled


aggregates would meet such requirements. Water absorption of coarse and fine recycled aggregates must be determined in the

laboratory before any mix design of recycled aggregate concrete can be attempted. Forwhat concerns coarse recycled aggregate this may be done according to ASTM C127,‘Standard test method for specific gravity and absorption of coarse aggregate’. Kreijger (63) found a parabolic relation between water absorption and density of recycled aggregates as shown in Figure 7.4.

Fig. 7.4 Water absorption as a function of density of recycled concrete aggregate (63).

It is more difficult to determine water absorption capacity and water content of fine recycled aggregate than of coarse recycled aggregate. Hansen and Marga (135w) found the use of ASTM C 128 ‘Standard test method for specific gravity and absorption of fine aggregate’ to be inappropriate and highly inaccurate when used to assess when fine recycled aggregates are in a saturated and surface-dry condition. The material is much too sticky. As a consequence it is difficult to control the effective water-cement ratio of a concrete production whether in the laboratory, in a ready mixed concrete plant or on site,if concrete is produced with fine recycled aggregate. Considering that fine recycledaggregates also increase the water demand of fresh concrete and lower the strength andprobably the durability of hardened concrete, it is not recommended to use recycled fineaggregate for production of quality concrete.

Puckman and Henrichsen (135a) has suggested an alternative method to the ASTM


procedure for measuring water absorption of fine recycled aggregate. This method mustbe investigated further before it is used in practice.

Due to high water absorption of recycled aggregates, it is sometimes suggested to usepre-soaked aggregates for production of recycled aggregate concretes in order to maintain uniform quality during concrete production. Practical ways of pre-soaking aggregates are discussed by Goeb (85). However, it has not been studied how fully saturated recycledaggregate will affect the freeze-thaw resistance of hardened recycled concrete.

7.5 Los Angeles abrasion loss and British Standard crushing value

It will be seen from Table 7.1 that Hansen and Narud (1) found Los Angeles (LA) abrasion loss percentages ranging from 22.4% for 16–32 mm coarse recycled aggregate produced from a high strength original concrete, to 41.4% for 4–8 mm coarse recycled aggregate produced from a low strength original concrete. Corresponding L.A.uniformity numbers L100/L500 were 0.24 and 0.38. BS aggregate crushing values were20.4% and 28.2%, respectively.

In Table 7.3, Hasaba et al (16) report BS aggregate crushing values ranging from 23.0% for a 25–5 mm coarse recycled aggregate produced from an original high strengthconcrete to 24.6% for a 25–5 mm coarse recycled aggregate produced from an original low strength concrete. Corresponding BS 10% fineness values were 13.3 tons and 11.3tons.

B.C.S.J. found Los Angeles abrasion loss percentages ranging from 25.1% to 35.1%for coarse recycled aggregates from 15 different concretes of widely different strengths,which were crushed in different ways. Similar values were found by Bauchard (135–1) who also found Sand Equivalent Values ranging from 28 to 68 for crushed concrete fines.

Yoshikane (19) (Table 7.4) found Los Angeles loss percentages ranging from 20.1%for a 13–5 mm coarse recycled aggregate produced from an original high strength (40 MPa) concrete to 28.7% for a 13–5 mm recycled aggregate produced from an original low strength (16 MPa) concrete.

Similar results were found by Ravindrarajah and Tam (65). According to ASTM Designation C 33, ‘Standard specification for concrete

aggregates’, aggregate may be used for production of concrete when the Los Angeles

Table 7.4 Relationship between compressive strengths of original concretes and Los Angeles loss percentages of corresponding recycled aggregates, from Yoshikane (19).

Sample C A B E F D

Compressive Strength MPa 15 16 21 30 38 40

L.A.Abrasion Loss Percentage 28.7 27.3 28.0 25.6 22.9 20.1


abrasion loss percentage does not exceed 50%. Crushed stone for road constructionpurposes is usually required to have LA loss values not exceeding 40%.

According to British Standard 882, 1201, Part 2,1973, ‘Specifications for aggregates from natural sources’, aggregates may be used for production of concrete wearingsurfaces when the aggregate crushing value does not exceed 30%, or 45% for otherconcrete, as determined according to BS 812, ‘Methods for sampling and testing of mineral aggregates’. Alternatively, BS 882 specifies that the BS 10% fines values should be more than 5 tons for normal concrete, more than 10 tons for concrete wearingsurfaces, and more than 15 tons for granolithic floor finishes.

Considering the results reported above, it may be concluded that recycled concreteaggregates produced from all but the poorest quality concrete can be expected to passASTM and BS requirements to L.A.abrasion loss percentage, BS crushing value, as wellas BS 10% fines value even for production of concrete wearing surfaces, but probably notfor granolithic floor finishes.

7.6 Sulfate soundness

ASTM C33, ‘Standard specification for concrete aggregate’, limits the loss in weight when aggregate is subjected to five cycles of alternate soaking and drying in a sulfatesolution. The test is carried out according to ASTM C88, ‘Standard test method for soundness of aggregates by use of sodium sulfate or magnesium sulfate’. When magnesium sulfate is used, ASTM C33 limits the weight loss of coarse and fineaggregate to 18% and 15%, respectively. Corresponding weight losses are 12% and 10%when sodium sulfate is used.

Strand (68) found a sulfate soundness loss of 3% for coarse recycled concrete aggregate compared with 5% for corresponding virgin aggregates.

B.C.S.J. (12) found sodium sulfate soundness loss percentages after five cycles rangingfrom 18.4% to 58.9% for coarse recycled aggregates from 15 original concretes ofdifferent compressive strengths and crushed in different ways. Sulfate soundness losspercentages for corresponding fine recycled aggregates ranged from 7.4% to 20.8%.These results were confirmed by Kaga et al. (135m). Thus, Kaga et al. (135m) claim that most recycled aggregates would be less durable than original aggregates, and thatrecycled aggregates would fail to meet ASTM C 33 requirements to a sodium sulfatesoundness of not more than 12% loss for coarse aggregate.

Contrary to this, Fergus (7e) found magnesium sulfate soundness losses ranging from 0.9% to 2.0% for coarse recycled aggregates produced from concrete, which was derivedfrom a number of different pavements. Corresponding loss values of fine recycledaggregates ranged from 6.8% to 8.8%. Losses of 3.9% and 7.1% were measured fororiginal coarse and fine aggregate used to produce original concretes.

On the basis of these and other results, Fergus (7e) concluded that coarse recycled aggregates were superior to control natural gravel in those tests designed to evaluate thepossible effect of aggregate properties with respect to the durability of concrete. Fergus(7e) also concludes that durability of fine recycled aggregate was comparable to


durability of control natural sand. Thus, American results indicate that the durability characteristics of recycled

aggregates generally are improved over those of natural aggregates, while Japaneseresults indicate that the opposite is true. However, Kasai (66) concludes that the sulfate soundness test is unsuitable for evaluation of the durability of recycled concreteaggregates. As durability properties of exposed recycled aggregate concretes are ofutmost importance, it is suggested that additional studies be made of the durabilitycharacteristics of recycled aggregates versus original aggregates.

See also Section 9.2 for frost resistance of recycled aggregate concrete.

7.7 Contaminants

7.7.1 General

One of the problems inherent in use of recycled aggregates for manufacture of newconcrete is the possibility of contaminants in original demolition debris passing into newconcrete. Contaminants may be clay balls, bitumen joint seals, expansion joint fillers,gypsum, periclase refractory bricks, chlorides, organic materials, chemical admixtures,tramp steel and other metals, glass, lightweight bricks and concrete, weathered or firedamaged particles, particles susceptible to frost or alkali reactions, industrial chemicalsands, reactive substances and high alumina cement concrete.

B.C.S.J. (12) and Mukai et al. (4) report results of a study of the effect on concrete strength of various contaminants which were added independently and in variousquantities to a natural and a recycled aggregate.

Table 7.5 shows the volume percentage of each of six contaminants which, whenadded to the aggregate, gave 15% reduction of compressive strength compared to controlconcretes.

From the results of the B.C.S.J. study (12) it may be concluded that impurities in the formof tiles and window glass have little influence on the compressive strength of recycledaggregate concrete. However, blast furnace slag aggregate may give slightly lower

Table 7.5 Volume percentages of impurities which gave 15 per cent reduction of compressive strength compared to control concretes, from (6).

Impurities Lime Plaster

Soil Wood (Japanese cypress)

Hydrated Gypsum

Asphalt Paint Made of Vinyl Acetate

Volume percent of aggregate

7 5 4 3 2 0.2


concrete strength. Concrete with 3% by weight of gypsum plaster reduces strength by15% when concrete is dry cured and by up to 50% when concrete is wet cured. This isbecause gypsum plaster is softened and weakened by water immersion. Clay, acetic vinylpaint, asphalt, and wood also reduced concrete strength.

On the basis of such results, the Japanese Proposed Standard for the ‘Use of recycled aggregate and recycled aggregate concrete’ (6) limits the amounts of injurious impurities contained in recycled aggregates to the values shown in Table 7.6.

It may be concluded that provided the usual limits of cleanliness are applied to recycledaggregates and a strict limit is imposed on the total amount of allowable impurities, thenof those contaminants, only glass is likely to remain a potential problem. Waste glass is aproblem because it is alkali reactive with cement paste under wet conditions. This ismade more serious by the lack of suitable means of removing glass contaminants.Therefore, it is preferable to ensure that no glass is present in the original debris. Plateglass windows should always be removed from buildings before demolition.

In great detail Yanagi et al. (135z) studied the properties of hardened concrete made from unwashed and washed coarse recycled aggregate from two different recycling plantsin the Tokyo area. Contaminants included asphalt, plastics, wood, paper, textiles, soil,clay and crusher fines. Three different methods of washing were employed. It was foundthat the compressive strength of recycled aggregate concrete is increased by the washingof coarse aggregate, but that the carbonation depth increases at the same time, probablydue to removal of fines. Thus, the concrete becomes stronger but more permeable. Thereappears to be no difference in drying shrinkage of concretes made with washed andunwashed recycled concrete aggregates.

7.7.2 Bitumen

According to Japanese results obtained by B.C.S.J. (12), the presence of asphalt in aggregates seriously reduces concrete strength. Addition of 30 volume per cent of asphaltto recycled aggregate reduced concrete compressive strength by approximately 30%.

Similar results obtained by Fergus (7e) are presented in Table 7.7. Here an addition of

Table 7.6 Maximum allowable amounts of injurious impurities, according to (6).

Type of Aggregate

Plasters, Clay Lumps and Other Impurities of Densities < 1950

kg/m3

Asphalt, Plastics, Paints, Cloth, Paper, Wood, and Similar Material Particles

Retained on a 1.2 mm Sieve. Also Other Impurities of Densities < 1200 kg/m3

Recycled Coarse

10 kg/m3 2 kg/m3

Recycled Fine

10 kg/m3 2 kg/m3


30.8 volume per cent of bituminous concrete to recycled aggregate resulted in a 36.6%reduction of concrete compressive strength which is in good agreement with Japanesefindings.

Fergus (7e) also found that recycled aggregate concrete containing bituminous concrete reacts normally to the addition of air entraining admixtures. Ray (20), on the other hand, reports on a case where a mixture of recycled aggregates from concrete and asphaltproduced lean concrete with so much entrained air that a detraining agent had to be usedto keep the amount of entrained air within specified limits.

Gerardu and Hendriks (70) state that recycled aggregates should not contain more than1% asphalt because asphalt reduces the compressive strength of concrete.

It would appear from the results of these investigations that bituminous aggregate particles in recycled aggregate concrete reduce the strength in the same way as any otherlow strength lightweight aggregate particles would reduce strength of conventionalconcrete. As such strength reductions will become apparent during the process of trialmixing, and as bituminous aggregate particles almost certainly are frost resistant, thereare no obvious reasons why very stringent limits should be imposed upon the allowablecontents of bituminous aggregate particles in recycled concrete aggregates.

Even so, it must be considered good practice to remove bituminous concrete overlay materials from concrete pavements for example by cold-milling before recycling the concrete. This will probably be done anyway because it is economically advantageous torecycle bituminous concrete separately in an asphalt plant. Any bitumen which remainson the old concrete surfaces after removal of the overlay is probably without muchimportance for the quality of recycled aggregate concrete.

Table 7.7 Reduction in compressive strength of recycled aggregate concrete as a function of volume per cent bituminous concrete in recycled aggregates, from Fergus (7e).

Bituminous Concrete in Vol. Percent of Coarse Recycled

Aggregate

Bituminous Concrete in Vol. Percent of

Fine Recycled Aggregate

Compressive Strength (psi)

Percent Reduction in

Strength

0 (control) 0 (control) 4910 0

143 0 4790 2.4

17.0 0 4390 10.6

21.7 0 4130 15.8

30.8 0 4130 15.8

30.8 30.8 3110 36.6

100 100 1100 77.5


7.7.3 Gypsum

Nixon (5) reviewed several systematic studies of the deleterious effects on recycledaggregate concrete of gypsum plaster in recycled aggregates due to sulfate expansions.

On the basis of these and later investigations it may be concluded that stringent limitson the gypsum content should be included in standard specifications for recycledaggregates.

In many countries in the Middle East, codes and standards limit the sulfate content of aggregate either to 0.5% by weight of both the fine and the coarse aggregate fraction or to4% by weight of cement including sulfate in cement. Both percentages should becalculated as equivalent SO3 contents. However, attention is called to the much largeramount of sulfate considered to be acceptable by Samarai (60). On the safe side it is suggested to apply above mentioned limits to recycled aggregate and recycled concrete.Furthermore, it is recommended to use Sulfate Resistant Portland Cement for productionof recycled aggregate concrete whenever recycled aggregates may be contaminated bygypsum.

7.7.4 Organic Substaoces

Many organic substances such as wood, textile fabrics, paper, joint seals and otherpolymeric materials are unstable in concrete when submitted to drying and wetting orfreezing and thawing. Other organic substances such as paint may entrain considerableamounts of air in concrete.

As a consequence, stringent limits on the content of organic contaminants should beimposed in standard specifications for recycled aggregates and recycled aggregateconcrete.

Until more experience has been gained, it would seem reasonable to apply a limit valueof 2 kg/m3 for substances lighter than 1200 kg/m3, such as it is suggested in the JapaneseProposed Standard (6). 2 kg/m3 correspond to approximately 0.15% of organic substance by weight of aggregate. It should be kept in mind that organic impurities are usuallyrelatively light, which increases their content in concrete in terms of parts per volume.

7.7.5 Chlorides

Chlorides in concrete can give rise to severe reinforcement corrosion. Original concretescan be contaminated by chlorides in several ways. Chloride ions can penetrate fromoutside, as is the case in marine structures or highway bridges, parking structures andpavements which have been exposed to de-icing salts. Chlorides can also be entrained inthe original fresh concrete by use of accelerating admixtures or poorly washed marineaggregates or desert sands.

On a Michigan pavement restoration project, Fergus (7e) measured up to 1.12 kg/m3

NaCl in recycled aggregate from 20-year old 23 cm thick pavement sections which had


been removed and were to be replaced due to mechanical failure, and which had beenexposed to de-icing salts for many years: 1.12 kg/m3 NaCl corresponds to 1.12×35.45/58.44=0.68 kg/m3, or approximately 0.68×100/2300=0.03% of chloride ion by weight of concrete. As the original concrete was produced with 335 kg/m3 cement, the overall chloride ion content in the old pavement was approximately0.03×2300/335=0.2% by weight of cement.

Peterson (21) measured 12 kg/m3 of chloride ion at the top of a 12–year old 27.5 cm thick flat slab of a parking structure, decreasing to approximately 1.3 kg/m3 of chloride ion at the bottom of the slab. Assuming that the concrete was produced with 350 kg/m3 of cement, this would correspond to 3.4% of chloride ion by the weight of cement at the topof the slab and 0.37% at the bottom.

Strand (68) measured 2.4 to 3.0 kg/m3 of sodium chloride in samples of concrete frompavements with various years of service in Wisconsin. Concern about rapid steelcorrosion due to chloride content of the salvaged concrete, as well as from future wintermaintenance, led to the decision to use epoxi-coat all steel in the new recycled aggregateconcrete pavement.

Bergholt and Hansen (22) found chloride ion contents as high as 7.5% by the weight of cement in a structure located in the State of Bahrain in the Arabian Gulf, where theoriginal concrete had been produced with chloride contaminated desert sand.

Hansen and Hedegaard (23) added 4% of water-free calcium chloride, corresponding to 2.56% of soluble chloride ion by the weight of cement, as an accelerating admixture toan original concrete. After 38 days of accelerated curing, the original concrete wascrushed. It was found that the 30–20 mm fraction of crushed concrete contained 0.21% of chloride ion, the 20–10 mm fraction contained 0.22% of chloride ion, and the 5–10 mm fraction contained 0.23% of chloride ion, all by weight of recycled aggregate. Crushedconcrete fines below 5 mm contained 0.39% of chloride ion. On the basis of these results,it was estimated that 1.41% of soluble chloride ion by weight of cement would beintroduced into a recycled aggregate concrete, similar in composition to the originalconcrete, by way of recycled coarse and fine aggregate.

It is recommended that standard specifications for recycled aggregate and recycled aggregate concrete should impose stringent limits on chloride contents of suchaggregates. However, the threshold chloride concentration, below which there is no riskof reinforcement corrosion, remains a controversial issue. Therefore, no specific limits onchloride concentration in recycled aggregates shall be recommended in this report.

ACI Committee 201 (27) currently recommends the following limits for chloride ion in concrete prior to service exposure, expressed as a percentage by weight of cement:

1) Prestressed concrete 0.06% 2) Conventionally reinforced concrete in a moist environment exposed to

chloride 0.10% 3) Conventionally reinforced concrete in a moist environment but not exposed to

chloride 0.15% 4) Above ground building construction where concrete will stay dry no limit

The Japanese Proposed Standard for the ‘Use of recycled aggregate and recycledaggregate concrete’ (6) suggests that essentially the same maximum limits should apply


to recycled aggregates. It may be concluded that new concrete, produced from recycled coarse aggregate

which has been produced from old chloride-contaminated concrete in many cases would fail to meet current recommended limits for chloride ion in concrete. Use of fine recycledaggregate with coarse recycled aggregate will increase the risk of reinforcementcorrosion in the new recycled aggregate concrete.

For winter concreting purposes it has been common practice in the past to use 2% of flaked calcium chloride dihydrate (CaCl2.2H20) by weight of cement as an accelerating admixture to concrete. Two per cent of calcium chloride dihydrate corresponds toapproximately 1% of chloride ion in concrete by weight of cement. It should be studiedwhether there is any risk of exceeding current ACI recommended limits when suchconcretes are recycled as coarse aggregate for production of new concrete. Judging fromthe results of Hansen and Hedegaard (23) there is a risk of exceeding current ACI recommended limit for chloride ion concentration in concrete prior to service exposure,when such concretes are recycled as coarse aggregate for production of new concrete.

7.7.6 Chemical and mineral admixtures

Hansen and Hedegaard (23) studied the properties of recycled aggregate concretes as affected by chemical admixtures in original concretes. They concluded that as long asplasticizing, air entraining and retarding admixtures are used in quantities not exceedingmanufacturers’ recommended dosages, the presence of such admixtures in recycled aggregates has no significant effect on slump, air content, or setting time of freshrecycled aggregate concrete, or on compressive strength of hardened recycled aggregateconcrete. Apparently, such admixtures should not be considered as contaminants inspecifications for recycled aggregate. Effects of chloride-containing accelerators are discussed in Section 7.7.5.

It remains to be studied how the lack of air entrainment in original concretes may affect the frost resistance of recycled aggregate concretes.

Although no studies have been made, it is not believed that the presence- of common mineral admixtures such as agricultural lime, pulverized fuel ash or condensed silicafume in original concretes will have any deleterious effects on recycled aggregateconcretes.

7.7.7 Soil and filler materials

Demolished concrete is frequently contaminated by organic soil or clay. Clay lumps areparticularly difficult to remove once they are incorporated in the material, but also clayminerals as such can be deleterious. There are no reasons to believe that recycledaggregates which are contaminated by soil should behave any differently in recycledaggregate concrete than ordinary aggregates which are similarly contaminated wouldbehave in conventional concrete.

Therefore, the usual requirements to cleanness, which form part of standard


specifications for concrete aggregates in most countries, can also be applied to recycledaggregates. Such requirements include maximum allowable limits on contents of organicimpurities, clay lumps, coal and lignite, and material finer than the ASTM No. 200 (0.075micron) sieve.

On a large recycling project in Belgium, Morlion et al. (135t) report that the quantity of fine material below the 75µm sieve was successfully reduced to 0.3% of the totalweight of aggregate. This was done by means of water sprinklers which were mountedover the belt conveyors and sieves. When necessary, the material was passed severaltimes over the sieves. In some cases the length of the loop over the conveyors waschanged.

7.7.8 Metals

Small amounts of reinforcing steel or bits of wire in recycled aggregates may causestaining or surface damage due to rusting when close to the surface of recycled aggregateconcrete, particularly if chlorides are present. Pieces of zinc and aluminium fromflashings, frames and conduits might cause problems due to release of hydrogen in freshconcretes, or they may give rise to cracking due to internal expansions.

However, it is unlikely that significant quantities of steel or other metals would remainin recycled aggregate. Steel can be readily removed by magnetic separation, and this willusually be done because of possible damage to crushers which are used to process the oldconcrete. The salvage value of most other metals is so high that flashings, frames,conduits, plumbing components and fixtures usually will be removed before the crushingof building rubble. As most metals are ductile materials, they will probably not befragmented in the crushers and larger pieces of metal will therefore be screened out at anearly stage of the processing procedure.

7.7.9 Glass

Plate glass from windows may contaminate demolished concrete, but no figures areavailable as to the levels that might be expected, or can be tolerated in such debris. Sincethe density of glass is similar to that of concrete or aggregates, separation would be verydifficult.

Plate glass could be a potentially dangerous contaminant because it can take part in alkali-silica reactions. Such glass is reactive because it is a non-crystalline metastable silica; in addition, the usual presence of abundant alkali in such glass could lead todeleterious alkali-silica reactions even if low-alkali cements were used.

7.7.10 Fragmented brickwork and lightweight concrete

When recycled aggregate concrete is contaminated by less than 5 weight per cent offragmented brick rubble or lightweight concrete, changes in mechanical properties ofrecycled aggregate concretes are probably insignificant. However, from the point of view


of durability the situation may be different. A serious problem with certain types of crushed bricks, more specifically refractory

bricks with a high content of periclase, MgO, has been reported in ENR (25). The problem involved ready-mixed concrete from six plants, provided to more than 100 objects in the San Francisco Bay area in California. The plants used aggregate from a 35000 ton pile of slag on which 4 tons of discarded refractory bricks had accidentally beendumped. Damage amounting to 25 000 US dollars or more was suffered by each of 20projects although the refractory bricks were present in a concentration as low as 0. 01%.The refractory brick fragments expanded when the periclase particles slaked, causing‘pop-outs’ in the concrete ranging up to 35 cm in diameter and 5 cm deep.

This may be an unusual case, which probably could not have been avoided, no matter how stringent specifications had been imposed. Rather, it stresses the need for rigorousplant supervision when recycled aggregates are produced. It is not difficult to envisionthat similar problems may be encountered if recycled aggregates were used containingunslaked lime (CaO) or brick rubble susceptible to frost damage.

The density of cement mortar and therefore recycled aggregate, is seldom below 2000 kg/m3, and the density of common bricks is seldom above 1900 kg/m3. Thus, it should be possible to separate most brick rubble, lightweight concrete, and other potentiallydeleterious particles from recycled concrete aggregate in a heavy medium at a density ofapproximately 1950 kg/m3, such as is suggested in the Japanese Proposed Standard for the ‘Use of recycled aggregate and recycled aggregate concrete’ (6).

It is suggested that standard specifications on recycled aggregate should include maximum limits on contents of brick rubble and fragmented lightweight concrete below1950 kg/m3, similar to the maximum limits on other potentially deleterious particles below 2400 kg/m3 which are common in standard specifications for conventional aggregate to be used in the production of concrete which will be exposed to severe ormoderately severe weather (see for example ASTM C33).

Aggregates which are produced from crushed concrete which contains more than 5weight per cent of fragmented bricks or other rubble is not considered recycled concreteaggregate in the context of this report. So-called brick rubble aggregates, aggregatesproduced from sand lime bricks, and mixed concrete and brick rubble aggregates aretreated separately in another RILEM TC–37DRC state-of-the-art report (53) also published in this book.

7.7.11 Parcticles damaged by weathering or fire

Recycled aggregates may be produced from original concrete which is so severelydamaged by alkali- or sulfate reactions, frost or other weathering agents, fire or other deleterious physical or chemical agents, that the resulting aggregate is unsuitable forproduction of recycled aggregate concrete from the point of view of mechanicalproperties. Such mechanical defects may show up in standard tests for soft and friableparticles, in the Los Angeles abrasion test, or in the sulfate soundness test. However, nopractical experience or experimental results are available, and it is recommended thatresearch should be carried out to clarify possible unfavourable effects on recycled


concrete properties. In principle, the method of detecting such mechanically weakparticles in recycled aggregate would be no different from the detection of othermechanically soft or weak particles in natural aggregates.

It is an entirely different question whether the same physical or chemical mechanisms which may have destroyed an original concrete, such as alkali-silica reactions, will continue to destroy a recycled aggregate concrete due to introduction of some of thephysically or chemically unsound aggregate particles from the original concrete in therecycled aggregate concrete. Such problems are dealt with in Sections 7.7.12 and 7.7.13.

7.7.12 Particles susceptible to frost damage

Mechanically strong, but physically or chemically unsound aggregate particles whichmay not have caused any problems in an original concrete, for example because of mildexposure, could be introduced into recycled aggregate concrete through the recycledaggregates. This might give rise to problems if the new concrete were to be severelyexposed. In particular, it is problems concerning frost damage and alkali silica reactionswhich attract attention.

When original concretes were made with chert sand and gravel which was highlysusceptible to frost damage, Buck (26) found that the freeze-thaw resistance of corresponding recycled aggregate concretes was greatly improved. Table 7.8 shows an improvement from a durability factor of 3 according to ASTM C666 after 300 cycles to afactor of 23. It is usually considered that a durability factor below 40 means that theconcrete is unsatisfactory with respect to frost resistance. Forty to 60 is the range forconcrete with doubtful performance, and above 60 the concrete is probably satisfactory.Frequently durability factors above 80 are required in specifications. Thus, it may beconcluded that although recycling improved freeze-thaw resistance, it by no means rendered the recycled aggregate concrete frost resistant.

Yrjanson (7g) and Nelson (7h) report on laboratory research and field performance which indicate that the crushing of a potentially ‘D’ cracking aggregate to a smaller size substantially reduces the ‘D’ cracking potential of concrete made with the aggregates. With this in mind, the Minnesota Department of Transportation specified crushing of theoriginal concrete to a 19 mm maximum size on a recycling project.

Thus, it may be concluded that coarse recycled aggregates do benefit from the crushing

Table 7.8 Frost resistance of recycled aggregate concrete, Buck (26).

Type of Aggregate Used No. of Cycles Durability Factor

New chert gravel and sand (I) 300 3

Coarse recycled aggregate and natural sand (I) 300 23

Coarse and fine recycled aggregate (I) 300 28


operation. This is probably due to the elimination of porous and weak particles in thecrusher. In addition there is a dilution effect, as a relatively smaller volume percentage ofunsound particles from the original concrete are introduced into the recycled aggregateconcrete.

Both crushing and dilution should improve frost resistance of recycled aggregatesbeyond that of original aggregates. However, such beneficiation may not in itself besufficient to ensure frost resistance of recycled aggregates, as will be seen from Section 9.2 on frost resistance of hardened concrete. It is evident that more research on frost resistance of recycled aggregates is required to clarify matters.

See also Section 9.2 on frost resistance of recycled aggregate concrete in general.

7.7.13 Alkali-reactive aggregate particles

No experimental data are available which make it possible to evaluate the effect onrecycled aggregate concrete of potentially alkali reactive particles in recycled aggregates.The problem of alkali reactions is probably even more difficult to deal with than theproblem of frost resistance because both crushing and dilution may bring theconcentration and gradation of reactive particles in the recycled concrete closer to thepessimum content than in the original concrete and thus create more unfavourableconditions in the recycled aggregate concrete than in the original concrete. However, this has never been shown experimentally and in practice. More research is required to clarifythese matters.

See also Section 9.4 on alkali-silica reactions in recycled aggregate concrete.

7.7.14 Industrial chemicals and radioactive substances

Recycled aggregate concrete should not be contaminated by malodorous, toxic, orradioactive substances in recycled aggregates. Neither should recycled aggregates containoil- or water-soluble chemicals to such an extent that normal setting, hardening, orstrength development of recycled aggregate concrete is reduced or concrete durability isendangered.

Standard specifications for concrete aggregates normally take into account relatively few contaminants, commonly found in natural aggregates such as humus, chlorides, andsulfates. However, when demolished concrete is taken from chemical plants or otherindustrial plants where chemicals have been employed, recycled aggregates may becontaminated by a wide variety of substances which, if soluble, could affect theproperties of recycled aggregate concrete (27), or which could pose health hazards. No standard specifications could possibly include maximum limits on contamination ofrecycled aggregates by the wide range of chemicals which is used in modern industry.

In most cases it will probably be found that only surface layers of old concrete are affected, so that no more than traces of potentially harmful contaminants will be found inthe bulk of recycled aggregate concrete. Under other circumstances potentially harmfulcontaminants may not be water-soluble, which in reality makes them harmless in


recycled aggregate concrete. Even so, original concrete from any plant where chemicals or radioactive material have

been used should be considered suspect until proved innocuous.

7.7.15 High alumina cement

Recycled aggregates from structures where high alumina cement has been used in lieu ofPortland cement should probably not be used for production of recycled aggregateconcrete for structural purposes.

7.8 Repeated recycling of recycled aggregate concrete

Fergus (7e) investigated a case where aggregates were produced from a recycled aggregate concrete which had experienced 300 cycles in a freeze-thaw chamber, commonly used for durability tests. In other words, Fergus was concerned with a‘repeatedly recycled aggregate concrete’. Test results for both aggregate properties andconcrete properties proved such repeatedly recycled aggregate concrete to be bothdurable and of good quality in all respects.

Therefore, one may project that existing concrete structures, in addition to providing an aggregate source for the immediate future, may continue to generate an adequate supplyof aggregates for concrete construction in the more distant future after once beingrecycled.

7.9 Recycled concrete aggregates for other purposes than production of new

concrete

Once the concrete has been crushed, sieved and if necessary decontaminated it can findapplications as 1) general bulk fill, 2) fill in drainage projects, 3) sub-base material in road construction or 4) aggregate for new concrete. Until now we have only discussedrecycled aggregate for production of new concrete. In the following we shall consider theuse of crushed concrete for other purposes.

Building Research Establishment in the UK (138) has outlined the choice and use of materials for general bulk fill. Ideally a material for use as fill should be a hard granularmaterial with a fairly large particle size that consolidates easily and remains free draining.It should also be chemically inert and not subject to significant changes in dimensionswith changing moisture.

Clean graded crushed concrete meets these requirements admirably and is frequentlyused in the construction of foundations for houses, garages and other light buildings.However, crushed concrete with high sulphate or timber contents should be avoided forcritical applications. Inferior material can be used for less demanding applications such aslandscaping, levelling or the construction of acoustic barriers, provided there is no risk of


contamination of ground water, Mulheron (135h). Requirements for material used in road construction in the UK are set out in the

‘Specifications for highway works’, Department of Transport (139). At present the only recycled material included in this specification is crushed concrete which is allowed asgranular fill for a wide range of applications such as:

1) Drainage works, permeable backing to earth retaining structures, material for filter drains, and backfill to pipebags and above pipe surround material.

2) Earth works, such as fill to structures, drainage layers to reinforced concrete structures, bedding material for buried steel structures, and unbound or cement-lime bound capping layers.

3) Road base and sub-base layers, as Type 1 or 2 granular sub-base material.

Research results and practical experience have shown that given the correct grading andother properties, crushed concrete can be successfully used for the production of bothcement bound materials and lean concrete. The current UK specifications for cementbound materials includes four categories of material with minimum strength at 7 daysranging from 4MPa to 15 MPa. Of these materials only CBM1 and CBM2 can bemanufactured with recycled aggregates since the specifications for CBM3, CBM4, andall categories of wet lean concrete require the aggregate to be either a naturally occurringmaterial complying with BS 882 (1983) or crushed air-cooled blast furnace slag complying with BS 1047 (1983). This represents a change from previous editions of thespecifications which required aggregates for cement bound materials to be a washed orprocessed granular material. This included the use of recycled materials. It is not knownwhat has prompted this change.

8. Mechanical properties of recycled aggregate

concrete

8.1 Compressive strength and rate of strength development

Before attempting to review mechanical properties and durability of recycled aggregateconcrete it may be appropriate to mention that Japanese researchers (135bb), (135e), (135z), (135y) and (135u) agree that up to 30 percent of natural aggregate can be replaced by recycled concrete aggregate without significantly changing the properties of newconcretes as compared to corresponding control concretes made with natural aggregates.If this is so, it may be the simplest and most economical way to get recycled concretesinto general use.


8.1.1 Recycled aggregate concrete made with coarse recycled aggregate and natural

sand

On the basis of his review of earlier research, Nixon (5) concluded that the compressive strength of recycled aggregate concrete is somewhat lower (in some cases up to 20%lower, but usually less) compared with the strength of .control mixes of conventionalconcrete.

Later, B.C.S.J. in Japan (12) arrived at the same conclusion on the basis of experimental results which showed compressive strength of recycled aggregate concreteto be between 14% and 32% lower than that of conventional concrete. These experimentsand their results are described in more detail by Kakizaki et al. (135f) and by Kawamura and Torii (135g).

Fig. 8.1 Compressive strengths of recycled aggregate concretes as a function of the strength of original concretes, from (28).

Wesche and Schulz (28) compiled earlier results obtained by Buck (26), Malhotra (29), Schulz (30, 31), and Frondistou-Yannas (32). Apparent correlation was found betweencompressive strengths of conventional and recycled aggregate concretes. It will be seenfrom Figure 8.1 that recycled concretes consistently had 10% lower compressive strengththan control concretes made with conventional aggregate. Later Ravindrarajah and Tam(65) found recycled aggregate concretes to have between 8% percent and 24% lower compressive strength than corresponding concretes made with conventional aggregates.Gerardu and Hendriks (70) report the compressive strength of recycled aggregate


concretes made with coarse recycled aggregate and natural sand to be 95% or more of thestrength of conventional concretes. Kashino and Takahashi (135e) found a 10% reduction in strength for some mixes while there was no strength reduction for other mixes.However, Kakizaki et al. (135f) found a strength reduction of 14% for NS-RC concretes and 32% for Rs-Rc concretes as compared to control concretes made with naturalaggregates. Similar figures from Ikeda et al., (135n) were 15% and 40%. Yamato et al.(135y) found that recycled aggregate concrete with both fine and coarse recycledaggregate had about 20% lower strength than comparable control concretes made withnatural amphibole aggregate.

Similar results were found by Nishibayashi and Yamura (135p). Such results have given recycled aggregate concrete the reputation of being somewhat inferior toconventional concrete, and perhaps unfit for production of structural concrete. However,this is not always so.

Hansen and Narud (13) prepared one high-strength (H: w/c=0.40), one medium-strength (M: w/c=0.70), and one low-strength (L: w/c=1.20) concrete which were curedin water at 40°C and tested for compressive strength after 38 days. The three concretes were passed through a laboratory jaw crusher. The crusher products were screened andrecombined into three qualities of coarse recycled aggregate, H, M, and L, ofapproximately the same grading as the original conventional aggregate. High-strength, medium-strength, and low-strength concretes were then prepared with the same mixproportions as the three original concretes, but with all nine possible combinations ofaggregates. All nine recycled aggregate concretes were cured in water at 40°C and tested for compressive strength after 38 days. In these experiments all recycled aggregateconcretes were made with coarse recycled aggregate and natural sand.

It will be seen from the results which are presented in Table 8.1a that in three independent series of experiments, recycled aggregate concretes made with coarserecycled aggregate and natural sand obtained approximately the same strength and in

Table 8.1 a Compressive strength in MPa of original and recycled aggregate concrete made with natural sand and coarse recycled aggregate after 38 days of accelerated curing. Symbols H, M, and L indicate original high-strength, medium. strength, and low-strength concretes made with natural gravel. Symbol H/M indicates a high-strength, recycled concrete made with coarse recycled aggregate produced from medium-strength concrete, etc. From (13).

Series Compressive Strength of Original and Recycled Aggregate Concretes, in MPa

H H/H H/M H/L M M/H M/M M/L L L/H L/M L/L

1 56.4 61.2 49.3 34.6 34.4 35.1 33.0 26.9 13.8 14.8 14.5 13.4

2 61.2 60.7 36.0 36.2 14.5 13.6

3 58.5 60.6 33.2 36.0 15.0 12.8


some cases higher strength than corresponding control concretes which were made withthe same mix proportions, but entirely with natural aggregates (H/H versus H, M/Mversus M, and L/L versus L in Table 8.1a). Similar results were obtained by Malier and Mazars (84). However, it will be seen from Table 8.1a that when high-strength concrete (H) was produced from low-strength recycled coarse aggregate (L) and natural sand, the compressive strength of the recycled concrete mix (H/L) was 39% lower than thecompressive strength of the recycled concrete mix (H/H) which was produced with high-strength coarse recycled aggregate and natural sand.

The fact that concrete made with recycled coarse aggregate can in fact have higher compressive strength than identical control concretes made with the same water-cement.

ratio was confirmed by Yoda et al. (135b) who found an increase of 8.5% for a recycledconcrete above a similar corresponding concrete made with natural aggregate. Kawai et al. (135q) also found that it was possible to produce recycled aggregate concrete, withcoarse recycled aggregate and natural sand with the same compressive strength ascomparable original concrete, made with natural aggregates and the same water-cement ratio.

Hansen and Narud (13) concluded that the compressive strength of recycled aggregate concrete depends on the strength of the original concrete, and that it is largely controlledby a combination of the water-cement ratio of the original concrete and the water-cement ratio of the recycled concrete when other factors are essentially identical. If the water-cement ratio of the original concrete is the same as or lower than that of the recycledaggregate concrete, then the strength of the recycled aggregate concrete can be as good asor higher than the strength of the original concrete.

Hansen and Narud (13) also found it quite feasible to make recycled aggregateconcrete with a water-cement ratio of 0.40 having around 34 MPa compressive strengthafter 14 days of standard curing and after 38 days of accelerated curing using recycled

Table 8.1 b Compressive strength in MPa of original and recycled concretes made with both coarse and fine recycled aggregate.

Compressive strength of original and recycled aggregate concretes in MPa

Series Curing Time


4 14 days in water at 20 C

49.5 37.3 33.6 33.7 23.9 16.1 17.2 19.1 9.7 5.5 4.5 6.8

5 204 days in water at 20 C

56.1 51.4 45.7 38.9 38.9 24.9 25.8 24.3 17.0 9.3 6.8 10.3


aggregate from an original concrete with a water-cement ratio of 1.20 having a compressive strength of approximately 14 MPa at crushing, see Table 8.1a. This confirmed earlier results by Buck (26) which showed that it is possible to make recycledaggregate concretes which are stronger than corresponding original concretes from whichthe recycled aggregates are derived.

It will be seen from Table 8.2 that B.S.C.J. (12) obtained somewhat similar results using coarse recycled aggregate and natural sand.

Rasheeduzzafar and Khan (52) attempted to produce high-strength concrete (40 MPa or higher) from medium-strength (23 MPa) coarse recycled aggregate. They found thestrength of recycled aggregate concretes to be lower than that of corresponding controlconcretes made with the same water-cement ratio but with natural aggregate, when the strength of such control concretes exceeded the strength of the original concrete (23MPa). For water-cement ratios below 0.40, no increase in compressive strength ofrecycled aggregate concretes was observed with further decreasing water-cement ratios. When recycled aggregate concretes were produced with water-cement ratios giving compressive strengths at or below 23 MPa, there was no difference in strength betweensuch recycled concretes and corresponding control concretes.

These observations are explained by Rasheeduzzafar and Khan (52) on the basis of photomicrographs of the fracture patterns of recycled aggregate concrete. When thestrength of control concretes made with conventional aggregate was above the strength ofthe old concrete, the strength of the new mortar and the new mortar-aggregate bond in

corresponding recycled aggregate concretes is higher than the strength of the recycledaggregate or the bond between the old mortar and the original aggregate, thereby makingthe recycled aggregate the weaker and, therefore, the strength-controlling links of the composite system. On the other hand, when the strength of control concretes made withconventional aggregate was below the strength of the old concrete, the inferior quality ofthe new mortar in corresponding recycled aggregate concretes or its bond with the

Table 8.2 Compressive strength of original concretes and recycled aggregate concretes made from the same original concretes using recycled coarse aggregate and various proportions of recycled fine aggregate and natural sand, from (12).

w/c Compressive Strength of Concrete (MPa)

Natural coarse and fine

aggregate (original concrete)

Recycled coarse

aggregate and 100% natural

sand

Recycled coarse aggregate, 50%

recycled fine aggregate, and 50%

natural sand

Recycled coarse aggregate and 100% recycled fine aggregate

0.45 37.5 37.0 34.0 30.0

0.55 28.9 28.5 25.0 21.5

0.68 22.0 21.0 17.5 13.0


recycled aggregate form the weaker link, and hence control the failure. On a smaller scale Karaa (93) studied the bond between mortar and recycled coarse

aggregate which he found to be ‘satisfactory’. Malhotra (47), Buck (46), and Ravindrarajah and Tam (65) found the strength

development with age to be similar for conventional and recycled aggregate concretemade with coarse recycled aggregate and natural sand.

8.1.2 Recycled aggregate concrete made with coarse and fine recycled aggregates

Hansen and Marga (135w) have repeated the experiments, which are reported in (13) and summarized in Section 8.1.1. The experiments were repeated with identically the same raw materials and original concretes; but this time all recycled concretes were producedwith both coarse and fine recycled aggregates. The results are presented in Table 8.1b.

Hansen and Marga found that based on equal water-cement ratios the use of both coarse and fine recycled aggregates on average reduced the compressive strength ofrecycled concretes by approximately 30% compared to control concretes made withnatural sand and gravel. Thus the use of fine recycled aggregate always has a detrimentaleffect on the compressive strength of recycled concretes.

Ravindrarajah, R.S. and Tam C.T. (135aa) found that the detrimental effect of usingcrushed concrete fines in recycled concrete can be mitigated by partial replacement of thecrushed concrete fines with natural sand or fly ash.

Rasheeduzzafar and Khan (52) found no significant difference in compressive strength between a recycled aggregate concrete made with recycled coarse aggregate and naturalsand and a corresponding recycled aggregate concrete made with both coarse and finerecycled aggregates. However, they stand alone with their findings which are in sharpcontrast to the results obtained by de Pauw (10), Morlion (135t), Bernier, Malier, and Mazars (84), and B.CS.J. (12).

It will be seen from Table 8.2 (from(12)) that the compressive strength of recycledaggregate concretes made with coarse recycled aggregates and a blend of 50% finerecycled aggregate and 50% natural sand was 10–20% lower than the strength of a corresponding recycled concrete made with coarse recycled aggregate and 100% naturalsand. When recycled aggregate concretes were made with coarse recycled aggregate and100% fine recycled aggregate, the compressive strength was 20–40% lower than the strength of corresponding recycled aggregate concrete made with coarse recycledaggregate and 100% natural sand. The other authors who are mentioned above foundsimilar results.

Gerardu and Hendriks (70) report the compressive strength of recycled aggregate concrete made with both coarse and fine recycled aggregates to be 85% of the strength ofconventional concrete, while that of recycled aggregate concrete made with coarserecycled aggregate and natural sand is 95 percent of the strength of conventional concreteor more.

In a personal communication to the author, Hendriks reported the results of another investigation where a concrete which was made with coarse and fine natural aggregatewith an aggregate density of 2600 kg/m3, a water-cement ratio of 0.47 and 320 kg/m3 of


cement had a 28 days compressive strength of 40 MPa. When identical concretes weremade with coarse and fine recycled aggregates having combined aggregate densities of2320 kg/m3 and 2050 kg/m3, the 28 days compressive strengths were reduced to 32 MPaand 27 MPa respectively.

Soshiroda (33) reports the results of other investigations made by B.C.S.J. (12) where various proportions of fine natural aggregate were replaced with fine recycled aggregatein recycled aggregates and where the effect on concrete compressive strength wasdetermined.

Fig. 8.2 Compressive strength of recycled aggregate concretes made with a water: cement ratio of 0.65 where various volume percentages of natural sand were replaced by fine recycled aggregate, from (33).

It will be seen from Figure 8.2 that one particular recycled aggregate concrete lost half its compressive strength when all natural sand in the mix was replaced by fine recycledaggregate. It will also be seen from Figure 8.2 that loss of strength is much more severewhen natural sand is replaced by fine recycled aggregate in the entire grading spectrum ofthe sand (lower curve in Figure 8.2) than when replacement takes place in the coarser fractions only (upper curve in Figure 8.2). In other words, it appears to be the fractionsfiner than 2 mm of recycled aggregate which bring about the largest strength reductionsof recycled aggregate concrete.

As fine recycled aggregate also has a tendency to reduce the frost resistance ofrecycled aggregate concrete and to give rise to other problems which have beenmentioned earlier, it is recommended to screen out and waste all material below 2 mm inrecycled aggregates or perhaps to avoid the use of fine recycled aggregate below 4–5 mm altogether.


McCarthy and MacCreery (67) report that the Michigan Department of Transportationhas limited the allowable amount of fine recycled concrete aggregate to 25% or 30% oftotal sand on Interstate Highway rehabilitation projects and plan completely to prohibitthe use of recycled fines on some future work. This is because tests have shown somerecycled aggregate concretes to have unsatisfactory strengths where a high proportion ofcrushed concrete was used in the concrete fines. No further details are reported.

8.1.3 Effect of dry mixing of aggregate

It is perhaps not surprising that Kasai et al. (51) found the fineness modulus of recycledaggregates to be reduced with increasing time of dry-mixing in the concrete mixer before cement and water was added (see Figure 8.3).

Fig. 8.3 Reduction of fineness modulus of coarse recycled aggregate as a function of dry mixing time, from (51).

It is more surprising that in the same investigation Kasai et al (51) found the compressive strength, tensile strength, and modulus of elasticity of recycled aggregate concretes, madewith recycled aggregates which had been dry-mixed prior to production of concrete, to be considerably higher than the strengths and modulus of elasticity of correspondingconcretes made with recycled aggregates which had not been dry-mixed prior to addition of water and cement (see Table 8.3).

In Table 8.3 results for concretes produced with dry-mixed aggregates are shown in percentage of results for concretes produced with recycled aggregates which had not beendry-mixed prior to addition of cement and water. Before dry-mixing, recycled aggregates were produced by the crushing to a grading between 5 mm and 25 mm of an original


concrete in an impact crusher. Kasai et al. (51) suggest that the effects observed after dry-mixing may be due to one

or more of the following reasons:

1. shape of coarse aggregates is improved by dry-mixing. 2. old mortar which is attached to the surface of recycled aggregate particles is removed

by dry-mixing. 3. fine particles of old cement which are liberated during dry-mixing of recycled

aggregates accelerate the hydration of fresh cement similar to a chemical nucleating agent.

See also Section 11.

8.2 Coefficient of variation of compressive strength of recycled aggregate concrete

B.C.S.J. (12) and CUR (11) found the coefficient of variation for compressive strength of recycled concrete in the laboratory not to be much different from that of conventionalconcrete when one and the same recycled aggregate was used throughout production.This was later confirmed by Hansen and Narud (13) and Coquillat (38).

This may well be so under controlled conditions in the laboratory, but in practice larger variations will probably be found because of difficulties in maintaining a constant freewater-cement ratio in recycled aggregate concretes which are produced with aggregatesof high water absorption capacity. Even when recycled aggregates are pre-soaked, larger strength variations will probably persist.

When recycled aggregate concretes are produced from original concretes of differentqualities, the coefficient of variation for compressive strength is much larger than when

Table 8.3 Effects of dry mixing of recycled aggregates prior to addition of cement and water, on strengths and modulus of elasticity of recycled aggregate concretes, from (51).

Dry Mixing

w/c Slump (cm)

Compressive Strength in % of

controls

Tensile Strength in %

28 Day

Modulus Elasticity in %

28 Day

3 Day

7 Day

28 Day

No 0.5 6.5 100 100 100 100 100

Yes 0.5 6.5 177 130 111 136 96

No 0.6 18.1 100 100 100 100 100

Yes 0.6 19.1 162 156 135 123 108


the same recycled aggregate is used in all batches. Typical results illustrating this point are presented by de Pauw (34) in Table 8.4.

De Pauw (34) found variations in 28–day compressive strength from 32.0 MPa to 49.1 MPa when concretes of identical mix proportions were produced with recycledaggregates from twelve 15–year old concretes of widely different quality. The meancompressive strength of all recycled concretes in Table 8.4 is 41 MPa, and the standard deviation is 5 MPa, giving a coefficient of variation of 12%.

High coefficients of variation must be expected by ready-mixed plants attempting to produce concrete with recycled aggregate from recycling plants which use mixedconcrete rubble as raw materials in an indiscriminate way, whether from old buildings,pavements, sidewalks, driveways, curbs, or gutters.

As an example, let us assume that a ready-mixed concrete plant were to produce and test 12 batches of medium-strength concrete from recycled aggregate of unknown origin. If by accident six batches were of type M/H (i.e. medium-strength concrete produced with high-strength recycled aggregate) in Table 8.1a and the rest were of type M/L (i.e. medium-strength concrete produced with low-strength recycled aggregate), then the coefficient of variation would be approximately 14% based on the results in Table 8.1a. If

Table 8.4Compressive strengths of one and the same recycled concrete produced with recycled aggregate from old concretes of different quality, from (34).

Water-Cement Ratio

of Original Concrete

Original Concrete when crushed after 15

years. Compressive Strength MPa

Water-Cement Ratio of recycled aggregate concrete

Recycled Aggregate Concrete at 28 days.

Compressive Strength MPa

0.53 75.1 0.57 49.1

0.67 51.5 0.57 40.3

0.65 59.3 0.57 43.1

0.80 38.9 0.57 38.0

0.50 73.1 0.57 47.4

0.59 62.4 0.57 43.3

0.65 67.9 0.57 41.8

0.81 42.1 0.57 32.0

0.50 61.9 0.57 39.8

0.50 84.8 0.57 36.8

0.53 73.4 0.57 44.0

0.50 64.1 0.57 35.2


the exercise was repeated for concretes of type H/H (i.e. high-strength concrete produced with high-strength recycled aggregate) and H/L (i.e. high-strength concrete produced with low-strength recycled aggregate), the coefficient of variation would be 25% for the 12 test results presented in Table 8.1a.

Hendriks (64) reports variations in compressive strength between 41 MPa and 50.6MPa for concretes of identical mix proportions, but produced with recycled concreteaggregates manufactured by various Dutch producers. Also coefficients of variationaround 25% were found.

Large standard deviations and correspondingly high coefficients of variation always make it expensive in terms of cement consumption to meet requirements to characteristicstrength in modern concrete codes and specifications; and compliance criteria for highstrength concrete cannot be met at all if the coefficient of variation is above a certainlevel. For example, according to the Danish concrete code (116) it would require production of concrete with a mean strength of more than 60 MPa in order to meetcompliance criteria for a characteristic compressive strength of 25 MPa if the coefficientof variation was 25% and four specimens were tested in each series. This would make italmost impossible to produce structural concrete from mixed demolition rubble inDenmark.

8.3 Modulus of elasticity, damping capacity and stress-strain relationship

Due to the large amount of old mortar with a comparatively low modulus of elasticitywhich is attached to original aggregate particles in recycled aggregates, the modulus ofelasticity of recycled aggregate concretes is always lower than that of correspondingcontrol concretes made with conventional aggregates.

Frondistou-Yannas (32) found up to 33% lower modulus of elasticity for recycledaggregate concretes made with coarse recycled aggregate and natural sand compared tothe modulus of elasticity of corresponding control concretes made with conventionalaggregates.

Kakizaki et al. (135f) found the elastic modulus of recycled aggregate concretes to be 25% to 40% lower than for regular concrete, depending on the respective qualities of theoriginal concrete and the recycled concrete. A minimum value for the modulus ofelasticity of recycled aggregate concrete Ec to be used in the design of structures made from such concrete can be calculated from Equation 8.1 when the compressive strengthof the recycled aggregate concrete fc and the density a of the concrete is known:

Gerardu and Hendriks (70) report a maximum of 15% lower modulus of elasticity ofrecycled aggregate concretes made with coarse recycled aggregate and natural sandcompared with corresponding conventional concretes. If the sand is also replaced withcrushed concrete fines, a maximum of 40% reduction in modulus of elasticity was

(8.1)


observed. Ravindrarajah and Tam (96) found that use of fine recycled concrete aggregate instead

of natural sand reduced the 28-days static modulus of ordinary concrete by about 15%. Ravindrarajah, Loo and Tam (107) later expanded their conclusions as follows:

Modulus of elasticity of recycled aggregate concrete is lower than that of naturalaggregate concrete and the difference increases with strength. For a medium strengthwater cured concrete, the reductions in the static and dynamic modulus of elasticity areabout 25% while they are about 35% for air cured concrete. Recycled fine aggregatereduces the modulus of elasticity by a similar amount as recycled coarse aggregate.

Wesche and Schulz (28) found up to 19% lower modulus of elasticity for recycledaggregate concretes made with the same water-cement ratio and coarse recycled aggregates containing two different natural aggregates, compared to the modulus ofelasticity of conventional control concretes.

Rasheeduzzafar and Khan (52) found up to 18% lower static modulus of elasticity inrecycled aggregate concretes made with coarse recycled aggregate and natural sandcompared to the modulus of elasticity of corresponding control concretes made withconventional aggregates.

Fig. 8.4 Modulus of elasticity as a function of water:cement ratio of original and recycled aggregate concretes, from (16).

Zagurskij and Zhadanovskij (83) and B.S.C.J. (12) report between 10% and 30% lower modulus of elasticity of recycled aggregate concretes made with coarse recycledaggregate and natural sand, compared to the modulus of elasticity of correspondingoriginal control concretes. When recycled aggregate concretes were made with coarserecycled aggregate and 100% fine recycled aggregate, the modulus of elasticity was 25%


to 40% lower compared to the modulus of elasticity of corresponding original controlconcretes. The Japanese results are presented in Figure 8.4. Hansen and Boegh (35) prepared one high-strength (H: w/c=0.40), one medium-strength (M: w/c=0.70), and one low-strength concrete (L: w/c=1.20) which were cured in waterat 40°C and tested for modulus of elasticity after 47 days.

The three concretes were passed through a laboratory jaw crusher. The crusher products were screened and recombined into three qualities of coarse recycled aggregate,H, M, and L, all of the same grading as the original aggregate. High-strength, medium-strength, and low-strength concretes were then prepared with the same mix proportions as the three original concretes, but with all nine possible combinations of coarse recycledaggregates. All nine concretes were cured in water at 40°C and tested for modulus of elasticity after 47 days of curing in water at 40°C.

It will be seen from the results in Table 8.5 that both dynamic and static modulus of elasticity are from 14% to 28% lower for recycled aggregate concretes than for controlconcretes made with the same conventional aggregate. However, it is evident thatdifferences in modulus of elasticity would have been much larger if the high-strength concrete (H) had been made with a stiffer aggregate (such as quartz) and the low-strength concrete (L) had been made with a softer aggregate (such as soft limestone) than thenatural aggregate which was actually used in the experiment. In one particular case

Table 8.5 Static and dynamic modulus of elasticity of original and recycled aggregate concretes after 47 days of accelerated curing. Symbols H, M, and L indicate original high-strength, medium-strength, and low-strength concretes made with natural gravel. Symbol H/M indicates a high-strength, recycled concrete made with coarse aggregate produced from mediumstrength concrete, etc., from (35).

Type Modulus of Elasticity of Original and Recycled Aggregate Concretes, in GPa


Dynamic Modulus

46.7 40.3 37.6 39.1 42.3 36.4 35.8 35.0 36.6 31.0 28.8 28.0

% Reduction below controls

0 13.7 19.5 16.3 0 13.9 15.4 17.2 0 15.3 21.3 23.4

Static Modulus

43.4 37.0 36.3 34.8 38.5 33.0 32.0 30.0 30.8 27.5 22.3 22.6

% Reduction below controls

0 14.7 16.4 19.8 0 14.7 16.9 22.1 0 10.7 27.6 26.6


Hansen and Boegh found the modulus of elasticity of a recycled aggregate concretewhich was made with recycled aggregate that consisted of a low quality crushed-mortar to be 45% lower than the modulus of elasticity of a corresponding control concrete madewith conventional aggregates.

Coquillat (38) found 28% lower dynamic modulus of elasticity for a recycled aggregate concrete made with both fine and coarse recycled aggregate compared with acorresponding conventional concrete.

In essence, above-mentioned results are confirmed by Ravindrarajah and Tam (65) and by Karaa (93). In addition, Ravindrarajah and Tam (65) found the relationship between compressive strength and modulus of elasticity for recycled aggregate concrete to bedifferent from that for conventional concrete proposed by various authorities such asCEB, FIP, and the British concrete code, CP-110.

It may be concluded that the low modulus of elasticity of recycled concrete aggregates results in a recycled aggregate concrete with a modulus of elasticity comparable to that ofconventional lightweight aggregate concrete.

Nishibayashi and Yamura (135) found an almost straight line relationship betweencompressive strength and modulus of elasticity of recycled aggregate concrete. They alsofound that the modulus of elasticity of recycled aggregate concretes made with coarserecycled aggregate and natural sand was 65–85% that of normal control concrete.

Henrichsen and Jensen (120) found that the stress-strain relationship for recycled aggregate concrete is similar in shape to that of ordinary concrete. Thus structures madefrom recycled aggregate concrete can be designed according to the theory of plasticityjust like structures made from ordinary concrete.

Schulz (135) has demonstrated that a linear relationships exists between particle density of recycled concrete aggregates and modulus elasticity of recycled aggregateconcrete.

Bernier, Malier, and Mazars (84) found the ultimate strain at compressive failure to be 2.6×10− 3 for recycled aggregate concrete made with both coarse and fine recycledaggregate while it was 1.7×10− 3 both for an original control concrete and for a recycled aggregate concrete made with coarse recycled aggregate and natural sand.

Ravindrarajah and Tam (65) found the damping capacity expressed in terms of thelogarithmic deerement to be between 16% and 23% higher for recycled aggregateconcrete than for conventional control concretes made with virgin aggregates. Thedamping capacity for both types of concrete increased with the decrease in compressivestrength.

8.4 Creep

Wesche and Schulz (28) found creep of two recycled aggregate concretes, made with coarse recycled aggregate and natural sand, to be 50% higher than creep of correspondingcontrol concretes made with conventional natural and crushed aggregate, see Figure 8.5. This is not surprising, considering the fact that the recycled aggregate concretescontained 50% more mortar than control mixes. Creep of concrete is proportional to the


content of cement paste or mortar in concretes. Ravindrarajah and Tam (65) found creep of recycled aggregate concretes made with

coarse recycled aggregate and natural sand to be 30–60% higher than creep of conventional control concrete.

CUR (11) found creep of recycled aggregate concretes to be 25% respectively 45%higher than for comparable natural aggregate concretes with compressive strengths ofapproximately 50 MPa and 25 MPa.

Fig. 8.5 Total deformation of original and recycled concretes (per MPa) versus time under load, from (28).

Gerardu and Hendriks (70) state that in the laboratory, creep of recycled aggregate concrete may be up to 40% larger than for conventional concrete made with virginaggregates.

Kasai (66) reports that Nishibayashi found creep of recycled aggregate concrete made with coarse recycled concrete aggregate and natural sand to be 20–30% higher than for conventional control concretes.

Nishibayashi and Yamura (135p) later reported that the creep per unit of stress (specific creep) of recycled aggregate concrete was greater than that of conventionalconcrete. The differences developed over a period of 250–300 days after loading. Then the rate of increase in creep strain for both concretes gradually became smaller with afurther increase in time. Creep strain increased considerably with an increase in thewater-cement ratio, but the difference in creep between recycled aggregate concrete andordinary concrete remained almost constant at any water-cement ratio and at any sustained load level. Thus, it is not expected that creep of recycled concrete shall giverise to any problems, provided its increased magnitude is taken into account.

It can be expected that the creep of recycled concrete could be much larger if such concretes were produced with both fine and coarse recycled aggregate, but more research


is needed to confirm this expectation.

8.5 Drying shrinkage

According to Figure 8.6, Hasaba et al. (16) found drying shrinkage of recycled aggregate concrete (Ns-Rc) made with a cement content of 300 kg/m3, with coarse recycled aggregate (Rc), and with natural sand (Ns) to be 50% larger than drying shrinkage oforiginal concrete (Ns-Ng) made with natural sand (Ns) and natural coarse aggregate (Ng).When both coarse (Rc) and fine (Rs) recycled aggregates were used, drying shrinkage ofrecycled aggregate concrete (Rs-Rc) was 70–80% larger than that of a control concrete(Ns-Ng) made with natural fine and coarse aggregate.

These results are confirmed by Fujii (135cc), Fujii also found that shrinkage ofrecycled aggregate concrete is reduced by secondary crushing of the aggregate.

Coquillat (38) found 73% higher drying shrinkage for a recycled aggregate concretemade with both fine and coarse recycled aggregate than for a corresponding conventionalconcrete.

Ravindrarajah, Loo and Tam (107) report drying shrinkage of recycled aggregateconcretes at 90 days to be twice that of the natural aggregate concrete. The same authors

Fig. 8.6 Drying shrinkage of original and recycled aggregate concretes as a function of time of drying, from (16).

report that recycled fine aggregate reduces the modulus of elasticity and increases dryingshrinkage by an amount similar to that of recycled coarse aggregate. Nishibayashi andYamura (135p) and Morlion (135t) as well as Puckman and Henrichsen (135aa) confirmed that drying shrinkage of recycled concrete is much larger than that of ordinaryconcrete.


Wesche and Schulz (28) found drying shrinkage of two recycled aggregate concretesmade with coarse recycled aggregate and natural sand to be 40% larger than dryingshrinkage of control concretes made with conventional aggregates. This is not surprisingconsidering that the recycled aggregate concretes contained 50% more mortar thancontrols, and that drying shrinkage increases with the contents of cement paste or mortarin a concrete.

Zagurskij and Zhadanovskij (83) report 20% to 30% higher shrinkage for recycled aggregate concrete made with coarse recycled aggregate and natural sand compared tocorresponding control concretes made with conventional aggregates.

CUR (11) found the shrinkage of recycled aggregate concrete to be 35 respectively 55% higher than for comparable natural aggregate concrete with compressive strength ofapproximately 25 and 50 MPa.

Similar experiments which were carried out by Ravindrarajah and Tam (65) resulted in shrinkage values between 14% and 95% higher for recycled aggregate concretes than forconventional concretes. At the end of 70 days of drying, the difference between originaland recycled aggregate concretes was greater for higher-grade concretes than for lower-grade concretes.

Karaa (93) found shrinkage after 90 days to be approximately 50% higher for recycled aggregate concrete made with both fine and coarse recycled concrete aggregate than forcorresponding concrete made with natural sand and gravel. Karaa (93) also compared the rates of shrinkage and swelling of normal and recycled concrete and found that the rate ofshrinkage slowed down for recycled aggregate concrete because of the water held in theaggregate particles. This confirms earlier findings by CUR (11).

Kawamura and Torii (135g) found particularly high drying shrinkage of recycled aggregate concretes made with both fine and coarse recycled aggregates.

Hansen and Boegh (35) prepared a high-strength (H: w/c=0.40), a medium-strength (M: w/c=0.70), and a low-strength concrete (L: w/c=1.20) from the same conventional aggregates. Original concretes were cured in water at 40°C. After 47 days the three concretes were passed through a laboratory jaw crusher. The crusher products werescreened and recombined into three qualities of coarse recycled aggregate, H, M, and L,of approximately the same grading as the original conventional aggregates. High-strength, medium-strength, and low-strength concretes were then prepared with the same mix proportions as the three original concretes, but with all nine possible combinations ofcoarse recycled aggregate and natural sand. All nine concretes were cured in water at 40°C. Four 10×10×80 cm beams from each of the nine recycled aggregate concretes were dried at 40% RH and 25°C for six months. During this period the drying shrinkage was measured.

It will be seen from the results which are presented in Table 8.6 that the drying shrinkage of all recycled concretes (except for one erratic result for L/M) wasapproximately 50% higher than for corresponding control concretes made with the sameconventional aggregates, regardless of mix proportions and type of recycled aggregateused. In one particular case Hansen and Boegh found the drying shrinkage of a recycledaggregate concrete which was made with recycled aggregate that consisted of a lowquality crushed mortar to be three times that of a corresponding control concrete madewith conventional aggregate.


It may be concluded that drying shrinkage of recycled aggregate concrete made with coarse recycled aggregate and natural sand is approximately 50% higher than shrinkageof corresponding control concretes made with conventional aggregate. When both coarseand fine aggregates are used, drying shrinkage of recycled aggregate concrete issomewhat higher, perhaps 70% higher (16), than shrinkage of corresponding control concretes made entirely with conventional aggregates.

Mulheron (142) found that the irreversible shrinkage of concretes, subjected tocomplete drying and then wetting to saturation, are almost independent of aggregate type.However, the reversible shrinkage of the recycled aggregate concretes were generallyhigher than those of the controls.

8.6 Tensile, flexural, shear and fatigue strength

B.C.S.J. (12), Mukai et al. (37), and Ravindrarajah and Tam (65) found the indirect tensile, so-called cylinder splitting strength of recycled aggregate concrete made with coarse recycled aggregate and natural sand not to be significantly different from that ofconventional concrete. However, when both coarse and fine recycled aggregates wereused, the tensile strength of recycled aggregate concretes was down to 20% lower thanthat of conventional concrete. On the other hand, Coquillat (38) found no significant difference in tensile strength between conventional concretes and recycled aggregateconcretes when both coarse and fine recycled aggregates were used.

Gerardu and Hendriks (70) report down to 10% lower indirect tensile strength for

Table 8.6 Shrinkage after drying for 13 weeks at 40 per cent RH and 25° C of original and recycled aggregate concretes. Symbols H, M, and L indicate original high-strength, medium-strength, and low-strength concretes made with natural gravel. Symbol H/M indicates a high-strength, recycled concrete made with coarse recycled aggregate produced from medium-strength concrete, etc., from (35).

Item Shrinkage after 13 weeks of drying at 40% RH and 25° C of original and recycled aggregate concretes


Total shrinkage

3.4 5.1 4.9 5.3 3.5 4.9 5.3 5.2 4.5 6.8 5.7 6.8

% increase in shrinkage above controls

0 50 44 56 0 40 51 49 0 51 27 51


recycled aggregate concrete made with coarse recycled aggregate and natural sandcompared with conventional control concretes made with virgin materials. If the sand isalso replaced with crushed concrete fines, the reduction may be down to 20%. Kawamuraand Torii (135g) found very little difference between the tensile of recycled and ordinary concretes. The same was true for flexural strengths.

B.C.S.J. (12) found that the flexural strength of recycled aggregate concrete is somewhere between 1/5 and 1/8 of its compressive strength, similar to what is the casefor conventional concrete, but no experimental data are presented.

Ravindrarajah and Tam at first (65) found no significant difference in flexural strengthof conventional concrete and recycled aggregate concrete made with coarse recycledaggregate and natural sand. However, later Ravindrarajah and Tam (107) report that both tensile and flexural strength of recycled aggregate concrete is consistently 10% lowerthan for natural aggregate concrete. Malhotra (47), Karaa (93), and Ikeda et al. (135n) all found lower flexural strengths for recycled aggregate concretes than for conventionalconcretes. Karaa (93) found the flexural strength of recycled aggregate concretes produced with both fine and coarse aggregate to be reduced by 26% while the tensilesplitting strength was reduced by 35%. The large differences found by different authorsare probably due to differences in quality of the recycled aggregates used.

Ikeda et al. (135n) found that reductions in strength caused by the use of coarse recycled concrete aggregate are approximately 6% for tensile strength, 0% for flexuralstrength and 26% for shear strength compared to corresponding strengths for ordinaryconcrete. When both coarse and fine recycled aggregates are used, tensile strengths,flexural strengths and shear strengths were reduced by 10%, 7% and 32% respectively.Karaa (93) also found the ratio between compressive strength and tensile strength to be lower for recycled than for ordinary concrete.

Hironaka, Cline and Shoemaker (117) found that aged portland cement concrete pavements can be recycled into new surface courses that have the same fatiguecharacteristics as those constructed with virgin aggregates.

On the other hand Kawamura and Torii (135g) found that the flexural fatigue strengthof concretes made with natural sand and coarse recycled aggregates was higher than thatof comparable natural aggregate concretes. Visual inspection of the fracture surfacesshowed that most failures in natural aggregate concrete occurred along the interfacebetween cement mortars and aggregate grains, while in recycled aggregate concretefailure occurred within cement mortar portions of recycled coarse aggregate grains.Taking into consideration the difference in failure process between the two types ofconcerte, it can be concluded that high flexural fatigue strength in recycled aggregateconcrete is due to the strong bond between cement mortar matrix and recycled aggregateparticles.

Generally, when a pavement is used for traffic the bearing capacity is graduallylowered due to the fatigue by cyclic loading. However, Yoshikane (135z) found that this trend can be reversed in the case of base course material made from recycled concreteaggregate stabilized with fly ash, ground granulated blast furnace slag or waste sludgefrom ready mixed concrete plants. The positive effect is due to slow hydration of themixture of crushed concrete fines and the stabilizing agents.


8.7 Other mechanical properties

Gerardu and Hendriks (70) report that in highway construction the resistance to polishingof coarse recycled concrete aggregates is higher than for many conventional crushedaggregates.

Ravindrarajah, Loo and Tam (102) found that the ultrasonic pulse velocity and therebound value for concrete are reduced by the use of recycled concrete aggregates insteadof natural aggregates. In their investigation it was also found that the relationshipbetween compressive strength and ultrasonic pulse velocity as well as betweencompressive strength and rebound value for concretes made from natural aggregates andrecycled aggregates may be represented by exponential functions. Use of recycledconcrete aggregates instead of natural aggregates in concrete did not affect the strength-rebound value relationship, whereas the strength-ultrasonic pulse velocity relationship was affected. For the same value of pulse velocity the recycled concrete showed higherstrength than natural aggregate concrete and the strength difference increased with theincrease in pulse velocity. However, the combined method of pulse velocity and reboundvalue gave fairly good estimates for the strength of concrete, independent of theaggregate type used.

CUR (11) found the range of values of thermal expansion coefficients for recycledaggregate concretes to be similar to that for natural aggregate concretes. Mulheron (142) also found that the thermal expansion coefficient of recycled aggregate concretes aresimilar to or lower than control concretes.

No information was found in the literature on other mechanical properties of hardenedrecycled aggregate concrete such as impact resistance, fire resistance or acousticproperties.

8.8 Reinforced concrete

Mukai et al. (36) found the bond strength between steel and recycled aggregate concrete to be equivalent to that of conventional concrete both under static and fatigue loading,when coarse recycled aggregates were used with natural sand. However, when both fineand coarse recycled aggregates were used, cracks appeared at 15% lower flexural loadthan when conventional aggregate was used, and the ultimate flexural strength ofreinforced concrete was 30% lower due to bond failure. Shear strength followed a similarpattern.

Mukai and Kikuchi (135u) also found that for what concerns shear strength ofreinforced concrete with few stirrups, concretes using recycled aggregates were slightlyinferior to ordinary concretes. However, when the number of stirrups was increased equalstrength could be obtained.

Kakizaki et al. (135f) found that the bonding strength of vertical bars is between 2.4and 3.7 times that of horizontal reinforcing bars. Moreover, it is 25% lower for vertical


bars in recycled aggregate concrete compared with vertical bars in regular concrete andcorrespondingly 3–35% lower for horizontal bars in recycled aggregate concrete compared with horizontal bars in regular concrete.

It is concluded that coarse recycled aggregate can be used in reinforced concrete without much inconvenience, but that fine recycled aggregate should be avoided. Itappears that up to 30% of natural coarse aggregate or crushed stone can be replaced bycoarse recycled aggregate without any negative effects at all.

8.9 Dry and wet lean concretes. Unbound road base materials and stabilized road

base materials

Dry lean concrete differs from conventional structural concrete in two main respects. Ithas an earth-moist consistency, due to its lower water content so that it can only becompacted by rolling. Also, it contains a relatively small quantity of cement,approximately 100–140 kg/m3 with an aggregate-cement ratio in the range of 15:1 to 20:1. This may be compared with conventional concrete mixes with aggregate-cement ratios between 6:1 and 4:1. The average cube strength of dry lean concrete for themanufacture of road bases is required to lie within the range of 10–20 MPa.

Mulheron (103) found that suitably graded recycled aggregates can be used to produce lean concretes that satisfy the strength and density requirements of current Britishspecifications for road base construction (104), although these specifications do notcurrently allow the use of recycled aggregates for such purposes. Such use would dependon an understanding and a clear appreciation of the characteristic properties and problemsassociated with recycled aggregates.

Mulheron found that the physical and mechanical properties of lean concretemanufactured using recycled aggregates reflect the porous, low modulus materialspresent in such aggregates. Thus, when compared to a control concrete, lean concretemanufactured using recycled aggregates has a lower elastic modulus, and exhibitsconsiderably higher creep and shrinkage.

Moreover, Mulheron (103) found that the durability of lean concrete manufacturedusing recycled aggregates, where subjected to freeze-thaw conditions, appears to be similar to an equivalent control concrete made with natural gravel.

Kawamura and Torii (135g) studied the properties of high fly-ash wet lean concretes made with coarse recycled aggregates from an old pavement concrete with a compressivestrength of 43 MPa, natural sand and portland cement with 30, 50 and 70 weight per centreplacement by fly ash. 200 kg/m3 of cement plus fly ash was always used and new concretes were produced with a slump of 3 cm and with an air content of 7%.

For a required slump the water requirement of high fly ash concrete was 10–15% lower than the water requirement of corresponding concretes without fly ash. However, thisbeneficial effect is largely offset by correspondingly higher water requirement ofrecycled aggregate concrete, which was 8 to 15% higher than that of natural gravelconcretes. The use of recycled aggregates did not influence the air entraining ability ofthe concretes. The negative influence of the use of recycled aggregates on the


compressive strength of lean concrete is not as significant as in ordinary concrete, whilethe modulus of elasticity is significantly lower and drying shrinkage is higher for recycled aggregate concretes than for ordinary concretes.

Although the compressive strength of high fly ash lean concrete is smaller than that oflean concrete without fly ash at early ages, high fly ash lean recycled aggregate concreteshows continuous strength development after 28 days. The extent of strengthdevelopment in high fly ash lean recycled aggregate concrete increases with thepercentage of replacement of cement by fly ash.

When it comes to frost resistance the Durability Factor according to ASTM C666drops from 87% for normal concrete, to 84% for Ns-Ng concretes with 50% fly-ash replacement, 48% for Ns-Rc concretes, 40% for Ns-Rc with 50% fly ash replacement, 52% for Rs-Rc concretes and 40% for Rs-Rc concretes with 50% fly ash replacement. Thus, the frost resistance of wet lean recycled aggregate concretes is considerably lowerthan that of ordinary wet lean concretes. This may not be important in practice becausethe lean concretes used as base course material will usually not be exposed to severefreezing and thawing conditions except for the portion of pavement shoulder. Thus, theauthors conclude that high fly-ash lean concretes with 50% fly-ash replacement can be used as base course material in all combinations of recycled aggregates.

According to Yoshikane (135c) it is estimated that about 130 000 tons/year of wasteconcrete material was used in Japan in 1986 as recycled base course material forroad construction. In view of the total amount of waste concrete generated in Japan(about 10 million tons/year) and in view of the positive results obtained there are greatexpectations seen for advancing its practical use for this purpose.

The quality standard for recycled base course material in Japan is found in (140). Fundamentally, the same standard values are applied as those for new base coursematerial, but the Los Angeles abrasion test and the stability test using sodium sulphatehave been omitted.

Yoshikane (135c) warns that when asphalt-concrete waste is mixed into the wasteconcrete materials, when the ratio of asphalt concrete in the mix is more than 30 weightper cent, and when the depth is shallow of the layer below the pavement surface in whichthe recycled base course material is used as mechanically stabilized granular base, thenthe bearing capacity of the base course as a whole is lowered due to the heat which istransmitted from the surface. Therefore, when a base course is constructed where thetemperature rises above 40°C, it is recommended to increase the value of modified CBR by about 10 points. When the ratio of mixing of asphalt-concrete waste in the recycled granular base course material is less than 30 weight per cent, or when the granularmaterial is stabilized by binders, such considerations are probably irrelevant.

Yoshikane (135c) has made field density tests and studied modified CBR-values of mechanically stabilized granular base materials as well as crusher-run materials made from crushed concrete. In every instance he found both the field-density test results and the modified CBR-value of the materials to exceed specification requirements. He alsofound cores of such base course materials from actual pavements to increase inunconfined compressive strength up to 4 MPa after three years of cyclic loading bytraffic.

Yoshikane (135c) also made a very thorough investigation of granular base course


materials made from crushed concrete but stabilized with portland and blended cements,fly ash, ground granulated blast furnace slag and waste sludge from ready mixed concreteplants. Compared to materials stabilized by means of portland cements, the earlystrengths of many of the materials was somewhat low at 7 and 28 days, but in many casesthe long-term strengths were excellent due to reaction between lime in the crusher finesand the pozzolans which were used. This certainly merits further investigation.Yoshikane (135c) also presents a flow chart of a plant for production of recycled road base materials on the basis of crushed concrete, which is actually in operation in Japan.

Goerle and Saeys (135i) studied seven test roads and 84 samples from ten different Belgian crushing plants, in order to evaluate crushed concrete as an unbound road basematerial when compared to traditional materials. It was found that most of the materialstested were suitable for road bases or subbases according to Belgian specifications.However, some of the materials were too coarse which causes problems duringconstruction. Additional crushing of the concrete to specifications would add very little tothe cost of the material.

It was noticed that the specific density of crushed concrete aggregates is lower than for traditional materials, which must be taken into account in the specifications for thedensity of road bases or subbases using these materials.

The crushed concrete aggregates were compared with the conventional materials for bases and sub-bases, from the point of view of deformation under repeated loading in atriaxial test. The elastic modulus was calculated after a sufficient high number of cyclesto obtain a constant reversible deformation and thus a constant value. The elastic modulusof the crushed concrete behaved better than traditional materials from the point of view ofpermanent deformations. Also the modulus of elasticity of many materials showed animportant increase in the period of several weeks after construction.

Goerle and Sayes (135i) also found that from an economical point of view, the recycling of crushed concrete from demolished plain concrete pavements is a veryadvantageous procedure, especially if crushing can be carried out on site and if theaggregate obtained can be used in situ as an unbound road base or subbase material. Totalsavings of up to 45% have been achieved on Belgian projects.

Seventy per cent of the total savings comes from reduced transport costs, 20% from the lower cost of materials and 10% from avoided dumping costs. In this comparison, theaverage distance from the job to the waste dump and the extraction site for the newmaterial was 15 and 35 km respectively.

The comparative cost analysis has also revealed that breaking down the concrete to blocks of sufficiently small size during demolition not only changes the cost of thedemolition operation very little, but it also encourages the use of a mobile crusher whilerespecting the optimum ratio between the size of the waste concrete to be processed andthat of the aggregate to be produced.

Special attention must be paid to the feeding of the crusher, which accounts for 70% of the total cost of the crushing operation; the cost of sieving the crushed material andcarrying it off by conveyor belts is relatively less important.

Busch (135j) reports on the reconstruction of a runway at Copenhagen Airport,Kastrup, Denmark, reusing materials of both the original portland cement concretepavement and the subsequently added asphalt overlays. The concrete was reused as an


unbound base course layer. The project demonstrated that the portland cement concretecould be processed to fulfil requirements in the Danish standard specifications forgrading.

9. Durability of recycled aggregate concrete

9.1 Permeability and water absorption

The rate of most kinds of concrete deterioration depends on concrete permeability. This isbecause water absorption is indirectly related to permeability of hardened concrete, andpenetration of water into concrete is required for most deterioration mechanisms to beeffective.

Kasai (66) reports that B.C.S.J. (12) conducted water permeability tests on concretes which were made with water-cement ratios of 0.5–0.7 and with slump values around 21cm. The results show that the water permeability of recycled aggregate concrete is 2–5 times that of conventional control concretes and that the scatter of results is larger. Ivanyiet al. (127) also found comparatively higher water-permeability of concretes made with mixed concrete and masonry.

Rasheeduzzafar and Khan (52) compared water absorption of recycled aggregate concretes made with different water-cement ratios and with coarse recycled aggregate and beach sand to water absorption of corresponding control concretes made with thesame water-cement ratios but entirely with conventional aggregate. The old concretefrom which the coarse recycled aggregates were derived had a compressive strength of 23MPa. It may be inferred from the results that a concrete compressive strength of 23 MPacorresponds to a water-cement ratio of approximately 0.55 when concrete is producedwith natural materials in Saudi Arabia. 30-minute water absorption was measuredaccording to British Standard methods of testing hardened concrete for other thanstrength, BS 1881—Part V. It may be inferred from Figure 9.1 that there may be no significant difference between the water absorption (and thus presumably no significantdifference in permeability) of recycled aggregate concretes and corresponding controlconcretes made with conventional aggregate when both concretes are produced withwater-cement ratios higher (and therefore lower compressive strengths) than those of theoriginal concrete from which the recycled aggregate is derived.


Fig. 9.1 30 minutes water absorption for recycled aggregate concretes and conventional concretes made with different water: cement ratios, from (52). All recycled aggregate concretes were made with recycled aggregates from an original concrete which was produced with a water: cement ratio of approximately 0.55.

However, the situation is different when both recycled aggregate concretes andcorresponding control concretes made with natural aggregate are produced with water-cement ratios lower (and therefore higher compressive strengths) than those of theoriginal concrete from which the recycled aggregate is derived. In this case, waterabsorption (and thus presumably permeability) of recycled aggregate concretes may beup to three times that of corresponding conventional concretes made with naturalaggregate. This is not surprising when considering that such recycled aggregate concretescontain a large volume fraction of more porous coarse recycled aggregate which isdistributed in a relatively dense matrix, while control concretes contain original coarseand comparatively dense natural aggregate in the same relatively dense matrix.

In the particular case which was studied by Rasheeduzzafar and Khan (52), it appears that the low strength and correspondingly high water absorption (and thus presumably thehigh permeability) of the recycled coarse aggregate could be compensated for by


producing recycled aggregate concretes with 0.05 to 0.10 lower water-cement ratios than conventional concretes. If the original concrete had been produced with a lower water-cement ratio and thus a higher strength, it is evident from the results reported in (52) that less of a decrease in water-cement ratio of recycled aggregate concretes would have beenrequired to achieve equal water absorption in recycled aggregate concretes andcorresponding control concretes.

It may well be that in situations where recycled aggregate concretes and concretes made with conventional aggregates are made to have equal strength, they may have equalpermeability. However, this remains to be shown.

9.2 Frost resistance

Malhotra (29) and Buck (26) compared frost resistance of original and corresponding recycled aggregate concretes, which were produced with a variety of water-cement ratios. Their results were reviewed in some detail by Nixon (5). Neither of the two authors found the freeze-thaw resistance of recycled aggregate concrete to be significantly lower than that of corresponding control concretes, and in many cases it was higher. Coquillat (38) and Karaa (93) arrived at essentially the same conclusion. Rottler (99) also found this to be true when concretes were exposed to de-icing salts under repeated freezing andthawing. Rottler also found the frost resistance of all recycled concretes to increase withdecreasing maximum size of coarse aggregate.

McCarthy and MacCreery (67) report that freezing and thawing tests were made onrecycled aggregate concrete following the provisions of ASTM C666. Water-soaked beams were frozen in air and thawed in water through 300 cycles. Both elongation andsonic modulus of elasticity were used to evaluate changes in concrete. Although no details are given, it is reported that test results showed recycled aggregate concrete tohave very high durability.

Strand (68) reports results of tests on concrete specimens cast with coarse recycled aggregate and natural sand which indicate that recycled aggregate concrete is as durableas concrete made with virgin aggregates. Many of the recycled mixes tested, exhibitedbetter durability than concrete made with virgin materials.

Hendriks (64) reports no significant difference in frost resistance of cores drilled fromtwo concrete pavements near Helmond in the Netherlands. One pavement was made withconventional concrete and the other with recycled aggregate concrete.

B.C.S.J. (12) found that air entrained recycled aggregate concrete made with coarserecycled aggregate and natural sand had almost the same resistance towards freezing andthawing as corresponding original concretes. However, when both coarse and finerecycled aggregates were used, the freeze-thaw resistance of recycled aggregate concretes was much reduced.

Hasaba et al. (16) found the freeze-thaw resistance of air entrained concretes madewith recycled concrete aggregates always to be inferior to that of control concretes madewith natural sand and gravel. This was true whether recycled aggregate concretes weremade with coarse recycled aggregates and natural sand or with both coarse and fine


recycled aggregates, see Figure 9.2. But recycled concretes made with both fine andcoarse recycled aggregates deteriorated much faster than recycled concretes made withcoarse recycled aggregate and natural sand. Rottler (99) found frost resistance of concrete made with coarse and fine recycled aggregates to be slightly inferior to frost resistance ofconcrete made with coarse recycled aggregate and natural sand. Kasai et al. (135x) arrived at the same conclusion and suggested that fine recycled aggregate concrete shouldnot be used under severe exposure. By visual inspection, Hasaba et al. (16) observed that it is the cement mortar adhering to the original aggregate particles in recycled aggregateswhich deteriorates due to freezing and thawing.

Kawamura et al. (15) also found somewhat lower frost resistance for air entrained recycled concretes than for air entrained control concretes made with natural aggregates.Moreover, these authors found that the frost resistance of recycled aggregate concreteswas lower when a recycled aggregate from comparatively low quality structural concretewas used, than when higher quality recycled aggregate from a pavement was used.

Mulheron (103) and Mulheron and O’Mahony (137) reports that when subjected to alternating freeze-thaw conditions unbound recycled aggregates are less durable thannatural river gravels. Interestingly, when concretes made from such aggregates weretested

Fig. 9.2a Frost resistance of air-entrained concretes made with 300 kg/m2 cement and natural as well as recycled aggregate, from (16).

under the same conditions of freezing and thawing, it was observed that the recycledaggregate concrete exhibited the superior durability.

Kawamura and Torii (135g) found the frost resistance of their 4% air entrained naturalsand and gravel concretes to be frost resistant when tested according to ASTM C 666.However, comparable air entrained recycled concrete aggregate concretes made withnatural sand and coarse recycled concrete aggregate started deteriorating after a fewcycles of freezing and thawing, and failed completely after less than 300 cycles. Visualobservation of the fracture surfaces of recycled aggregate concrete revealed that


deterioration took place along the interface between cement mortars and originalaggregate particles or cement mortar stuck on original aggregate grains. This is a strongindication that the original concretes which were used in this investigation had not beenair entrained. If this is true, it provides a warning that even air entrained recycledaggregate concretes cannot be expected to be frost resistant unless the original concretefrom which the recycled aggregates are produced has also been air entrained. Althoughthis would seem a logical conclusion it has never been experimentally proved in aconclusive way.

According to Kleiser (141) adequate freeze-thaw and de-icing resistance of recycled aggregate concrete can be obtained for practical purposes if the water-cement ratio of the recycled concrete is sufficiently low and both old and new concrete has been adequatelyair entrained.

Kabayashi and Kawano (135v) found that when natural aggregate was used for both fine and coarse aggregates concretes showed good frost resistance with a Durability Factor of 96% after 300 cycles, when tested according to the ASTM C 666, Method A.When recycled concrete aggregate was used for fine aggregate only, there was noproblems either. However, when the recycled aggregate was used for coarse aggregateonly, the Durability Factor dropped to 70% of that of the original aggregate concrete, andwhen recycled concrete was used for both fine and coarse aggregates, the DurabilityFactor became approximately 50% of the original aggregate concrete. Furthermore, inthis test, the use of recycled aggregate resulted in more scaling of the concrete surface.This scaling was particularly pronounced when the recycled aggregate was used for boththe fine and coarse aggregate. The reason seems to be the low-strength paste of the original concrete which was stuck on recycled aggregates.

Kashino and Takahashi (135e) found that when the ratio of recycled aggregate mixedin coarse aggregate was lower than 30%, the frost resistance of recycled aggregateconcrete to frost damage was practically unchanged compared with conventionalconcrete.

Yamato et al. (135y) found that the freezing and thawing resistance of air entrainedrecycled aggregate concretes always was lower than that of control concretes. Thereduction in the freezing and thawing resistance was dependent upon the proportion ofreplacement of coarse aggregate by recycled aggregate. For a replacement ratio of therecycled aggregate less than 30%, the reduction was small.

Nishibayashi and Yamura (135p) found the resistance to freeze-thaw deterioration of recycled aggregate concrete to be very much inferior to that of normal concrete, and theresistance was scarcely improved by air entrainment.

On the basis of extensive tests on highway concrete, Puckman and Henrichsen (135c) concluded that the frost resistance of recycled concrete can be negatively affected, if themortar of the original concrete is not frost resistant. Thus, it is not recommended torecycle concrete pavements which are badly damaged by frost.

While American, French, and Dutch results on frost resistance of recycled aggregateconcrete are encouraging, Japanese results are less conclusive. It is recommended thatmore research should be carried out to clarify under what circumstances recycledaggregate concrete is frost resistant and under what circumstances there may beproblems. The difference between Japanese and American results may be due to the fact


that Japanese results frequently were obtained on fairly low quality original concretes,while original concretes in American experiments were old, high-strength pavement grade concretes.

The Minnesota, North Dakota and Oklahoma State Highway Departments all conducted studies (97) before they tried to recycle problem D-cracked pavements. All three Highway Agencies used recycled material crushed to 3/4 inch or less. Also, the useof fly ash has improved the performance of D-cracking susceptible aggregates. Both Minnesota and Oklahoma replaced 15% of the portland cement in the mix with 20percent fly ash by weight. North Dakota replaced 15% of the cement in its concrete mixwith 15 percent fly ash by weight. The phenomenon of D-cracking of concrete pavements was studied in more detail by Schwartz (121).

Fig. 9.2 b Comparison between frost scaling of recycled concretes and control concretes when a mixture of crushed concrete and masonry was used as coarse aggregate while natural sand was used, from (127).

Figure 9.2a from Ivanyi, Lardi and Esser (127) shows that recycled aggregate concretemade with mixed concrete and masonry debris is far less frost resistant when exposed todeicing salts than similar concretes made with natural aggregates. This clearly shows thatfrost resistance of recycled aggregate concrete may be a problem unless expertly handled.


It is recommended that the problem of frost resistance of recycled aggregate concrete should be studied in more detail.

9.3 Carbonation and reinforcement corrosion

B.C.S.J. (12) studied the rate and extent of carbonation of recycled aggregate concrete inair at 20°C and 60% relative humidity. The air contained 20% carbon dioxide.

It was found that the rate of carbonation of a recycled aggregate concrete made with recycled aggregate from an original concrete which had already suffered carbonation was65% higher than that of a control concrete made with conventional aggregate. In principlethis result is confirmed by Karaa (93) who found rust after two months on reinforcement bars with a 2–3 cm cover of recycled aggregate concrete.

B.C.S.J. (12) concluded that reinforcement in recycled aggregate concrete may corrodefaster than reinforcement in conventional concrete. However, such increased risk ofcorrosion can be offset by producing recycled concrete with a lower water-cement ratio than conventional concrete.

Fig. 9.3 Half cell potentials of steel bars embedded in specimens made from recycled aggregate concrete and concrete made from conventional aggregates, from (52).

These conclusions are supported by Rasheeduzzafar and Khan (52) who monitored corrosion of 25 mm reinforcement bars cast into 305 mm by 203 mm by 38 mm concreteslabs subjected to 40 ponding and drying cycles. Each cycle consisted of two days of


ponding with a 5% sodium chloride solution followed by four days of drying.Reinforcement bar corrosion was monitored using a copper-copper sulfate half cell according to ASTM C 876, ‘Test for half cell potentials of reinforcing steel in concretes’. Two recycled aggregate concretes with water-cement ratios of 0.55 and 0.40 and two corresponding control concretes were tested. It will be seen from Figure 9.3 that for the same water-cement ratio, reinforcement bars corroded slightly more in recycled aggregate concretes than in corresponding control concretes. However, it will also beseen from Figure 9.3 that such increased corrosion can be compensated for by producing recycled aggregate concretes with slightly lower water-cement ratios than concretes made with conventional aggregates.

Mulheron (142) summarized results of tests on the durability of embeddedreinforcement as follows:

a) Under normal environmental conditions (20°C and 7 days wet/dry cycles) there is little or no difference between the time to onset of corrosion of bars embedded in conventional or recycled aggregate concrete—although the inclusion of demolition debris did reduce this time somewhat. Once corrosion had started, the rate of corrosion was independent of the type of aggregate. By far the most important factors under these conditions were the water-cement ratio, cement content and depth of cover to the reinforcement. Indeed, where the depth of cover was less than the maximum aggregate particle size, considerable variation in the time to onset was observed.

b) Under conditions of normal temperature and wet/dry ponding with solutions of NaCl the time to onset of corrosion decreased with decreasing depth of cover. The demolition debris concrete proved unable to prevent the onset of corrosion at depths of 40 mm even after as little as 7–10 cycles. For crushed concrete aggregate the onset of corrosion occurred between 25–40 cycles for bars at a depth of 25 mm cover compared with the 40+cycles required for a control concrete with the same mix design. The bars at 40 mm in both the recycled concrete aggregate and control aggregate mixes had yet to show signs of corrosion when the report was published.

In all cases the rate of corrosion at any depth of cover appears unaffected by the type ofaggregate used, once it has started.

B.C.S.J. (12) concluded that carbonation rates were 1.2 to 2 times higher than those of control mixes when recycled aggregate concretes were produced with recycled aggregatefrom original concrete made with blast furnace slag as original aggregate, or whenrecycled aggregates were contaminated with lime plaster or wood particles. This is incontrast to Kashino et al. (135e) who found little difference between the carbonation rate of recycled aggregate concretes and control concretes made with ordinary aggregates.

Risk of reinforcement corrosion in recycled aggregate concrete made with chloridecontaminated concrete was dealt with in Section 7.7.5. The rate of penetration of chlorides into recycled aggregate concrete has not been studied, as far it is known to theauthor.


9.4 Alkali-aggregate reactions

According to Forster (105) three things are necessary to cause damaging alkali-aggregate reactivity in concrete:

1. an aggregate with sufficient amounts of reactive constituents that are soluble in highly alkaline aqueous solutions;

2. enough water-soluble alkali from some source (usually the cement) to drive the pH-value of the pore liquid in the concrete up to 14–15 and hold it there so that swelling alkali-silica gel is produced; and

3. sufficient water to maintain the solutions and provide moisture for the swelling of the gel.

The consequences of using recycled material, which has suffered from alkali-aggregate reactions, as an aggregate in a new concrete have not been thoroughly defined.

In the special case of concrete recycling, several questions must be answered. How extensive is the reaction and the resulting distress at the time of recycling? Has thereaction gone to completion—that is, have the reactive constituents been used up?

If petrographic or other examinations seem to indicate that the reactive components have been used up, it may be safe to go ahead and use the material. If this is not so,merely the use of a low-alkali cement in the new concrete may not prevent further alkaliaggregate reaction with the recycled material, because the reaction may continue withinthe recycled material between old mortar and aggregates.

The only safe way to screen materials with this particular problem is to do long-term mortar bar expansion tests (ASTM C 227) with the recycled material in cements withvarious alkali contents in order to determine what level of alkali is acceptable. If reactionis taking place between the recycled materials, it may be that no level of alkali in thecement will be low enough to prevent reactions.

The addition of fly ash to the mix appears helpful in preventing the reaction. It has been speculated that the blending of limestone into the aggregate may reduce the probability of alkali-aggregate reactivity, but this has not yet been proven. Reduction inrecycled aggregate size may also be helpful in controlling the reaction problem. Thequestion of recycling of alkali-aggregate reactive material needs additional investigation.

Alkali reactive aggregates have been a problem in many areas of the Western UnitedStates (97). However, there has been some success in using these aggregates to producequality concrete. The Wyoming State Highway Department became aware of an alkalireactive aggregate problem in the early 1970s after several newly constructed portlandcement concrete pavements began to show the typical signs of alkali reactions, which isalligator cracking throughout the pavement slab. By the late 1970s it became apparentthat complete removal and replacement of these pavements would not be far off. Studieswere undertaken to determine the extent of the problem, and if the aggregates could beused with corrective measures.

Numerous mix designs using different cements with recycled coarse and fineaggregates were tested. ASTM Test C 227 was used to check on alkali-aggregate


reactivity of the mix designs. The test were run for 60 months and revealed that severalrecycled concrete mix designs were usable. The mix designs are presented in (97). The use of such recycled aggregates will change the properties of standard portland cementconcrete mixes, but with only minor changes quality mixes can be produced.

Mulheron (103) indicates that further tests are in progress in England on the use ofrecycled aggregates from original old concretes which have been affected by alkali-aggregate reactions. However, no results were available at the date of publication of thisstate-of-the-art report.

Puckman and Henrichsen (135a) have attempted to test alkali reactivity of someDanish recycled aggregates using a modified ASTM C 227 test. However, it is not knownwhether this method is applicable to recycled aggregates.

As there is as yet no recognized method for the testing of alkali reactivity of recycledconcrete aggregate, the limitation of total amount of alkali in concrete should be used,which is found in local specifications for production of concrete with reactive aggregates.

9.5 Sulfate resistance

Nishibayashi and Yamura (135p) has shown that the durability of recycled aggregate concrete under sulfate actions or in sea water is almost the same or slightly inferior to thatof ordinary concrete.


10. Properties and mix design of fresh recycled

aggregate concrete

10.1 Water requirement and workability

Mukai et al. (36) found that recycled concretes produced with coarse recycled aggregate and natural sand required approximately 101/m3 or 5% more free water than controlconcretes produced with corresponding natural aggregate, in order to achieve the sameslump. Approximately 25 1/m3 or 15% more free water was required when both fine andcoarse recycled aggregates were used. Similar results were found by Buck (26), Frondistou Yannas (32), Malhotra (29), Hansen and Narud (13), and by Ravindrarajah and Tam (65).

Rasheeduzzafar and Khan (52) found the workability of recycled aggregate concretes made with coarse recycled aggregate and beach sand to be somewhat improved comparedwith the workability of corresponding original concretes made with crushed limestonecoarse aggregate and beach sand. However, substitution of fine, poorly graded beachsand by well graded, fine recycled aggregate markedly reduced workability.

H. Lambotte and C. de Pauw (39) found addition of finely ground gypsum to reduce the slump of recycled aggregate concretes compared to control mixes.

Kasai (66) reports the results of experiments which show that the fineness modulus ofrecycled concrete aggregate gradually decreases with the time of mixing in the concretemixer. This is probably due to some of the old mortar being rubbed off the recycledaggregate particles. Thus, it is to be expected that the content of fines in fresh recycledaggregate concrete mixes will increase and that the slump of the fresh concrete thereforewill decrease with the time of mixing in the concrete mixer.

Concrete mixes which are made exclusively with coarse and fine recycled aggregatestend to be very harsh and not suitable for placing with a slipform paving machine. Thiscan be corrected by adding up to 25% natural sand. But mixes containing coarse recycledaggregate and natural sand produce the most desirable characteristics (7f).

Karaa (93) found that concrete produced with dry recycled concrete aggregates loosesits workability and sets faster than concrete produced with wet recycled concreteaggregates. However, for the same free water-cement ratio there was no effect on compressive strength or modulus of elasticity of the hardened concretes. This isconfirmed by Hansen and Narud (13). Ravindrarajah, Loo and Tam (107) also found that setting times of recycled aggregate concrete are slightly less than for comparable naturalaggregate concrete. Iványi, Lardi and Esser (127) arrived at the same conclusion but forconcretes made with mixed recycled concrete and masonry aggregate.

Kashino and Takahashi (135e) found that pre-wetting of recycled aggregate was


necessary when it was attempted to make ready-mixed recycled aggregate concrete. Morlion, Venstermans and Vyncke (135t) studied the time it takes to saturate recycled

concrete aggregates by immersion in water. They found that it takes 15 minutes tosaturate 4–28 mm coarse aggregate with a water absorption coefficient of 5%, 10 minutes to saturate 2–4 mm fine aggregate with an absorption coefficient of 10% and 5 minutes tosaturate 0–2 mm fine aggregate with an absorption coefficient of 17%. On a very large project where 80 000 m3 of crushed concrete was used for production of new concrete fora new lock in the port of Antwerp in Belgium, it was found necessary to pre-soak the aggregates in order to prevent a rapid decrease in concrete workability. Immersion of theaggregates in water for one hour prior to mixing turned out to be a very efficient solution.

Hansen and Narud (13) found that there was little or no difference in compressivestrength of recycled aggregate concretes produced with the aggregate in air-dry or saturated surface dry condition when the free water-cement ratios of the fresh concretes were the same. This was later confirmed by Kawai et al. (135q)

Thus, it may be concluded that in actual concrete production it may be necessary to pre-soak recycled concrete aggregates in order to avoid rapid slump loss and early setting of the fresh recycled aggregate concrete. This is conveniently done by immersing theaggregates in water for one hour prior to mixing. However, for what concernscompressive strength of the hardened recycled aggregate concrete there is no significantdifference whether the concrete is produced with the aggregate in air-dry or saturated surface dry condition, provided the two concretes are produced with the same free water-cement ratios allowing for full absorption of the recycled aggregates. Air-dry coarse recycled concrete aggregates apparently saturate themselves with mixing water from thefresh mix within the first 15 minutes. This is probably what causes rapid slump loss andearly setting of the fresh concrete, but it does not affect the compressive strength or otherproperties of the hardened concrete. If this conclusion is correct, it explains muchconfusion in the literature as well as in practice.

Hansen and Marga (135w) found that based on equal slump, the water requirement of recycled aggregate concrete made with both coarse and fine recycled aggregates was 14%higher than that of control concretes made with natural sand and gravel. When concretewas produced with coarse recycled aggregate and natural sand, the increase in waterdemand was only 6%.

Kawamura and Torii (135g) confirmed that the consistency of recycled aggregateconcrete is particularly low when both fine and coarse recycled aggregates are used.

10.2 Free water-cement ratio law

In an extensive series of investigations, Mukai et al. (37) found excellent straight-line relationships between the ratio of cement to free water and compressive as well as tensilestrength of recycled aggregate concretes made with coarse recycled aggregate and naturalsand, as well as with coarse and fine recycled aggregates, see Figure 10.1.

Ravindrarajah and Tam (107) confirmed the normal relationships between water-cement ratio and strength of concrete in compression, tension, and flexure. In other words


the water-cement ratio law applies to recycled aggregate concretes. This importantobservation is also confirmed by Kakizaki (135F).

It may be concluded that the basic water-cement ratio law, which is fundamental to all concrete mix design, applies without modification to all types of recycled concretes. Onlythe level of strength may in some cases be lower for recycled aggregate concrete than forconventional concrete.

Fig. 10.1 Relationship between cement:water ratio and compressive strength of concretes made with natural and recycled aggregates, from (37).

10.3 Cement content

Assuming, according to the findings in Section 8.1, that the compressive strength of recycled aggregate concrete made with coarse recycled aggregate and natural sand at bestis equivalent to the compressive strength of a similar concrete made with correspondingconventional aggregate and the same free water-cement ratio. Further, assuming that atleast 5% more water is required to achieve the same slump, it may be concluded thatrecycled aggregate concretes require at least 5% extra cement and probably more whenproduced with coarse recycled aggregate in order to obtain the same strength ascorresponding conventional concretes.

Under similar assumptions at least 15% more cement would be required if new


concrete is produced with both coarse and fine recycled aggregates. However, in realitymuch more than 15% extra cement is required to maintain the same compressive strengthwhen both coarse and fine recycled aggregates are used as for a correspondingconventional concrete which is made with natural aggregates. This is because finerecycled aggregate in itself is known to lower concrete strength by 10% at best and 50%at worst.

Thus, it may be concluded that recycled aggregate concrete, except for no-fines concrete made with recycled aggregate, always requires more cement than conventionalconcrete for equivalent strength and slump. It may also be concluded that it is veryuneconomical in terms of cement consumption to use fine recycled aggregate in concreteproduction.

10.4 Density and air content

Mukai et al. (4) found that the natural air contents of fresh recycled aggregate concreteswere higher and varied more than natural air contents of fresh control mixes made withconventional aggregate. Densities of fresh recycled aggregate concretes varied from 2020to 2210 kg/m3, which was between 85% and 95% of control mixes.

On the basis of systematic investigations, the results of which are reported in Table 10.1, Hansen and Narud (13) concluded that natural air contents of recycled aggregateconcretes may be up to 0.6% higher than natural air contents of fresh control mixes madewith conventional aggregate. Densities of fresh recycled aggregate concretes varied from2200 to 2250 kg/m3, which is more than 95% of control mixes.

In an additional series of experiments Hedegaard (17) found no significant difference in entrained air contents between control concretes and recycled aggregate concretesmade with coarse recycled aggregate from an original concrete with 6.5% entrained air.This is confirmed by Puckman and Henrichsen (135a), who also found that the use of recycled concrete aggregates does not impair the air void system in the recycledaggregate concrete.

Table 10.1 Density and air content of fresh original and recycled aggregate concretes. Symbols H, M, and L indicate original high-strength (w/c=0.40), medium-strength (w/c=0.70), and low-strength concretes (w/c=1.20) made with natural sand and gravel. Symbol H/M indicates a high-strength, recycled concrete made with coarse recycled aggregate produced from medium-strength concrete, etc. (Information additional to (13).)

Type Density kg/m3 Air Content %

H 2360 1.3

H/H 2250 1.5

H/M 2250 1.6


It is concluded that the natural air content of recycled aggregate concrete may be slightlyhigher than that of control concretes made with conventional aggregate. The density ofrecycled aggregate concretes is always lower than that of control mixes. Reduction indensity may vary from less than 5% to more than 15%. How much the natural air contentis increased and how much density is decreased in any particular case depends on mixdesign and efficiency of compaction. But it is certainly possible to produce recycledaggregate concrete in the laboratory with no significant increase in air content and lessthan 5% lower density, compared with control mixes.

Kreijger (63) found linear relations to exist between compressive strength and densityof recycled aggregate concretes as shown in Figure 10.2.

10.5 Ratio of fine to coarse aggregate

From the point of view of both economy and cohesion of fresh concrete, B.C.S.J. (12) found the optimum ratio of fine to coarse aggregate to be approximately the same forrecycled aggregate concrete as for conventional concrete.

10.6 Mix design of recycled aggregate concrete mixes

In principle, mix design of recycled aggregate concrete is no different from mix design ofconventional concrete, and the same mix design methods can be used. In practice slightmodifications are required.

Assuming for example that one were to use for design of recycled aggregate concretemixes, the DOE method (40), which is widely employed in the UK. In that case thefollowing modifications would be appropriate.

H/L 2250 1.9

M 2350 1.1

M/H 2250 0.9

M/M 2250 1.2

M/L 2240 1.6

L 2290 1.9

L/H 2210 1.5

L/M 2200 2.2

L/L 2200 2.2


Fig. 10.2 Compressive strength as a function of density of hardened concrete (63).

1. In order to determine a target mean strength on the basis of a required characteristic strength, a higher standard deviation must be employed when designing a recycled aggregate concrete made with recycled aggregates of variable quality than when recycled aggregate of uniform quality or conventional aggregate is used.

2. At the design stage, it may be assumed that the free water-cement ratio for required compressive strength will be the same for recycled aggregate concrete as for conventional concrete when coarse recycled aggregate is used with natural sand. If subsequent trial mixes show that the compressive strength is lower than assumed, an adjustment of the water-cement ratio must be made.

3. It can be assumed that for the same slump, the free water requirement of recycled coarse aggregate concrete is 10 1/m3 higher than for conventional concrete.

4. A maximum recycled aggregate size of 16–20 mm may be required for reasons of concrete durability.

5. Because of a higher free water requirement of recycled concrete mixes, the calculated cement contents will be somewhat higher for recycled aggregate concretes than the cement contents for corresponding conventional concretes.

6. Mix design must be based on the measured density of recycled aggregate at hand. 7. When estimating the ratio of fine to coarse aggregate, it can be assumed that the

optimum grading of recycled aggregate is the same as for conventional aggregate. 8. It is imperative that trial mixes should be made in order to adjust the free water content

necessary to obtain the required slump, the free water-cement ratio necessary to obtain


the required strength, and the ratio between fine and coarse aggregate necessary to achieve the best economy and cohesion of the fresh mix. Larger deviations from values estimated according to the original DOE method can be expected for recycled aggregate concretes than for conventional concretes, but in the author’s experience, it is nevertheless possible and convenient to use the DOE method for design of recycled aggregate concrete mixes.

11. Production of recycled aggregate concrete

Practical experience (7) has shown that recycled aggregate concrete is as easy to batch,mix, transport, place, compact, and finish as conventional concrete. However, because ofthe relatively high water absorption of recycled aggregate, it is sometimes recommendedto batch recycled aggregates in a pre-soaked state and as close to a saturated surface drycondition as possible, see (98) and (11). This presents practical problems to the concretemanufacturer, which according to Morlion et al. (135t) can conveniently be overcome byimmersing the aggregates for one hour in water before mixing. Kaga et al. (135m) foundthat more than 24 hours of immersion in water was neccesary for complete saturation ofrecycled coarse aggregates.

However, neither Hansen and Narud (13) nor Karaa (93) found any difference betweencompressive strength or modulus of elasticity of concretes made with dry or saturatedrecycled aggregates as long as they were made with the same free water-cement ratio.

The Dutch concrete code allows 20% of the total amount of aggregate in new concreteto consist of recycled concrete aggregates without any special measures being taken. TheJapanese suggest that up to 30% of the total aggregate in concrete mixes may consist ofrecycled aggregate without any ill effects.

However, for technical as well as economical reasons it is recommended to producerecycled aggregate concrete with coarse recycled aggregate down to no less than 2 mmand a fine natural sand for the rest. Use of crushed concrete fines below 2 mm has adetrimental effect on economy as well as on many technical properties of concrete.

As indicated above, Kashino and Takahashi (135e) found that when the ratio ofrecycled aggregate mixed in coarse aggregate is lower than 30 weight per cent, neithercompressive strength, modulus of elasticity, creep nor frost resistance are significantlychanged compared with ordinary concrete. Also the permeability of fresh concreteremains practically the same. However, problems are reported with stockpiling andsolidification during storage.

Mukai et al. (4) and Hansen and Narud (13) found bleeding of recycled aggregateconcretes to be slightly less than that of control mixes, probably due to the fact that someof the old mortar rubs off recycled aggregates during mixing and creates a slight excess offines in the mix. This is confirmed by Kashino and Takahashi (135e).

When coarse recycled aggregate was used with natural sand, Mukai et al. (4) found


little difference between the compressive strength of recycled aggregate concretes whichhad been low-pressure steam-cured at elevated temperatures and strength of conventional control concretes which had been cured in the same way. When both coarse and finerecycled aggregates were used, concrete compressive strengths were greatly reducedcompared to controls.

Surprisingly both Schulz (135) and Kaga et al. (135) found that five minutes of dry premixing the aggregate alone in the concrete mixer actually improved the workability ofthe fresh concrete without impairing the properties of the hardened concrete. This resultmay be explained by moderate abrasion and refining, with the grading curve movingupwards only slightly. The grading curve still remains within the range of good grading,but the aggregate particles get a better shape by abrasion.

Working from experience with ready-mixed concrete plants, Kashino et al. (135e) confirmed that:

1. Regarding mix proportioning of concrete, recycled aggregate can be handled in approximately the same manner as ordinary crushed stone.

2. Basically recycled aggregate concrete can be dealt with at the ready-mixed plant in the same way as placing ordinary concrete.

3. Placing and compaction of well-designed recycled aggregate concrete is not any different from placing and compaction of conventional concrete.

4. The strength characteristics of recycled aggregate concrete as obtained in the laboratory are reflected without change in actual structures.

In essence, it was found that recycled aggregate concrete gave no problems for whatconcerns workability and strength when they were manufactured and placed by methodssimilar to those used for ordinary concretes. There are, however problems which remainto be studied concerning stockpiles and setting of aggregates during stocking.

No information on the susceptibility of fresh concrete to plastic shrinkage cracking hasbeen found in the literature.

12. Use of crushed concrete fines for other purposes

than production of new concrete

It has been shown in this report that the use of fine recycled aggregate below 2 mm has adetrimental effect on economy as well as on many technical properties of recycledaggregate concrete. From the point of view of production of recycled aggregate concrete,fine recycled aggregate below 2 mm should be wasted. For this reason it has been studiedwhether crushed concrete fines can be used for other useful purposes than production ofnew concrete.


12.1 Setting and hardening of crushed concrete fines

Hansen and Narud (41) have shown that any unhydrated cement which may remain incrusher fines below 2 mm is so diluted that the fines have insufficient hydraulic bindingcapacity to harden a soil or granular mass.

The author of this state-of-the-art report later mixed 0–4 mm sand produced by the crushing of old concrete, with water to produce a mortar with a water-cement ratio of 0.50. Some of the mortar was cured for 28 days in a sealed container at 40°C. After drying it was evident that the mortar had neither set nor hardened. It had retained itsoriginal loose granular structure. Considering that the old concrete had been producedwith a cement content of 410 kg/m3 and a water cement ratio of 0.40, and that it had obtained a compressive strength of approximately 60 MPa at the time of crushing, it maybe concluded that crushed concrete fines do not have hydraulic properties due to possibleremaining unhydrated portland cement, which are sufficient to cause binding of granularmasses.

The rest of the mortar was allowed to dry out at ambient temperature in the laboratory. After 28 days the mortar had developed a hard but brittle crust which increased inthickness until the entire sample had hardened after approximately 180 days. On the basisof the results of such pilot tests it is suggested that the apparent setting of recycledaggregate with time in stockpiles or when used as unbound subgrade or subbase materialfor road construction is due to carbonation of calcium hydroxide in the crushed concretefines rather than to hydration of remaining cement.

Hansen and Narud (13) found crushed concrete fines to contain from 2% to 4% ofcalcium hydroxide depending on the cement content of the original concrete. Thus, whenmixed with water as mentioned above, crushed concrete fines can be expected to set andharden in the same way as a weak lime mortar. If this is so, the hardening process ofrecycled concrete aggregate could be enhanced by the addition of slaked lime, but noliterature was found to support this conclusion.

Yoshikane (135c) found that hardening due to carbonation alone can result in compressive strengths up to 4MPa in road base courses made entirely from compactedcrushed concrete aggregates without addition of any pozzolan or hydraulic binder. Suchuse is also described by Puckman and Henrichsen (135a). It makes recycled concrete fines unsuitable for drainage purposes unless material below 2 mm is screened out.

Hansen and Narud (41) found that calcium hydroxide in fine crushed concrete which isformed by hydration of original cement in old concrete by autoclaving at elevatedtemperatures can be brought to react with mineral particles in the fines, or withpulverized fuel ash or condensed silica fume to yield reaction products of a certainstrength, similar to what is the case in the production of calcium silicate bricks, see Table 12.1.

Considering that crushed concrete fines contain a certain amount of calcium hydroxideit could also be expected that the material without any addition of slaked lime, wouldobtain truly hydraulic properties at ambient temperatures when mixed with water andpozzolanic materials such as fly ash, silica fume or ground granulated blast furnace slag.


This is exactly what was observed by Yoda, Yoshikane, Nakashima and Soshiroda(135b).

12.2 Alternative cements produced from crushed concrete fines

Yoda et al. (135b) produced two types of hydraulic cement on the basis of crushedconcrete fines. One cement was produced by the drying of a mixture of crushed concretefines below 5 mm, ground granulated blast furnace slag, 2–3% gypsum and an inorganic accelerator. Another cement was produced by the drying of a mixture of waste cementsludge from ready mixed concrete plants, crushed concrete fines below 5 mm, 2–3% gypsum and an inorganic accelerator.

After wet curing for 4 weeks the compressive strength of concretes made with bothtypes of recycled cements was half that of concrete made with the same water-cement ratio and ordinary portland cement. Other concrete properties followed the same trend.

However, when comparing concretes having the same slump and compressive strengthbut made with recycled cements and Portland Blast Furnace slag cement it was found thatdevelopment of strength with time, drying shrinkage and frost resistance of the concreteswere almost the same, while heat of hydration was lower and rate of carbonation wasfaster for concretes made with recycled cements.

In 1988, 1500–2000 m3 of concrete made with recycled cements were commerciallyproduced in Japan per month and used in non-loadbearing structures such as foundations, low breast walls and mass concrete structures. The price of such recycled concrete isabout 4% less than that of normal concrete.

Following the same lead Hansen (136) produced an original concrete with 413 kgordinary portland cement, 540 kg natural sand, 1262 kg natural gravel and 165 kg freewater per cubic metre of concrete. The water-cement ratio was 0.40 by weight, the slump of the fresh concrete was 55 mm, and the compressive strength of the hardened concretewas 56.4 MPa after 38 days of accelerated curing in water at 40°C. The concrete was

Table 12.1 Compressive strengths of products made with crushed concrete fines, from (41) and (42).

Material Compressive Strength, in MPa (psi) after Curing

28 days at 20° C

28 days at 40° C

24 hours in autoclave at 8 Atm

Crusher Dust only 0 (0) 0 (0) 9.3 (1348)

Fly Ash only 0.1 (14) 1.3 (188) –

Crusher Dust - Fly Ash 4.2 (609) 9.7 (1406) 12.5 (1812)

Crusher Dust + Silica Fume

– – 24.4 (3538)


crushed in a laboratory jaw crusher, and the crusher products were screened into the samesize fractions of coarse and fine aggregates which had been used to produce the originalconcrete. Part of the fine material below 4 mm was wet ground in a ball mill for 20 hoursto a crusher dust of cement fineness.

New concrete was then produced with 275 kg of crusher dust, 275 kg of ASTM ClassF fly ash, 375 kg of fine recycled aggregate below 4 mm, 1263 kg of coarse recycledaggregate above 4 mm, and 238 kg of free water per cubic metre of concrete. The slumpof the fresh concrete was 100 mm and the cohesion of the mix was excellent. Eight 100 x200 mm cylindrical specimens were cast. When the first four specimens were tested after28 days of standard curing in water at 20°C. A mean compressive strength of 1.6 MPawas obtained. When the last four specimens were tested after three years of standardcuring in water at 20°C a mean compressive strength of 12.4 MPa was obtained.

12.3 Crushed concrete fines used for road construction and soil stabilization

Forster (105) mentions that ASTM minus No. 4 material (< 4.75 mm) can be used in roadconstruction as a stabilizing material in base courses, but Arnold (108) warns that recycled fines should not be used in drainage layers beneath a pavement. Some of thecementitious material attached to the surfaces of the fines go into solutions when waterpercolates through. A precipitate then forms in the drainage structure or on the geotextilefabric used to wrap the drain. Therefore the Michigan Department of Transportation nolonger allows the use of recycled fines in drainage layers of pavement bases.

Hansen and Angelo (80) showed that when crusher fines below 2 mm are blended into a plastic and wet clay, the soil is modified and somewhat improved beyond what can beexplained by the pure mechanical effect of blending the fine-grained clay with the coarser grained crusher fines. Such improvement is probably due to calcium hydroxide from thecrusher fines reacting with the clay minerals to form clots. However, the improvement isso slight that it may not be of any practical value.

12.4 Crushed concrete fines used for special purposes

Hansen (89) showed that crushed concrete fines make excellent cat litter which is free from odour, probably due to the presence of small quantities of slaked lime (calciumhydroxide) in the fines. The amount is so small that it will not hurt a cat’s paws. The material is heavy enough to fall off a cat’s paws in the container, so that the cat does not leave paw marks on the floor. Also crushed concrete fines are quite effective in removingfresh oil spills from garage floors.

Berger and Carpenter (90) suggested that crushed concrete fines can be used forneutralization of acid soils or waste water, and Scotts (91) and (92) reported on an Austrian ‘accident’ which occurred in 1983 when, during the resurfacing of an overpass, an area of sick forest beneath it was heavily coated with gravel dust to a depth of about 2


mm. Dismayed by the event, the owner expected the accidental coating to be the deathknell for the already weakened forest. Instead, years later, the coated area displayedvigorous growth and renewed health, contrasted clearly with the adjacent uncoated forestarea which remained sick. If one assumes that the accidental dusting simply supplied limeto fertilize the soil and neutralize acid rain, it does suggest two major benefits:

1.an abundant material, which is not the product of fossil fuels can rejuvenate ailing forests, and

2.one large application extends the effect over a period larger than one year without burning the nourishment system of the tree. Perhaps knowledge of this benefical accident will spur commercial interests in the timber industry and farming to explore the possibility of achieving reduced costs and improved yields by applying gravel such as it was suggested already by Julius Hensel in the 1890s (91) and (92).

Other possible uses, for which crushed concrete fines have been suggested by Berger andCarpenter (90), include trickling filters for waste water treatment, poultry grits,substitution for ground limestone in S02-scrubber filters in coal burning power plants, forstabilization of sewage sludge, or as a source of available silica in highly leached lateritic soils. However, it should be kept in mind that the concentration of calcium hydroxide incrusher fines from old concrete is very small, 4 weight per cent at the most. Because ofthe low concentration of calcium hydroxide, use of crusher fines may be uneconomical,even if it can be shown that beneficial effects do exist.

13. Products, codes, standards, and testing methods

for recycled aggregate concrete

13.1 Aggregate products which can be produced from recycled concrete

Lindsell and Mulheron (87) have reviewed the wide range of aggregate products which can be manufactured depending on the type of demolition debris being processed and thecapabilities of the recycling plant. For the purpose of comparison it is possible to classifythis range of products into four main categories.

(i) Crushed demolition debris—mixed crushed concrete and brick that has been screened and hand-sorted to remove excessive contamination, but still contains a proportion of wood or other impurities.

(ii) Clean graded mixed debris—mixed, crushed concrete and brick which has been graded and contains little or no contaminants.

(iii) Clean graded brick—crushed and graded clean brick and masonry containing less than 5% other stony material and little or no contaminants. (Stony material is used


here to mean concrete, brick, natural stone and ceramic materials.) (iv) Clean graded concrete—crushed and graded clean concrete containing less than 5%

brick or stony material and little or no contaminants.

It is important to note that the recycling of demolition debris can also produce a numberof useful by-products. These include recovered steel reinforcement, sold for its scapvalue, crusher fines, used to cover drainage or sub-base courses, and waste timber.

The major markets for recycled aggregate are:

1. General bulk fill 2. Base or fill in drainage projects 3. Sub-base or surface material in road construction 4. New concrete manufacture.

The suitability of the different types of recycled aggregate for such uses is discussedbelow.

Ideally, a material for use as fill should be a hard, granular material with a fairly largeparticle size that consolidates easily and remains free draining. In addition to this, itshould be chemically inert and not subject to significant changes in dimension withchanging moisture content.

Clean graded concrete easily meets all of these criteria and is highly sought for fill andsub-base applications in drainage and road construction projects. Clean graded brick isalso very suitable as a fill material provided it has sufficient hardness and durability.However, bricks with a significant quantity of adhering gypsum plaster or an acid solublesulphate content in excess of 0.5% should not be used. Refractory bricks are alsoundesirable because the periclase content can cause significant expansion when wet.Clean graded mixed debris and crushed demolition debris are usually suitable as generalfill, but may contain unacceptable levels of contamination. Thus, debris with a highgypsum plaster content should not be used as fill close to wet concrete structures, cementbound materials, or brickwork, since this can result in severe sulfate attack. Similarly,crushed debris with a significant timber content should be avoided since the timber canrot and leave voids in the fill layer.

The inclusion of recycled aggregates in the construction of road sub-bases appearswidely accepted in most countries provided the normal grading requirements are met andthe level of contaminants is acceptable. In practice, this usually limits the choice to eithercrushed brick or concrete. The use of these materials as aggregate for asphalt roadsurfacing has been investigated on a laboratory scale in Holland (15). The results indicatethat in principle it is possible to use crushed concrete for the coarse fraction of gravel andopen-graded asphalt. In contrast, crushed brick is not suitable owing to its high bitumenrequirement and high void content.

The acceptance of recycled aggregates for production of new concrete will depend onwhether they satisfy certain specifications. Whilst these may vary from country to countryit is possible to identify a number of general requirements which any aggregate must meetbefore it will be accepted. Firstly, its should be sufficiently strong for the grade ofconcrete required and should be dimensionally stable with changes in moisture content.Secondly, the aggregate should not react with cement or reinforcing steel, nor should it


contain reactive impurities. Finally, the aggregate should have a suitable particle shapeand grading to produce acceptable workability of the concrete mix.

13.2 United States

Since 1982, ASTM ‘Standard specification for concrete aggregates’, C 33–82, paragraph 8.1, defines coarse aggregate as including crushed hydraulic cement concrete, and ASTMC 125–79a ‘Standard definitions of terms relating to concrete and concrete aggregates’ defines manufactured sand as including hydraulic-cement concrete. Similarly, the US Army Corps of Engineers has changed its specifications and guides to encourage the useof recycled concrete as aggregate (Buck (43)). Thus, it may be concluded that there are no longer any national barriers to the use of recycled portland cement concrete asconcrete aggregate in the United States, and that the US is on the path to acceptance ofrecycled aggregate concrete pavement as a standard aggregate and routine, rather thanrequiring special testing of it as aggregate. According to an anonymous report (97) there have been no problems meeting standard aggregate specifications in the US for suchconcrete.

Some State Highway Departments in the United States have developed their own specifications for recycled aggregate concrete in pavements. More specifically, IowaDepartment of Transportation (7f) requires:

1. The existing pavement to be crushed and used as aggregate must be thoroughly evaluated by the contracting agency.

2. Where asphaltic concrete resurfacing is present, the asphaltic concrete shall be removed before the Portland cement concrete is removed. However, isolated areas of adhering asphaltic concrete up to one inch in thickness is considered acceptable.

3. During removal of the existing Portland cement pavement, care must be taken to assure minimum contamination of the salvaged concrete with underlying sub-base material or soil.

4. Processing equipment shall include a means by which excessive fines can be controlled so that the maximum material passing the ASTM No. 200 sieve in the total product does not exceed 5%. Washing the finished product is not normally considered necessary.

5. Reinforcing steel, if any, removed from existing pavement shall become the property of the contractor and shall be disposed of off the project.

6. Crushed concrete in the processed form may be suitable for use without the addition of virgin fines; however, finishing and workability will generally be enhanced by adding natural fine aggregate in amounts of approximately 25%.

7. Normal procedure is to proportion the mix so that coarse and fine crushed concrete may be consumed in the same ratio that they are produced; however, it may be necessary to add a certain amount of natural fine aggregate to produce acceptable workability.

8. Freeze-thaw durability of recycled concrete should be evaluated in accordance with ASTM C 666, Method B, modified to provide a 90-day moisture period. Durability


Factors from ASTM C-666, Method B, as modified, are considered acceptable if they are 80 or above.

13.3 Japan

The Building Contractors’ Society of Japan has issued a ‘Proposed standard for the use ofrecycled aggregate and recycled aggregate concrete’ (6).

The proposed standard introduces and defines the terms: original concrete, recycledaggregates, and recycled aggregate concrete as explained in Section 4 of this report.Although much of the Japanese standard is no different from what can be found in codesand standards for conventional concretes in other countries, there are a number ofrequirements which are specific to recycled aggregates. Some of the more interesting arementioned below:

1. Original concrete shall be sound, hard, normal-weight concrete. 2. As a rule, concrete of distinctly different qualities shall be used separately. 3. Finishing materials, reinforcements and dirt on original concrete shall be as removed

best they can. 4. Oven-dry specific gravity, percentage of water absorption, lost substances in a washing

test, and percentage of solid volume of recycled aggregates shall conform to qualities given in Table 13.1.

5. Recycled aggregates shall not contain injurious amounts of foreign matter which may adversely affect recycled aggregate concrete and steel used therein. Allowable amounts of injurious impurities are shown in Table 13.2.

Impurities are classified in two groups:

(a) Gypsum plaster, Shikkui (Japanese plaster) and other plaster material, clay lumps less than 1950 kg/m3.

(b) Asphalt, plastics, paint, cloth, paper and wood having a density less than 1200 kg/m3, and similar material particles which can be retained on a 1.2 mm sieve.

Injurious impurities can be determined in accordance with a proposed standard testmethod, which is based on visual inspection or separation in two heavy liquids atdensities of 1200 and 1950 kg/m3. It is interesting that this is the only testing methodfound in any country or state which has been specifically developed for recycled concreteaggregates.

6. Recycled aggregate concrete shall be classified according to types of aggregate used, as shown in Table 13.3.

7. Specified design strength of recycled aggregate concrete shall be determined according to the type of recycled aggregate concrete and shall be below the maximum value given in Table 13.3.

8. Table 13.4 lists typical uses for which recycled aggregate concretes are considered suitable.


9. An air entraining agent or an air entraining and water-reducing admixture shall be incorporated into any fresh recycled aggregate concrete mix. The air content of recycled aggregate concrete shall always be between 3% and 6%.

Table 13.1 Quality requirements to recycled aggregates according to Japanese proposed standard for the use of recycled aggregate and recycled concrete, from (6).

Test Item Recycled Coarse Aggregate

Recycled Fine Aggregate

Oven-Dry specific Gravity Not less than 2200 kg/m3 Not less than 2000 kg/m3

Percentage of Water Absorption

Not more than 7% Not more than 13%

Lost Substances in Washing Test

Not more than 1% Not more than 8%

Percentage of Solid Volume Not less than 53% –

Table 13.2 Allowable amounts of injurious impurities according to the Japanese proposed standard for the use of recycled aggregate and recycled aggregate concrete from (6).

Type of Aggregate Impurity I Impurity II

Recycled Coarse 10 kg/m3 2 kg/m3

Recycled Fine 10 kg/m3 2 kg/m3

Impurity I: Plaster of Paris, Japanese Plaster, clay lumps, lime mortars, and other plaster materials < 1950 kg/m3. Impurity II: Asphalt, plastics, paint, cloth, paper, wood, and similar materials < 1200 kg/m3 retained on a 1.2 mm sieve.


10. Required slump of recycled aggregate concrete shall not exceed 21 cm. 11. Water-cement ratio shall not exceed 0.70. 12. Cement content shall not be less than 250 kg/m3. 13. The smallest possible water content and ratio between fine and coarse aggregate

content shall be used which will produce a concrete with the required slump and

Table 13.3 Type of recycled aggregate concrete and maximum values of compressive strength, from (6).

Type of Recycled Aggregate Concrete

Type of Aggregate Maximum Allowable Value of Compressive Strength

Coarse Aggregate

Fine Aggregate Specified Design

Strength

Proportioning Strength

I Recycled aggregate (1)

Conventional aggregate

180 300 (2)

II Recycled aggregate (1)

Mixture of conventional aggregate and recycled aggregate

150 270 (2)

III Recycled aggregate (1)

Recycled aggregate 120 240 (2)

Note: (1) Including that mixed with normal weight aggregate (2) Provided the cement content will not become excessive, larger values may be used, for example if the slump is reduced.

Table 13.4 Suggested uses of recycled aggregate concrete according to the Japanese proposed standard for the use of recycled aggregate concrete, from (6).

Type of Recycled Aggregate Concrete

Principal Object of Usage

I Low-rise buildings in general, low-rise apartment buildings, single family houses, single storey commercial buildings, heavy foundations, etc.

II Foundations for precast concrete block construction, non-residential light construction, machinery foundation, etc.

III Foundations for wooden buildings, gates, fences, simple machinery foundations, slabs on grade, etc.


having proper cohesion.

A Japanese ‘Draft standard specification for recycled base course material’ is found inRef. (140). Fundamentally the same standard values are applied as those for new basecourse material, but the Los Angeles abrasion test and the sulphate soundness test areomitted.

13.4 The Netherlands

A proposed Dutch product standard for recycled concrete as aggregate for production ofplain, reinforced, and prestressed concrete (115), has been developed by CUR (11). Thisstandard specification of which the full text is included in (11), apply if more than 20% byweight of total coarse or fine aggregate consists of recycled concrete aggregate. If lessthan 20% by weight of coarse or fine aggregate consists of recycled concrete and theremaining part consists of natural sand and gravel or crushed natural materials, the totalaggregate is considered to be natural aggregate and the standard specifications do notapply. The above-mentioned product standard (115) is included in the draft for the newDutch concrete-code VBT 1986. The following main points are of interest:

1. Definitions

(a) Concrete rubble is defined as demolition waste which is derived from hydraulic cement concrete, reinforced or otherwise, and which has a dry density of not less than 2100 kg/m3.

(b)Stony materials are defined as:

– apport M83–1concrete made with natural gravel – brick – sand-lime brick – lightweight concrete – aerated concrete – ceramic materials (such as roof tiles, tiles, pottery, and sewage ware) – glass – natural stone – masonry mortar (excluding plaster or plaster-containing mortars)

2. Composition By definition, concrete rubble should contain at least 95 weight per cent of concrete. The remaining 5 weight per cent may consist of other stony materials such as natural stone, lightweight concrete, ceramic materials, bricks or mortar and a maximum of 1 weight per cent of bituminous material.

3. The producer of recycled concrete aggregate must record the origin of the material. The record must include information on location and type of the demolished structure.

4. In order to arrive at a better understanding of the composition, specimens of the rubble must be screened on the 8 mm sieve. For what concerns the fraction above 8 mm, the


weight percentages of the following constituents must be determined by visual analysis and weighing:

– Concretes made with natural aggregate – Lightweight aggregate concretes and aerated concretes, or both – Clay bricks – Sand-lime bricks – Lime mortar or cement mortar – Ceramic products – Natural stones – Glass – Rubber – Wood – Synthetic materials – Asphalt – Other materials

The composition of the fraction above the 8 mm sieve is considered to be representativeof the composition of the entire mass of aggregate.

5. Table 13.5 shows requirements with apply for grain size distribution of the aggregates: 6. The amount of soft and friable material which is ground to powder by hand as

determined by the method given in the Dutch standard specification for sand and gravel, NEN 3542, should not exceed 0.1 weight per cent of the dried material.

7. The amount of organic materials in fine recycled aggregates must be such that the addition of sodium hydroxide, in accordance with the method described in NEN 3542, does not give rise to a darker colour than the standard colour given in the above-mentioned standard, unless it can be shown that the impurity which gives rise to the color is harmless (see Item 15).

8. The weight percentage of water-soluble chlorides in recycled aggregates as determined according to the method presented in NEN 3542 should not exceed the values given in Table 13.6.

Table 13.5 Required grading for recycled aggregates according to the Dutch proposed standard for the use of recycled aggregate and recycled aggregate concrete (11).

Size Fraction in mm of Recycled Aggregate

Percent retained on sieve (mm)

> 31.5

> 16

> 8 > 4 > 2 > 1 > 250µ

> 63µ

0–4 – – – 0–0 25–31

50–62

80–87 96–100

4–16 – 0–5 55– 85– 95– – – 99–


9. The content of calcium carbonate in recycled aggregate as determined according to the method presented in NEN 3542 should not exceed 25% by weight of the 0–4 mm fraction and 10% by weight of the fraction above 4 mm.

10. The content of sulfate in recycled aggregates, as determined according to the method presented in NEN 3542, should not exceed 1 weight per cent of particles dried at 98°C.

11. For some applications, such as exposed concrete surfaces, recycled aggregates must be free from constituents which are objectionable from an aesthetic point of view (for example asphalt, water-soluble iron or vanadium compounds).

12. The content of wood and other matter of organic origin in recycled aggregates, as determined according to DIN 4226 (Test for Lightweight Particles), should not exceed 0.5% by weight of the 0–4 mm fraction and 0.1% by weight of the fraction above 4 mm.

13. Certain requirements and limit values are introduced concerning dimensional stability, retardation, staining, cubicity, and frost resistance of recycled concrete aggregates.

14. On the basis of information of the origin of the demolition rubble and the visual analysis, it must be determined whether there are impurities in the rubble which may give rise to internal expansion of the concrete (for example particles of calcium or magnesium oxide, as determined by the autoclave method for detection of lime instability (BS 1047), iron instability (BS 1047) or alkali-reactive materials (ASTM C–586, C–295, C–289, and C–227)).

15. If the origin, the visual analysis, or the result of the test which is described under Item 7 gives rise to doubt, a water extraction of the rubble must be made in order to determine whether the material contains water-soluble or acid-soluble compounds which could adversely affect setting or hardening of concrete. Adverse effects on setting time are determined by preparing two sets of cement paste specimens, one with the extracted water, and one with distilled water. Any difference in setting time as determined by the standard Vicat test is assumed to be due to contaminants in the extracted water. Similarly, the compressive strength is determined on two sets of

57 100 100 100

4–31.5 0–5 32–44

70–75

90–100

– – – 99–100

Table 13.6 Maximum allowable contents of water-soluble chlorides (Cl−) in recycled aggregates according to (11).

Fraction mm

Unreinforced Concrete

Reinforced Concrete

Pre-stressed Concrete

0–4 – 0.1% 0.015%

> 4 – 0.05% 0.007%


specimens made from the same standard mortar, but with extracted water, respectively distilled water. Differences in setting time and compressive strength of specimens prepared from extracted water and distilled water should not exceed 15% for the recycled aggregate to be accepted.

16. The content of flat pieces in coarse recycled aggregates as determined according to the vibration table test of the Organization for Applied Scientific Research in the Netherlands (TNO) should not exceed 30% by weight of total coarse aggregate.

17. If the rubble is to be used in asphaitic concrete, the requirements laid down in Items 5, 7 to 11, 13, 14, and 15 shall be waived. If used for construction of highway sub-bases, recycled aggregate must satisfy the requirements under paragraph 3.8 of the Dutch 1978 Requirements. For use in base courses or surface layers, the rubble must satisfy the requirements under paragraph 3.7 of the Dutch 1978 Requirements.

18 A proof of origin must be supplied with the rubble. The certificate must state:

a) date of dispatch by the supplier b) name of the haulage contractor c) type of aggregate d) size fraction e) standard requirements which the material is guaranteed to satisfy f) location and type of origin

When these product specifications are used, it is required in the draft of the new Dutchconcrete code VBT 1986 that ‘for stuctural members whose dimensions are governed bythe maximum permissible deflection it will be necessary to allow for 10% greaterthickness or depth in order to ensure adequate stiffness’. This is required in order toaccount for the lower modulus of elasticity and creep of recycled aggregate concretecompared with natural aggregate concrete. However, if only 20% of natural aggregateinstead of 100 percent is replaced by recycled concrete aggregate, this additionalthickness or depth of the members is not required.

13.5 United Kingdom

The new British Standard Guide 6543, ‘Use of industrial by-products and waste materialsin building and civil engineering’, covers the use of demolition waste and other wastematerials in both road construction and buildings. While not up to date in terms oftechnology, it does consider crushed concrete to be suitable for a wide range of sub-baseand base course applications. It even goes as far as approving, in principle, the use ofclean concrete and brick rubble for use as aggregate for concrete subject to minimumstrength requirements. This is a considerable step forward for recycling in the UK.

The current situation in the UK has been reviewed by Lindsell and Mulheron (87) andby Mulheron (135h).


13.6 USSR

In 1984, NllZbh of the USSR Research Institute for Concrete and Reinforced Concretehas published the first Russian ‘Recommendations on the recycling of sub-standard concrete and reinforced concrete products’.

According to the recommendations, coarse recycled concrete aggregates can be usedfor:

1. macadam bases for the floors and foundations of buildings and structures and for asphalt pavements of all grades,

2. production of 5–15 MPa concrete and reinforced concrete, 3. production of up to 20 MPa concrete and reinforced concrete when mixed with 50%

conventional crushed aggregate.

It is recommended that the crushed concrete fines be used as filler in the production ofasphalt concrete. It is not recommended to use crushed concrete fines for production ofnew concrete.

It is not allowed to use recycled concrete aggregates for production of prestressed concrete due to high shrinkage and creep as well as low modulus of elasticity.

13.7 Federal Republic of Germany

In the Federal Republic of Germany it is not allowed to use recycled concrete aggregatefor production of new concrete. Because of their density, such aggregates are too heavyto be classified as lightweight aggregates, and with a crushing strength of less than 100MPa, they are too weak to be classified as natural or crushed aggregate for production ofconventional concrete. At the present time permission is required for each individualproject to use recycled concrete aggregate for production of new concrete, but nopermissions have yet been granted.

However, during the period 1945–1955 large quantities of brick rubble werereprocessed and used in the production of new concrete. This resulted in the publication of a German Standard DIN 4163, written specifically to cover the production and use ofconcrete made with crushed brick. Under this Standard, concrete of a density between1600 and 2100 kg/m3 could be obtained with a maximum strength of 30 MPa and anelastic modulus of 15 GPa. Authorities in the Federal Republic of Germany are nowreconsidering their position on use of recycled aggregate concrete.

It is worth mentioning that there exists a West German Standard Specification for the use of recycle demolition waste in road construction (128).


13.8 Denmark

In 1990 Denmark will issue an amendment to the regular concrete code (116) which will allow the use of recycled aggregate concrete for certain structural purposes in mildenvironments. The amendment distinguishes between concretes having characteristiccompressive strengths up to 20 MPa (GP1) and concretes having characteristic strengthsup to 40 MPa (GP2).

GP1 recycled materials are required to have saturated and surface dry densities above2200 kg/m3. Such materials typically consist of crushed structural grade concrete.

GP2 materials are required to have densities above 1800 kg/m3 and typically consist of clean demolition rubble, typically a mixture of masonry and concrete.

Both materials are required to conform to the regular Danish codes for aggregate andconcrete for what concerns freedom from deleterious materials.

For the purpose of structural design the modulus of elasticity of GP1 concrete shall be assumed to be 80% of the prescribed values for conventional concrete and 50% forconcrete made with GP2 materials. Alternatively the true modulus of elasticity can bedetermined experimentally. The same coefficients of safety can be used for GP1 and GP2as for conventional concrete.

It has been established by experiments that the stress-strain relationship of recycled aggregate concrete is not significantly different from that of conventional concrete.Therefore, the same design criteria can be used for recycled aggregate concrete as areprescribed in the concrete code for conventional concrete. However, there are differencesfor what concerns design for instability of columns and walls as well as for deformationsin general. It is also assumed that the coefficient of variation of compressive strength testresults will be somewhat larger for recycled aggregate concrete than for conventionalconcrete.


14. Economic aspects of concrete recycling

Economic aspects of recycling of concrete have been analysed by Frondistou-Yannas (44, 45, 50) for what concerns the United States, by CUR (11) for what concerns the Netherlands, and by Drees (95) for the Federal Republic of Germany. The following conclusions can be drawn on the basis of these three studies:

Conditions which are conducive to successful operation of recycled aggregate plantsinclude:

1. Abundant and constant supply of demolition rubble 2. High dumping costs for demolition rubble 3. Easy access for heavy trucks 4. Suitable industrial land available, preferably next to a sanitary land fill. 5. Inaccessibility or scarcity, and therefore high cost of good quality natural sand and

gravel or crushed stone. 6. Ready market for products.

Considering these factors, it is not surprising that one of the largest recycling plants in theworld is located in West Berlin (54) and that densely populated countries such as parts of the United States, the Netherlands, Belgium, West Germany, and Japan are among thefirst to consider large-scale recycling of demolition waste.

Pavements and runways present favourable cases for recycling of concrete because large quantities of relatively clean concrete rubble are generated over a short period oftime. It is generated within a very limited area, and transportation along still existingparts of pavements presents no problem. Moreover, such rubble can be processed insimple plants without washing or elaborate sorting and cleaning.

In almost all practical cases where concrete pavements or runways have been crushed and recycled, considerable savings have been achieved compared to the combined cost ofdumping the old concrete and hauling in new base or sub-base material from pits and quarries or producing new concrete from conventional aggregate (7). Obviously, the largest savings have been achieved where conventional aggregate was locallyunavailable, and for that very reason most of the recycling projects that have been carriedout so far have been located in areas with a shortage of natural aggregates.

However, concrete used in streets and highways typically accounts for only about 15–20% of total concrete consumption in industrialized countries (44, 45). In order to operate recycling plants at high capacities, thereby realizing economies of scale, the largequantities of concrete rubble generated from the demolition of old buildings, pavements,sidewalks, driveways, curbs, gutters, etc. are also required, and it must be processed into aggregate for production of new concrete which can be accepted by the constructionindustry as a reasonable alternative to conventional aggregate.


The economy of large-scale recycling of mixed concrete rubble in metropolitan areas isvery much different from the economy of recycling of pavements and runways. For onereason it introduces the problem of contamination as the demolition rubble is mixed withgypsum, wood, plastics, and steel (49) which must be removed before the recycled product can be used for production of new concrete. Thus, much more elaborate plantsare required to process mixed demolition rubble than clean concrete from highwaypavements. A flow chart illustrating the design of a plant which is capable of producingconcrete aggregate from mixed demolition debris is shown in Figure 6.2.

The macro-economics of plants capable of processing mixed concrete debris in the United States were studied by Frondistou-Yannas (44, 45, 50).

Frondistou-Yannas found that a prerequisite for the economic justification of concreterubble recycling is the presence of sufficiently large quantities of concrete debris so that arecycling plant of optimal size can be operated at high utilization factors. Accordingly,several researchers (48, 49) have assessed the quantities of concrete debris producedlocally in the United States. It has been found that, on the average, 0.27 tons of concreterubble per capita are generated each year in the United States. It follows that in urbanareas with a population greater than half a million people, the amount of concrete debrisgenerated annually is of the order of a few hundred thousand tons. By contrast, a singlehighway demolition project produces only a few tens of thousand tons of debris.

On the basis of an economic analysis, Frondistou-Yannas found that in order to realize economics of scale, a plant should process at least 110–275 tons of debris per hour, and in order to produce a reasonable return on investment, the plant should process and sellno less than 200 000 tons of recycled aggregate per year. This implies that urban areas ofat least one million people are needed to support the operation of a concrete recyclingplant in the United States. There are no reasons to believe that this requirement would besubstantially different in other industrialized countries.

Frondistou-Yannas suggests for economical and other reasons that the most favourablelocation of a recycling plant would be at a fixed position near a large city, preferably nextto a sanitary land fill so that trucks that bring in debris on their way back will carryaggregate. The adjacent sanitary land fill additionally reduces transportation costs asconcrete contaminants do not have to be transported to a distant dump. Portable unitsshould be used so that the plant can be relocated to a different site next to a new sanitaryland fill when the capacity of the old fill is exhausted. However, recycled concreteaggregate can be sold only if it compares favorably with its competitor, natural aggregate.

CUR (11) has analysed economic aspects of recycling of concrete in the Netherlands and attempted to make a comparison between the two types of aggregate on the basis oftwo concrete members of equal performance, one made with recycled concrete aggregateand the other with natural aggregate.

Table 14.1 shows the main factors adding up to the total cost of recycled aggregates. CUR (11) found that:

1. The extra work on the demolition site which is required in order to prepare demolition debris for recycling is equivalent to 25% of the regular demolition costs (S1).

2. Dumping charges (s2) depend very much on local circumstances. In the Netherlands in 1982 they varied from 3 Dfl (Dutch guilders) to 30 Dfl per m3.

3. The extra costs for preparation, processing, inspection, storage, and sale of recycled


aggregates, s7=12 Dfl, which appear in Table 14.1 and later in Table 14.2, are based on an average of estimates made in 1982 by a number of Dutch companies actually engaged in commercial processing and sale of recycled aggregates.

Table 14.2 gives the Dutch cost comparison between concretes of equal strength,produced with natural gravel and recycled concrete aggregate. All costs quoted are basedon experiences from real productions in the Netherlands, and they are quoted in 1982prices in Dutch guilders. Costs of transportation are assumed to be equal for all fourconcretes.

It will be seen from Table 14.2 that when dumping charges for demolition debris areleft out of consideration, recycled building rubble was not competitive for concreteproduction in the Netherlands in 1982 as compared to natural gravel.

The 1982 market prices which are quoted in Table 14.2 for recycled aggregates applyto rubble aggregates used as road-base materials. For such purposes rubble aggregate iscompetitive because crushed natural rock which is required for road construction is moreexpensive than natural gravel. In 1982 nearly two million tons of demolition rubble wereprocessed into recycled aggregates and used for unstabilized road bases in theNetherlands.

In order to be competitive for concrete production it appears from Table 14.2 that in theNetherlands, recycled aggregates would have to sell for approximately 25% less, insteadof 50% more than natural gravel in order to compete with natural gravel for concreteproduction.

In 1982 recycled concrete aggregates produced by the only large scale plant in Franceat Limeil-Brevannes near Paris was selling at twice the cost of natural materials (94). For

Table 14.1 Comparison of cost elements in the processing and handling of natural aggregates and recycled aggregates (D.fl.=Dutch guilders).

Natural Aggregates D.fl. Re-Use of Rubble Granules D.fl.

Excavation costs n1 Extra treatment of debris at the demolition site

s1

Production costs (including interim storage)

n2. Dumping charges (negative) for demolition debris

s2

Bulk transport costs n3 Costs of transport of demolition debris to dump (negative)

s3

Costs of transport to building site

n4 Costs of transport of debris to processing plant

s4

Processing costs for recycled aggregate s5

Costs of transport of recycled aggregate to building site

s6

Extra costs for inspection, storage, and sale of recycled aggregate

s7


comparison, Frondistou-Yannas found that in the United States recycled aggregates would have to sell for at least 50% less than natural gravel in order to compete on equalterms with natural gravel for concrete production. Even at this price an unprejudicedperson would be indifferent to natural aggregate or recycled aggregate.

However, there are good reasons why a person could be prejudiced against recycledaggregate. For one, experience with it is limited and uncertainties remain concerning theperformance of recycled aggregates in concrete. Secondly, extra costs andinconveniences are involved in the use of recycled aggregates for concrete productionsuch as for example costs of pre-soaking, extra inspection, and costs of compensating for lower strength and higher creep, shrinkage, and elastic deformation of recycled aggregateconcrete. Some of these costs may be offset by lower density or better thermal insulationof recycled aggregate concrete. Even so, the price of recycled aggregates will have tocome down from today’s level in order for the material to be competitive with conventional aggregate.

There are two ways in which this can come about.

1. The extra cost of 12 Dfl/ton, which was charged in the Netherlands when the report was prepared for the processing of old concrete and building rubble into recycled aggregate, can be lowered once the initial developing phase is over. Already in 1982 this would have brought the price of recycled aggregate down to a level where it would have been competitive with natural gravel provided the customer was unbiased.

Total

Total

Requirement for recycled aggregate to be competitive provided the buyer is unbiased: ∑s

i≤∑ni

Table 14.2 Cost comparison between concretes made with natural gravel, recycled concrete aggregate, brick rubble, and mixed concrete and brick rubble aggregate in the Netherlands (1982).

1. Natural gravel concrete with 1080 kg of gravel at Dfl 22/ton Dfl 23.76/ton

2. Concrete made with recycled concrete aggregate

– 900 kg of recycled concrete aggregate (4–32 mm) at Dfl 17/ton (production and processing costs)

Dfl 15.30/ton

– 40 kg of cement at Dfl 125/ton Dfl 5.00/ton

– Extra costs for inspection, storage, and sale) at Dfl 12/ton Dfl 12.00/ton

Total Dfl 32.30/ton


2. The price of conventional aggregates will continue to rise as raw materials get scarcer and transportation costs higher. More important, dumping charges for demolition debris are expected to rise steeply as the quantity of demolition debris and particularly that of concrete debris will continue to increase rapidly throughout the next decades. Without crushing, concrete debris packs very poorly and tends to render sanitary fills unsuitable for future use as building sites.

All in all it can be expected that the use of recycled aggregate for concrete production willincrease in the future as both the demand for roadbase material and the price of recycledaggregate is foreseen to decrease in most industrialized countries.

Drees (95) found that in West Germany one may count on the generation of 0.3 tons ofdemolition rubble suitable for recycling per person per year. This makes for a total of 18million tons per year. It is considerably less than what is assumed in the optimisticestimates which have been made by other authors. Compared to a total yearly productionof 500 million tons of raw materials of mineral origin in West Germany, 18 million tonsis a small part. However, it is significant, because demolition waste amounts to 2/3 byweight, or 1/4 volume of the total yearly deposits on city dumps. The costs of manuallysorting the demolition waste would amount to 25 DM/m3 in 1989 prices. Mechanicalsorting would reduce the costs to 8–10 DM/m3 in 1989 prices.

At the present time economical use of clean demolition rubble is only sensible for roadconstruction or as fill. Use of crushed and cleaned demolition rubble as aggregate forproduction of structural concrete is not economically viable and probably not technicallydesirable because of its lower quality compared to conventional aggregates.

When building structures are demolished and it is desired to reuse the concrete, allcomponents which contain deleterious materials such as wood, plastics, glass, lightweightmaterials and metals should be removed as far as this is economically possible beforedemolition of the load carrying structure itself. However, Drees (95) does not believe intotal selective demolition based on the demounting of buildings in the reverse order ofconstruction. He feels that this is considerably more expensive than pre-sorting of themixed demolition rubble at the recycling plant and later wet or dry separation ofdeleterious components in the recycling plant itself.

After a thorough review of different lay-outs and equipment of recycling plants fordemolition waste, Drees (95) arrives at the conclusion that the total cost of a stationaryplant itself would be 3.2–4.5 million DM in 1989 prices without including the cost of realestate. This is considerably more than what has been assumed by others, but probably arealistic estimate. Mobile and semimobile plants would cost between 700 000 and 900000 DM in 1989 prices according to Drees.

Production costs of marketable recycled demolition rubble depends on the requiredquality of the material produced. The least expensive is demolition rubble produced by amobile plant on the demolition site, where the product is only intended for use as fill. Thesame is true for reuse of demolition rubble on site for road construction purposes.According to Drees (95) production costs for such materials would typically besomewhere between 5 and 7 DM/t in 1989 prices. For cleaned and processed buildingdemolition waste produced to high quality requirements in stationary plants the costswould typically be 10–12 DM/t and could rise to more than 15 DM/t if the plant runs atlower than optimum capacity.


Charges for receiving demolition rubble at dumps, and sales prices for end productsdepend on local conditions. If there is a long distance to the nearest dump, high dumpingcharges of 8–11 DM/t can be expected for reception of the rubble. If at the same timetransport distances for virgin fill and aggregates are long, crushed and clean recycledmaterials can possibly be sold for 10 DM/t. Under less favourable conditions charges forreceiving demolition waste may be as low as 3–4 DM/t and the sales price for processed material may have to be as low as 6–8 DM/t. In order to break even, it is estimated thatthe difference between dumping charge and sales price should be at least 10 DM/t for astationary plant. For existing plants this difference was frequently only 9–9.5 DM/t in 1989. Thus, the processing of demolition rubble is not yet a profitable business.

Drees (95) is not in favour of government interference, but he does recognize thatgovernment regulation of dumping charges for demolition waste in heavily populatedareas must be regulated if recycling plants are going to have a realistic chance to survive.He also recommends that any requirements to recycled products which are superfluousfrom a technical point of view, should be abandoned. Furthermore, he belives that therisk of pollution of ground water by seepage from clean demolition waste is exaggeratedand that many current requirements to cleanness of such materials could be relaxed. Thiswould certainly promote more extensive use of recycled demolition waste.

15. Energy aspects of concrete recycling

Copple (7e) compared the energy required for production of recycled aggregate concrete with the energy required for production of conventional concrete with virgin aggregate.Energy requirements which are common to both types of concrete as well as energyrequirements which are unique to each type of concrete were considered.

Energy requirements which are unique to conventional mixes include hauling and disposal of old concrete, production of virgin aggregates, and hauling of virginaggregates. Energy requirements which are unique to recycled aggregate concrete includemoving crusher to the job site, crushing and screening of concrete, and transporting oldconcrete to crusher and from crusher to plant if machines are at different sites.

Results are plotted in Figure 15.1. It will be seen that energy savings are realized for recycled aggregate concretes even when virgin aggregates must be hauled only a fewmiles. As haul distances increase, so do savings.


16. Practical case histories

Ray (20) has traced developments in recycling of concrete pavements through current demonstration projects sponsored by the Federal Highway Administration in the UnitedStates. Projects discussed include highways and airports. The use of recycled concrete in

Figure 15.1 Energy savings (per cent) of recycled as compared to conventional concrete, from Ref. (7e).

sub-bases, cement-treated sub-bases, lean concrete bases, and concrete pavements is alsodescribed.

At Love Field, Dallas, Texas, a new runway was placed on a 15 cm cement treatedsub-base in 1964. The mix used 72% of crushed concrete from the old pavement on the site of the new runway, 28% natural sand, and 4% cement by weight.


The first use of recycled concrete in a lean concrete (Econocrete) sub-base for a new concrete pavement was in California. The lean mix concrete which used a mixture ofrecycled concrete and asphalt required 8% cement. The average 28-day compressive strength was 5 MPa.

In 1977 crushed concrete was used as aggregate in a lean concrete sub-base for a keel strip at the Jacksonville, International Airport, Florida.

The first successful use of recycled aggregate for production of new concrete was in Iowa in 1976. A 41-year old concrete pavement was crushed and used as aggregate in production of concrete for a new one-mile long and 22.5 cm thick highway pavement.

In another project in Iowa in 1978, crushed old concrete was used as aggregate for production of a new 17-mile long and 20 cm thick highway pavement. The mix designcalled for 638 kg/m3 of recycled coarse aggregate, 375 kg/m3 of recycled fine aggregate, 551 kg/m3 of natural fine aggregate, and 369 kg/m3 of cement.

In Connecticut in 1980, a 1000-feet long section of a 24–year old reinforced concrete pavement was recycled into a new 22.5 cm thick reinforced concrete pavement. Theresulting mix showed flexural strengths over 3.5 MPa at 28 days.

Also in 1980, the Minnesota Department of Transportation recycled a 16–mile plain concrete pavement into a new concrete pavement on a trunk highway. The pavement wassuffering severe distress from ‘D’ cracking. Studies in the Department laboratoriesproved that concrete made with the recycled concrete would provide suitable durability ifthe maximum aggregate size was set at 19 mm. The use of recycled concrete in the newpavement has saved the Minnesota Department of Transportation in excess of US$600000.

The largest concrete pavement recycling project to date is the Edens Expressway reconstruction job in Illinois. Here 15 miles of six-lane pavement was recycled and placed as new sub-base material in 1979 and 1980.

In 1983 the Minnesota DOT awarded two adjoining projects on Trunk Highway 15—a total of 11 miles. These were also a ‘D’ cracked pavement—similar to the 1980 project. The equipment and techniques for these projects corresponded to those used before.

Oklahoma became the first state to recycle a full-size project on the Interstate System. They took alternative bids on a 7.7-mile, 4-lane project on Interstate-40 east of Oklahoma City. The base bid called for three layers of asphalt totalling 8 3/4 inches. The alternativewas for removal and recycling of 220 382 square yards of the existing 9-inch plain concrete using the crushed ‘D’ cracked pavement as the aggregate in a new 10-inch slab. As in Minnesota, the maximum size specified for the coarse aggregate was 1 inch (90%to 100% of the material passing the 3/4-inch sieve) to prevent ‘D’ cracking in the new pavement. This work was carried out by paving alternate roadways in two 4-mile sections while traffic used the opposite side.

Michigan also awarded a major Interstate recycling project in 1983. In less than fivemonths 5.7 miles of four-lane divided pavement (‘D’ cracked 25-year old concrete) was replaced. The bid prices on this project were so good that Michigan advertised a secondproject on Interstate 75. The new 10-inch pavement with tied shoulders was built oneroadway at a time to accommodate traffic. Information on developments in the UnitedStates was received from Gordon K.Ray (20) who also provided a list of additional pavement recycling projects in the U.S. in 1984 and 1985, see Table 16.1.


As a result of these and other pioneering efforts, the Federal Highway Administration hasset up several two- or three-man teams to travel around the United States contacting StateHighway Departments to encourage them to recycle old pavements and offering tounderwrite part of the costs involved. Also, as mentioned in Chapter 13, the ASTM and the US Army Corps of Engineers have removed all national barriers to the use ofrecycled Portland cement concrete as concrete aggregate.

In just one construction season, the Michigan Department of Transportation (MDOT) has removed, recycled and replaced more than 400 000 m3 of 10 in. concrete pavement on one of Detroit’s busiest highway stretches (109) and (110). MDOT made use of the

Table 16.1 Concrete recycling projects in the US in 1984 and 1985.

State Route Location Length in miles

Quantity in square yards

1984

Wisconsin 1–90/94 Madison N. 31.70 798500.00

Wyoming 1–80 Evanston 4.50 200000.00

Oregon 1–5 N. Albany 7.00 210250.00

Michigan 1–75 NB

Monroe Co. 6.00 211134.00

Michigan 1–94 Van Buren 9.20 402312.00

Michigan 1–75 Wayne Co. 10.00 381977.00

Illinois Fwy 412 Macon Co. 3.34 100220.00

Minnesota 1–90 Austen 2.50 82196.00

Minnesota 1–90 N.D. line 3.80 122663.00

North Dakota 1–94 EB Eckelston 13.10 311634.00

1985

Wyoming 1–80 Green Ri. 5.90 263000.00

Wyoming 1–80 Pine Bluff 7.10 315000.00

North Dakota 1–29 NB

Blanchaard 10.40 84400.00

Michigan 1–94 Kalamzoo 8.66 443976.00

Kansas 1–70 Abilene 9.30 420000.00

Kansas 1–235 Wichita 15.50 700000.00

Wyoming 1–80 Rock Springs

9.50


lessons learned from 14 previous recycling jobs where more than 2 500 000 m3 of old concrete were recycled. The old concrete from the Lodge Freeway recycling projectproduced 200,000 tons of coarse aggregate, more than enough for 380 000 m3 of 25 cm thick reinforced concrete pavement and 84 000 m3 of reinforced concrete shoulders placed during reconstructions. The 67 000 tons of crushed concrete fines below 5 mmwere not used in the concrete mix, but the steel recovered from the old pavement wasclean enough to be melted down and recycled. From a technical as well as an economicalpoint of view the fact that this project was successfully carried out is evidence that therecycling of concrete has moved from an experimental stage to a cost effective way ofconserving resources.

With approximately 60 million cubic yards of concrete now utilized yearly in US roadbuilding, and with more expected for rebuilding of 3.8 million miles of roads andhighways under the additional $5.5 billions a year provided by the Surface TransportationAssistance Act of 1982, the volume of recycling is expected to increase rapidly in the US(113).

With barriers removed, the many concrete recycling plants which operate in andaround major cities in the United States are brought into focus. Here old concretesalvaged from old buildings, pavements, sidewalks or curbs and gutters is crushed,stockpiled, and sold to contractors. Most of this material is used as unstabilized base orsub-base at the present time, but as concrete aggregate becomes scarcer and more expensive, its use may be extended to new concrete. Tests by many agencies on recycledconcrete as aggregate for new pavement show excellent strength and durability.

The numerous commercial concrete recycling plants in major metropolitan areas around the United States are of greater economic significance than concrete pavementrecycling projects.

The economic feasibility of concrete recycling is discussed in Section 14. The technology of concrete recycling is well established in the United States and is

well documented in Anon. (97). Recycling of Portland cement concrete has proven itselfto be a cost effective alternative for road construction purposes. In 1987 there had alreadybeen over 1000 lane miles of portland cement concrete pavements recycled into newpavements. Whenever reconstruction of a concrete pavement is contemplated, recyclingshould be considered as an alternative. In most cases recycling of concrete has provenmore economical than the alternative of using virgin aggregate. However, in some casesthe condition of the existing pavement and local aggregate availability and cost, willindicate that recycling of the in-place concrete is not the best option. Life cycle cost studies may result in a complete reconstruction using new concrete pavement with virginaggregates. There always remains the option of using the old concrete in the sub-base or as improved granular subgrade or for reconstruction of appurtenances other than pavements such as drainage, side slopes, shoulders or backslopes.

There is a paucity of published information on recycling projects in the rest of the world. Yrjanson (7g) reports that an urban expressway north of Paris, France, has been recycled and used in a lean concrete base and porous concrete shoulders.

A number of other recycling projects in France are reported in Refs. (131)–(134) and an excellent general review of the state-of-the-art in France including case histories is presented by Bauchard (135l).


Hendriks (64) reports that in Europe by far the largest quantities of demolition debris are recycled in the Netherlands. It is estimated that 0.43 tons of debris is generated eachyear per person, and more than 60 stationary and mobile recycling plants have beenestablished in the Netherlands. The largest stationary plant with a yearly capacity of 200000 tons is located in Rotterdam. Van Eck (81) reports that wood is sorted out from concrete and masonry rubble which is then crushed, washed, screened, and sold for roadconstruction purposes. In the future 50,000 tons of wood waste a year from the Rotterdamplant will be processes in a pyrolysis plant which will generate charcoal, tar, and woodgas.

From January 1985 it has also been allowed to use recycled aggregates for production of concrete for general construction purposes in the Netherlands. Hendriks (57) reports that the first use of recycled aggregate concrete in the Netherlands was in Amersfoortwhere such concrete was used for partition walls in an apartment building. The concretewas produced with the same cement content as regular concrete and met requirements toa characteristic strength of 22.5 MPa. The water requirement was slightly higher thanwould have been the case for regular concrete, and the concrete required vibration for asomewhat longer time. Relatively high drying shrinkage of recycled aggregate concretedid not result in any cracking of walls.

Hendriks (64) also reports that at the Volkel Airfield in the Netherlands coarserecycled aggregate concrete was used for a lean concrete base course and concretepavement. The compressive strength was 10% to 20% lower than what would have beenexpected for a conventional concrete of the same mix proportions. At Maastricht Airport,also in the Netherlands, a concrete pavement was made with recycled aggregate concrete.The concrete met requirements to a characteristic strength of 37.5 MPa.

At the Copenhagen International Airport in Denmark recycled concrete aggregate hasbeen used as base course for a new runway and on an experimental basis in the concretepavement for new aprons (79).

Schulz (82) reports that there are 60 recycling plants in the Federal Republic ofGermany with a total capacity of 10 million tons a year or more than two-thirds of all available demolition rubble. However, only 2.7 million tons a year of recycled aggregateis used primarily as sub-base material, so the plants are working much below their full capacity. In the Federal Republic of Germany it is not allowed to use recycled concreteaggregate for production of concrete. Such aggregates are too heavy to be classified aslightweight aggregates; and with a crushing strength of less than 100 MPa, they are tooweak to be classified as natural or crushed aggregate for production of concrete.

It is regrettable that outdated concrete specifications prevents the use of recycled concrete in new concrete in the Federal Republic of Germany. Schulz (135d) reports on an abortive attempt in 1987 to obtain a single permit to reuse 5 000 tons of recycledconcrete for production of new concrete in West Berlin. However, such materials is beingextensively used as unbound as well as cement bound sub-base material in road construction as evidenced by two recent publications (111) and (112) which describe the use of such materials in the restoration of motorways in Western Germany.

Kasai (66) reports that recycled aggregate is used for road construction in Japan. There is no production of recycled aggregate for concrete production because the authoritieshave not yet approved the Japanese Proposed Standard for the ‘Use of recycled aggregate


and recycled aggregate concrete’ (6). However, Kasai (66) reports that the Building Research Institute of the Ministry of Construction in Japan has constructed a small houseas part of its technological development work on reusing construction waste forconstruction activities. In this test recycled concrete aggregate was used for ready-mixed concrete, and no problems developed regarding slump, air content, workability orcompressive strength. The behavior of the concrete in the structure is currently underobservation.

Zagurskij and Zhadanovskij (83) report that in the USSR, recycling plants with a total yearly capacity of 720 000 m3 are currently in operation. The plants are located at 18different precast concrete factories in various parts of the country, including four inMoscow. Coarse recycled concrete aggregate is used for foundation purposes and forproduction of new structural concrete up to a characteristic strength of 20 MPa. Crushedconcrete fines are also used as mineral filler in asphalt.

Krejcirik (122) reports that the Czechoslovakian State Railways crush reinforcedconcrete sleepers that can no longer be used for track construction. This paper describesthe recycling process and shows how the materials recovered can be put to economicaluse.

Trevorrow et al. (135r) has reported on the current situation in the UK and they have included some case histories in their paper.

Morlion et al. (135t) reports on the successful construction of the embankment walls ofthe new ‘Berendrecht’ lock using demolished concrete from the old ‘Zandvliet’ lock in the harbour of Antwerp in Belgium.


17. Recycling of fresh concrete wastes

Recycling of alkaline waste water and waste aggregate from ready-mixed concrete plants are important from the point of view of preventing public nuisance and the saving ofnatural resources.

About 50 million m3 of ready-mixed concrete is produced in the Federal Republic of Germany each year. Roughly 3% of this quantity (i.e. 1.5 million m3) arises as waste concrete, which at the present time is largely disposed of by dumping. Riker (73, 74) and Friesenborg et al. (75) describe in detail how fresh waste concrete can be recycled. However, it is beyond the scope of this state-of-the-art report to deal with requirement forrecycled fresh waste concrete.

A survey which was carried out in the United States revealed that dumping was themost practical method of disposal of left-over ready-mixed concrete (123). However, some recycling does take place.

If waste water was recycled in all of the ready-mixed concrete plants in Japan with anannual production of 150 million m3 of concrete, over 25 million m3 of fresh water and more than 2.5 million m3 of aggregate could be saved annually. The Japanese Standard Specifications for Ready-mixed Concrete, JISA 5308, has been modified to make thispossible, and at the present time 52% of all Japanese plants are recycling clarified waterand 17% successfully recycle slurry water. Results of investigations which led to thisdevelopment are reviewed by Kasai (76).

Grelk (124) has prepared a comprehensive state-of-the-art report on the recycling of concrete waste reviewing 34 literature references from all over the world. He has alsoconducted his own research (125). Grelk concludes that only slump and setting time offresh concrete are affected by the use of up to 15 weight per cent of waste concrete fines< 0.3–0.5 mm suspended in the mixing water for new concrete. No other properties of fresh concrete or properties of hardened concrete were significantly affected. However,setting time of fresh concrete can be reduced by more than one hour and slump of thefresh concrete was typically reduced by 10 mm for each 2% of waste concrete fines in themixing water. An amendment to the Danish Concrete Code is being prepared allowingthe use of waste-water from ready-mixed concrete plants containing up to 15 weight percent of waste concrete fines to be used for production of new concrete provided properprecautious are taken. Reclaimed, washed and screened sand and gravel from waste readymixed concrete can be used as normal aggregates without further treatment.

Culuknoise (77) has studied the recycling of rebound from shotcrete.


18. Conclusions and recommendations

1. Numerous laboratory experiments, field tests, and full scale pavement rehabilitation projects have shown that it is possible to recycle concrete to produce aggregate for drainage material, shoulders, stabilized as well as unstabilized base courses, bituminous concrete, lean mix, and econocrete sub-bases as well as new concrete pavements.

Recycling of concrete to produce structural grade concrete for other purposes than pavements is technically feasible provided certain precautions are taken. Giving contractors the option to recycle will determine the economic feasibility of such operations.

2. Plants for production of recycled concrete aggregates are not much different from plants for production of crushed aggregate from other sources.

First generation processing plants incorporate various types of crushers, screens, and transfer equipment. With the possible exception of a magnet for the separation of reinforcement and other ferrous matter, they have no facilities for removal of contaminants. Such plants are frequently used on pavement rehabilitation and recycling projects. In most cases uncontaminated recycled concrete aggregate can be used for production of new concrete without being washed. Second generation plants incorporate various kinds of sorting devices for dry or wet removal of foreign matter from concrete. Such plants are in commercial operation. In the third generation processing plants of the future all demolished material should be supplied to the installation and processed into saleable products without there being any need to transport residual matter to dumping sites either from the demolition site or from the processing installation. Such plants are not yet in operation.

3. Operation of a crushing and screening plant is always accompanied by the generation of noise and dust. Therefore, in the selection of plant location, environmental conditions of the vicinity, and legal requirements must be carefully studied and necessary countermeasures taken. However, the early concern about noise and dust problems when crushing concrete in mobile plants in urban areas has apparently been somewhat exaggerated.

4. Plain as well as reinforced concrete can be crushed in various types of crushers to provide a crushed aggregate with an acceptable particle shape. When crushed in one pass, the grain size distribution of recycled concrete aggregate frequently approximates a Fuller curve.

5. Impact crushers provide the best grain size distribution of recycled concrete aggregate, and they are less sensitive than jaw crushers to material which cannot be crushed such as reinforcing bars.


When it comes to other properties of recycled concrete aggregates, jaw crushers perform better because they crush a smaller proportion of original aggregate particles in the old concrete than impact crushers.

6. There was some concern expressed initially about the removal of steel from reinforced concrete, particularly pavements with heavy mesh. Through the innovation of contractors in developing breaking, removal and crushing equipment and procedures, this problem has largely been overcome.

7. Approximately 30% by volume of old mortar is attached to 16–32 mm coarse recycled aggregate. Corresponding figures are 40% for the 8–16 mm fraction and 60% for the 4–8 mm fraction. Fine recycled aggregate below 4 mm contains approximately 20% by weight of old cement paste, while the filler fraction 0–0.3 mm may contain as much as 65% of old cement paste.

8. Because of the large content of old mortar in the crushed material, the density of recycled concrete aggregates are from 5 to 10% lower than the density of corresponding original aggregates.

Water absorptions of 5–10% are typically found for recycled aggregates. Relatively high values are found for fine recycled aggregate. Relatively low values are found for coarse recycled aggregates. Due to high water absorption of recycled aggregates, it is sometimes recommended to use pre-soaked aggregates for production of recycled aggregate concretes in order to maintain uniform quality during concrete production. However, it has not been studied how fully saturated recycled aggregate will affect freeze-thaw resistance of new concrete. Because the density is lower and the water absorption is higher, and because the range of densities and water absorption is higher for recycled concrete aggregates than for conventional aggregates, it is imperative that density and water absorption of recycled concrete aggregates be carefully determined before it is attempted to design a mix of recycled aggregate concrete. Moreover, it is important that the two properties be carefully monitored during concrete production. This must be done in order to avoid large variations in properties of hardened concrete as well as in yield of fresh concrete. This is fairly easy when coarse recycled concrete aggregate is used with natural sand, but difficult when fine recycled concrete aggregate is used. It is very difficult to determine the free water content of fine recycled aggregates. That is one of many reasons why it is not recommended to use fine recycled concrete aggregate for production of new concrete. It is very difficult to determine the free water content of fine recycled aggregates.

9. Recycled concrete aggregates, produced from all but the poorest quality of concrete, can be expected to pass ASTM and BS requirements to LA abrasion loss percentage, BS crushing value as well as BS 10% fines value, even for production of concrete wearing surfaces, but probably not for granolithic floor finishes.

10. American results indicate that the sulfate soundness of recycled concrete aggregates generally is lower than ASTM maximum allowable limits. Japanese results indicate that the opposite is true. Further research is required in order to determine whether the sulfate soundness test is suitable for evaluation of the durability of recycled concrete aggregates, and in order to explain the large discrepancy between American and Japanese results.


11. In standard specifications on recycled concrete aggregates it is recommended to impose maximum allowable limits on the content of contaminants such as bitumen, gypsum, organic substances, soil, chlorides, metals, and glass. See Section 7.7.

12. In the laboratory it is found that compressive, tensile, and flexural strength of recycled aggregate concrete can be equal to or higher than that of original concrete when the recycled aggregate concrete is made with the same or lower water-cement ratio than the original concrete. However, in practice and often in the laboratory, strengths of recycled aggregate concretes are found to be lower than those of corresponding original concretes. This is particularly important when it is attempted to produce structural-grade or high-strength recycled aggregate concrete from original low strength concrete or when recycled fine aggregate is used with recycled coarse aggregate. In such cases the compressive strengths of conventional structural concrete and corresponding recycled aggregate concrete made with the same water-cement ratio may vary by as much as 50% or more depending on the quality of the recycled concrete from which the recycled aggregate is derived. More commonly the compressive strength of recycled aggregate concretes is found to be 5–10% lower than that of corresponding concretes made with conventional aggregates.

Differences in strength between the two types of concrete are smaller and less important when lower strength foundation grade-recycled aggregate concretes are produced. However, it is recommended always to make trial mixes in order to determine the strength potential of any recycled aggregate before it is used in production.

13. When a recycled concrete aggregate of uniform quality is used, the coefficient of variation of compressive strength between mixes of recycled aggregate concrete is no different from that of original concrete.

When recycled aggregates of non-uniform quality are used, the coefficient of variation of compressive strength between mixes may be very high for structural grade concretes, but lower for foundation grade concretes. This may be the case when recycled aggregate is delivered from a central crushing plant in an urban area which accepts concrete rubble from many different demolition sites simultaneously. Considering that acceptance criteria for structural concrete in modern concrete codes frequently are based on the standard deviation or the coefficient of variation of compressive strength test results, it may not be economical, though technically feasible, to produce structural grade concrete from recycled aggregate of non-uniform quality. Thus, in the future such recycled aggregates may be limited to production of lower grade concretes, if only for economic reasons.

14. There is some evidence that coarse recycled aggregates can be used in reinforced concrete without any inconveniences at all. Use of both coarse and fine recycled aggregate may lower bond strength between concrete and reinforcing bars by 15% and ultimate flexural strength of reinforced concrete by as much as 30% due to bond failure, when compared to bond and flexural strength of corresponding reinforced concrete made with conventional aggregates. Further investigations into this matter are recommended.

15. Due to the large amount of old mortar which is attached to original aggregate particles in recycled aggregates, the modulus of elasticity of recycled aggregate


concretes is always lower than that of corresponding control concretes. Values from 15% to 40% lower are reported. Comparatively high values of elastic modulus are reported for recycled aggregate concretes produced with coarse recycled aggregate and conventional sand. Comparatively low values of elastic modulus are reported when both coarse and fine recycled aggregates are used.

16. Due to the large amount of old mortar which is attached to original aggregate particles in recycled aggregates, drying shrinkage and creep of recycled aggregate concrete are always from 40% to 80% higher than for corresponding control concretes which are made with conventional aggregates. Comparatively low drying shrinkage is reported for recycled aggregate concretes produced with coarse recycled aggregate and conventional sand. Comparatively high drying shrinkage is reported when both coarse and fine recycled aggregates are used.

As the effects of high drying shrinkage and high creep tend to cancel out in restrained structural members which are made from recycled aggregate concrete, such members appear to be no more prone to cracking due to drying shrinkage than members which are made from conventional concrete.

17. It is generally accepted that when natural sand is used, up to 30% of natural crushed aggregate can be replaced with coarse recycled aggregate without significant changes in the mechanical properties of concrete.

18. When new concrete is produced from coarse recycled aggregate, the presence of plasticizing, retarding, and air entraining admixtures in the old concrete has no significant effect on the properties of the new concrete. However, when calcium chloride has been added to the old concrete as an accelerating admixture, approximately 30% of the original chloride content can be traced as free chlorides in the new concrete. This may significantly accelerate strength development of the recycled concrete. Also, when parking or bridge structures have been submitted to de-icing chloride containing salts, or when marine structures have been exposed to sea water for long periods of time, fairly large amounts of chlorides can be traced in recycled concrete aggregates.

Considering the fact that specification limits on chloride content in concrete for the purpose of protecting reinforced structures against corrosion tend to become even more strict, chloride contamination may eventually turn out to be a serious obstacle towards more widespread use of recycled aggregates in concrete production.

19. On a more positive side it appears that small amounts, up to 1% by weight, of bitumen from asphaltic concrete surfacing which remains in coarse recycled aggregate will not seriously affect the properties of recycled aggregate concrete.

20. Surprisingly perhaps, there is evidence to support the fact that when recycled aggregate concrete is produced with coarse recycled aggregate which originates from structural grade concrete, frost resistance of the recycled aggregate concrete will be as good as, or better than the frost resistance of the original concrete.

There is also some evidence that repeated recycling of such concrete may continue to improve frost resistance. Therefore, one may project that existing concrete structures, in addition to providing an aggregate source for the immediate future, may continue to generate an adequate supply of aggregates for concrete construction in the more distant future after once being recycled.


However, when both coarse and fine recycled aggregates are used, or when low-grade recycled aggregates are used, frost resistance of a recycled aggregate concrete may be lower than that of corresponding control concretes made with conventional aggregates. Frost resistance of recycled aggregate concrete is reported to be improved when 16–19 mm maximum size coarse recycled aggregate is used rather than 32–38 mm maximum size. Further studies of the frost resistance of recycled aggregate concretes are urgently recommended, particularly the use of air entrained recycled aggregate concrete made with recycled aggregates which originate from original concretes of different qualities and which have not been air entrained.

21. No studies have been reported on the susceptibility to alkali reactions of recycled aggregate concrete produced from recycled aggregates which originate from original concrete that has been damaged by alkali reactions. Such studies are also urgently needed.

22. For equal water-cement ratio, the water permeability, the rate of carbonation and therefore the risk of reinforcement corrosion seems to be somewhat higher for recycled aggregate concretes compared to conventional concretes. However, it appears that such undesirable effects can be offset if recycled aggregate concretes are produced with slightly lower water-cement ratios than corresponding conventional concretes.

23. No attempts have been made to compare rates of chloride penetration into recycled aggregate concretes and corresponding conventional concretes. Such studies are urgently needed.

24. In principle, mix design of recycled aggregate concrete is no different from mix design of conventional concrete, and the same mix design procedures can be used. In practice, slight modifications are required as shown in Section 10.6. Slightly more water and cement may be required for recycled aggregate concretes than for corresponding concretes made with conventional aggregates in order to obtain same workability and strength.

There is one major difficulty though. It is not possible to determine water adsorption, free water content or density in saturated surface dry condition of fine recycled concrete aggregate sufficiently accurately by any existing testing method. This is due to high water absorption and high cohesion of such materials. Thus, it is very difficult to control the quality of concrete produced with such aggregate, and it is not possible to know with any degree of certainty what is the free water-cement ratio of such concrete. Therefore, it is not recommended to use fine recycled concrete aggregate for production of new concrete.

25. For technical as well as economical reasons it is recommended to produce recycled aggregate concretes with coarse recycled aggregate down to no less than perhaps 4 mm, or definitely not less than 2 mm, and conventional sand for what concerns the rest. Use of crushed concrete fines below 2 mm appears to have a detrimental effect on economy as well as on many techncial properties of new concrete.

Fortunately, when there is a shortage of aggregate in a region, shortage of coarse aggregate is more common than shortage of fine aggregate.

26. Practical experience has shown that recycled aggregate concrete is as easy to batch,


mix, transport, place, compact, and finish as conventional concrete. However, because of the relatively high water absorption of recycled aggregate, it is generally recommended to batch recycled aggregates in a pre-soaked condition, and in a state which is as close to saturated and surface dry as possible.

27. Susceptibility to plastic shrinkage cracking of fresh recycled aggregate concretes remains to be studied.

28. Crushed concrete fines contain so little unhydrated cement that such fines do not qualify as hydraulic cements. When mixed with water, a slight setting, but no real hardening of the concrete is observed. This is so, even when pastes are cured in water at 50°C for prolonged periods of time.

On the other hand, crusher fines below 4 mm may contain up to 4% by weight of calcium hydroxide which is formed by hydration of original cement in the old concrete. When mixed with water and left to dry in the laboratory, the product will gradually harden much like a weak lime mortar would do. Such hardening is probably due to formation of calcium carbonate when calcium hydroxide in the fines reacts with atmospheric carbon dioxide. It may give rise to caking in stockpiles.

29. When mixtures of crusher fines, water, and pulverized fly ash, or condensed silica fume are prepared and autoclaved, calcium hydroxide from the fines can be brought to react with mineral particles in the crusher fines, with fly ash or with silica fume to form reaction products of considerable compressive strength, much like calcium silicate bricks.

30. In principle, crusher fines may also be used for soil stabilization or soil modification purposes. Other possible uses include trickling filters for waste water treatment, poultry grit, cat litter, acid soil or waste water neutralization, substitution for ground limestone in SO2 scrubber filters in coal burning power plants, stabilization of sewage sludge, or as a source of available silica in highly leached lateritic soils. However, because the concentration of calcium hydroxide in the crusher fines is very low, use of crusher fines for most of these purposes may be uneconomical, even if it can be shown that beneficial effects do exist.

31. Recycling of alkaline waste water and waste aggregate from ready-mixed concrete plants is possible. For environmental reasons this will probably be required in many countries in the future.

Recycling of rebound from shotcrete is also possible, but probably not economical. 32. Codes, standards, and testing methods for recycled aggregates and recycled aggregate

concretes have been prepared in the United States, Japan, the Netherlands, the United Kingdom and Denmark. See Section 13.

33. At the time when this document was prepared, practical experience had shown that the use of recycled concrete aggregate is economical for pavement reconstruction purposes under all but extreme circumstances, when compared with the use of conventional aggregates.

However, use of recycled concrete aggregate for general construction purposes still remained more costly than the use of conventional aggregate even in a country like Holland, where there is a shortage of conventional aggregate. In most countries this situation is expected gradually to change in favour of recycled aggregates. For one thing, it is expected that the extra cost which is now commonly charged for the


processing of old concrete and mixed demolition rubble can be lowered once the initial developing phase is over. Also, the price of conventional aggregates will probably continue to rise in the future as raw materials get scarcer and transportation costs continue to rise. Moreover, dumping charges are certain to rise steeply over the next decades as the quantities of demolition debris continue to increase, at the same time as the number of accessible dumping sites continues to decrease.

34. This state-of-the-art report spells a bright future for the recycling of concrete, provided that all parties involved proceed with reasonable prudence in order to avoid set-backs which may reflect in unfavourable ways on the reputation of recycled aggregate concrete.

19. Acknowledgments

The author wants to express his thanks to all members of RILEM Technical Committee37-DRC, without the help of whom it would not have been possible to prepare thisdocument.

In particular, the author is indebted to Dr. Stamatis Frondistou-Yannas of Newton,Massachusetts, for her contribution to Section 14 on economic aspects of concreterecycling, to Mr. Gordon K.Ray, Concrete Pavement Consultant, Arlington Heights,Illinois, and Mr. Alan D.Buck, Research Geologist, US Army Engineering WaterwaysExperiment Station, Vicksburg, Mississippi, for keeping me informed aboutdevelopments in the United States; to Dr. Ch. F.Hendriks of Rijkswaterstaat, Delft, TheNetherlands, for his assistance with Dutch documents, and to Professor Y.Kasai of NihonUniversity, Japan for valuable material from Japan which he and his co-workers havereviewed and translated in order to facilitate preparation of this state-of-the-art report.


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(63) Kreijger, P.C. (1983), Hergebruik van Bouw- en Sloopafval als Toeslagmateriaal in Beton. TH-Eindhoven, Afdeling Bouwkunde, Rapport M83–1 .

(64) Hendriks, C.F. (1985), The use of concrete and masonry waste as aggregates for concrete production in the Netherlands. EDA/RILEM Demo-Recycling Conference. Proc. Vol. 2 Re-Use of Concrete and Brick Materials , Rotterdam, European Demolition Association, Wassenaarseweg 80, 2596 CZ Den Haag, the Netherlands.

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(79) Hartmann, L., and Jakobsen, J.B. ( Private communication ) Cowiconsult, Teknikerbyen 45, DK2830 Virum, Denmark.

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(81) Van Eck, H. (1985), Recycling of demolition wood. EDA/RILEM Demo-Recycling Conference, Reuse of Concrete and Brick Materials , Rotterdam, European Demolition Association, Wassenaarseweg 80, 2596 CZ, Den Haag, the Netherlands.

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Haag, the Netherlands. (83) Zagurskij, V.A., and Zhadanovskij, B.V., (1985) Breaking reinforced concrete and

recycling crushed materials. Special Technical Report. Research Institute for Concrete and Reinforced Concrete (GOSSTROY) , Moscow, English translation available from European Demolition Association, Wassenaarseweg 80, 25% CZ, Den Haag, the Netherlands.

(84) Bernier, G., Malier, Y., and Mazars, J., (1978) New material from concrete demolition waste—the Bibeton. Proceedings of the international conference on the use of by-products and waste in civil engineering, Paris, pp. 157–162 (in French).

(85) Goeb, E., (1985) Pumping structural lightweight concrete. Concrete Construction , 30, No. 6, pp.505–510.

(86) Anon. (1984), Recommendations for recycling sub-standard concrete and reinforced concrete products. Special Technical Report, Research Institute for Concrete and Reinforced Concrete , (NIIZhB) GOOSTROY, 2nd Institutskaja Str. 6, 109389 Moscow.

(87) Lindsell P. and Mulheron M., (1985) Recycling of demolition debris, Institute of Demolition Engineers, 18 Station Approach, Virginia Water, Surrey GU25 4AE, United Kingdom.

(88) German Standard DIN 4163, (1951) Concrete made with broken brick. Specification for production and use.

(89) Hansen T.C., (1989) Cat litter and a method for production of cat litter on the basis of crushed hardened concrete, cement mortar and cement paste, UK Patent GB 2169484B.

(90) Berger R.L. and Carpenter S.H., (1981) Recycling of concrete into new applications, Chapter 6.1 in: Adhesion problems in the recycling of concrete. NATO Conference Series, Series VI Materials Science , Plenum Press, New York, pp. 325–339.

(91) Scott, F., (1985) A fortuitous accident International Laboratory , p. 6. (92) Scott, F., (1986) Further reports on a fortuitous accident, International Laboratory ,

pp. 6–8. (93) Karaa, T., (1986) Evaluation technique des possibilites d’emplois des dechets dans

la construction—recherche experimentale applique au cas de bèton fabrique a partier de granulats de bétons recycles. These de doctorat de Université Paris 6. CSTB 4 Avenue du Recteur Poincaré 75782 Paris Cedex 16, France. (In French).

(94) Anon., (1982) Recyclage de béton armé de la décharge a la chaussée. Carrières et Materiaux No. 207, pp. 32–33. (In French).

(95) Drees, G., (1989) Recycling von Baustoffen in Hochbau, Geräte, Materialgewinnung, Wirtschaftlichkeitberechnung. Bauverlag GMBH. Wiesbaden und Berlin (in German).

(96) Ravindrarajah, S.R. and Tam, C.T., (1986) Concrete with fly ash or crushed concrete fines or both. Paper distributed at ACI-CANMET . Second. International Conference on the use of fly ash, silica fume fine, slag and natural pozzolans in concrete , Madrid, Spain. (Paper not included in the offizial Proceedings of the Symposium).

(97) Anon., Recycling Portland cement concrete. Demonstration Projects Program DP no. 47 FHWA-DP 47–85 , Demonstration Projects Office of Highway Operations, Federal Highway Administration HHO 42, 400 Seventh Street, SW, Washington DC 20590. USA.

(98) Büchel, R., Wiederverwendung alter Baustoffe. Beton 2/87 , p. 66. (In German). (99) Rottler, G., (1985) Dauerhaftigkeit von Recyclingbetonen bei Frost-Tausalz-

Beanspruchung, Diplomarbeit , Institut für Massivbau und Baustofftechnologie,


Universität Karlsruhe, Postfach 6380, 7500 Karlsruhe 1. Bundesrepublik Deutschland. (In German).

(100) Reinhardt, H.W., Demountable building with concrete. Betonwerk und Fertigteil-Technik 5/1985 pp. 300–5. (In English).

(101) Svenson, A., Der Backenbrecher Steinbruch und Sandgrube 1/85 pp. 17–21. (In German).

(102) Ravindrarajah, R.S., Loo, Y.J. and Tam, C.T., (1988) Strength evaluation of recycled-aggregate concrete by in-situ tests. Materials and Structures (RILEM), Vol. 21, No. 124, pp. 289–295.

(103) Mulheron, M., (1986) A preliminary study of recycled aggregates. The Institute of Demolition Engineers. 18 Station Approach, Virginia Water, Surrey GU25 4AE, UK.

(104) Department of Transport, (1983) Specification for road and bridge works. 6th Ed, UK.

(105) Forster, S.W., (1986) Recycled concrete as aggregate. Concrete International -Design and Construction (ACI) pp. 34–40.

(106) Heck, J., (1983) Study of alkali-silica reaction tests to improve correlation and predictability for aggregates. Cement Concrete and Aggregates (ASTM), Vol. 5., No. 1, pp. 47–53.

(107) Ravindrarajah, R.S., Loo, Y.H. and Tam, C.T., (1987) Recycled concrete as fine and coarse aggregates in concrete. Magazine of Concrete Research . 39, No. 141, pp. 214–220.

(108) Arnold, C.J., (1988) Recycling concrete pavements. Concrete Constructions , pp. 320–326.

(109) Kuennen, T., (1987) Lodge freeway recycling—nine miles in eight months. Roads and Bridges . 25, No. 7, pp. 44–45.

(110) Pearsson, R.I., (1988) Recycling Detroit’s Lodge freeway. Concrete International (ACI) , pp. 16–19.

(111) Anon., Instandsetzung mit Recycling Beton. Erneuerung der BAB1 Beton 9/88 , p. 373.

(112) Schulte, H.P., Erneuerung einer Betonfahrbahndecke. Verwendung von Recyclingmaterial bei der BAB 7 Beton 8/88 , p. 315.

(113) Roth, L., (1984) Concrete recycling—the way of the future. Highway and Heavy Construction , Barrington, Illinois, USA, 127 No. 2. p. 34–37.

(114) Schroeder, C.J., (1982) Breaking, removal and crushing Portland cement concrete for recycling. Public Works (U.S.) 113 No. 3, pp. 80–82.

(115) C.U.R., (1984) Betonpuingranulaat als toeslagsmateriaal voor beton, V.B. Aanbeveling 4 CUR Postbus 420, 2800 AK Gouda, The Netherlands. (in Dutch). These recommendations are included in ref. 11.

(116) DIF, (1989) Proposed amendment to the Danish concrete code: use of recycled demolition rubble, Dansk Beton , 6, No. 4.

(117) Hironaka, M.C., Cline, G.D. and Shoemaker, N.F., Recycling of Portland cement concrete airport pavements. Report No.: NCEL-TN-N–1766, DOT/FAA/PM-86/23 , Naval Civil Engineering Laboratory, Port Hueneme, California, USA.

(118) World Patent Index: Patents on concrete crushers, access numbers 87–131087/19, 87–082100/12, 86–156094/24, 86–054906/08, 85–088125/15, GB8705, GB2146918, 84–211301/34, 83–770932/38, 83–H7653K/23.

(119) Ridout, G., Valori’s nutcracker breaker with tradition-prestressed concrete crushing machine, Serial Dat. 1982–02–25 . 305, No. 5341. Contact J. Sutter, UK, ISSN 0010–7859.


(120) Henrichsen, A., Jensen, B. and Thorsen, T., Styrkeegenskaber for beton med genanvendelsesmaterialer, (internal report) Danmarks Ingenior Akademi, Bygningsafdelingen, Afdelingen for Fysik og Materialer, Bygning 373, DK 2800 Lyngby (in Danish).

(121) Schwartz, D.R., (1987) D-cracking of concrete pavements, National Cooperative Highway Research Program, Syntheses of Highway Practice 134 . Transportation Research Board, National Research Council, Washington DC.

(122) Krejcirik, M., (1986) Recycling von Betonschwellen bei der Tsechoslowakischen Staatsbahn’, Eisenbahningenieur , 37. No. 2. pp. 69–71.

(123) Hurd, M.K., (1986) What happens to left over ready mix. Concrete Construction , 31, No. 3. pp. 299–305.

(124) Grelk, B., Genbrug af frisk betonspild—State-of-the-art-report, available from Byggeteknik , Teknologisk Institut, Gregersensvej, Taastrup, Denmark. Technical Report 1988–09–06, bg/ema 89/63 (in Danish).

(125) Grelk, B. and Jensen, P., Genbrug af frisk betonspild—Projektrapport, available from Byggeteknik , Teknologisk Institut, Gregersensvej, Taastrup, Denmark, Technical Report beg/bir 64/1 (in Danish).

(126) Kuhlman, R.H., (1989) Soil cement from recycled pavement, Concrete International . pp. 35–38.

(127) Ivanyi, G., Lardi, R. and Esser, A., (1985) Recycling beton. Forschungsbericht aus dem Fachbereich Bauwesen No. 33, Universität-Gesamthochschule, Essen.

(128) Gütegemeinschaft Recycling Baustoff e.V., Recycling-Baustoffe für den Strassenbau, Gütesicherung. RAL-RG 501–1 , Beuth Verlag, Berlin.

(129) Anon, (1985) Merkblatt über die Verwendung von industriellen Nebenprodukten im Strassenbau, Teil: Wiederverwendung von Baustoffen Forschungsgesellshaft für den Strassen und Verkehrswesen, Bonn.

(130) Dohmann, M., Gefahren durch Bauschuttrecycling, Entsorgungs-Praxis , 10/87. (131) Anon, (1986) An innovating solution for the demolition material treatment of all

kinds in the Gennevilliers Port, Chantiers de France No. 187, pp. 24–29 (in French). (132) Anon, (1985) Une installation-pilote de bergeaud pour le traitement de materiaux

de demolition en beton armé, Chantiers de France , No. 185, pp. 43–45. (133) Laure, D., Pelletier, J.L. and Stotzel, J., (1985) Reinforcement de la RN6 en Seine-

et-Marne: recyclage des produits de demolition de structures de beton armes. Rev. Gen. Routes Aerodr . 59, No. 615 pp. 113–117 (in French).

(134) Anon, (1975) Dechets et sous-produits industriels: elimination-recyclage-valorisation, Journees d’Information , Institut National des Sciences Appliquees, Villeurbanne. Available from CSTB Library.

(135) Proceedings of the Second International RILEM Symposium on demolition and reuse of concrete and masonry . 2: Reuse of demolition waste. (ed. Y.Kasai), Nihon Daigaku Kaikan, Tokyo, Japan, Chapman & Hall, London.

135a Puckman, K. and Henrichsen, A., Reuse of concrete pavements, Ibid, Ref, 135, pp. 746–755.

135b Yoda, K., Yoshikane, T., Nakashima, Y. and Soshiroda, T., Recycled cement and recycled concrete in Japan, Ibid. Ref. 135, pp. 527–536.

135c Yoshikane, T., The instances of concrete recycled for base course material in Japan. Ibid. Ref. 135 , pp. 756–765.

135d Schulz, R.R., Concrete with recycled rubble-development in West Germany. Ibid. Ref. 135 , pp. 550–509.

135e Kashino, N. And Takahashi, Y., Experimental studies on placement of recycled


aggregate concrete. Ibid. Ref. 135 , pp. 557–564. 135f Kakizaki, M., Harada, M., Soshiroda et al. Strength and elastic modulus of recycled

aggregate concrete, Ibid, 135 , pp. 565–74. 135g Kawamura, M. and Torii, K., Reuse of recycled concrete aggregate for pavement.

Ibid. 135 , pp. 726–35. 135h Mulheron, M., The recycling of demolition debris: current practice, products and

standards in the United Kingdom. Ibid. Ref. 135 , pp. 510–519. 135i Goerle, D. and Sayes, L., Reuse of crushed concrete as a road base material, Ibid.

Ref. 135 , pp. 736–745. 135j Busch, J., Crushed concrete used as base course material on runway 04r-221 at

Copenhagen Airport. Ibid. Ref. 135 , pp. 766–774. 135k Jakobsen, J.B., Elle, M. and Lauritzen, E.K., On-site use of regenerated demolition

debris, Ibid. Ref. 135 pp. 537–46. 135l Bauchard, M., The use on roads of aggregates made from demolition materials, Ibid,

135 , pp. 719–725. 135m Kaga, H., Kasai, Y., Takeda, K. and Kemi, T., Properties of recycled aggregate

from concrete, Ibid. 135 , pp. 690–698. 135n Ikeda, T., Yamane, S. and Sakamoto, A., Strengths of concrete containing recycled

aggregate, Ibid. 135 , pp. 585–594. 135p Nishibayashi, S. and Yamura, K., Mechanical properties and durability of concrete

from recycled coarse aggregate prepared by crushing concrete, Ibid. 135 , pp. 652–659. 135q Kawai, T., Watanabe, M. and Nagataki, S., Preplaced aggregate concrete made

from demolished concrete aggregates, Ibid. 135 , pp. 680–689. 135r Trevorrow, A., Joynes, H. and Wainwright, P.J., Recycling of concrete and

demolition waste in the UK, Ibid. 135 , pp. 520–524. 135s Kakizaki, M., Harada, M. and Motoyasu, H.., Manufacturing of recovered aggregate

through disposal and recovery of demolished concrete structures, Ibid. 135 , pp. 699–708.

135t Morlion, D., Venstermans, J. and Vyncke, J., Demolition of the Zandvliet lock as aggregates for concrete, Ibid. Ref. 135 , pp. 709–718.

135u Mukai T. And Kikuchi M., Properties of reinforced concrete beams containing recycled aggregate. Ibid. Ref. 135 , pp. 670–679.

135v Kabayashi, S. and Kawano, H., Properties and usage of recycled aggregate concrete, Ibid. Ref. 135 , pp. 547–556.

135w Hansen, T.C. and Marga, M., Strength of recycled concrete made from coarse and fine recycled concrete aggregates. Ibid. 135 , pp., 605–612.

135x Kasai, Y., Hisaka, M., and Yanaga, K., Durability of concrete using recycled coarse aggregate, Ibid. Ref. 135 , pp. 623–632.

135y Yamato, T., Emoto, Y., Soeda, M. and Sakamoto, Y., Some properties of recycled aggregate concrete, Ibid. Ref. 135 , pp. 643–651.

135z Yanagi, K., Hisaka, M., Nakagawa, M. and Kasai, Y., Effect of impurities in recycled coarse aggregate upon a few properties of the concrete produced with it. Ibid. Ref. 135 , pp. 613–620.

135aa Ravindrarajah, R.S. and Tam, C.T., Methods of improving the quality of recycled aggregate concrete, Ibid. 135 , pp. 575–584.

135bb Kikuchi, M., Mukai, T. and Kozumi, H., Properties of concrete products containing recycled aggregate, Ibid. 135 , pp. 595–604.

135cc Fujii, T., Strength and drying shrinkage behavior of concrete crushed aggregate, Ibid. 135 , pp. 660–669.


136 Hansen, T.C., Recycled concrete aggregate and fly ash produce concrete without cement”. Accepted for publication in Cement and Concrete Research , 1989.

137 Mulheron, M. and O’Mahony, M., (1987) Recycled aggregates. Properties and performance. The Institute of Demolition Engineers, 18 Station Approach, Viginia Water. Surrey GU25 4AE.

138 Building Research Establishment, (1983) Hardcore, Digest 276 , Department of the Environment.

139 Department of Transport, (1986) Specifications for highway works. HMSO, (UK). 140 Japan Road Association, (1984) Technical guideline for utilizing work pavement

materials (Draft) 141 Kleiser, K., (1986) Wiederverwendung von Bauschutt als Betonzuschlag. Vortrag in

Rahmen der Fachveranstaltung: Aufbereitung und Wiederverwendung von Bauschutt, Haus der Technik , Essen, (In German).

142 Mulheron, M., (1989) Update on recycled materials in the UK. ( Private communication ).


21. APPENDIX A. Literature reviewed in first state-

of-the-art report 1945–77. Nixon (5)

Nixon, P.J., (1976) The use of materials from demolition in construction, Resources Policy , pp. 276–283.

Buck, A.D., (1976) Recycled concrete as a source of aggregate. Proceedings of the Symposium on Energy and Resource Conservation in the Cement and Concrete Industry , Canada Center for Mineral and Energy Technology, Ottawa.

Glushge, P.L., (1946) The work of the scientific research institute, Gidrotskhnicheskoge Stroiteistvo No. 4 , pp. 27–8 (USSR). Brief English summary in Engineer’s Digest , 7, No. 10, p.330.

Graf, O., (1948) Uber Ziegelsplittbeton, Sandsteinbeton und Trümmerschuttbeton, Die Bauwirtschaft , No. 2, No. 3, No. 4, (Germany). Crushed brick concrete, sandstone concrete and rubble concrete, Trans. No. 73–1 , (1973) US Army Engineer Waterways Experimental Station, C E. Vicksburg, Miss.

Ploger, R.R., (1947) An investigation of the compressive strength of concrete in which concrete rubble was used as an aggregate. Unpublished thesis, Cornell University.

Malhotra, V.M., (1976) The use of recycled concrete as a new aggregate. Proceedings of the Symposium on Energy and Resource Conservation in the Cement and Concrete Industry Canada Center of Mineral and Energy Technology, Ottawa.

Buck, A.D., (1973) Recycled concrete. Highway Research Record No. 430 . Frondistou-Yannas, S., (1977) Waste concrete as aggregate for new concrete, ACI

Journal, pp. 373–374. studies in the reuse of demolished concrete (1975) Committee for Research on the Reuse of Construction Waste , Building Contractors Society, Tokyo, ( personal communication by F. Tomasawa).

Gaede, K. Deutscher Ausschuss für Stahlbeton 109, (1952) and 126, (1957). Newman, A.J. (1946) The utilization of brick rubble from demolished shelters as

aggregate for concrete, Inst. Mun. Eng. J. 73, No. 2, pp. 113–121.


PART TWO RECYCLING OF MASONRY

RUBBLE Dr R.R.SCHULZ

Institute for Building Materials Testing, Waldkirch, Germany

and

Dr Ch.F.HENDRICKS

Road Engineering Division, Rijkswaterstaat, Delft, The Netherlands

List of Abbreviations and Symbols

Abbreviations

Symbols

cal calculated f guilder (Dutch monetary unit) g aerated concrete HOZ blast furnace slag cement HS slag aggregate brick or block KS sand-lime brick or block k-Wert grading value (the sum of the percentage retained

particles on the entire set of sieves divided by 100) LB lightweight concrete M.-% % by weight Mio million Mz sold baked clay brick NB normal concrete NE-Metall non-ferrous metal obs measured PZ Portland cement RAL German Insititute for Quality Assurance and Quality

Marking V solid blocks made from lightweight rubble Vol.-% % by volume

B degree of certainty

DZ degree of crushing by compression

E modulus of elasticity N/mm2

Eb modulus of elasticity of concrete N/mm2

g aggregate kg/m3

mns natural sand content –Z

n number –

r correlation coefficient –

SE

Recycling of masonry rubble 141

standard error of estimate *

V volume m3

W water content kg/m3

W30 water absorption after 30 minutes % by vol

W24h water absorption after 24 hours % by vol

z cement content kg/m3

βD compressive strength N/mm2

βBZ flexural strength N/mm2

βDmz brick or block compressive strength N/mm2

βsz tensile splitting strength N/mm2

γ aggregate/cement ratio –

λ thermal conductivity W/(Km)

t’b concrete density kg/m3

tRg particle density kg/m3

( s bulk density kg/m3

ω water/cement ratio

* unit of associated mean value


1 Introduction

Recycling and re-use of building rubble present interesting possibilities for economizing on waste disposal sites and conserving natural resources. RILEM Technical Committee37-DRC has contributed to the elimination of existing technical barriers and promotion of the use of mineral materials from building rubble. To provide a basis for this work, twostate-of-the-art reports have been prepared, summarizing available literature and analysing it with a view to suitable practical applications.

In formulating the aim, it became obvious that a subdivision into at least two distinct groups of building materials would be necessary in order to ensure an optimum use ofbuilding rubble. Concrete rubble resulting from the breaking up of roads and other civilengineering concrete construction works contains few other building materials thanconcrete. But rubble from building structures contains generally many other types ofmaterials such as masonry. The properties of concrete rubble and mixed masonry rubbleare so different that they need to be treated separately. For this reason it has beennecessary to present separate reports on aggregates based on recycled concrete rubble andon recycled masonry rubble. Part One of this volume contains the report on aggregates based on recycled concrete rubble. The present report on crushed masonry and recycledconcrete made with crushed masonry as aggregate draws largely on knowledge acquiredon the use of rubble from buildings destroyed in the Second World War. More recentresearch (4, 42, 40, 50) published in the Netherlands has contributed substantially to theextending and updating of this part of the report. The reader is frequently referred toliterature reference (4) which summarizes the results of a major study of mixed demolition rubble which was made in the Netherlands. A brief summary of the propertiesof the raw materials used in this study and the results obtained on correspondingconcretes are presented in Appendix A.

2 Historical survey

“Concrete” (Opus Caementitium) buildings made with crushed brick have been known since Roman times (24 to 29). The concrete channels of the Eifel water supply toCologne are an example of this type of structure in which the binder is a mixture of limeand brick-dust or other pozzolanas. Crushed brick concrete with portland cement was used in Germany from 1860 for the manufacture of concrete products. Systematic


investigations on the effect of the cement content, water content and grading of crushedbrick have been carried out since 1928. However, the first significant applications onlydate back to the use of rubble from buildings destroyed (11) in the Second World War.

During the period of reconstruction after the Second World War it was necessary onthe one hand to satisfy an enormous demand for building materials and on the other toremove the rubble from the destroyed cities. The amount of brick rubble in Germantowns was about 400 to 600 million cubic metres. Using this rubble made it possible notonly to reduce site clearing costs but also to contribute considerably to fulfilling the needfor building materials. Rubble-recycling plants in the Federal Republic of Germany produced about 11.5 million cubic metres of crushed brick aggregate by the end of 1955,with which 175000 dwelling units were built (29).

The statistics compiled by the Association of German Cities show that by the end of 1956, about 85% of all building rubble in the German Federal Republic had been cleared.In two-thirds of all municipalities clearance was complete at the beginning of 1957. Onlyin 15 large cities did about a million of cubic metres still remain by the end of 1955 (29). By about 1960, there was no longer any rubble recycling done in the Federal Republic.There are many technical and economical directives and guidelines dating from theperiod between 1945 and 1960 (the main one being DIN 4163 (1)) and also many publications. The German Society for the Use of Rubble issued a total of 437publications listed in reference (29).

In the UK also, rubble was recycled and used after the Second World War, although to a lesser extent than in Germany. It applied more particularly to redundant defencestructures, mainly to brick masonry constructions (30). These were very seldom rendered so that there was hardly any presence of impurities as would be the case with other typesof construction.

Although other parameters apply nowadays, both as regards the composition of rubbleand demolition and recycling technologies, the experience acquired during the post-war years remain interesting particularly in connection with recycling of masonry rubble foruse as aggregate for production of new concrete.

3 Prospects

Forecasts have been made about the use of rubble from demolitions in the comingdecades (78), on the basis of existing use of materials and an average life hypothesis. According to these forecasts, the annual concrete rubble production within the EuropeanCommunity (EC) is expected to increase from 55 million tonnes in 1980 to 162 milliontonnes in the year 2000, while that of brick rubble will remain more or less constant atabout 52 million tonnes. These figures may well be too high in view of the recession inthe building market and provide only a rough overall estimate (unless the newer members of the EC are included). It is very clear that the proportion of concrete rubble and


masonry rubble has shifted towards concrete rubble and is connected to the fact that, inthe last decades, concrete manufacture has increased steadily whilst production figuresfor bricks have hardly changed.

An example from another source is the Netherlands (4) (cf. (48)) where, at the beginning of the 1980s the annual figure was still 3 million tonnes of masonry rubble andonly 2 million tonnes of concrete rubble. If the forecasts are correct, the production ofconcrete rubble should dominate by the middle of the 1990s.

4 Walling materials

4.1 Types of walling unit

The term “masonry rubble” is a collective term for various mineral building materials resulting from the demolition of buildings and civil engineering structures (4). They include mainly:

Masonry rubble often also contains mortar rendering and burnt clay materials such asroofing tiles and shingles. Concrete rubble may contain undesirable contaminants such asmetals, asphalt, timber, plastics, glass and plaster.

4.2 Manufacture and composition

4.2.1 Ordinary concrete (NB)

Ordinary concrete consists of a mix of sand and gravel embedded in a cement matrix.Crushed natural stone and sand is sometimes used instead of rounded gravels and sands,depending on availability. According to the German standards the particle density ofnormal aggregate is between 2200 and 3200 kg/m3 and the strength exceeds 100 N/mm2.

ordinary concrete (NB); aerated concrete blocks (G);

bricks (Mz); blastfurnace slag bricks and blocks (HS) and

sand-lime bricks (KS); natural stone (NS).

lightweight concrete and lightweight concrete blocks (LB);


The properties of the concrete are determined mainly by the properties and amount of theweaker component, the cement matrix.

4.2.2 Masonry bricks (Mz)

Masonry bricks are made of clay or clayey soils with or without addition of mineralfillers or foaming agents, which are formed and burnt and in which hardening occurs innormal bricks by dry sintering (changes and reactions in the hardened state) and in hardburnt clinker by sintering or fusion (bond obtained through partial melting flow). Both density and compressive strength increase with increasing burning temperatures. Bricksused for the construction of walls are classified as lightweight bricks, high strength bricksand clinkers, according to their density and strength (16). Clinkers are bricks that have been sintered at the surface and have been shown by testing to possess a good frostresistance. The water absorption capacity of bricks may be up to about 7% (DIN 105 T3,(92).

4.2.3 Sand-lime bricks (KS)

Sand-lime bricks are made of lime and silica aggregates, pressed damp, and hardened inabout 6 to 7 hours in an autoclave under high water vapour pressure, generally at 16 barand at 200°C. The lime reacts with the SiO2 and produces calcium silicate hydrates (CSH) similar to the products of hydration of cement and resulting in high strength values(16).

4.2.4 Lightweight concrete and lightweight concrete blocks (LB)

Lightweight concretes with dense structures are made with lightweight aggregates in totalor in part. The density of the concrete depends mainly on the porosity of the aggregateparticles. If the aggregate particles are bonded with only a little cement paste at the pointsof contact, the result will be an open textured concrete or porous concrete. No-fines concrete, i.e. concrete made with all aggregates of a very similar particle size isparticularly porous. A combination of particle size and porosity gives a mixed porosity.

4.2.5 Cellular concrete (G)

Cellular concrete is usually made with cement, lime, finely ground quartz sand or otheraggregate with high silica content, water and a chemical agent (aluminium powder) andhardened under a pressure of about 10 bar with steam at temperatures of about 180°C (18). The reactive area of the aggregate has been increased by the grinding process and, when subjected to such high temperatures, it reacts with the CaO of the binder to formcalcium silicate hydrates similar to those that occur during hardening of cement (16).


4.2.6 Blastfurnace slag bricks and blocks (HS)

Blastfurnace bricks and blocks have slag as the main constituent (mostly in granulatedform) with lime, slag cement or similar hydraulic binders and sometimes also other silicamaterials. They may be solid blocks or blocks with hollows and are generally steamhardened or hardened in exhaust gases containing carbon dioxide (blastfurnace gases).

4.2.7 Natural stone (NS)

Natural stone for masonry work must be cut from sound stone only, but many types ofstone are suitable for this purpose. Not all natural stones used for masonry work arecompletely resistant to weathering. Such a requirement applies only for unprotectedmasonry exposed to the weather.

4.3 Properties

Table 1 shows the differences between various standardized materials used for masonrywork and also the differences within each type as regards various densities and strengthclassifications or both. The range of variation is much greater when older, non-standardized materials are included. Asphalt, which may be present in considerablequantity in building rubble, should be mentioned, although its effect on concrete is so badthat it is totally unsuitable for re-use as aggregate in concrete (3, 4).

5 Masonry rubble

5.1 Composition

Since there are very different types of material used for masonry work in the differentregions in Germany, it follows that the composition of rubble is also different from oneregion to another. As the investigations of Hoffmeister have shown (56), the rubble from North and Central Germany contains mainly brick and sand-lime brick; in the south, however, there were various amounts of natural stone as well (see Table 2). If the brick rubble varied considerably in physical properties (porosity and strength) and in chemicalcomposition (silicic acid, clay and gypsum contents), the differences were even greater inthe natural stone. This applied also to the sands used for mortars and renderings.


The end product of a single plant for the preparation of rubble to be used in building construction may well show considerable variations in composition. This was revealed bythe results of more recent investigations (see Tables 3 and 4) made on eight different installations in the Netherlands (4). Although these results refer to prepared rubble, they give indications about the composition of the untreated original rubble. Table 3 gives the result of visual examination showing differences observed during one day’s production run and Table 4 shows the range of variation for ten days taken at random between 1980and 1982. It may be seen that some plants show a preference for certain types of buildingmaterials. It appears also that in plants 1 to 5 there are considerable amounts of asphaltconcrete rubble and on average about 20% by weight of mortar. Sand-lime brick occurs only in small amounts.

A similar situation occurs in newer German recycling plants (see Tables 5 and 6). The amount of concrete rubble is particularly high in plants A and B (see Table 6), which seems to point to an initial preliminary sorting of the rubble.

Table 1. Properties of masonry bricks and blocks

Type of brick or block

Density Compressive strength

Modulus of

elasticity ×1000

Shrinkage DIN Specification

number

kg/m3 N/mm2 N/mm2 mm/m

Burnt clay bricks and blocks (Mz)

Lightweight hollow bricks

500–1,000

2–35 105 T2

Solid/hollow bricks

1,000–2,200

4–>35 (20–25)

7–18 up to 0.6 105 T1

High-strength bricks and clinker

1,000–2,500

36–>75 105 T3

Ceramic clinker 1,200–2,500

>60 105 T4

Sand-lime bricks and blocks (KS)

Solid, perforated & hollow bricks and blocks

500–2,200

4–>75 (20–25)

7–17 up to 0.7 106 T1


Facing bricks 800–2,200

12–>75 106 T2

Blast furnace slag bricks (HS)

Solid, perforated & hollow bricks

900–2,000

6–>35 5–10 up to 1.0 398

Aerated concrete bricks and blocks(G)

300–800 2–>7.5 (4)

1.25–3 up to 0.7 4,165

Lightweight aggr. & no-fines concretes (LB)

Perforated bricks

500–1,600

4–>15 (Pumice) 18,149

Hollow bricks 500–1,400

2–7.5 up to 2.3 18, 151

Solid bricks and blocks (V)

500–2,000

2 4 6

7.5

2.5–4 4–7

6–8.5

up to 1.0 (expanded

clay)

18,152

Concrete (NB) Hollow blocks

1,000–1,800

4–>15 18,153

Table 2. Composition of original debris sampled from ruins of two German cities (from (56))

Constituent in weight % Stuttgart Nürnberg

Cement-bound materials > 40 mm

Regular concrete 9.95 1.08

Lightweight concrete 0.08 0.02

Cement mortar 0.51 –

Blastfurnace slag concrete 0.03 –

Total of cement-bound materials 10.57 1.10

Ceramic materials > 40 mm

Hard burnt bricks – 1.20


Brick rubble 18.48 21.43

Burnt clay bricks, entire bricks 1.75 3.00

Other ceramic materials 0.95 0.23

Total of ceramic materials 21.18 25.86

Natural stone > 40 mm

Sandstone rubble 11.23 16.69

Sandstone, entire units 15.27 –

Slate 0.07 –

Granitic stone – 0.75

Total of natural stone 26.57 17.44

Contaminants > 40 mm

Gypsum plaster 0.07 0.01

Lime mortar 0.65 1.00

Blastfurnace slag 0.03 –

Glass 0.19 0.03

Non-ferrous metals 0.17 0.01

Steel 2.28 0.33

Wood 0.18 0.01

Textiles – 0.01

Total contaminants 3.57 1.40

Total grains > 40 mm 61.89 45.80

Total grains < 40 mm 38.11 54.20

Total of all components 100.00 100.00

Table 3. Variation in composition of processed building waste sampled during one particular day in 8 different processing plants. Figures are in weight % (from (4))

Processing plant N°

Constituent 1 2 3 4 5 6 7 8

Cement-bound

Regular concrete 2–75 97–100 16–38 18–70 5–6 31–34 4–18 2–4

Lightweight concrete 0–2 – – – 1–6 – – 0–1


Cement mortar 0–4 – – – – – 0–3 –

Lime mortar 3–12 – 0–2 4–12 6–14 3–11 7–28 7–24

Ceramic

Hard burnt bricks 9–79 – 0–1 – – 12–26 0–34 7–26

Brick rubble 9–45 – 1–2 9–30 71–81 12–22 34–70 56–65

Roofing tiles – – – – – 2–10 0–2 –

Ceramic tiles – – – – <0–3 0–1 0–1 –

Other

Asphalt 1–27 3 69–82 8–72 0–2 4–24 0–1 0–1

Sand-lime bricks – – – – 7–12 – – 0–2

Natural stone – – 0–3 6–23 – – – 2–4

Contaminants

Glass – – 0–0.2 – 0–1 – <0.1 <0.2

Metal 0–2 – – <0.2 <0.1 – 0–5 <0.3

Wood x – x x x x x x

Cardboard x – – – x – x –

Paper x – x x x – x x

Polymers – – x – – – x –

Reed – – – – x – – –

Limestone – – – – – – x –

Asbestos cement – – – – – – x –

Clay x – – x – – – –

Table 4. Variation in composition of processed building waste sampled during ten arbitrarily chosen days from 1980 to 1982 in 8 different processing plants. Figures are in weight % (from (4))

Processing plant N°

Constituent 1 2 3 4 5 6 7 8

Cement-bound

Regular concrete 61–91 51–83 45–83 33–93 17–73 8–48 7–35 3–17

Lightweight concrete 0–8 – – – – 0–2 – 0–1

Cement mortar – – – 0–9 – – – –


Lime mortar 0–8 2–11 1–14 2–4 4–20 7–22 7–35 14–32

Ceramic

Hard burnt bricks – – – – – – – –

Brick rubble 2–30 1–34 4–34 2–54 17–80 43–77 43–73 54–78

Roofing tiles – – 0–4 – 2–21 – – 0–2

Ceramic tiles – – 0–1 3–5 0–1 0–5 0–11 0–1

Other

Asphalt 0–8 12–28 4–19 0–37 0–11 – – 0–1

Sand-lime bricks – – – – – 0–3 0–8 –

Natural stone – – 0–8 12–21 – – – –

Contaminants

Glass <0.1 <0.2 <0.3 – <0.5 <0.4 <1.4 –

Metal – – – – – <0.2 0–2 –

Wood x x x x x x x x

Cardboard x x x – x – x x

Paper – x x x – x x –

Polymers – – – x – x x –

Reed – x x x – – – –

Limestone – – – – – – x –

Asbestos cement – – – – x x x –

Clay – – – – x – – –

Table 5. Composition of processed building waste sampled from 8 different West German processing plants (from (47))

Processing plant No

Constituents 1 2 3 4 5 6 7 8

Cement-bound

Concrete Other x –

o –

x –

x o

x o

x o

x o

x x

Ceramic and other masonry materials o – – x x x x x

Natural sand, gravel x o o x x x x x

Natural stone and slag x x x o x x x x


Other mineral product susceptible to weathering – – – – – x x x

Deleterious contaminants

Asphalt Wood, etc x –

x –

x –

o –

x o

x x

x x

x o

x in large quantities o in small quantities – in insignificant quantities

Table 6a. Constituents of building waste sampled after wet processing in plant A, compare Table 6b (from (35))

Useful sand and crushed stone

Sand suitable as fill

Wood and other contaminants

Steel Sediments

64 % 34 % 1 % 0,7 %

0.3 %

Table 6b. Composition of samples of processed building waste sampled from two West German processing plants (from (35, 45 and 46))

Constituents in weight %

Plants Type of processing

Concrete rubble

Brick rubble

Natural crushed

stone rounded

Slags and ashes

Other

A wet 52 12 8 16 5 7 (1)

B dry 50 15 15 10 5 5 (2)

(1) Asphalt (2) Sand-lime bricks and blocks, fire clay products etc.

Table 6c. Composition of samples of processed building waste. Particle size 2/45 mm from processing plant A (compare Table 6b). Samples selected from buyers at different locations (from (80))

Constituents in weight %

Sample N°

Concrete rubble

Brick rubble

Gravel and crushed stone

Slags and ashes

Other

deleterious harmless


5.2 Influence of composition

During the post-war years, preliminary sorting to remove the large sized impurities wasdone mainly by hand. The rubble was put on a conveyor belt and the operators removedany apparently unsuitable material. The effort required for collecting and sortingdepended on the choice of recycling process and on the quality of the rubble.

In modern plants, non-mineral materials such as wood, metal, remnants of textiles, etc.represent a disrupting element, but preliminary sorting by hand is no longer economicallyjustifiable although it cannot be avoided entirely (4). It is advisable to divide the rubble into three categories according to the nature of the main constituent: asphalt, concrete andmasonry rubble and to store them separately if convenient. If there is any suspicion thatthe rubble contains unwanted materials, these should be kept away from the three groups(4). This implies that the origin, amounts and overall composition of the rubble isrecorded on arrival. Production control should in any case include systematic visualexamination of the rubble (4). The type and composition of the rubble supplied can beregulated to a certain extent through the acceptance price or cost (32). The higher the grade of the demolition rubble, the lower the acceptance price or the higher theacceptance cost. With increasing shortage of dumping sites and increasing disposal fees,

1 69.6 5.2 22.6 2.5 < 0.1

2 72.3 3.0 22.0 2.5 0.1 < 0.1

3 65.1 14.2 20.3 1.0 0.5 0.3

4 68.2 6.9 17.7 5.9 1.0 0.3

Particle fraction 0/2 mm (counted under microscope): about 70% quartz; 10% burnt clay bricks; 5% basalt; 5% slag; 10% cement

Table 6d. Composition of processed building waste according to particle size distribution, from processing plant A, see Table 6b (from (80))

Constituents Particle size fraction, in mm 2–8 8–12 12–16 16–31.5 31.5–45

Gravel and crushed stone 16.8 23.0 26.0 30.4 14.5

Brick rubble 3.9 7.9 3.5 14.2 3.1

Concrete rubble 74.8 63.1 67.1 50.7 79.3

Slag 4.2 5.7 3.2 4.7 3.1

Other (harmless) – – 0.1 – –

Other deleterious 0.3 0.2 0.1 – —


there is an increasing possibility of influencing pre-sorting at the demolition site and hence also the composition of the rubble.

6 Preparation of masonry rubble

6.1 General

The preparation process for crushed masonry differs very little from that used for crushedconcrete. Reference should be made therefore to the relevant chapter in the report on“Recycled aggregates and recycled aggregate concrete” (31). This section presents mainly the experience of recycling rubble from the ruins left by the Second World Warand details taken from the literature on recycling of masonry rubble.

6.2 Preliminary sorting

In the dry recycling process for rubble from destroyed buildings, which consists mainlyof masonry bricks and hard burnt clinker bricks, in the original state or, sometimes, air-dried, the debris is separated into two or more grades, the fines being kept separate fromthe coarser grades. The limit according to reference (5) is between 40 and 50 mm diameter of the particles. On average, this gives a proportion of 45–55% of material below 40–50 mm. Sampling has shown that this fraction contains excessive amounts of impurities. This applies particularly to gypsum, the proportion of which at about 6–7% (sometimes more—Fig. 1), compared to 3% in the total rubble, is rather high (33). The fine material below 40–50 mm is considered to be unsuitable, not least because it contains not only gypsum but also clay, humus and other substances harmful to concrete.For this reason, any material with particle sizes less than 40 to 50 mm should be screenedout and possibly used as fill. Coarser materials with a gypsum content of about 1% (7), measured in terms of the SO3 content may then be subjected to further treatment. TheSO3 content of different size fractions of raw ruins-derived rubble from two cities in the North (N) and south (S) of Germany are shown in Figure 1.

6.3 Crushing

The most desirable grading curves for concrete aggregate (Fig. 2) can only be achieved by using a series of successive crushers and returning any over-size particles to the respective crusher (11, 40, 43). The most desirable particle shape can only be achieved by


primary, followed by secondary crushing (19, 23, 37). However, from an economical point of view, a single crushing process is usually the best (43, 32).

According to the paper referenced (39) hammer crushers are generally capable ofwithstanding any pieces of metal or other foreign bodies which may have beenoverlooked during the preliminary sorting of the rubble. Hammer crushers are capable ofreducing the material to the required particle size in a single operation. However, the

Fig. 1. SO3 content in different size fractions in raw ruins-derived rubble (from (56)) from two cities (N and S).


Fig. 2. Approximation to regular grading curves from crushings from brick rubble in single- and two-stage jaw crushers (according (11)).

best results have been obtained when all over-size particles are returned to the crusher.The results described in (4) show that both hammer crushers and impact crushers produced the largest amount of cubic particles from the masonry rubble investigated.

6.4 Classifying

After preliminary sorting, screening is necessary in order to avoid overloadingsubsequent secondary crushers (40).

6.5 Elimination of impurities

The most common impurities were gypsum plaster, iron and steel, non-ferrous metals, glass, timber and coal (6). Gypsum was found to be the most common impurity, and at the same time the impurity which it took most effort to eliminate in the pre-sorting process. There are three main processes for removing impurities and these are often usedin combination:

1. Dry process 2. Wet process 3. Thermal process (sintering)


6.5.1 Dry process

The dry process is the most generally used but also the least effective. In a plant inStuttgart (33) the raw material was put on a second conveyor belt after the preliminarysorting process and impurities were removed by hand. The material was then fed into acrusher installation where it was separated into the required particle sizes. According to(56) the critical particle sizes of less than 3 mm obtained through crushing, had an SO3content of less than 1%. However, Hoffmeister warned that this should not be taken toapply generally.

The gypsum content of rubble varied considerably in the different regions of Germany (see Figure 1). This is why the data sheet (37) recommends that a chemical analysis should be carried out before deciding which grades can be used immediately and whichgrades should be subjected to a special improving treatment (sintering for instance)before the processed rubble should be used as aggregate for concrete.

Separation by a compressed air process represents a considerable improvement over the usual dry process. In the compressed air process, constituents of different densitiesare separated out in sifting pipes with either horizontal or vertical flow. A necessarypreliminary requirement is that the rubble to be cleaned should already have been gradedinto separate sizes. This means that, for grades 0 to 40 mm, it is necessary to have aseparation into four or five sizes (33, 41). Another disadvantage is the release of largeamounts of dust requiring special protective measures (41). Apart from the usual crushing and screening installations, the use of magnets and metal detectors for extracting anynon-ferrous metals would be a useful item in completing the preparation process (32).

6.5.2 Wet process

In the wet process the rubble is subjected to washing, which should eliminate surfaceimpurities such as humus, clay, ash and any materials soluble in water (6). There is no separation into coarse and fine particles and the 80–90% recovery of material was considerably higher than for the dry process. However, Hoffmeister (6) found that hardly any gypsum was washed out in the wet process. He assumed that prolonged contact withwater would cause the gypsum to expand. This would mean that the water flows roundthe material under high pressure rather than through the material. Laboratory tests haveshown that subsequent treatment in a friction type mill could lower the gypsum contentconsiderably. The reduction in the gypsum content was attributed to the fact that thegypsum had been ground to a fineness where it could be washed out. However, the surestmethod to prevent contamination with gypsum was found to be initial dry crushing withelimination of all fines below 50 mm. With the wet process it was impossible, accordingto (43), to reduce the gypsum content of sizes 0 to 3 mm to less than 3% under any circumstances.

In the wet process generally used nowadays, the “Aquamator” (Fig. 3), unsuitable constituents such as timber, paper, plastics, lightweight concrete, etc. are separated fromthe heavier and desirable constituents partly by flotation, partly by spraying and retaining


on a screen (35, 41, 44, 53, 54). Overall, this requires about 160 cubic metres water per tonne of crushed rubble. Since the water is relieved of any floating materials in thecyclone classifier and re-circulated to the preparation process, the real supply of freshwater required is only about 2 cubic metres per hour. The German recycling plants usethe wet process only for the coarser sizes, but a plant in Amsterdam uses it also for thefines which gives a correspondingly high amount of sludge (35, 44). The wet process gives particularly good results for particle sizes of more than 8 mm specially where therubble contains large quantities of lightweight constituents. Since fines ranging from 0 to8 mm produce large amounts of sludge, it is advisable to provide early separation intofractions below and above 8 mm. If the fraction below 8 mm is wasted, this would alsoreduce the total amount of crushed rubble to be dealt with at later stages of the productionprocess (42, 44, 53, 54). The wet process does not release any dust and the content of suspended impurities to be washed out is also reduced. On the other hand, certaindisadvantages such as high water consumption and high cost of sludge disposal must betaken into account.

Fig. 3. Process diagram for wet processing building rubble with “Aquamator”, (manufacturer’s brochure Gfa, compare (44)).


6.5.3 Thermal process

By combining a dry process for the coarser sizes above 50 mm and sintering for the fines,it is possible to use nearly 100% of the rubble. However, this procedure is advisable onlywhen the cost of transporting and disposing of the fines exceeds that of the energyrequired for the thermal process (43).

6.6 Rentability

Mobile crushing plants with an output of about 5 m3/h have been found uneconomic because the machines could not be used to their full potential (34). Small plants are less economical than large ones (43) and there was an optimum output of about 20 and 60 m3/h. Larger plants provided practically no further improvement.

The best conditions are obtained with regular and full use of the plant. If a plant works only to a fraction of its capacity, the lower output must still carry the considerable fixedcosts which include the wages; variable costs are less important in recycling.

7 Properties of crushed masonry aggregate

The properties of recycled building rubble vary according to the composition of thematerial; conversely, the properties may be controlled to a certain extent by restrictingthese constituents. To this effect, it is necessary to make a distinction between the mainand the secondary constituents. In the post-war years, constituents other than brick andsand-lime brick rubble never had to be considered. If brick was the main constituent, an additional amount of sand-lime brick of about 15% by weight was thought to cause no difficulties (11). Even mineral materials such as mortar and rendering caused no disruption if they consisted of cement mortar, sand-cement mortar or lime mortar and therequired grading curves could be maintained (13, 55). It was only for the manufacture of very porous lightweight concrete for thermal insulation that the German standard DIN4163 (1) (which has since been withdrawn) specified that crushed brick and brick based sand should not contain more than 25% of the heavier particles of concrete, mortar,natural stone and sand-lime bricks.


7.1 Definitions

The Dutch draft standard CUR-VB, 1984 edition, (3) (See Appendix C), may be used as a model code for the classification of building rubble. It classifies as “crushed masonry” aggregate containing at least 65 weight% brick, sand-lime brick and concrete as main constituents and no more than 20 weight% lightweight concrete, 10 weight% cellularconcrete, 20 weight% ceramic materials such as roofing tiles, etc., 20 weight% naturalstone and 25 weight% mortar as secondary constituents. In contrast recycled building rubble containing at least 95 weight% of crushed concrete with a density of more than2100 kg/m3 and only 5 weight% of secondary constituents such as brick, sand-lime brick, lightweight concrete, cellular concrete, ceramic materials, natural stone and mortar isclassified as “concrete rubble”. It is possible that similar definitions may be devised for “crushed brick”, “crushed sand-lime brick” etc., when the amount of the main constituent is correspondingly high and that this is meant to characterize the properties of the crushedmaterial.

7.2 Grading

According to DIN 4163 (1), broken brick or rubble with the fines (particles less than about 30 mm) removed should be crushed and sieved in such a way that the particleshave as compact a shape as possible and can be supplied in the required grades andamounts, properly separated (see Figure 4). Suitable gradings are 0/3, 0/7, 3/7, 7/15, 15/30 and greater (all in mm). Reference should be made to the German standard foraggregate: DIN 4226–7.47 (Ref. 2). In deviation from the standard, the fraction below 0.2 mm could amount to a maximum of 5%. As mentioned before in Section 6.3, conformity to the required grading curves could be maintained only by returning over-size material to the crushing process and/or by using a series of preliminary and secondary crushing(11, 40, 43) (see Fig. 2).

It appears from (4) that production of a material which conforms to the grading curves is not without problems even with more modern plants. The gradings of 8/16 mm and16/31.5 mm shown in Fig. 5 do not completely correspond to the requirements (see Table C1). It should be taken into account generally that many existing plants include screeningdevices which are usually not designed to produce aggregate for making concrete and arebetter suited for road building purposes.


Fig. 4. Grading curve range according to DIN 4163 (1) compared with the grading curves according to DIN 1045 (88).

Fig. 5. Particle size distribution of recycled building rubble (crushed masonry a to d, from Tables 8 and 9, before the removal of the 0 to 4 mm fine particles, according to (4)).

For the gradings obtained with plants A and B (35, 45, 46) (see Table 6 b), the result after


elimination by calculation of fractions in excess of 32 mm, was still within the correctrange of the grading curves according to DIN 1045 for concrete aggregate (see Fig. 6).

7.3 Secondary natural constituents and natural sand aggregate

7.3.1 Fines

In recycling of rubble, subsidiary inorganic constituents may be tolerated provided thelimits of the grading curves specified can be maintained (55). They cause no difficulty for the properties of the concrete, at least as regards the physical and mechanical properties.This applies also to debris from mortars or renderings, as long as they are based oncement, lime-cement or lime mortars. After crushing, such constituents were found to occur mainly in the sand fraction. The same applies to sand fractions from floor fills.More doubtful were the loam fills from joist type floor constructions. Their remains, aswell as all fine suspended fractions which are capable of being removed by washingshould be kept within very narrow limits (see Section 7.8.1). The eight crushing plants investigated ((4), Tables 3 and 4) produced materials containing an average 20 weight%of masonry mortar.

Fig. 6. Particle size distribution of recycled building rubble, installations A and B (compare Table 6) referred to the relevant 0 to 32 mm range (according to (45)).


According to DIN 4163, it is permissible, for dense textured concrete, to replace all orpart of the crushed brick sand by natural sand if, for instance, it should be required inorder to improve the concrete strength. There were also other reasons for replacingcrushed brick sand up to 3 mm particle diameter: the fine fraction requires particularlyhigh amounts of water for good concrete workability, which incidentally was difficult toreproduce. The SO3 content of the crushed sand below 3 mm was partly in excess of 1weight% (7, 43, 56, 58). However, for reasons of economy, it was considered worthwhile to make full use of the rubble by using the fine fractions as well.

7.3.2 Natural sand

In many cases, attempts to replace brick sand by quartz sand of similar grading ((10) and also (9)), resulted in lower strengths. The reason was that the lower water requirementshad not been taken into account in a proper way. Differences in density were only veryroughly taken into account by assuming that the brick sand weighed only two-thirds of the natural sand (1). A similar experience was encountered when batching by volume for a concrete composition including natural sand with a density of 2,600 kg/m3 and crushed brick with an average density of 1,650 kg/m3. In reality the density of the crushed brick varied between 1,400 and 1,900 kg/m3, (19). In other words, for similar proportions by weight there was a reduction in volume of about 37%. Because of the manydisadvantages of the fine fractions of building rubble, it is generally recommendednowadays to restrict its use as aggregate for concrete to the coarser particles in excess of2 mm (or even better 4 mm). Recent investigations on concrete (for instance (4) and (8) used natural sand as fine aggregate.

7.3.3 Sand-lime bricks

Rubble front war-damaged buildings contains not only brick but also a certain amount of sand-lime brick. According to Hummel (11, 12, 52), crushed sand-lime brick is less suitable as an aggregate in its own right because of its higher density and because of thenature of its material structure. Sand-lime bricks absorb moisture just like baked clay bricks, but release it more slowly, which means that a higher permanent moisture contentis to be expected in the concrete. In the wet state, sand-lime brick rubble tends to clog up the screening plant. However, where ordinary masonry bricks have been crushed togetherwith sand-lime bricks, this does not seem to have been the case, or at least not to the same extent. Amounts of up to 15 weight% of sand-lime brick in crushed masonry aggregate are considered acceptable. Brandt (57) was unable to confirm the doubts about therecycling of sand-lime brick. In his opinion, crushed sand-lime brick is a suitable aggregate for concrete as long as carefully screened material is used from selected sand-lime brick rubble. Similar concrete compressive strength values were obtained as forcomparable concrete made with crushed brick, and a lower water absorption of aggregatemeant fewer problems with water content and processing. However, the increased densityresulted in a loss of thermal insulation properties. Consequently, insulating concrete


made with crushed brick and brick sand should not contain more than 25 weight% ofheavier particles consisting of concrete, mortar, natural stone, sand-lime brick or similar materials (1).

7.4 Density

Figures relating to the density of crushed brick and its mixes with quartz sand or rubblesand may be found in reference (9). According to (9), the density depends on the type of brick used (ordinary masonry bricks or hard burnt bricks) and on the amount of naturalsand used (Fig. 7) .

Fig. 8 gives a comparison between the absolute densities and particle densities of crushed brick and three different natural aggregates (grading 7/15 mm) commonly usedfor the manufacture of porous concrete (20).

Fig. 9 and Table A3 give particle densities and bulk densities for various crushed masonry materials (4). The particle densities are well below 2,200 kg/m3.

Fig. 7. Particle density of crushed brick rubble as a function of the natural sand content (according to (9))

The crushed brick mixes investigated thus fall within the range of “lightweight


aggregates”. There seems to be a linear relation between particle density and bulk density, which is particularly important for quality control. Wide variations in thecomposition of the crushed material require very frequent testing and this is why inpractice attempts have been made to replace the relatively cumbersome determination ofparticle density by bulk density, which is simpler and easier to measure. For practicalpurposes, it is necessary to confirm the relations thus obtained by further tests.

With the exception of a few types of natural stone and asphalt concrete, the absolutedensities of the materials investigated remain more or less constant between 2,600 and2,800 kg/m3. This means that the properties of the aggregate described below are mainly determined by their porosity.

7.5 Water absorption

Apart from hard-sintered clinkers, crushed brick and crushed rubble are highly absorbentaggregates and the higher the porosity of the original bricks, the higher the absorptioncapacity of the aggregate. According to reference (9), complete saturation of crushed brick before it is used in themanufacture of concrete is necessary in order to prevent the concrete from being “too thirsty”. A rough assumption of the water absorption of crushed brick is a value between22 and 25 weight% in relation to the dry material.

The test results in (4) show that crushed brick is already completely saturated with water after 30 minutes’ submersion in water.

Additional water absorption over a total period of 24 hours (w/24h) does not exceedabout 2 percentage points for low particle density values. There is a linear relationbetween water absorption and particle bulk density (Fig. 10). Since the relation of particle density to bulk density of the aggregate is also linear (see section 7.3) both water absorption and particle bulk density may be determined on the basis of the bulk density of the aggregate as a whole (Fig. 11). It should be pointed out again that further confirmation would be required before such relationships are used in practice.


Fig. 8. Characteristics of aggregate for crushed brick aggregate compared with natural lightweight and normal aggregates, size fractions 7 to 15 mm (according to (20))


Fig. 9. Relationship between bulk density and dry particle density of crushed masonry rubble (according to (4))


Fig. 10. Relationship between water absorption after 30 minutes (W30) and the dry particle density of crushed masonry (according to (4)).


The frost resistance of recycled rubble is important, particularly when the concrete is tobe exposed to the weather without any protection. Inside buildings, adequate frostresistance for moderate wetting is generally sufficient (2). Intended as protection against frost in road construction, the recycled material produced by plants A and B (Table 6) were certified to have sufficient frost resistance solely on the basis of grading andpetrological properties (45, 46). Investigations (80) on material produced by plant A gave different results for different test procedures. Alternate freezing and thawing generallyresulted in excessive spalling, but the frost resistance criteria of the frost heave test (CBRtest) were satisfied. Particularly good results were obtained for the 16/32 mm fraction,where spalling after freezing and thawing was well below the limit value. It is wellknown, however, that many bricks cannot withstand frost. In


Fig. 11. Relationship between water absorption after 30 minutes (w30) and bulk density of crushed masonry rubble (according to (4)).

rubble such bricks were relatively easily detected because of signs of weathering. Grafexpressed the opinion that weathered, frost sensitive bricks are crushed to such an extentin the process that they have no harmful effect in concrete (19).

7.7 Particle strength, degree of crushing

Direct determination of compressive strength of the constituents of building rubble ispossible only if the material is available in a form suitable for cutting out test pieces(cubes, prisms, cylinders). In many cases the material is available only in the crushedstate.

Hummel (20) carried out tests with a view to determining the average strength of the crushed material. The investigations included comparison between material obtained byimpact crushing and by compressive crushing. The material used was crushed brick withdifferent brick strengths; the amounts used in the steel testing cylinder were 0.5 litre ofmaterial with particle size 7–15 mm. Table 7 shows the mean values of the test results.Figures in parentheses represent the relation of the test results in percentages of thecorresponding test values in the second column of the table for crushed brick with a brick


compressive strength of 49.0 N/mm2. it may be seen that there is no correlation between the strength of impact crushed material and that of the bricks, whilst there is at least ageneral trend in common between the strength of the bricks and that of the materialcrushed in compression (21).

The other tests described in (21) show that (contrary to the case for impact crushing)the compressive crushing test enables a sufficiently accurate determination to be made ofthe particle strength of lightweight aggregates such as

crushed brick. The degree of compressive crushing was determined in terms of thedifference between the fineness value of the aggregate before and after compressivetesting according to DIN 52109 (93) . The fineness value is calculated from the sum of the residues (in weight%) on the sieves 7, 3 and 1 mm, divided by 100. The degree ofcompressive crushing of the aggregates tested showed a relation to the total volume ofpores of the mix (pores in the mix and pores in the particles) and also to the bulk density(Fig. 12).

Overall, the degree of compressive crushing diminishes with increasing cube strengthof the original material (Fig. 13) but the relation is not linear e.g. since it involves notonly the specific strength of the original material but also the influence of the shape of theparticles in the mix (21).

The investigations described in (4) do not show any relation, for crushed masonry mixes, between the degree of compressive crushing and the particle bulk density or theoverall bulk density (Table A2) .

According to the DIN standard 4226 which applied at the time (2) when the study was made, the uniformity of particle strength of aggregates for cellular concrete wasdetermined either by compressive tests on the concrete or

Table 7. Degree of crushing of processed brick rubble of different strengths depending on the method of testing. (Degree of crushing is defined as material retained on a 7 mm sieve, in weight % (from (21))

Test method Material retained on a 7 mm sieve, in weight % when compressive strength of original bricks or blocks, in MPa, was:

49.0(100)

20.8(42)

13.0 (27)

Impact test 77 (100)

81 (105)

60 (78)

Compressive test

87 (100)

79 (91)

60 (69)


Fig. 12. Relationship between degree of pressure crushing and bulk density for crushed brick and crushed sandlime stone (according to (21), correlation without KS).

by testing the strength of the particles by the cylinder method. This method resembles thecompressive crushing test but differs from it in that it determines the force required tocompress the aggregate inside the cylinder by 20 mm within about 100 seconds. So far,no test results for crushed masonry have been reported.

Fig. 13. Relationship between the degree of compression crushing and compressive strength of stones for crushed brick and sandlime stone (according to (21), correlation without KS).


7.8 Harmful constituents

7.8.1 Constituents liable to be removed by washing

According to Hummel (11, 12), the amount of remaining suspended matter after washingof recycled building rubble need not be as carefully restricted for lower strengthconcretes and lightweight concretes as it has to be for normal concrete. Although itshould not exceed 3 weight% according to data sheet (55), higher amounts would be permissible if tests show that the required compressive strength of the concrete has beenachieved. DIN 4163 (1) referred to the standard for aggregate, DIN 4226, applying at thetime but also allowed for higher amounts under certain conditions.

Using a wet crushing process makes it possible considerably to reduce the content ofsuspended particles. The fraction below 0.063 mm in recycled rubble prepared by a wetprocess (Plant A, Table 6) was 2.3 weight% of the total aggregate (45). Since it may be assumed that leachable particles occur mainly in the fines, where the limit values arehigher, it is probable that the overall requirements of DIN 4226 (Table B1) probably are fulfilled. When dry processes are used (air screening, Plant B, Table 6) the conditions, with 3.4 weight% of suspended particles (46), are less favourable. The required limitvalues are probably not always maintained in all fractions. In any case, it may beassumed that, by eliminating fines up to 4 mm, the content of leachable particles in thetotal aggregate would also be reduced to a harmless level. A series of tests (4) with fine fractions (0/4 mm) gave up to 13 weight% of leachable constituents (Table A6a). As mentioned in Section 9.3, this may cause serious difficulties in connection with theproperties of concrete.

Therefore it is recommended that no fine material below 4 mm should be used when producing aggregate for concrete production from masonry rubble.

7.8.2 Organic materials

As may be seen from Tables 3, 4 and A1(4), pieces of wood, vegetable matter, insulation material, paper, textiles, etc. generally amount to less than 0.1 weight% of the recycledmaterial. Values in Table 5 demonstrate that, depending on the type of plant and originalmaterial, it is not always possible to eliminate lightweight constituents in a satisfactorymanner.

No finely divided matter of organic origin was detected in the course of theseinvestigations. These materials were probably eliminated by preliminary screening andremoval of the 0/4 mm fraction. The same applies to substances liable to interfere withthe hardening of concrete.


7.8.3 Sulphur compounds

According to DIN 4161 the sulphate (SO3) content, due to the presence of mortar debris,pieces of gypsum, slag and other contaminants should not exceed 1 weight% of the driedaggregate when used with standard cement and binders of similar composition (see alsoDIN 4226 Parts 07.47 and 04.83).

Continuous chemical analysis is required, particularly in regions where gypsumrenderings are prevalent. In many places, the gypsum content of the aggregate gives riseto problems. Investigations in the Stuttgart region have shown that the gypsum contentmeasured as SO3, of the building rubble was between 1 weight% (grading > 40 mm) and6.5% (grading < 40 mm) (58).

Even before the Second World War in German standard specifications, the SO3 content of concrete aggregates had been restricted to 1 weight% (corresponding to 2.1weight% of gypsum) (19). To answer the question, whether it might be possible toincrease the permissible amount of SO3, and whether gypsum particles might be lessharmful than gypsum powder (19), Graf carried out the following tests (19):

Fairly porous concrete prisms measuring 40 mm x 40 mm x 160 mm were made with 137 kg/m3 Portland cement and w/c= 0.80. Gypsum was added as a finely groundpowder. Expansion of the prisms after they had been stored either for 28 days under wetconditions or seven days of wet storage followed by 21 days of dry storage, was at least3.5 mm/m. Addition of 1.5 weight% SO3 to the concrete, whilst the aggregate itself(crushed brick) contained 0.4 weight% of SO3 and the portland cement 1.8% SO3 showed that, with 1 weight% of SO3 and otherwise equal parameters, the expansion did notexceed 0.6 mm/m. No further changes in length were observed when the time of exposurewas increased from 28 days to 8.5 months. Further tests were carried out to determine theeffect of gypsum of various degrees of fineness. The tests were made with prismsmeasuring 100 mm×100 mm×560 mm and with 200 and 300 kg portland cement/m3. Inone case the gypsum was ground to the fineness of cement and in others it had a particlesize of 1–3 mm. In some cases the powdered gypsum produced more cracks and widercracks than the coarser fractions, but in general the particle size did not appear to be asignificant factor.

In further series of tests (19), the effect of gypsum on expansion of concrete specimensmade with various kinds of aggregate was investigated. With 300 kg of Portland cementand an SO3-content of 2 weight% of the aggregate, use of crushed brick did not result inany expansion or cracking. Using Rhine sand and Rhine gravel, all other parametersbeing equal, there was extensive cracking, with crack widths up to 0.3 mm. Investigationscarried out by Graf gave the following conclusions:

1. The lower the cement content, the greater the effect of gypsum on expansion and cracking of concrete.

2. Gypsum in particle form is just as harmful in its effect on expansion and cracking of concrete as in powder form, but the effect is felt much later.

3. When using lightweight aggregate, e.g. crushed brick, a much higher gypsum content could be allowed than for normal aggregate, due to the fact that


the gypsum content in the tests was calculated in percentage of the weight of the aggregate.

In contrast with the studies of Graf, Gaede (33) assessed the effects of gypsum in terms ofthe compressive strength of the concrete. His tests showed a sharp decrease in strengthwithin a narrow range of added sulphate, irrespective of the cement content. Above andbelow this area of sharp decrease in strength, the strength values remained more or lessconstant. The same sharp decrease could be shown for all mixes when the SO3 contentwas determined not in terms of the aggregate alone but of the amount of cement+14weight% of the aggregate. Gaede observed that for dense textured concrete, made withportland cement and natural aggregates, w/c ratios of 0.62, the addition of powderedgypsum resulted in a decrease in strength starting at an SO3 content of 1.2 weight% andending at an SO3 content of about 3.6 weight%. The following relationship wasestablished to represent these facts:

Critical sulphate content x, with respect to content of cement c+14 weight% aggregate,where:

Sulphate content y with respect to 100% aggregate, where:

where =cement/aggregate ratio by weight. g=total weight of aggregate per m3 of concrete It is possible to conclude that even with

a reduction of the SO3 content to a value as low as 1 weight% of the aggregate, there isstill an appreciable loss of compressive strength of concrete. This applies particularly tomixes with low cement contents. The investigations which are reported in (33) show thatthe loss of strength is about 50% greater with magnesium sulphate than with calciumsulphate (gypsum). Portland cement gave greater losses of strength than blastfurnace slagcement.

Comparison of the results obtained by Graf and Gaede shows that: Whilst Graf drew attention particularly to the expansion phenomena due to the

presence of gypsum and investigated changes in specimen length and crack widths, Gaedestudied changes in concrete strength. Graf thought that restricting the SO3 content ofaggregate to 1 weight% would be sufficient, but Gaede showed that damage may occur atmuch lower amounts of SO3. Contrary to Graf, Gaede was of the opinion that in practice,the larger gypsum particles are less active, but this was not confirmed by tests. It stillremains an open question which SO3 content will cause damage to concrete. As years ofpractice with a value of 1 weight% SO3 in relation to the weight of aggregate have notgiven rise to any problems, this value may be generally accepted. Particularly with mixesof high cement content, 1% of SO3 by weight of aggregate is on the safe side becausesulphate reactions occur by reaction with the cement and the cement alone. Therefore inthe end it is the cement content that is of importance.


7.8.4 Substances corrosive to steel (chlorides, etc.)

In recycling rubble from demolished buildings, hardly any attention has been paid to thepresence of chlorides and other salts which might give rise to corrosion of thereinforcement. Tables B1 and c1 give present day requirements for aggregate to be used in reinforced concrete.

7.8.5 Other impurities (asphalt, glass, metals, etc.)

Wet or compressed air recycling processes appear to clean the rubble so thoroughly that,according to the data in (35), (45) and (46) the total content of lightweight constituents such as wood, insulating materials, etc. in the fractions above 2 mm of the recycledrubble does not exceed 0.5 weight% (Table 6). The amount of asphalt however which, according to (3) and (4), has to be considered as an impurity is certainly too high at about 7% (Plant A—Table 6). As shown in Tables 3 to 5, considerable amounts of asphalt are always to be expected in demolition rubble. The problem may be solved by preliminarysorting. Apart from a very few exceptions, glass occurs only in small quantities up toabout 0.5 weight% and metal up to 0.3 weight% ((4), Tables 3 and 4). Self-cleaning magnet type separators and metal detectors (32) make it possible to eliminate metals to a large extent.

7.9 Loss on ignition

When crushed brick is the main constituent of recycled rubble, the loss on ignition is lessthan 5 weight% according to published test results (4) (Table A2) . If sand-lime brick or concrete are the main constituents, the limit value of 5 weight% is clearly exceeded (2).

7.10 Transfer of deleterious organisms

There was initially a certain fear that the recycling of rubble from demolished buildingsmight propagate fungi that could attack timber, but tests have shown that no fungi cansurvive the process of concrete manufacture (9, 59, 60).

7.11 Quality control

Even at the time when rubble from war-damaged buildings was being recycled, strict quality control measures were applied to rubble aggregate in order to protect the user


against the application of inferior building material. By strict quality control it wasintended to prevent failures which might have brought recycled rubble materials intodisrepute (77, 82 , 83).

It was for similar reasons that, in 1985, the Association for Quality Control of Recycled Building Materials was established in the Federal Republic of Germany (81). The Association grants the manufacturers of recycled building materials the right to usethe RAL quality stamp—at present only for road construction purposes. To this effectvarious quality and test requirements were developed, with which the beneficiary of thequality stamp must comply. These requirements specify the type and extent of testing of recycled materials for road construction. They ensure that manufacturing proceduresremain constant and provide a sound basis for uniformity in assessment and designation.The quality control includes manufacturer’s quality control and surveillance by an external body (85, 86, 87).

Irrespective of the field of application (aggregate for concrete or road construction), quality control of crushed building rubble makes sense only if due consideration is givento the specific properties of this type of material. Production of recycled rubble may showgreat variations in the course of a day’s production. The frequency of manufacturer’s quality control according to DIN 4226 Part 4 (2) is insufficient to take this into account. On the other hand, it would be difficult to justify the cost of increasing the frequency ofquality control beyond that required for natural aggregates. Therefore it is necessary inthe future to provide suitable preliminary sorting, storage and mixing in order to ensurethat a day’s production may be regarded as a single batch.

8 Fresh concrete—composition and properties

8.1 Water requirement

In the early days water absorption by porous crushed rubble or crushed brick presentedconsiderable problems from the point of view of concrete technology. During the periodof recycling war rubble, the concept of a distinction between surface moisture andabsorbed moisture was still unusual. In line with the terminology for normal denseaggregates, terms such as water requirement and free water were in use. This explains thestatement in (11) “Water requirements of 6 to 14 weight% for gravel sand concrete are tobe compared to 20 to 35 weight% for crushed brick concrete”. Not only does this deal far too roughly with the problems of water absorption and water content and their relation totime after mixing and consistency of concrete, but it does not take into accountdifferences in density of various materials. It was pointed out, however, that waterrequirements were lower when natural sand was used as fine aggregate. Sand from rubblewhich consists mainly of concrete or lime-mortar waste had an absorption capacity


somewhere between that of natural sand and that of brick sand (9). It was known that the absorption capacity of bricks decreased with increasing strength of the brick, i.e. withdecreasing porosity (11, 12). This is why the absorption capacity of hard burnt bricks wasset at only about 15 to 24 weight% (9). It was also known that the particular part of the mixing water which was absorbed and stored in the crushed brick aggregate wasconsequently not available for hardening of the cement but, in dense concretes, subsequently helped to achieve hardening of the concrete at later ages. Particularly forstiff concrete mixes, it was recommended that the amount of mixing water should becalculated carefully in order to prevent lack of water for cement hydration (11, 12).

Hummel (11, 12) warned against pre-wetting of crushed brick because it seemed doubtful that the moisture would be evenly distributed throughout the crushed aggregate.The “Technical Data Sheet for the Manufacture of Crushed Brick Concrete” (55) (preliminary to DIN 4163) recommended that, if the amount of mixing water is increased,part of this water should be poured into the mixer drum at the start of the mixing process.Suitable proportioning of total mixing water should be determined by leaving anexperimental mix for half an hour in order to determine whether the fresh concrete hadstiffened more than was required for placing.

According to a proposal by Charisius (10), the concrete should be mixed in such a way that the aggregate is first thoroughly moistened with a given amount of water, then leftfor half an hour, after which enough water is added to produce concrete with a slump of45 mm. The authors of (9) stress that complete saturation of crushed brick aggregate is a necessary prerequisite to ensure against loss of strength due to lack of water for hydrationof the cement paste (compare this with the findings in (62)). Tests were carried out in which the crushed brick was wetted and left for half an hour in the mixer. The descriptionof the tests makes a distinction between free water and bound water, which was not soobvious at the time. It was known that the water requirement value, which was to beequated with the water absorption of the aggregate, depended on the nature of theaggregate, the shape of particles, the grading and the surface texture of aggregate. At thattime an empirical determination of the water absorption was seldom made in practice.Instead, the water absorption was based on estimated values of between 22% and 30% ofthe dry weight of aggregate.

8.2 Free or effective water/cement ratio

In the discussion of test results in (9) it was found that the water/cement ratios, calculated on the basis of total water minus the assumed water absorption sometimes were below thevalues required for complete hydration of the cement. In extreme cases, calculatedwater/cement values of 0.1 to 0.2 were obtained. Correspondingly high compressivestrength values were observed for such concretes.

However, in order to dermine the free or effective w/c ratio of brick-concrete it is necessary by way of experiments to determine reliable values for water absorption of allaggregates. Absorption after 30 minutes’ immersion in water (w30) was found to be a sufficiently accurate indication of the true value of water absorption and this practice has


also proved reliable in practice (ASTM C127 (Ref. 89) and ASTM C128 (Ref. 90)). Account should be taken of the fact that maintaining a specified w/c ratio is made moredifficult by the fact that water absorption capacity of concrete aggregate depends onconcrete consistency. For high slump values and correspondingly higher availability ofwater, porous aggregates may absorb larger amounts of water (61, 69).

If, however, the aggregate is pre-wetted for instance by spraying, so that it neitherabsorbs nor releases water during concrete manufacture or during the early stage aftermixing of the concrete, regular determination of water absorption becomes unnecessary.The aggregate is said to be in a saturated and surface dry condition. However, in practice,it is not always possible to achieve uniform and complete saturation of porous aggregates(compare this with Section 8.1).

8.3 Cement content

According to DIN 4163 (1), the binder content of crushed brick concrete should be related to the quality of the binder and the concrete strength required. It should bedetermined by trial mixes, for instance according to DIN 1045 (88) applied to reinforced concrete made with crushed brick.

In the current edition of DIN 1045 (88), minimum binder contents for dense concrete with cement contents of 300, 270 or 240 kg/m3 are specified, depending on grading of aggregate and other conditions. Cement contents of 270 to 330 kg/m3 have been recommended (11, 12). Laboratory tests have been carried out with cement contents up to 350 kg/m3 (9, 13, 15).

8.4 Workability

8.4.1 Dense crushed brick concrete

Crushed brick concretes with reasonably dense texture can be made with all freshconcrete consistencies in the ranges from very stiff to plastic .

Compaction of concrete is facilitated by increasing the amount of mixing water (11, 12). According to DIN 4163 (1), the consistency of the fresh concrete should be adjustedto the type of building component and its extent of reinforcement. For reinforced concretecomponents, which are manufactured without vibration, a flowing concrete is generallyused in order to ensure good embedding of the reinforcement and proper corrosionprotection of the reinforcement by the concrete itself (1).

Reference (9) reports more favourable water contents and better workability of mixes using crushed brick and rubble sand, compared to mixes with natural sand. Compaction isalso described as being easier with brick rubble sand than with natural sand. Densecrushed brick concretes which were produced with rubble sand tended to show highercompressive strengths than mixtures produced with natural sand, probably due to the


pozzolanic activity of the crushed brick sand. Less definite, but still positive, was theassessment of the use of rubble sand in reference (13). Mixes with natural coarse aggregate and rubble sand, like those with natural sand, achieved higher compressivestrengths than those containing crushed brick only.

8.4.2 Porous crushed brick concrete

For all concretes where high porosity is required, it is necessary to prevent the cementpaste from becoming too fluid and it is necessary to restrict the amount of mixing waterin the concrete in such a way that the cement paste does not sink into the voids and fill upthe pores. According to DIN 4163 the amount of mixing water is correct, if the aggregateparticles are coated with a film of binder. The consistency of porous crushed brickconcrete in the fresh state was generally within the range of stiff to very plastic, and thiswas generally seen as satisfactory in practice because it is desirable to remove theshuttering as soon as possible after casting.

8.5 Compaction

Investigations of the extent and type of compaction of crushed brick and crushed rubbleconcrete are described in reference (9). The effect of various parameters on concretecompressive strength was determined. In view of what is known nowadays, theconclusions reached at the time, i.e. that vibrated concretes generally reached higher bulkdensities and strengths than those compacted by hand by rodding or tamping will come asno surprise.

In reference (9), the basic assumption was a figure of 1.5% naturally embedded air pores in concrete which was not intentionally air-entrained. But in reference (4) surprisingly high values of 3.3% to 6.2% (Table A2) were quoted, probably in error.

8.6 Bulk density

Wet densities of fresh concretes investigated in reference (9) varied between 1,780 and 2,100 kg/m3 and depended on the type of crushed brick and the extent of replacement ofbrick sand by quartz sand or rubble sand. Increasing the amount of quartz sand alwaysgave higher bulk densities for fresh concrete.

For sand-lime brick concrete, the bulk densities of the fresh concrete were higher, withfew exceptions, than for comparable concrete mixes which were produced with crushedbrick (9)—See also Table A2 (4).


8.7 Composition of the concrete

8.7.1 Dense crushed brick concrete

According to DIN 4163 (1), aggregate grading should be decided according to the type ofconcrete required, but particularly according to whether dense or porous concrete wasrequired.

For dense crushed brick concrete, the grading should be within the range of the cross-hatched area of grading curves in Fig. 4. DIN 4163 (1) quoted corresponding ranges for fractions 0/7 mm and 0/15 mm. These ranges are narrower than required for naturalaggregate according to DIN 1045. It was necessary to lower the upper limit of the gradingcurves because the finest fraction of the rubble requires too much cement paste. Thelower limit took account of the possibilities which were available for compaction of theconcrete at the time. It was feared that concrete with high proportions of coarse aggregatewould be too harsh to be workable. Increased compaction used for such harsh mixeswould also present the risk of destruction of aggregate particles (11, 12). In spite of narrowing the grading range of fine aggregate, it proved difficult to control the waterrequirements for the absorbing aggregate and hence also the w/c ratio of the resultingconcrete. It turned out that even small modifications in the grading curves gave rise tolarge deviations from the specified w/c ratios (9) (compare this with Section 8.2).

8.7.2 Porous crushed brick concrete

According to DIN 4163 (1), the grading for porous crushed brick concrete should bedesigned to produce as large a void content as possible between aggregate particles,which means a fundamental difference from the grading for dense concrete.

Leaving out or restricting the fraction between 0 and 3 mm already ensures a certain concrete porosity, but it is only by using fractions 3/7 or 7/15 or 15/30 mm exclusivelythat a suitable high porosity is achieved (Fig. 15). The average binder content of porouscrushed brick concrete varied according to the quality of the binder and the requiredconcrete strength. The binder content varied widely and should therefore be decided ineach individual case by production of trial mixes.

The cement content of very highly porous crushed brick concrete varied between 130 and 170 kg/m3. It should be chosen rather low to prevent any filler effect and in order to ensure cementing of the aggregate only at the points of contact. In order to improvestrength but at the cost of losing part of the volume of voids, it was recommended toincrease the cement content of such concretes to about 200 to 230 kg/m3 (11, 12).


9 Properties of the hardened concrete

9.1 Dense concrete

9.1.1 Bulk density

Crushed brick concretes with bulk densities between 1,000 and 2,100 kg/m3 gavecompressive strengths of 2 to 32 N/mm2 (11, 12, 14). The bulk densities depend not only on the cement content (Fig. 18) but also on the grading and the density of the actualrubble fragments. Shortly after the war, lightweight concrete was made with bulk densityon average only 69% to 75% of that of normal concrete but which still reachedcompressive strengths of 12 to 16 N/mm2. The bulk densities at 28 days were generallybetween 1,600 and 2,100 kg/m3. Because of the high water absorption of the aggregate itwas possible to reduce these values by a maximum of 400 kg/m3 by drying. It wasknown that only the dry bulk density was reproducible (11, 12).

9.1.2 Compressive strength—influences

9.1.2.1 W/c ratio

The problems concerning water absorption of crushed rubble described in Sections 8.1and 8.2 make it difficult to achieve any desired constant w/c ratio of concrete. The post-war literature mentions excessively high, as well as excessively low, w/c ratios which it isdifficult to reconcile with the concrete strengths, even with present-day knowledge. Water absorption of crushed brick or rubble caused unwanted changes in thewater/cement ratios, so that many concretes achieved surprisingly high strength values,even exceeding those of gravel sand concretes with similar composition (11, 12). Since these factors overlap the true parameters, only rough trends appear in Fig. 14, but the analysis showed that in a series of tests not enough water remained available for thehardening of cement. The strengths were correspondingly low; the maximum beingobtained for a w/c ratio=0.4


Fig. 14 Compressive strength of crushed masonry concrete with and without the addition of natural sand as a function of the effective water-cement ratio (according to (9)).

as would be expected. At higher w/c ratios the strength dropped in the expected manner.In any case the corresponding curve is located well below the curve for normal concretemade with a cement z 25 according to DIN specifications. This is due mainly to a lowercement strength of only about 30 N/mm2 which was normal in Germany in the 1940s and 1950s. The results in Fig. 15 (9) follow largely the shape of the w/c ratio curves of Walz,but are situated slightly lower, again for the same reasons as mentioned before. Thefigure also shows the effect of various cement contents.

The results of more recent investigations on crushed brick concrete with natural sand (8) are shown in Fig. 16. To convert the standard cylinder strengths into standard cube strengths the same proportion values were used as determined in the tests. Since thecompressive strengths


Fig. 15. Compressive strength of crushed brick concrete without the addition of natural sand as a function of the effective water-cement ratio (according to (9))


Fig. 16 Cube compression strength of crushed brick concrete with additional natural sand as a function of the effective water-cement ratio (according to (8), for comparison: Normal concrete with Z25 and Z35 (according to (18)).

are higher than those of comparable normal concrete, the possibility cannot be excludedthat in these tests there were difficulties in accurately determining the w/c ratios. Thisassumption is supported by the fact that the results for similar crushed brick concretes inreference (4) (see Table A2) only reach the lower limit of the range of normal scatter (Fig. 16).

9.1.2.2 Bulk density

Although there seems to be no direct correlation between particle density andcompressive strength for lightweight concretes, there exists such a relation within thevarious types of aggregate. Fig. 17 shows that at a constant cement content of 350 kg/m3, there appears to be a linear relation between compressive strength of concrete and densityof aggregate. Analysis of available data for crushed brick concretes without natural sand(Fig. 19) shows that concrete compressive strength increases with particle density ofaggregate. The relation is not linear, however, and the correlation is poor. The largescatter may be due to differences in cement content and w/c ratio among concretes. The


same applies to crushed brick concretes which are produced with natural sand (Fig. 18).

Fig. 17. Compressive strength of crushed brick concrete with different additions of natural sand as a function of the particle density (air-dried) at a constant cement content (according to (9, 15)).


Fig, 18. Compressive strength of crushed brick concrete with different additions of natural sand and cement contents as a function of the particle density (air-dried), according to (9, 13, 15).


Fig. 19. Compressive strength of crushed brick concrete without addition of natural sand as a function of particle density (air-dried).


Fig. 20. Compressive strength of crushed brick concrete with and without addition of natural sand as a function of particle density.

Figure 20 shows that the resulting curves for concrete with and without natural sand are fairly similar in shape and are displaced only slightly in relation to each other.Consequently, the effect of natural sand on concrete compressive strength does not seemsignificant. As will be seen from Fig. 21, this applies in the first place to natural sandcontents of less than 700 kg/m3 . Increasing amounts of natural sand produce an increasein concrete strength, but this is not clearly seen in the regression function chosen.

It was not possible, on the basis of the available data (4) to establish a correlation for practical application between aggregate particle density and density of concrete, betweenaggregate particle density and concrete compressive strength, or between density ofcrushed masonry rubble and that of concrete. Neither could this be done for thecorrelation between aggregate particle density and compressive strength of concrete.


9.1.2.3 Strength of bricks

For recycled rubble concrete with low cement contents between 200 and 270 kg/m3, the specific strength of crushed brick was found to have only slight or no effect at all on thecompressive strength of concrete. This is probably explained by the fact that the requiredconcrete

Fig. 21. Compressive strength of crushed brick concrete as a function of natural sand content (according to (9)).

consistency was obtained solely by adjusting the amount of mixing water, and thatconsequently concretes with low cement contents had low w/c ratios and resultingconcrete blocks had a low strength. On the other hand when cement contents were aboveabout 350 kg/m3 (Fig. 22) there was a strong correlation between compressive strength ofthe original bricks and that of concrete. Maximum strengths were obtained with arelatively low standard cement strength of about 30 N/mm2


9.1.2.4 Nature of the crushed material

Tests of the suitability of crushed sand-lime bricks as aggregate for production of newconcrete (9) showed that a compressive concrete strength class of DIN B 10 could only be reached with a cement content of 300 kg/m3 and a particle size distribution of the aggregate corresponding to DIN 4163 (see Fig. 4, cross-hatched area). For lower cement contents and for particle size distributions outside the required grading curve, concretecompressive strengths were only 2 to 8 N/mm2. 1:1 mixtures of crushed sand-lime bricks and baked clay bricks gave the same or in some cases higher concrete compressivestrengths in spite of lower particle densities than concretes produced from pure sand-lime brick rubble.

Fig. 22. Compressive strength of crushed brick concrete as a function of block compression strength (according to (9, 15)).

Unfavourable properties of crushed sand-lime brick rubble concretes (9) were not confirmed by more recent experiments (4). In the later investigations some of theconcretes made with crushed sand-lime brick aggregate gave better results than those for concretes made with crushed baked clay bricks (see Table A2). The lowest strengths occurred when crushed lightweight concrete aggregate was used. It should be noted that these experiments always included only one sample of each type of the recycled material.


Also, when selecting crushed masonry, for practical purposes, the lowest possible qualitywas always used (4).

9.1.2.5 Cement content

Figure 23 shows the effect of cement content on crushed brick concretes without addition of natural sand. In these experiments the strength of cement and aggregates did not varysignificantly.

In order to obtain the same concrete strength, depending on the type and composition of the crushed masonry aggregate, the cement requirement may be up to 20% higher thanfor normal concrete. If fine crushed masonry rubble (size fraction 0/4 mm) is used, evenmore cement is required to achieve the equivalent concrete strength.

Fig. 23. Compressive strength of crushed brick concrete as a function of cement content (according to (9, 15)).

9.1.2.6 Particle size distribution

In order to investigate whether the particle size distribution of crushed brick rubble (9) influences concrete compressive strength, the grading curves shown were evaluated bymeans of the fineness modulus FM (see Fig. 24) .


As a comparison the FM values for the grading curves B32 and C32 were also plottedon this graph. It can be seen that there are few changes in the vicinity of curve B whilenear curve C distinctive influences on the compressive strength can be noted. However, ifthis graph is assessed taking the effective w/c ratio into account, the only fact whichremains of the indicated influence is that with an increasingly fine fraction, the waterrequirement increases, and if a specified workability is maintained, the w/c ratio alsoincreases. With a constant w/c ratio and the same degree of compaction, the influence ofthe particle composition is noticeable.

Charisius et al (9) have shown that neither the influence of particle size distribution ofbrick rubble nor the influence of recycled concrete is significant.

Fig. 24. Compressive strength of crushed brick concrete without the addition of natural sand as a function of the k-value of the grading curves and of the cement content (according to (9, 10)).

9.1.2.7 Strength development

According to Charisius et al (9), the increase in compressive strength of recycled brickrubble concrete from 28 days to 90 days was 30% to 40%. For recycled concretesproduced with crushed hard-burnt brick, the increase in compressive strength of concretes produced with crushed hard-burnt bricks (clinker) the increase in compressive strength was as much as 67%. This increase in concrete compressive strength at later ages isprobably due to some pozzolanic effect of the finely ground burnt brick.


9.1.3 Tensile, flexural and tensile splitting strength

The flexural strength of concretes produced with crushed brick rubble follows a patternsimilar to the compressive strengths (9). The flexural concrete strength increases withincreasing cement content of the concrete and with concrete density (see Figs. 25 and 26).

Fig 25. Relationship between flexural strength and compressive strength of concrete for crushed brick concrete with additional natural sand (according to (9))


Fig. 26. Relationship between flexural strength and concrete density for crushed brick concrete with additional natural sand (according to (9)).

Fig. 27. Relationship between flexural strength and compressive strength of concrete for crushed brick concrete with additional natural sand (according to (8)), (conversions from cylinder to cube compressive strength have been made using factors given in (8)).

Figures 27 and 28 show relationships between on the one hand flexural strength and cylinder tensile splitting strength, and on the other hand compressive strength of crushedbrick concrete. In general, flexural and tensile splitting strengths of recycled brickaggregate concrete are about 10% higher than corresponding values for normal concrete


(8).

Fig. 28. Relationship between splitting tensile strength and compressive strength of concrete for crushed brick concrete with additional natural sand (according to (8)), (conversions from cylinder to cube compressive strength have been made using factors given in (8)).

9.1.4 Modulus of elasticity

The modulus of elasticity for dense crushed brick concretes with a compressive strengthof 32 N/mm2 were about 15,000 N/mm2 compared with 30,000 to 35,000 N/mm2 for normal concretes of equivalent composition and strength. For porous crushed brickconcrete, the modulus of elasticity was much lower, as would be expected. For no-fines concrete with 1–3 mm brick sand and cube compressive strength of 3.5 N/mm2, the modulus of elasticity was 4000 N/mm2 (11, 12).

It will be seen from Fig. 29 that the modulus of elasticity of crushed brick concrete is only between half and two-thirds that of normal concrete of the same strength. Figure 29also shows that there is a linear relationship between compressive strength and modulusof elasticity of brick rubble concrete. Figure 30 shows that the values for the modulus ofelasticity of brick rubble concrete do not conform with the stipulated values forlightweight concrete according to DIN 4219 (17). Although the relationship between modulus of elasticity of brick rubble concrete and bulk density is linear, the measured


values are below the area suggested in DIN 4219.

Fig. 29 Modulus of elasticity of crushed masonry concrete with natural sand as a function of the compressive strength of concrete (according to (4 , 8)).


Fig. 30. Modulus of elasticity of crushed masonry concrete with natural sand as a function of dry particle density (according to (4, 8)).

Figure 31 and reference (42) indicate that formulae for the calculation of modulus of elasticity of brick rubble concrete on the basis of bulk density and compressive strengthmake useful estimates of the modulus of elasticity of brick rubble concrete possible.

9.1.5 Creep

In -order to examine creep, shrinkage and strength under sustained loading, crushedmasonry concrete and control specimens of normal concretes of roughly the sameconsistency and compressive strength were produced. Experimental results from crushedmasonry concrete specimens are marked e, f and g in Tables A2 to A4. Results of corresponding compressive strength and modulus of elasticity tests can be seen in TableA2 and Figs 9 to 11. Creep is higher for all crushed masonry concretes than for normal concretes as shown in Fig. 32 and Table A4b. The relatively small difference for crushed lightweight concretes can be explained by the different w/c ratios (4).


Fig, 31. Relationship between the measured modulus of elasticity and that calculated in accordance with the CEB/FIP guidelines for crushed masonry concrete (compare fig. 29)).


Fig. 32. Relative deformation due to load and independent of load of crushed masonry concrete after one year of exposure (according to (4)).

9.1.6 Shrinkage

Measurements of shrinkage were carried out jointly with creep tests described in Section 9.1.5. The results show (Fig. 32) that in only two cases shrinkage of crushed masonryconcrete after one year is higher than that of ordinary concrete. One might have expectedthat higher shrinkage would have been observed for all recycled crushed masonryconcretes, because such aggregates offer less deformation resistance to the shrinkage ofthe cement paste due to a lower modulus of elasticity of crushed masonry. Also, theshrinkage of crushed lightweight concrete is increased due to the fact that the aggregateitself is subject to shrinkage. It must be noted, however, that this effect only becomesapparent after a certain period, because drying shrinkage is delayed by continuedhydration due to the presence of internal moisture in the aggregate (see Fig. 32 and Tables A4 and A5). It appears that an experimental period of about one year isinsufficient for crushed brick concrete to eliminate the effect of additional internalhydration. In the post-war years it was therefore wrongly assumed that the shrinkage of rubble concrete is lower than that of ordinary concrete. For an ordinary concrete with acompressive strength of 32 N/mm2 and a modulus of elasticity of 15000 N/mm2, the shrinkage was only 0.35 mm/m after 180 days compared with 0.60 mm/m for an ordinaryconcrete of the same composition (11, 12). However, the situation is eventually reversed.


It is hardly possible to estimate the shrinkage of masonry rubble concrete because it depends on numerous factors and because the modulus of elasticity of the concrete is notgenerally known. The normal assumption that shrinkage depends on the total watercontent of concrete does not apply to concrete made with such porous particles. Finaldrying shrinkage of crushed masonry concrete is about 40% larger compared withordinary concrete (4) (in particular: about 20% to 60% for crushed brick concrete, about 40% for crushed sand-lime brick concrete and about 40% for crushed lightweight aggregate concrete).

9.1.7 Strength under sustained loading

For lightweight concrete with a dense structure it can be assumed that the strength undersustained loading is about 70% to 75% of the instantaneous compressive strength, whilefor ordinary concrete this figure is about 80% to 85%. This is also confirmed by Dutchexperiments (4) for crushed masonry concrete. For loads up to 70% of the instantaneouscompressive strength after 28 days, no cracking had occurred after 1 year.

After sustained loading for 28 days longitudinal cracks with a maximum width of 0.03mm appeared on all sides of the masonry rubble concrete prisms. The width of thesecracks increased to 0.06 mm after 1 year. No comparative tests were carried out withordinary concrete because the long-term creep strength of such concrete is well known.The strength under sustained loading of the examined crushed masonry concretes areconsidered adequate for construction purposes because general formation of micro-cracks is not unusual at such load levels (4).

9.1.8 Watertightness

Tests for watertightness (4) in accordance with DIN 1048 (2 days at 1 bar, 1 day at 3 bar and 1 day at 7 bar water pressure) resulted in water penetration depths as shown in Fig. 33 after splitting of the specimens. These depths are up to 50% higher in crushed brickand sand-lime brick concretes than in normal control concrete. In concrete produced with lightweight concrete aggregate, there was no clear boundary in the split specimensbetween dry and wet concrete. Therefore no data is recorded for such concrete.

9.1.9 Appearance of exposed concrete surfaces

It is not possible to work with differently coloured aggregates for exposed concrete (4). Also when changing from production of brick rubble concrete to production of ordinaryconcrete, severe difficulties arise because the entire mixing plant must be cleaned.


Fig. 33. Bulk density of the individual size fractions of crushed brick as a function of the largest particle diameter (according to (9)).

9.2 Concrete with porous structure

9.2.1 Porosity and density

When thermal insulating properties are required and concrete strength is unimportant, theporosity of concrete can be increased by increasing the voids between aggregate particles.The combination of particle and matrix porosity is called “mixed porosity”.

A reasonably high porosity can be obtained simply by omitting the 0/4 mm fraction,but a very high porosity can only be obtained with gap-graded concretes which contain only one of the fractions 4/8, 8/16 or 16/32 (see Fig. 33). Such concrete is called no-fines concrete. No-fines brick rubble concretes with a mixed particle composition andmaximum particle sizes of 30, 40 or 50 mm in which the fine fractions were omittedreached densities between 1,400 and 1,700 kg/m3 in air-dry condition. When restricting the size of coarse particles to about 7 or 10 mm, it was possible to reduce the density to1,200 to 1,400 kg/m3. With gap-graded concretes made with 1/3 mm brick rubble it waspossible to obtain concrete densities as low as 1,000 to 1,250 kg/m3 provided the cement


content did not exceed 170 kg/m3 11, 12) .

9.2.2 Compressive strength

For no-fines brick rubble concrete the strength class which can be reached is somewhere around DIN LB 5 ((18), compare (11, 12)). As for concretes with a dense structure, thestrength is affected by the water/cement ratio of the cement paste. With an increasingwater/cement ratio, the strength decreases. If the cement paste is too dry, e.g. earth dry orbarely plastic, only imperfect bond between the aggregate particles can be obtained,which also results in a reduction of concrete strength (28, 62). The concrete compressive strength increases linearly with increasing cement contents in the range between 80 and200 kg/m3 (see Fig. 34) (14, 20). Winternitz (62) emphasized the importance of “inner curing” for the compressive strength of concrete blocks. With high moisture content ofthe aggregate, even without external curing, concrete strengths were obtained which wereequivalent to those of concretes which had been normally wet cured.

9.2.3 Shrinkage

For lightweight concretes with high contents of mixed pores, shrinkage up to 0.4 mm/mmust be expected. For concretes made with shrinkable aggregates, for instance concretemade with crushed pumice, considerably larger expansion and shrinkage may beexpected (16).


Fig. 34. Compressive strength of porous crushed brick rubble concrete as a function of cement content (according to (14)).

According to (11) gap-graded concrete with a mix ratio of 1:8 or 1:10 by volume exhibited the following shrinkage after 180 days of storage in air:

Walz (28) as well as Wedler and Hummel (11) found that the shrinkage was lower for no-fines crushed brick concrete than for comparable ordinary and lightweight concrete. Forconcrete produced with dense limestone which had small water absorption, a shrinkagevalue of 0.17 mm/m is reported. This value was independent of particle shape, cementcontent and water/cement ratio. For ordinary concrete the expected values underequivalent conditions are about 0.3 to 0.5 mm/m. For no-fines crushed brick rubble concretes (7/15 and 15/30 mm particles) the measured shrinkage was only 0.06 mm/m(28). These results differ considerably from those obtained by other authors, because thedimensions of the specimens were different. Concrete shrinkage as a function of time isdetermined largely by the drying conditions. Small samples of 40×40×160 mm, as used by Graf (19), yielded considerably greater shrinkage over a period of 50 days than those

Brick rubble concrete 0.2 to 0.3 mm/m

Pumice concrete 0.6 to 0.7 mm/m

Aerated concrete 1.0 to 1.8 mm/m


produced by Walz (28), which were 800×750×25 mm. Shrinkage may be greatly delayed in the first months depending on the extent of water saturation of the aggregate. However,this effect largely disappears after about 1 year (18) .

In order to eliminate this effect the experimental periods for larger samples must be correspondingly longer.

9.2.4 Thermal conductivity

For good thermal insulation, the required concrete densities should be as low as possible.Figure 35 shows the coefficient of thermal conductivity of air-dried, no-fines brick rubble concrete as a function of density. Thermal conductivity of a no-fines brick rubble concrete which has a density of 1,050 kg/m3 and an aggregate moisture content of 5.5 weight% corresponds roughly to the thermal conductivity of a high quality pumiceconcrete (11, 12). For dense brick rubble concrete with a density of 1,630 kg/m3 and an aggregate moisture content of 4.5 weight%, the coefficient of thermal conductivity was0.77 W/(K m) which was very good at that time, compared with figures of over 1.75 W/(K m) for ordinary concrete.

Fig. 35. Thermal conductivity of porous crushed brick rubble concrete as a function of particle density (according to (11)).


9.2.5 Abrasion resistance

Abrasion resistance of air-dried, no-fines brick rubble concrete is similar (19) to that of concrete made with natural sand. Depending on cement content, type of cement andorigin of the brick rubble, the abrasion can be reduced even further. When water is added, the abrasion of brick rubble concrete rises well abovethat of normal concrete (19).

9.3 Concrete containing fine sand from crushed masonry rubble

The harmful effect on concrete of brick rubble sand has already been mentioned, butalways in a purely qualitative way. In order to quantify the effect of brick rubble sand onthe properties of concrete, an extensive Dutch experimental study (4) was made of different types of concrete which contained 0 to 4 mm brick rubble sand and coarsenatural gravel. The sands used corresponded to the types of rubble labelled e”, f” and g” in Table A6a. As can be seen from Table A6a these sands, which were produced by the removal of coarse particles by screening contained unacceptably high proportions offines. For that reason, control concretes were also produced with brick rubble sandswhere the fraction below 0.063 mm had been reduced to 4 weight% (mixes e“ ’, f“ ’ and g“ ’). The consistence and cement content of all the concretes were the same. As theincreased water requirement of brick rubble sand was compensated for by the addition ofwater, water/cement ratios of the concretes were different.

The results which are presented in Table A6a show that the concrete compressive strengths are reduced due to the increased w/c ratios compared with ordinary concretemade with natural sand. For concretes including sand-lime brick rubble sand, the reduction in compressive strength is the lowest. Reduction of the amount of fines hadlittle effect on compressive strength of the concretes. The effect of brick rubble sands onconcrete shrinkage is shown in Fig. 36 and 37. As could be expected, the shrinkage ofmixes made with brick rubble sands is larger than shrinkage of concrete made withnatural sand. For concrete containing brick and sand-lime brick sand, the shrinkage is reduced considerably by reducing the proportion of fines.


10 Durability of crushed masonry concrete


Dense brick rubble concrete having a compressive strength above 15 N/mm2 was considered to be frost resistant when measured according to the standard freezing andthawing test of the 1940s (11, 12). In the tests described in (9)

Fig. 36. Shrinkage of crushed masonry concretes produced with rubble sand and natural gravel as coarse aggregate (according to (4)).


Fig. 37 Shrinkage of crushed masonry concretes with rubble sand and natural gravel as coarse aggregate (according to (4)), with content of fines below 0.063 mm reduced to a value below 4% by weight.

spalling of the surface could only be observed in places where crushed brick particleswere located just below the surface.

In more recent freezing and thawing experiments (4), it was found that concrete containing crushed brick, crushed sand-lime brick and crushed lightweight concrete do not pass standard tests when compared to controls of normal concrete. The damagegenerally appears in the form of cracks, but sometimes also in the form of scaling and bythe removal of aggregate particles close to the surface. After 25 freezing and thawingcycles the water content of concrete made with masonry rubble was about twice as highas that of normal concrete. Water absorption during freezing and thawing cycles (4) was sometimes higher than what was found with regular water saturation (see Fig. 38).

It is well known how important particularly the moisture regime is for the frost resistance of lightweight concrete. The less water the porous aggregate absorbs, thehigher the frost resistance of the concrete ought to be. Favourable influences are, forexample, high cement paste density and the presence of plaster on external walls whichprevents soaking of the concrete.

Freezing and thawing tests (4) were carried out on 200 mm brick rubble concrete cubes, which were cut in half (mixes e, f and g, in Table A1). One half of each specimen .


Fig. 38 Dry particle densities of different crushed masonry concretes and water absorption after 25 freezing and thawing cycles (according to (4)).

was stored wet at 20°C until the 28th day after removal of the forms. The other half was stored dry in the laboratory at 20°C and 65% relative humidity. Freezing took place for16 hours at -15°C in air. In order to make the tests as close to real conditions as possiblethe samples were placed in a gravel bed and covered on the sides to the height of theexposed surface. During the period of freezing a surface zone, about 30 mm thick, cooleddown to the ambient temperature. The assessment of frost damage was made by visualchecks and by measuring the dynamic modulus of elasticity according to the resonancefrequency method. Frost resistance of the specimens was also determined on the basis ofvolume changes of samples dried at 105°C. It appeared that during the experimentalperiod concretes made with brick rubble were slightly damaged due to the formation ofcracks and due to scaling, while the ordinary control concretes were hardly damaged atall. Concretes made with crushed lightweight concrete and sand-lime bricks as aggregate developed fine cracks which were not confined to the surface. Baked clay brick concretesuffered extensive scaling above aggregate particles close to the surface. For baked claybrick rubble concretes, moist storage before the tests was more severely damaging thandry storage. It may be concluded that concretes containing crushed lightweight concrete or sand-lime bricks are reasonably frost resistant, while the frost resistance of crushedclay brick concretes is inadequate. Unfortunately the water saturation differed and thecement content was not uniform in this series of tests.

Frost resistance was also measured on drilled cores from the pavement of a bicycle track (4). The concrete of this test track was produced with 65% by volume of 3/30 mm crushed clay bricks, 35% by volume of natural sand and 365 kg of portland cement A


(w/c ratio 0.47). The cores were drilled at the age of 28 days. After 40 cycles of freezingand thawing by application of de-icing salt, the weight loss of the crushed brick rubble concretes was eight times that of the normal control concretes. Judging from the resultsof these tests the resistance to freezing and thawing by application of de-icing salt to brick rubble concretes is considerably lower than that of ordinary control concretes.However, in practice, the bicycle track has never been damaged due to frost action.Therefore it may be assumed that the laboratory test method used was too severe (4).

According to (11), no-fines brick rubble concretes are not frost resistant when saturated. Therefore it is recommended that external walls of such concrete should beprotected against soaking.

10.2 Protection of reinforcement

It is known that completely dry and completely wet concretes are not subject tocarbonation (18). However, at relative humidities between 50% and 70% the rate ofcarbonation is at a maximum. Apart from that, the rate of carbonation only depends onthe resistance to diffusion or the gas permeability of the concrete and on the content ofsubstances (like cement) which can combine with CO2. This means that the depth ofcarbonation of recycled concrete does not differ markedly from that of normal concretewhen the greater porosity of the recycled aggregate is compensated for use of densercement paste or higher cement contents or both.

The results of the Dutch experiments (4) which are shown in Fig. 39 demonstrate that after an experimental period of one year and under conditions particularly conducive tocarbonation, there is hardly any difference in depth of carbonation between ordinaryconcrete, crushed brick concrete and crushed sand-lime brick concrete. In recycled concrete made with crushed lightweight concrete, the depths of carbonation were evenless than for ordinary concrete. This is explained by the higher cement content and lowerw/c ratio of the recycled concrete.

According to DIN 4163, reinforced recycled concrete products were required to have adense structure and a proper cover over the reinforcement in order to obtain adequateprotection against corrosion of the reinforcement (compare Section 8.4).


Fig. 39. Depth of carbonation and water penetration for crushed masonry concrete compared with normal concrete (according to (4)).

10.3 Fire resistance

The fire resistance of crushed masonry concrete is good (55) provided it can be kept sufficiently dry. When wet, the internal steam pressure which is created in the case of firecan cause spalling of the concrete. Owing to the lower thermal conductivity of crushedmasonry concrete compared with regular concrete, reinforced concrete is better protectedagainst early heating in the case of fire. Also the duration of fire resistance of lightweightconcrete structures is improved markedly by its low coefficient of thermal expansion andthe low modulus of elasticity.

The behaviour of crushed brick concrete when subjected to fire was considered to be positive owing to the nature of the production process of the bricks themselves, providedthe concrete had dried out sufficiently (11).


11 Applications

11.1 Products made with crushed brick concrete

According to DIN 4163 (1), crushed brick concrete with a dense structure was allowed tobe used for concrete and reinforced concrete building units. According to (1, 11, 12, 55, 64, 65, 68), crushed brick concrete with a dense structure is suitable for the production of strip footings, basement walls, concrete piles, chimneys, all types of precast reinforcedconcrete products, large-size roofing elements and concrete blocks and concrete roofing tiles. Porous crushed brick concrete was considered where thermal insulating propertieswere most important but strength requirements were low, and crushed brick rubblelightweight concrete was specially suitable for thermally insulated walls and lightbuilding components, according to DIN 4163. For walls made of porous concrete, DIN4232 (70) applied, and still applies today. An appendix to DIN 4163 gave a survey of the applications for dense and porous crushed brick concrete. Both types of concrete could beused both for local construction on site and for production of precast components (11). Nowadays crushed bricks are used primarily as aggregate for production of lightweightconcrete exposed to high temperature, for instance in chimneys (18).

11.2 Production of concrete blocks

Experiments made with the production of roofing tiles from crushed brick concrete haveshown (63) that with a cement content of 400 kg/m3, the requirements of that time, a flexural strength of 3 N/mm2 was obtained. No increase in strength was obtained by increasing the cement content above 450 kg/m3. Additions of coarse crushed brick sand, while not increasing the flexural strength of the hardened concrete did improve theworkability of the fresh concrete. Additions of 0/4 mm quartz- or slag sand, and a cement content of about 400 kg/m3 produced a considerable increase in flexural strength. At acement content of 600 kg/m3 an average value of 5.5 N/mm2 was obtained. Increasing the vibration time beyond 1 minute and adding up to 3% of coloured pigment by weightof cement did not affect the strength of the roofing tiles. The only possibilities forimproving the mechanical properties further were considered to be the use of hard-burnt bricks or a higher-grade cement.

In order to answer the question, to what extent concrete blocks made with crushed masonry complied with the Dutch specifications for concrete blocks, a series of testswere made using brick rubble, crushed lightweight concrete and natural sand and gravelas aggregate. In this series the concretes were all produced with 235 kg/m3 of


blastfurnace slag cement, class A, Z 35 according to the Dutch cement specifications. Shrinkage was determined as the difference between the lengths of specimens after

storage in water for four days and after drying at 50°C and 17% relative humidity. Also the compressive strength was measured after a storage period of 50 days. The resultslisted in Table A5 show that the blocks comply with the Dutch Standards Class 30 (5% Fractile is 25.5 N/mm2). Due to the presence of concrete roofing tiles in the crushedmasonry, the shrinkage is higher for recycled aggregate concrete blocks than for blocksmade with natural sand and gravel. It was shown that the presence of crushed masonry inconcrete does not necessarily require a higher cement content in order to achieve thesame strength as normal concrete.

Tests were also made in order to determine what effect the variation in quality of the crushed brick rubble has on the properties of the blocks produced from such rubble.Three concrete manufacturers produced concrete blocks with crushed bricks using 320kg/m3 of Class A blastfurnace slag cement. The desired concrete strength class B was22.5. In the course of three days’ production, the 28 days’ compressive strength of the concrete produced varied between 24.9 and 29.8 N/mm2. The standard deviation between the batches of the individual manufacturers was on average 2.4 N/mm2. This showed that the effect of different qualities of crushed masonry is relatively small and that the scatterof compressive strength results for recycled brick concrete is not necessarily greater thanwhen natural aggregate is used.

11.3 Problems in practical applications

Cases of damage on buildings constructed with crushed brick concrete in Berlin after theSecond World War and reported in the 1980s must not lead to the disparagement ofbuilding materials made with building rubble. There have always been violations ofestablished regulations in building construction but, as the good state of the majority ofthe buildings made of ruins-derived concrete show, the damaged buildings are not typicalof structures made with building rubble. Grün drew attention (75) to certain sources of defects in the production of porous ruins-derived rubble concrete. These referred particularly to inadequate removal of impurities, which occurred mainly in smaller, badlyequipped recycling installations, and which were due to processing defects which led tosegregation and insufficient water for hydration of the cement paste.

12 Ground powder from masonry rubble as binder

It has been known since Roman times that ground brick powder is a pozzolanic material,which when mixed with slaked lime achieves hydraulic properties. However, experiments


which were carried out by Hummel and Charisius (11, 12) in order to demonstrate this effect turned out to be an almost total failure.

Replacement of slaked lime by 20% to 30% of air-dried ground brick powder in air-stored quartz sand or brick sand mortar hardly produced any increase in compressivestrength of the mixture. With an addition of 40% ground brick powder the compressive strength of the mortars dropped considerably. It was not possible to measure anyhydraulic effect of the ground brick powder. In steam-cured quartz sand mortars increasing replacement of the percentage of slaked lime by ground brick powder led to anincrease in compressive strength. On the other hand in steam-cured brick rubble mortar, the compressive strength decreased considerably in samples which contained groundbrick powder. The reactivity of ground brick powder which has been heated to a red-hot state is no higher than that of powder which has not been heated (11, 12).

The overall result of the work carried out in this context was summarized by Hummel and Charisius (11, 12) as follows: compared with trass or ground granulated blastfurnaceslag, the addition of ground brick powder cannot be expected to produce any significanthydraulic effect even under the most favourable conditions of storage or curing. In steam-cured quartz sand mortar the addition of brick powder can lead to an improvement incompressive strength, but this is not the case for steam-cured mortars produced from crushed brick rubble.

In spite of these discouraging results a commercial installation was actually established in Düsseldorf for the production of masonry units made with ground brick powder andlime by steam curing (71). Tests had shown that the recycled ruins-derived rubble contained sufficient reactive silica which strengthened the particle structure by formingcalcium silicate hydrate in the course of the autoclave treatment, after mixing in of anappropriate quantity of calcium hydroxide. The compressive strength of the blocksproduced was around 13 N/mm2; they were classified as Mz 10. Improvements in compressive strength were possible by mixing in appropriate amounts of lime and byincreasing the curing time. Water absorption of the blocks was 17%. By using almostpure crushed brick, the properties of the blocks is said to have come very close to theproperties of baked clay bricks (71).

13 Standards, guidelines and instructions for

production of crushed masonry aggregates and crushed masonry concrete

13.1 Federal Republic of Germany

Use of crushed bricks from ruins-derived rubble from the Second World War was first


regulated by an instruction sheet for crushed brick concrete (55). The text of that sheet was used as the basis for the preparation of DIN 4163. This standard was withdrawn afterthe rubble deposits from the ruins of German cities had been exhausted. According to thecurrent state-of-the-art, crushed brick should be used like lightweight aggregate and therefore comes under the jurisdiction of DIN 4226 04.83, parts 2 and 3 (2). The most important requirements of this standard for aggregates with a porous structure aresummarized in Table B1. Crushed masonry made from different types of stone may notnecessarily fall under this standard. In individual cases the approval of the GermanBuilding Authorities may be required (69). Specifications for manufacture and monitoring of lightweight concrete with a dense structure, which also apply to crushedbrick concrete with a dense structure, can be found in DIN 4219 (17).

13.2 The Netherlands

Based on fundamental investigations (4), subcommittee B 29 of the Dutch StandardsAssociation Committee 13 “Materials for Aggregates” prepared a draft standard for “Masonry Rubble for Concrete” which in its present edition (3) can be regarded as a standard recommendation. This draft is only valid in connection with acceptance testswhich must be carried out in accordance with NEN 3880 (VB 1974/1984, part G). Thedraft standard includes those particle mixtures for the production of concrete which haveas their primary constituent at least 65% by weight of crushed masonry and as secondaryconstituent to a limited extent also crushed lightweight concrete, aerated concrete, brickproducts such as roofing tiles, crushed natural stone and masonry mortar (withoutgypsum). The most important requirements are shown in Table C1.

It is common to many parts of the draft standard that it is required to carry out additional tests, e.g. concrete trial mixes, depending on the origin of the building wasteand on the results of a visual inspection. This applies particularly if, after the aggregates have been tested, there remain any doubts regarding the presence of harmful constituents.

14 Economic aspects of the recycling of masonry

rubble

14.1 Economics of utilization of masonry rubble

The pre-selection of whole bricks or blocks from ruins was considered by Wedler (11, 12) to be uneconomical and a waste of manpower. In his opinion the removal of wholebricks or blocks from the ruins should be confined to an absolute minimum and it should


only be done under specially favourable conditions. Moreover, the work should berestricted to the upper layer of the heaps of ruins. It was not possible in this way toachieve the kind of outputs and economies which were required for the tremendous post-war reconstruction effort. Recycling of the ruins into crushed brick was considered to bemuch more effective as the work could be done mechanically. However, the questionwhether it was more economical to recover building materials from the ruins or to dumpall debris from the ruins at disposal sites and to produce new materials in conventionalways had to be decided with a view to the local conditions. Faced with the mountains ofruins in many places and the lack of supplies of new building materials, the problems andquestions of reuse were very different from today’s situation.

The economics of utilization of the ruins were greatly influenced by the continuity of the flow of material and the possibility of preventing the deleterious fine rubble fromreaching the recycling plant. It was possible to lower the cost of transporting thedeleterious fines by some kind of pre-sorting at the building site. Disposal of the finerubble represented an unavoidable cost (74, 77, 79) and any intermediate storage had to be avoided. Full utilization of plant capacity had a decisive effect on the price of theaggregates (see Fig. 40) (74, 79). Favourable conditions for economic production such ascontinuity of supply and adequate quality of the end product did not exist in smallinstallations (34, 79). Even in some of the large installations there were blatant contrasts between the cost of the plant machinery and the quantity of material produced (79).

Fig. 40. Prices of ruins-derived crushed material as a function of the utilisation of the capacity of recycling installations (according to (74 and 79)).


One recommendation which most probably applies even today is to combine directly arecycling plant with a concrete block manufacturing plant (11, 66, 67, 77). The advantages are obvious, because the final price of the recycled rubble is largelydependent on the cost of transportation and the cost of intermediate storage of the crushedmasonry rubble. Moreover, acceptable costs of the final products to a large extentdepends on a high and uniform utilization rate of the recycling plant.

14.2 Study based on figures from 1982

In order that economic appraisals may be made, overall considerations are sufficient (4). What is decisive is the permissible processing cost of the rubble. Re-use of waste material must be cheaper than the use of natural sand and gravel. Table 8 shows the main factors which determine the price of these products.

According to experience from practice, the additional cost of the required pre-selection of rubble should not be more than 25% of the recycling cost. Disposal charges varywidely for different regions but generally show a rising trend. In 1982 storage costs inHolland varied between f 3.00 and f 30.00 per cubic metres (where f=Dutch guilders). Aspart of the additional processing costs the wear of the mixer must be taken into account,which is affected by the angularity of the crushed aggregate. Additional costs are forextra storage space, for cleaning the plant when changing the aggregate, the cost of pre-wetting the aggregate, additional costs of the inspection and extra administration due tovariations in quality of the rubble.

Constantly changing coloured aggregates such as crushed brick rubble requiresfrequent cleaning of the mixer. Also the buyer of the concrete must count on extra costsfor compacting concrete made with crushed aggregate as compared with those forcompaction of concrete made with aggregate with rounded particles. In order to ensureproper durability, a greater concrete cover or a higher cement content of concrete or bothmay become necessary. Also additional measures to compensate for increased creep andshrinkage may lead to additional costs. On the positive side, there are savings in weight,better thermal insulation properties and higher fire resistance of recycled brick concretethan of normal concrete.

On the basis of the 1982 price level and based on the results of technical properties ofconcrete (based on equal compressive strength) a comparison of the cost of mixescontaining gravel and crushed masonry was made (4). The transport costs for the different concretes were considered to be equal. Table 9 shows the “cost differences” which refer only to coarse aggregate for the production of 1 cubic metre of concrete. Itwas assumed that natural sand was used as fine aggregate. It will be seen from the costsurvey that crushed masonry concrete in 1982 could not compete with normal concrete ifdisposal charges were not included. It must also be taken into


Table 8 . Comparison of cost elements in the processing and handling of natural aggregates and recycled aggregates (D.fl.=Deutch Guilders)

Natural aggregates D.fl Re-use of Rubble Granules D.fl, Excavation costs n1 Extra treatment of debris at the demolition

site s1

Production costs (in-cluding interim storage)

n2 Dumping charges (negative) for demolition debris

s2

Bulk transport costs n3 Costs of transport of demolition debris to dump (negative)

s3

Costs of transport to building site

n4 Costs of transport of debris to processing plants

s4

Processing costs for recycled aggregate s5

Costs of transport of recycled aggregate to building site

s6

Extra costs for inspection, storage, and sale of recycled aggregate

s7

– –

Total

Requirement for recycled aggregate to be competitive, provided the buyer is unbiased: ∑s

i=∑n

i

Table 9Cost comparison between concretes made with natural gravel recycled concrete aggregate, brick rubble and mixed concrete and brick rubble aggregate in The Netherlands (1982)

1. Natural gravel concrete with 1080 kf of gravel at Dfl 22/ton Dfl 23.76/ton

2. Concrete made with recycled concrete aggregate

– 900 kg of recycled concrete aggregate (4–32 mm) at Dfl 17/ton (production and processing costs)

Dfl 15.30/ton

– 40 kg of cement at Dfl 125/ton Dfl 5.00/ton

– Extra costs for inspection, storage and sale at Dfl 12/ton Dfl 12.00/ton

Total Dfl 32.30/ton


account that the 1982 market prices for crushed masonry aggregate were aimedspecifically at the market for materials for road bases. In 1982 almost 2 million tonnes ofbuilding wastes were recycled in the Netherlands to produce crushed masonry aggregatefor unbound road bases. Considering the declining demand for base materials in roadconstruction and the increasing production of crushed masonry aggregate, it can beassumed that the sales of crushed masonry aggregate for concrete will become moreimportant in the future. The additional costs which appear in Table 9 are based on the average estimated figures from several recycling plants.

This leads to the conclusion that crushed masonry aggregate for concrete manufacture is less favourable from the economic point of view than use of natural sand and gravel,but that this picture may change if disposal charges are increased and if it proves possibleto reduce the costs of processing of crushed masonry.

15 Conclusions

1. Dutch draft standard recommendations (3) contain recommendations, specifications and rules for testing and assessing the suitability of crushed masonry rubble as aggregatefor concrete. However, compliance with these specifications is not sufficient in itself andacceptance tests must be carried out in any case. In the Federal Republic of Germanyaccording to DIN 4226 crushed brick rubble may be used as aggregate for production oflightweight aggregate concrete. However, crushed masonry rubble made from differentsorts of bricks and blocks may not necessarily fall under the jurisdiction of that standardand an authorization is required for their use in each individual case.

2. The proportion of harmful impurities in crushed masonry rubble should not exceedthe limiting values according to (3) or DIN 4226, part 2. According to the Dutch draftstandard the proportion of paper, plastic, glass, etc. should be limited to a maximum of1% by weight and 1% by volume.

3. Reliable figures for the water absorption of the aggregate must be determined wherethe characteristic value after 30 minutes is not reliable. An accurate estimate of the waterabsorption necessary for maintaining the consistency of fresh concrete and formaintaining the required water/cement ratio is made difficult by the varying value of thewater absorption of aggregates. For mixes with a fluid consistency and produced withlarge water contents more water may be absorbed by the aggregate and should bededucted from the quantity of mixing water when the free water/cement ratio iscalculated, than would be the case for stiff mixes.

4. Wherever possible, it is recommended that porous crushed masonry rubble shouldbe pre-wetted, for instance by means of sprinklers in a star silo. Care must be taken toensure that the water saturation of the aggregate is uniform. This requires sufficient time.

5. Aggregate must not be used for production of concrete while soaking wet, in ordernot to lose control of the free water/cement ratio.


6. The particle density of crushed brick rubble is between 1,200 and 1,800 kg/m3 and the bulk density is between 1,000 and 1,500 kg/m3. The particle density compared withother lightweight aggregates may be characterized as medium. For crushed masonryaggregates, the expected range of particle densities is even larger. Where the proportionof crushed concrete is large, the upper limit of 2,200 kg/m3 as defined by DIN 4226 for particle density of lightweight aggregate is reached.

7. The concrete strength classes which may be reached by dense lightweight brickrubble concrete and no-fines concrete are LB 25 and LB 5, respectively.

8. The modulus of elasticity of crushed masonry concrete can be estimated accordingto the CEB/FIP guidelines from concrete density and compressive strength (Ref. 91). The values calculated according to DIN 4219 are unsuitable for crushed masonry concrete.

9. Shrinkage and creep are higher for recycled masonry concrete than for ordinaryconcrete, as would be expected. However, the shrinkage process can be delayed by thelarge moisture content of the rubble aggregate. Suitable experiments have not yet beencarried out which will allow estimates to be made of long-term deformations. At the present time the procedure recommended is the same as for lightweight aggregateconcrete (compare DIN 4219).

10. The rate of carbonation of recycled masonry waste concrete is greater than forordinary concrete due to the porosity of the aggregate under otherwise similar conditions.However, there is a possibility of compensating for the lower resistance to diffusion byincreasing the cement content of the concrete.

11. Crushed brick concrete may be recommended for products which are not exposeddirectly to the weather. The frost resistance is adequate for moderate exposure.

12. The competitiveness of processed brick rubble aggregate compared with otherconcrete aggregates is improved in areas with large disposal charges for building waste.Another contribution to competitiveness is a uniform and high degree of utilization of therecycling plants. Confidence in crushed masonry aggregate can be reinforced by suitablequality control. There is no question that crushed brick aggregate is a useful material, butat the present time it would appear that the use of crushed masonry aggregate fromdifferent types of rubble can be most profitably used in the precast concrete blockindustry. The experience gained there could then be used for applications elsewhere. It isvery important that recycling technology should become accepted somewhere in thebuilding industry in order to become accepted by other parts of the industry at a laterstage.

16 References

1. DIN 4163, Ausgabe 02.1951: Ziegelsplittbeton. Bestimmungen für die Herstellung und Verwendung. (withdrawn)

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76. Hampe, H.: Zahlenunterlagen für die Aufbauarbeit. Der Bauhelfer 4 (1949), Nr. 6, S.162–164

77. Winternitz: Stand der Trümmerräumung und -verwertung in der Bundesrepublik.


Aus: Mitteilungen der Deutschen Studiengesellschaft für Trümmerverwertung, Nr. 37, 1950, Okt., S. 282–286. Die Bauwirtschaft 4 (1950), Oktober

78. Environmental Resources Limited: Demolition Waste. The Commission of the European Communities. The Construction Press, Lancaster, London, New York, 1980

79. Schleif, E.: Praktische Erfahrungen über die Wirtschaftlichkeit der Trümmerverwertung und der dabei anfallenden Kosten. Aus: Mitteilungen der Deutschen Studiengesellschaft für Trümmerverwertung, Nr. 29, (1950), Feb., S. 212–218. Die Bauwirtschaft 4 (1950), Februar

80. Nendza, H., Heckkötter, C.: Die Verwendung von aufbereitetem Bauschutt im Erd- und Strassenbau. Aus: Mitteilungen aus dem Fachgebiet Grundbau und Bodenmechanik. Hrsg.: Prof. Dr.-Ing. H.Nendza, Universität-Gesamthochschule-Essen, Heft 11, Dez. 1985

81. N.N.: Gütegesicherte Recycling-Baustoffe. RAL-Anerkennungsverfahren erfolgreich abgeschlossen. In Das Baugewerbe (1985), Nr. 9, S. 46–48

82. Moser, E.: Aktuelle volkswirtschafliche Fragen der Trümmerverwertung. <Versammlung der Bezirksgruppe “Nord’ der Deutschen Studiengesellschaft für Trümmerverwertung am 16.02.50 in Hamburg> Mitteilungen der Deutschen Gesellschaft für Trümmerverwertung e.V.

83. Vitt: Überwachung von Betonaufbereitungsanlagen für die Herstellung von Betonzuschlagstoffen aus Bautrümmern. Nr. 36 (1950), Sept., S 276–277. Die Bauwirtschaft 5 (1951), Oktober

84. Hansen, T.C.: Opening of the conference on recycling. EDA/RILEM Conference 1985, Proceedings II: Re-use of concrete and brick materials, 3rd June 1985

85. Verband Deutscher Baustoff-Recycling-Unternehmen e.V.: Recyling von “Altbaustoffen”, eine Herausforderung unserer Zeit, Broschüre des Verbandes, Bonn, 1985

86. Gütegemeinschaft t Recycling-Baustoffe e.V.: Güte- und Prüfbestimmungen, Recycling-Baustoffe für den Strassenbau, Bonn, 1985

87. Nakkel, E.: Recycling und Wiederverwendung—vom Nebenprodukt zum gütegesicherten Baustoff. Das Baugewerbe (1985), Nr. 13/14, S. 38–41 und Nr. 15, S. 35–40

88. DIN 1045, Ausgabe 12.78. Beton und Stahlbetonbau, Bemessung und Ausführung (für Trümmerverwertung massgebende Ausgabe: 03.43)

89. ASTM C 127. Standard Test Method for Specific Gravity and Absorption of Coarse Aggregate

90. ASTM C 128. Standard Test Method for Specific Gravity and Absorption of Fine Aggregate

91. CEB-FIP Model Code for Concrete Structures, Comité Euro-International du Béton (CEB), 3rd Edition 1978, 227

92. DIN 105 T3 Mauerziegel, May 1984 93. DIN 52109


APPENDIX A. Data from Dutch Investigation of Recycled

Masonry Concrete (4)

Table A1. Composition of crushed masonry rubble used for experimental studies. Compare Tables A2 to A6 (from (4))

Designation according to main component

Constituents Burnt clay bricks

Burnt clay bricks

Sand-lime bricks

Concrete Burnt clay bricks

Sand-lime bricks

Concrete

a b c d e f g

Cement-bound

Regular concrete

1.0 1.0 3.1 – 18.0 0.8 –

Lightweight concrete

0.1 – – 94.4 – 0.6 100

Masonry mortar

17.6 12.9 8.3 3.5 11.2 1.2 –

Ceramic

Hard burnt clay bricks

12.8 – 1.9 1.0 – – –

Burnt clay bricks

60.9 85.7 – 0.4 68.4 15.4 –

Ceramic products

– – 0.1 – 2.4 0.8 –

Other

Asphalt 0.2 – – – – – –

Sand-lime bricks

0.3 – 86.7 0.4 – 81.0 –

Natural stone 1.6 0.4 – – – – –

Contaminants

Glass 0,3 – – – – 0.1 –


Wood x x – – <0.1 – –

Paper x x – – <0.1 – –

> 8 mm 97.3 80.6 83.4 84.6

< 8 mm 2.7 19.4 16.6 15.5

x only present in very small quantities

Table A2. Properties of aggregates, and composition and properties of crushed masonry concretes with dense structure. See Tables A1, A3 and A4 (from (4))

Designation according to main component Burnt

clay brick

Burnt clay brick

Sand-lime brick

Concrete Burnt clay brick

Sand-lime brick

Concrete

a b c d e f g

Properties of aggregate 1)

Particle 4-8 Wt. % 7 14 11 14

size 8-16 Wt. % 41 28 27 26

distrib. 16-32 Wt. % 52 58 62 60

Moisture content

Wt. % 3.8 15.6 8.5 19.8 13.3 7.3 7.4

Water absorption

Wt.% 9.6 11.9 8.1 21.7 10.6 10.8 15.2

Particle density

kg/m 1,877 1,690 1,948 1,294 1,838 1,839 1,049

Bulk density kg/m 978 1,053 667 996 1,007 516

Crushing factor

0.67 0.64 0.64 0.60 0.67 0.60 0.63

Loss on ignition

Wt.% 4.7 3.2 7.1 11.4

Sulphate content 2)

Wt. % 0.38 0.11 0.99

Concrete mix composition

Type of cement

HOZ HOZ HOZ HOZ HOZ HOZ HOZ

Compres. strength 3)

N/mm2 35 35 35 35 35 35 35


Cement content

kg/m 320 326 324 324 311 323 409

Coarse aggregate content 4)

kg/m3 783 706 812 538 756 751 408

Nat. sand content 4)

kg/m3 788 802 798 798 795 796 744

Total water content

kg/m3 241 290 249 290 273 254 235

Water absorption

kg/m3 81 91 72 121 84 80 62

Free water/cement

ratio 0.50 0.61 0.55 0.52 0.61 0.54 0.42

Properties of fresh concrete

Slump mm 90 100 100 90 110 110 110

Flow table value

mm 390 410 380 350 430 430 420

Density kg/m3 2,132 2,184 1,952 1,950 2,135 2,125 1,796

Air content % 4.1 3.3 3.6 5.3 3.1 4.6 6.2

Properties of hardened concrete

Density (7d) kg/m3 2,156 2,145 2,206 1,991 – – –

Density (28d) kg/m3 2161 2,160 2,216 1,984 2,079 2,072 1,770

Compressive strength (7d)

N/mm2 22.3 22.1 23.9 19.4 – – –


N/mm2 30.7 30.7 35.1 25.9 32.2 32.8 28.1

Splitting tensile strength (28d)

N/mm2 2.8 3.0 3.7 2.9 2.7 2.8 2.1

1) crushed masonry in 4/32 mm size fraction 2) SO3 - content 3) Minimum strength of cement after 28 days 4) content of dry aggregate

Table A3a. Mix composition and properties of reference concretes for series a to g according to Tables A1 and A.2 (from (4))

Concretes made with natural sand, used as reference concretes to concretes


made in series a through g a a b-d b-d e-g e-g


Type of cement HOZ HOZ HOZ HOZ HOZ PZ

Compressive strength 1) N/mm2 35 35 35 35 35 45

Cement content kg/m3 320 285 320 285 263 370

Coarse aggregate content 2) kg/m3 1,082 1,100 1,082 1,101 1,102 1,046

Natural sand 2) kg/m3 787 800 787 801 802 761

Total water content kg/m3 167 168 167 168 176 167

Water absorption kg/m3 13 13 13 13 87

Free or effective water/cement ratio

0.48 0.54 0.48 0.54 0.60 0.43


Slump mm 100 110 100 110 110 100

Flow table value mm 460 470 420 450 440 400

Density kg/m3 2,355 2,355 2,356 2,356 2,333 2,344

Air content % 1.7 1.5 2.2 1.8 1.6 2.3


Density (7d) kg/m3 2,378 2,371 2,379 2,375 – –

Density (28d) kg/m3 2,376 2,375 2,386 2,383 2,311 2,343

Compressive strength (7d) N/mm2 25 .8 21 .2 27 .6 23.0 – –

Compressive strength (28d) N/mm2 35 .0 31 .5 39 .2 34.8 30.6 53.4

Splitting tensile strength (28d)

N/mm2 3 .4 3 .0 3 .9 4.0 3.3 4.0

1) Minimum strength of cement after 28 days 2) Content of dry aggregate

Table A3b. Particle size distribution of aggregate for all test series in Tables A1 to A3 (from (4))

Sieve size in mm 0.125 0.25 0.5 1.0 2.0 4.0 8.0 16.0 31.5

Material passing in Vol-% 1 6 18 28 36 40 51 76 100

Table A4a. Deformational properties of masonry rubble concrete with dense structure.


Reference is made to Tables A1, A2 and A3 (from (4))

Designation according to main component of aggregate Burnt

clay brick

Burnt clay brick

Sand-lime brick

Concrete Burnt clay brick

Sand-lime brick

Concrete

Age a b c d e f g

Modulus of elasticity

N/mm2 28d – – – – 20700 18200 17100

Shrinkage mm/m mm/m mm/m mm/m

7d 28d 91d

360d

0.10 0.23 0.44

–

0.11 0.32 0.54

–

0.14 0.28 0.45

–

0.14 0.24 0.45

–

– 0.03

– 0.31

– 0.03

– 0.47

– 0.15

– 0.72

Creep mm/m 336d – – – – 0.70 0.72 0.48

Table A4b. Deformational properties of reference concretes, for series a to g. See Tables A1- A3 (from (4))

Reference concretes with natural sand for series a to g

Age a a b-d b-d e-g (e-g)

Modulus of Elasticity N/mm2 28d – – – – 33,000 32,300

Shrinkage mm/m 7d 28d 91d

360d

0.16 0.26 0.39

–

0.15 0.26 0.39

–

0.15 0.26 0.35

–

0.14 0.24 0.29

–

– 0.12

– 0.37

– 0.15 0.41

–

Creep mm/m 336d – – – – 0.65 0.70

Table A5a. Properties of aggregates, and composition and properties of crushed masonry concretes with porous structure. See Table A1, aggregates b to d (from (4))

Main component of aggregates Burnt clay

bricks Sand-lime bricks

Concrete

b′ c′ d′



Type of cement PZ PZ PZ

Compressive strength 1) N/mm2 35 35 35

Cement content kg/m3 183 182 181

Coarse aggregate content 2) kg/m3 938 1047 707

Natural sand kg/m3 466 455 453

Total water content kg/m3 235 182 238

Water absorption kg/m3 117 89 157

Free or effective water/cement ratio

0.64 0.51 0.45


Compaction factor mm 1.39 1.33 1.31

Density kg/m3 1,816 1,867 1,577


Density (7d) kg/m3 1,837 1,861 1,560

Density (28d) kg/m3 1,842 1,885 1,620

Compressive strength (7d) N/mm2 7.4 9.1 6.2

Compressive strength (28d) N/mm2 7.9 10.6 8.4

Tensile splitting strength (28d) N/mm2 1.4 1.3 1.0

Shrinkage (7d) mm/m 0.05 0.12 0.11

Shrinkage (28d) mm/m 0.31 0.32 0.38

Shrinkage (91d) mm/m 0.51 0.44 0.64

1) Minimum strength of cement after 28 days 2) Masonry rubble 4/16mm. Content of dry aggregate

Table A5b. Grain size distribution of aggregate for all test series in Table A5a (from <4a))

Sieve size in mm 0.125 0.25 0.5 1.0 2.0 4.0 8.0 16.0

Material passing in Vol-% 0.5 4 11 16 21 23 54 100

Table A6a. Composition and properties of concretes made with crushed masonry sand and natural gravel. Series e′ ′ to g′ ′ with original content of fines. Series e′ ′ ′ to g′ ′ ′ with reduced content of grains smaller than 0.063 mm (from (4))


Designation according to main component of the sands Natur.

sand Burnt clay bricks

Sand-lime bricks

Concrete Burnt clay bricks

Sand-lime bricks

Concrete

e′ ′ ' f′ ′ ' g′ ′ ' e′ ′ f′ ′ ' g′ ′ ′

Concrete mix composition (reference material)

Type of cement

HOZ HOZ HOZ HOZ HOZ HOZ HOZ

Compres. strength 1)

N/mm2 35 35 35 35 35 35 35

Cement content

kg/m3 320 324 328 321 323 321 322

Coarse natural content 2)

aggregate kg/m3

1,129 1,126 1,175 1, 241 1,141 1,181 1,246

Masonry rubble sand 2)

kg/m3 752 3) 511 544 336 518 546 337

Particles < 0.063 mm 4)

Wt. % 1 12.7 5.6 11.1 4 4 4

Total water content

kg/m3 160 258 216 227 247 209 237

Water absorption

kg/m 61 54 62 62 59 62

Free or effective

ratio 0.50 0.61 0.49 0.51 0.57 0.47 0.54


Slump mm 100 100 110 100 110 110 100

Flow table value

mm 410 410 420 450 460 450 450

Density kg/m3 2,361 2 ,219 2,263 2 ,125 2,229 2,258 2,144

Air content % 2.4 2.3 2.6 4.6 2.2 2.2 4.4


Density (7d) kg/m3 2,376 2 ,252 2,272 2 ,174 2,257 2,296 2,179

Density (28d)

kg/m3 2,383 2 ,258 2,302 2 ,182 2,263 2,289 2,182


N/mm2 30.1 20.1 26.6 16.9 19.2 22.3 17.0



N/mm2 42.6 29.0 36.4 27.8 30.0 32.8 28.0

1) Minimum strength of concrete after 28 days 2) Content of dry aggregate 3) Natural sand 4) In sand

Table A6b. Material passing , in vol. % for aggregates in Table A6a

Sieve size in mm 0.063 0.125 0. 25 0.5 1.0 2.0 4.0 8.0 16 .0 31.5

4)

Series Ref. 1 1 6 18 27 34 38 49 76 100

e″ 12.7 5 10 22 31 38 40 49 76 100

f″ 5.6 2 8 22 31 39 40 49 76 100

g″ 11.1 6 11 15 20 30 39 49 76 100

e″′ 4 2 7 21 30 37 40 49 76 100

f″′ 4 2 8 21 31 39 40 49 76 100

g″′ 4 4 8 13 19 30 39 49 76 100


APPENDIX B. Requirements for lightweight aggregate according

to DIN 4226 Part 2 (2)

Table B1

Grain size distribution According to Table 1, DIN 4226 Part 2

Frost resistance by moderate exposure of concrete (partly saturated concrete)

Material passing required sieve < 4 weight %

Deleterious components

– Sediments Grain size fraction Particles < 0.063 mm weight % max.

0/2, 0/4 5.0

0/8, 2/4, 2/8 4.0

0/16, 0/25, 4/8, 4/16 3.0

8/16, 8/25, 16/25, 16/32

2.0

– Finely distributed constituents of organic origin (for instance humus)

Liquid : colourless or pale gold

– Constituents which may expand for instance coal and wood

max. content 0.5 weight% for particles < 4 max. content 0.1 weight% for particles > 4

– Constituents which may influence the hardening process, for example sugar etc,

Compressive strength of trial mixes max. 15 % less than control

–Sulfuric compounds, for example gypsum and anhydrite

Sulphate content, calculated as SO3 < 1 weight %

–Corrosive compounds, for example chlorides and nitrates

Content of salts which may give rise to corrosion of reinforcement < 0.04 weight %, for prestressed concrete < 0.02 weight %

– Alkali soluble silicic acid If suspected, conduct tests according to German recommendations entitled : “Vorbeugende Massnahmen gegen schädigende Alkalireaktionen im


Beton”

Loss on ignition Loss in ignition < 5 weight %

Freedom from deterioration by expansion

Percentage of crumbling particles by sieving on the next smaller sieve size to the size tested, < 0.5 weight %

additional, increased and reduced requirements

Additional requirements to lightweight aggregate for lightweight aggregate concrete in strength class LB 8 and higher, as well as lightweight concrete in various density classes

Requirements to uniformity

– Bulk density Max. deviation from required value < 15 %

– Particle density Max. deviation from required value < 15 %

– Particle strength

Compressive strength of concrete or cylinder strength according to DIN 4226 Part 3. Max. deviation from required value < 15 %

Increased requirements (e)

Requires separately agreed and measurable requirements on the basis of the special conditions of use and environmental exposure of the concrete particularly for what concerns

– expanding components (eQ)

– content of water-soluble chlorides (eCl)

– uniformity (eG)

Reduced requirements (v)

When not included in the general specifications, special testing by the contractor for what concerns:

– frost resistance (vF)

– content of dispersible particles (vA)

– content of finely distributed organic matter (vO)

– content of sulfates (vS)

When the SO3 is larger than 1 weight % demonstration by a recognized laboratory that the material can be safely used


APPENDIX C. Extract from the proposed Dutch Standard “Masonry Rubble for Concrete” Table C1.

Table C1

a. Main component

– At least 65 weight % crushed masonry rubble

b. Secondary components

– Maximum total of 20 weight % lightweight concrete, ceramic products and natural stone Maximum of 10 weight % aerated concrete and maximum of 25 weight % mortar

c. Particle sizes – 0/4, 4/8, 4/16, 8/16, 4/32, 16/32 mm

d. Particle size – The particle size distribution according to NEN 5916 (i.e. material retained on each sieve) must be within the limits shown in the following table

Material in weight % re t ained on each sieve in mm. Allowable maximum and minimum values ar e given for each part icle frac tion

Particle fraction

31.3 22.4 16 8 4 2 1 0.25

0/4 – – – 0 2–10 – 15–50 80–100

4/16 – 0 0.5 35–70 85–100 95–100 96–100 –

4/32 0–2 5–30 25–55 60–85 90–100 – 96–100 –

4/8 – – 0 0–10 80–100 98–100 – –

8/16 – 0 0–10 80–100 98–100 – – –

16/32 0–10 – 80–100 98–100 – – – –

e. Contaminants

1. Dispersible fines

– The content of dispersible fines according to NEN 5917 in particle size fraction O/4 must not exceed 4 weight %. In the other size fractions, the content of such material must not exceed 2 weight %. Contents of dispersible fines are allowed if it can be shown that they are harmless

2. Organic matter – According to NEN 5919 organic fines must not lead to dark colouring of the aggregate sample which is above no 11 on the Gardner-Colour scale


3. Chloride content

–The chloride content of crushed masonrry rubble must not exceed the following values 2masonry

Particle fraction Maximum chloride content in weight % of dry material

Plain concrete Reinforced concrete Prest ressed concrete

0.4 1.0 0.10 0.015

Other 1.0 0.05 0.007

: In order to determine the chloride content, indicator paper can be used according to method B in NEN 5921. Because of inaccuracies in this procedure, the following limit values are recommended in practice

Particle fraction

Maximum chloride content in weight % of dry materials

Classification

Reinforced concrete Prestressed concrete

0.04 < 0.08 > 0.11

< 0.012 > 0.017

acceptable not acceptable

Other <0.04 >0.055

< 0.006 < 0.008

acceptable not acceptable

If the use of indicator paper is not possible,the chloride content must be determined according to method A in NEN 5921

4. Sulphate content – According to NEN 5930, the content must notexceed 1 weight %

5. Non-mineral components – Contents of lightweight particles such as wood, remnants of plants, insulating materials, paper, textile must be determined according to NEN 5933 and must not exceed 1 % either by weight orvolume – the content of bituminous matter, rubber, metal, glass and heavy polymers which must be determined according to NEN 5942 must not exceed 1 weight %

f. Soft particles – According to NEW 5918, the content of particles


which can be crumbled by hand must not exceed 0.5 weight % for normal concrete and 0.2 weight % for exposed concrete, both values in percent of dry material

g. Discoloration – When aggregate is used for exposed concrete the content of potentially discolouring iron and vanadium compounds must not exceed a defect index of 20 as defined in NEN 5923

h. Components which may delay setting or hardening of concrete

– When setting time is measured according to the Vicat procedure there must not be more than 15% difference in the Vicat values from those obtained on reference mixes

i. Particle form – Content of flat particles must not exceed 30 weight % according to NEN 5941

j. Frost resistance – Weight loss in freez ing and thawing tests P articles must not exceed 3 weight % accordingto NEN 5924


PART THREE BLASTING OF CONCRETE: LOCALIZED CUTTING IN

AND PARTIAL DEMOLITION OF CONCRETE STRUCTURES

C.MOLIN

Trimex, Sweden (formerly Swedish National Testing Institute) and

E.K.LAURITZEN

Demex, Consulting Engineers Ltd, Denmark

The purpose of this report is to highlight the present state of knowledge in the area ofconcrete blasting. Special emphasis is laid on research and development results duringthe last decade.

Experimental and practical experience indicates that blasting with drilled-in charges is an interesting method for localized cutting and partial demolition of concrete structures.For the time being, however, lay-on charges can be used only in special circumstances,and these lay-on charges should preferably be shaped charges. It might also be possible touse explosives for fragmentation when concrete is to be reused.

Total demolition of buildings with explosives, which is an accepted method, is not dealt with.

Keywords; Localized Cutting, Partial Demolition, Concrete Structures, Drilled-in Charges, Blasting Technique, Damage, Hazards.

This section was first published in 1988 as Report 1988:09 by the Swedish National Testing Institute, P.O. Box 5608, 114 86 Stockholm, Sweden, (ISBN 91-7848-096-5, ISSN 0248-5172).

1 Foreword

One of the publications of the RILEM Committee “Demolition and Reuse of Concrete, 37DRC” is a report entitled “Demolition Techniques”, May 1985. The Chairman, Professor T.C.Hansen and the other members have considered it desirable to publishadditional information regarding engineering blasting methods. This report may beregarded as a state-of-the-art report on concrete blasting.

The work has been financed by the Swedish Council for Building Research and the National Swedish Testing Institute and by the Danish company Demex. Valuableobservations have been made by Bengt Vretblad, head of research at the SwedishFortification Administration in Eskilstuna, and by Conny Sjöberg, chief consultant at Nitro Consult AB in Stockholm. The original report was typed by Irene Persson andMaria Daversjö and the drawings were prepared by Lars Melin, all from the National Swedish Testing Institute.


2 Summary

2.1 General

Experimental and practical experience indicates that blasting with small drilled-in charges is an interesting method for localized cutting and partial demolition of concretestructures. At present, lay-on charges can be used only in special circumstances, andthese should preferably be shaped charges. It should also be possible to use explosives forthe fragmentation of concrete for reuse. The aim of this report is to highlight the presentstate of knowledge in the area of concrete blasting. Special emphasis is laid on researchand development work during the past decade. Demolition of whole buildings byblasting, which is an accepted method, is not dealt with.

Explosives are chemical compounds or mixtures of compounds which, by the supply of a certain amount of initiation energy, can be made to react and to evolve energy. Theymay be gaseous, liquid or solid. Explosives can react in two ways, by deflagration ordetonation. In both cases the reaction occurs in a thin zone which moves through theexplosive. When the velocity of this zone is lower than the velocity of sound, thephenomenon is called deflagration. When an explosive is drilled into a material, the gaspressure produces an explosive effect in conjunction with both deflagration and detonation. In detonation there is a simultaneous effect due to the shock wave produced.The shock wave subjects the material to a very complex and extremely rapid stress cycle.Cracking towards the free surfaces opens the way for the gas pressure front followingbehind the shock wave to widen these cracks and break up the material. The shock wavestage is of very short duration, of the order of 10 microseconds. The duration of the gasexpansion stage is longer, of the order of milliseconds.

2.2 Techniques

It is not possible at present to set up a theoretical model that will describe the stress andstrain cycle in a realistic manner. Determination of the necessary quantity of explosive isbased on empirical formulae and on experience. The endeavour is to utilize the energy ofthe explosive in an optimum manner and to reduce the damage to the structure or theenvironment to a minimum. The most common problem is to determine the size and typeof the charge which is needed to produce the intended explosive effect.

For conventional concrete structures, compressive strength probably expresses the resistance of the material to blasting reasonably well. The quantity of explosive must beincreased as the strength increases. However, it is probable that for high strengths of

Blasting of concrete 243

about 50 MPa and above, the resistance decreases. Then the blasting effort can bereduced. It is probable that the fracture energy of the material better expresses itsresistance even at high strengths.

Reinforcement is of great significance for the blasting of concrete. Reinforcementusually retards the shock wave or provides a framework for the concrete, which meansthat more explosive must be used when the structure is heavily reinforced. Small strongcharges of high detonation velocity are the most effective. For various safety reasons,weaker charges must sometimes be used at the expense of effectiveness.

It is generally assumed that the burden (the distance to the free surface in the direction of blasting) is the most important parameter for calculating the charge. In the variousformulae to be found in the literature, the necessary weight of charge is expressed as afunction of the burden. These formulae take no account of reinforcement conditions.However, both the cracks produced by the shock wave and the work done by the gaspressure are affected by reinforcements.

The spacing of the charges is often made equal to the burden. The aim is to use charges as small as possible, which means that the spacing of the charges must be reduced if acertain explosive effect is to be achieved. A larger number of charges must be used, witha greater amount of drilling as a result. The spacing also has a bearing on the sizedistribution of the crushed material.

2.3 The effect on concrete and the environment

At present, lay-on charges cause far too much damage to be suitable. Mainly drilled-in charges are therefore discussed in the following. Without special precautions, a crackzone extending 200–400 mm from the charge can be expected. Cracks mainly occurparallel to the plane of the construction. Vertical cracks occur only at points of structuralweakness such as openings. In most cases, the final stage in interval blasting is towards afree face, and the extent of cracking can therefore be reduced. Provided that small orweak charges are used, the strength of material is only slightly affected.

Broadly speaking, 1–30 g of detonating charges may be regarded as small charges. In the vicinity of blasting, high levels of vibration occur due to detonating charges.Deflagrating charges, on the other hand, are stated not to give rise to vibration problems.The velocity of vibration decreases rapidly with distance. The vibrations do not normallycause any damage to concrete structures in the vicinity of blasting. Blasting nearstructural elements and installations sensitive to vibration should, however, be avoided.The vibrations that can be permitted are considerably greater than those due tounderground blasting nearby. Provided that normal precautionary measures are taken,drilled-in charges do not give rise to harmful air blast or flyrock. Lightweight materialsuch as mineral wool can be used to advantage to attenuate air blast. A blanket consistingof strong netting of fine mesh size often provides good protection against flyrock.

Blasting gives rise to a lot of dust. Dust control measures are sometimes necessary.Flooding with water can bind visible dust completely. In normal cases, however, openingof windows should be adequate. In confined spaces where a lot of blasting is carried out,


problems may be encountered due to oxides of nitrogen. In the context of the applicationsdiscussed here, however, these gases should cause no difficulties since the quantities ofexplosives used are small. The gas concentrations can, therefore, be kept below thepermitted threshold values.

2.4 Development needs

Theoretical knowledge of blasting in reinforced concrete is limited. More research wouldtherefore, be desirable, for example, in the area of fracture mechanics. Some researchtasks of developmental orientation are indicated below.

– Production of recommendations for blasting with the emphasis on safety and liability aspects

– Development of small and practical charges of variable shape and strength – Development of small and cheap detonators with appropriate delay times and little

scatter in firing times – Development of simple and lightweight devices which markedly reduce air blast and

dust and prevent flyrock.

3 Background and objectives

During the past decade, construction activity in the industrialized world has increasinglyconcentrated on repair and refurbishment. The alterations which must be made in existingbuildings involve localized cutting and partial demolition of the loadbearing structure. Atpresent there is no method which is in all respects superior to the others. The choice ofthe right method or combination of methods is, therefore, an important initial stage inwork of this kind. Factors which are of essential significance in choosing the method tobe used for localized cutting and partial demolition are

– the strength of the structure – transport facilities in the building – repair needs after cutting – sensitivity of the surroundings to disturbance – the extent of the work

At present, blasting is used only to a very limited extent and mainly for foundations andsimilar elements of construction. The method is, however, fairly often used for thedemolition of entire tall buildings. In a refined and suitable form, however, it can also beused for localized cutting and partial demolition of most large elements of construction ina building.


The object of this report is to set out the present state of knowledge in the field of concrete blasting as regards localized cutting and partial demolition of concretestructures. Special emphasis is placed on R&D results during the past ten years.

4 The principles of disintegration

4.1 Concrete structures and the rate of loading

Concrete has a complex internal structure, the principal constituents of which areaggregate, cement paste and a phase boundary region. This region, the thickness of whichis 15–25m next to the surface of the aggregate, consists of large crystals of calcium hydroxide embedded in a sparse matrix of the reaction products of cement gel. Severalobservations suggest that the phase boundary region has a weaker structure than thepaste.

The strength of concrete is considerably affected by the rate of stress/strain. It has been shown that the rate of loading has a considerably greater effect on tensile strength than oncompressive strength, see e.g. Reinhardt (1982) and Suaris and Shah (1982).

In certain cases, the compressive strength can be doubled and the tensile strength quadrupled at very high rates. This increase in strength can be explained by means of afracture mechanics approach. Under very rapid loading conditions, a lot of energy issupplied in a short time. Cracking is forced to occur along paths with stronger zones, forinstance through aggregate. There is less time for cracks to find their way to the weakestzones such as the existing microcracks and the phase boundary regions between cementpaste and aggregate; see e.g. Zielinski and Reinhardt (1982).

In cases where vibration measurements have been made, the relationship between the particle vibration velocity and the material stress along a wave front where strain isunidimensional can be used.

According to this formula, fairly high stresses occur in the near zone. In spite of thesehigh stresses in the near zone, the ultimate strength is not exceeded under normal loading rates. This can probably be explained by the above-mentioned elevated strength of the concrete at high rates of loading.

(1)


4.2 Explosives

The term explosion can be defined simply as the mechanical or thermal effect of thedetonation or deflagration of the explosive.

Explosives are chemical compounds or mixtures of compounds which, by the supply of a certain amount of initiation energy, can be made to react at a high rate and to evolveenergy. They may be gaseous, liquid or solid.

Explosives can react in two ways, by deflagration or detonation. In both cases the reaction takes place along a thin zone which moves forward through the explosive. Whenthe velocity of this zone is lower than the velocity of sound, the phenomenon is calleddetonation. A shock wave is then propagated through the explosive at supersonicvelocity. The velocity of detonation may range between 3000 and 9000 m/s. Highpressures are evolved, with estimated values ranging from 1 to 40 GPa.

Table 1 sets out essential data for some typical explosives.

4.3 The effect of exploding charges

4.3.1 Drilled-in charges

When an explosive is drilled into a material, the effect due to the gas pressure can beobtained in conjunction with both deflagration and detonation. In detonation, the effect ofthe shock wave is added to this. The explosive effect, expressed in 2erms of the materialremoved by blasting, increases with the energy of the explosive since this can be utilizedto a high degree. The energy due to volumetric expansion of the gases formed can beutilized.

Table 1. Explosives data

Explosive

CRC Urbanite Gurit Dynamite TNT PETN

Maker Asahi Nippon 011 Nitro Nobel – – –

Country Japan Japan Sweden – – –

Density kg/m3 – 1300 1000 1500 1600 1650

Detonation velocity m/s 60 2000 3000 6000 6500 7500

Explosive energy MJ/kg – – 3.8 4.6 4.1 6.1

Gas volume m3/kg (at 0ºC) 0.050 – 0.400 0.750 0.690 0.780


4.3.1.1 Detonation

A detailed description of the effect of drilled-in charges is given in e.g. Molin (1984 (A)).The shock wave subjects the material to a very complicated and extremely rapid stresscycle. The material in the immediate vicinity of the charge is crushed by the shock waveat a very high velocity. As the distance from the charge increases, the crush zone changesinto regions with plastic and gradually elastic deformation. Theum (1978) and Gercke(1952) and others have constructed relatively simple analytical models. Owing to thevery complex character of the problem, however, these must be regarded asapproximations. Several authors mention impedance as an important factor in thetransmission of the compressive wave. If the impedance of the explosive is equal to thatof the material and if the materials are in contact, direct transmission of the compressivewave from the explosive to the material can be expected. Differences in impedance giverise to reflections and thus a loss of energy. Where the charge detonates in the vicinity ofa free face, the primary compressive wave is reflected at the solid material/air boundary.Tensile stresses are set up which, in turn, can cause spalling of the material. This isdescribed by, inter alia, Thum (1978). The crack system which is caused by thecomplicated stresses is shown in Fig. 1.

(a) Radial cracks caused by the primary shock wave (b) Radial cracks at the surface as a result of interaction between the compression wave

and reflected tension waves (c) Tangential cracks caused by tensile stresses due to the reflected waves (d) Tangential cracks caused by direct compressive/tensile waves

Fig. 1. Crack propagation close to free surface.

Cracking adjacent to free faces opens the way for the gas pressure behind the shock wave


to widen the cracks and throw off the material. The shock wave stage is of very shortduration, of the order of 10 microseconds. The duration of the gas expansion stage islonger, of the order of milliseconds. The failure mechanism is treated by Johansson andPersson (1970), Henryck (1979) and others.

In blasting, it is only a small proportion of the developed energy which is utilized in breaking up the material. Rascheef (1973), for instance, is of the opinion that not morethan 25% of the gas pressure energy is utilized for fragmentation. Energy conversion isillustrated in Fig. 2.

Fig. 2. Blast energy conversion.

4.3.1.2 Deflagration

In deflagration, no shock wave is developed in the material. In the same way as indetonation, a crush zone is formed near the charge by the high compressive stresses. Thisis however much smaller than in detonation. Breakup is caused by compression andprincipal tensile stresses. High temperatures but relatively small gas volumes are


developed. Stringent demands are placed on the stemming. It must be strong and seal thedrill-hole hermetically. Sand and clay are not sufficient. Rapid hardening cement mortar can be used. Attention must be paid to the setting time required. A more detailed description ofthe failure mechanism in plain concrete is given in Ito, Sassa, Tanimoto (1972).Engineering use of deflagrating explosives has been described in the Japanese literature.A brochure on CCR powder, published by Asaki Chemical Industry Co Ltd, may bementioned as an example of the literature on which detailed descriptions are given ofcompleted blasting projects.

4.3.2 Lay-on charges

A lay-on charge is a charge which is applied to the surface of an object. Deflagrating charges do not normally cause any deformation in concrete since the

gases evolved can expand freely in the ambient air. The object is, however, given animpulse in the direction explosive-object.

When an explosive detonates in direct contact with an object, this is subjected to ashock wave. The pressure at the explosive/material interface is equal to the detonationpressure (in solid and liquid explosives up to 40 GPa). No material known at present canstand up to such high pressures without undergoing yield/deformation. The effect of theshock wave induced in the material is prolonged if the charge is covered by a material ofsufficient mass, e.g. sand or clay. The effect on a structural material is determined by thedetonation pressure of the explosive and the contact area of the charge. When a charge isdetonated on a structure of moderate thickness which is exposed to the air on both sides,an effect, spalling of material, is obtained on the opposite side also, see Fig. 3. This is due to partial reflection of the shock wave as it passes from the medium of higher density tothe one of lower density. This gives rise, inter alia, to tensile stresses which causespalling of the material if they exceed the ultimate tensile strength.

5 Blasting techniques

5.1 Methods


It is not possible at present to set up a theoretical model which describes the stress andstrain cycle in a realistic manner. Determination of the quantity of explosive required isbased on empirical formulae and on experience. The aim is


Fig. 3. Spalling on the opposite side at detonation.

to achieve optimum utilization of the energy of the explosive and to reduce the risk ofdamage (disturbance) to the structure or the environment to the minimum.

The most common problem is usually determination of the size of the charge needed for the breakout (intended explosive effect) to be achieved. Fig. 4 sets out the results of tests using charges of four different sizes, with the other conditions remaining unchanged.

Fig. 4. Blasting result as a function of the size of charge

The following parameters govern the results of blasting.

Concrete parameters

Thickness


Weichelt (1969) gives a calculation method for quantification of some of the aboveparameters. Langefors and Kihlstrom (1978) present a detailed review of the assumptionson which calculation of charge size for rock blasting is based. These data are, however,not directly applicable to the blasting of concrete structures.

5.1.1.1 Concrete parameters

A lot of the knowledge gained in rock blasting, particularly the blasting of granite, can beused in the blasting of concrete. The properties of concrete are not very different fromthose of granite. See Table 2.

Strength

Reinforcement

Charge parameters

Strength of explosive

Weight

Spacing of charges

Interaction/interval

Stemming

Geometrical parameters

Constriction

Burden

Diameter of drill-hole

Coupling ratio

Table 2. Comparisons of materials

Property Concrete Granite

Compressive strength (MPa) 10–70 70–300

Modulus of elasticity (MPa) 20–35·10s 40–60–10'

Velocity of sound (m/s) 4000–4500 5000–6000

Impedance (kg/m2.s) 8.8–10–5·106 13.5–18.0·106

Fracture energy (J/m2) 70–140 80–1401

1 Bohus granite


According to Weichelt’s formula for the blasting of concrete, more explosive is needed for weak concrete than for strong concrete. In systematic blasting tests on còncrete of varying strengths, the opposite was found, i.e. a stronger concrete required a higherspecific charge on constant charging. It is stated, however, that at very high strengths thespecific charge can be reduced, see Molin (1984 (A)). The change probably occursaround a strength of 50 MPa. It is also suggested that the ultimate tensile strength ofconcrete might be a relevant parameter with regard to the resistance of concrete toblasting. The fracture energy of a material is a function of its strength and its deformationcapacity. Fibre reinforced concrete has a high fracture energy. It has also beendemonstrated in some tests that fibre reinforced concrete is difficult to blast. At presentvalues of the fracture energy are not readily available. In the strength region which isapplied for normal structures, there is good correlation between fracture energy and thecompressive strength.

Cracks and other inhomogeneities are significant with regard to the results of blasting.Cracks can often hinder blasting. Undesirable results such as insufficient explosive effectmay be obtained.

5.1.1.2 Reinforcement

Reinforcement is of great significance for the blasting of concrete. Sassa et al.(1972)have carried out blasting tests on reinforced concrete. It is evident from these thatcracking which initiates failure is a function of reinfor cement. Charges of normal sizemay be expected to cause little damage to the reinforcement itself. It is not cut and itsdeformation is small or moderate. Reinforcement usually retards the shock wave orprovides a framework for the concrete, which means that more explosive is needed as theamount of reinforcement increases. In conjunction with blasting towards a free face, i.e.when the principal blasting direction can be made parallel to the plane of thereinforcement, the amount of explosive is independent of the reinforcemnt. For further.information, reference is to be made to Molin (1984 (A)). Reinforcement, particularlywhen it is placed at the centre of the section, may increase unintended cracking.Deformation of heavy reinforcement may cause spalling of remaining adjacent concrete.

5.1.1.3 Charge parameters

(a) The strength of the explosive The strength of an explosive is not a concept that is well defined. Langefors andKihlstrom (1978) define the strength of an explosive as a function of energy and gasvolume. The detonation velocity of the explosive, i.e. the velocity at which the detonationwave is transmitted through the explosive, is often included in the expression for thestrength of the explosive. The magnitude of the gas pressure in the drill-hole during an explosion is determined by the heat of detonation and the gas volume.

The shock wave effect in the material is dependent on the velocity of detonation. The detonation pressure is directly proportional to density and to the square of the velocity of


detonation. When blasting in built-up areas, indoors and in elements of construction that must not

be damaged, it is important that side effects should be reduced as far as posible. Severalmanufacturers have, therefore, developed explosives for careful blasting. Specialemphasis has been placed on reducing the velocity of detonation and gas pressure. InSweden, for instance, Gurit has been produced by Nitro Nobel. In Japan, developmenthas progressed a stage further and explosives with velocities of detonation below 2000m/s and gas volumes less than 0.1 m3/kg have been produced. An example which can bementioned is Urbanite manufactured by Taisei. The product Concrete Cracker (CCR) hasa velocity of deflagration of 60 m/s and produces a gas volume of 0.05 m3/kg. The explosive deflagrates. Its action is produced only by a quasi-pressure, see Sassa (1972). There are explosives whose velocities of deflagration are even lower. These deflagratingexplosives are well suited to blasting plain concrete.

(b) Coupling ratio The coupling ratio is defined as the drill-hole diameter to explosive diameter ratio. Itaffects transmission of the shock wave to the surrounding material and development ofpressure in the drill-hole. As the coupling ratio increases, there is a considerable drop in the effectiveness of the explosive but also a reduction in unwanted damage to theenvironment. In practice, the coupling ratio can be increased by e.g. using narrow Guritcartridges or detonating cord in 20–30 mm holes. In accordance with data supplied by thecompany that manufactures the low velocity detonating explosive Urbanite, the relationship between drill-hole pressure and coupling ratio is as set out in Fig. 5.

(c) Stemming Closure of the drill-hole by some material in order to enhance the explosive effect is termed stemming. The materials used for stemming detonating explosives are clay, sandmixed with plaster or compacted well graded sand. Stemming has little influence on theshock wave effect. However, it confines the gases which can, therefore, widen andlengthen the cracks more effectively. In thin structures and shallow holes, however, it isdifficult to stem holes satisfactorily. Low velocity detonating charges and deflagratingcharges require good stemming since the explosive effect is dependent on thedevelopment of gas pressure in the drill-hole.

(d) Interaction between charges Blasting is normally carried out with several charges. It is advantageous to make use ofthe interaction that can be achieved between the charges. This can be done byinstantaneous or delay firing. In practice, detonators with delays of 20–30 ms are used. This delay is, however, too long for direct interaction to occur. Considerably shorterintervals are required of 1 or 2 ms and, in addition, little scatter in firing time, see Rustan(1978). Detonators that satisfy these requirements are available in the market at presentalthough they are expensive. Delay firing is applied in order to reduce vibrations and airblast.


Fig. 5. The relationship between drill-hole pressure and coupling ratio.

5.1.1.4 Geometrical parameters

(a) General Fig. 6 sets out the most important geometrical parameters in blasting.

Fig. 6. Important geometrical parameters in blasting.


(b) Burden, f It is generally assumed that the burden is the most important parameter in calculating thecharge. In the various formulae to be found in the literature, the required weight of chargeis, therefore, often expressed as a function of the burden.

Langefors and Kihlstrora (1978) give the series

where k0, k1 and k2…are constants. It is shown that k0 and k1 are equal to zero and that the next three terms are significant.

k2 and k3 are stated to depend on the elastoplastic properties of the materials. k4 isdefined as a function of the weight of the expelled material. Weichelt (1969) and othersare content with using the third degree term which produces the simple formula

k3 is a constant which is the product of the parameters relating to the material, the properties of the explosive and geometrical conditions. According to Hopkinson’s scaling law,

This expression agrees with the equation (5). The following simple formula is acceptable as a rule of thumb:

These formulae seem to work in practice for granite and plain concrete. They take noaccount of reinforcement conditions although these are significant. Both crackingproduced by the shock wave and the work done by gas pressure are affected by thereinforcement.

(2)

(3)

(4)

(5)

(6)

(7)


(c) Spacing of charges, c The distance between charges is often made equal to the burden. The endeavour is to usecharges as small as possible which means that the spacing of charges must be reduced if acertain blasting effect is to be achieved. The number of detonators must, therefore, beincreased and more drilling must be done. Spacing is significant with regard tofragmentation and the quality, i.e. smoothness and cracking, of the contour.

(d) Diameter and depth of drill-hole db and hb

For practical reasons, the drill-hole diameter is normally made a little larger than thecharge diameter. In conjunction with extra careful blasting, the coupling ratio is madelarge for instance 2, which means that the drill-hole diameter is double the charge diameter. From the production point of view, the drill-hole diameter should be as small as possible so that easily handled equipment can be used. However, diameters les than 10mm are not likely to be used at present.

In walls and floors, the drill-hole is often drilled so that the charge is at the centre ofthe construction or its depth is made the same as the burden.

(e) Constriction An explosive charge is most effective when the shock wave and the gas pressure aredirected at right angles to the free faces of the element of construction. In his formula ofthe weight of charge, Weichelt gives a range of 0.8 to 4. This indicates the greatsignificance of constriction for the quantity of explosive required.

In making openings, constriction is considerably greater for the first charges which must break out the initial cavity than for the subsequent charges. Localized cutting,mainly in thick structures, is often similar to the blasting technique applied in tunnelling.


For the present it is difficult to make use of lay-on charges in blasting concrete. Theygive rise to strong air blast and cause shallow breaks on the rear face. Blasting cord, seeFigs. 7 and 8, is slightly better.

Fig. 7. Blasting cord, schematic.

Owing to the shape of the cross section and the metal lining, for instance copper, acertain cutting effect is obtained, see Molin (1983 (C)). Blasting cords have in actual fact


been developed for cutting steel. The directional effect is used for military purposes, forinstance to penetrate armour.

Fig. 8. Cutting in a wall with blasting cord, rear side,

Lay-on charges need no drilling. They can be applied easily to the appropriate surface. Atleast for thin structures of 100–200 mm, it should be possible to simplify this blastingmethod. Development work with the aim of optimizing shape, metal lining and stand-off is required. Particular attention should be paid to reduction of the air blast effect bymeasures which should preferably be incorporated in the charge.

6 The effect on nearby concrete

6.1 Cracking

As mentioned above, blasting by means of detonating charges subjects the material tovery high compressive, tensile and shear stresses. The primary shock wave normally


causes only local damage around the drill-hole. It is the shear and tensile stresses which cause cracking. When the compression wave reaches the free face, it is reflected in theform of a tension wave. Particularly when the geometry is symmetrical, interferencephenomena may occur, see Rinehart (1959). Colliding tensile stresses can then give rise to concentric cracking inside the structure. See the example in Fig. 9.

Propagation of these parallel cracks is affected to a high degree by the way in which blasting is carried out. As a rough estimate, a zone 200–400 mm from the charge may be damaged by cracking by a charge of about 30 g. The extent of cracking increases with thereinforcement ratio but decreases with strength. Cut blasting gives rise to considerablylarger cracks than blasting towards a free face. The final stage of interval blasting is inmost cases free face blasting. Crack propagation can be appreciably reduced byprecautionary measures. For a given type and weight of charge, the length should beincreased, the diameter reduced and the drill-hole diameter increased. The requirementregarding detonation stability imposes a minimum diameter. The use of shaped chargesor the provision of holes between the drill-holes also reduces damage. The proposedmeasures also have the effect of reducing the extent of spalling, particularly if the lengthof the charge can be made the same as the thickness of the concrete structure. Adescription of the extent of the damage and proposals for preventive measures are givenin e.g. Molin (1984 (A)). These have been summarized in Fig. 10.

Deflagrating charges cause considerably less damage. There are no investigationsreported in the literature which

Fig. 9. Crack formation in structure due to interference between colliding tensile waves.


Fig. 10. Crack propagation and external concrete damage for various blasting modes.

show the extent of damage. Nor has a study been made of whether sufficient explosiveeffect is achieved. Through cracks can in some cases be formed by a corner charge ifthere is a point of weakness in the vicinity, since the crack finds its way to this. The riskof unintended cracking is great in thin unreinforced structures, such as certain walls withholes and services entry points.


6.2 Strength

Apart from the cracks referred to in Subsection 6.1, the strength of the material is littleaffected provided that the charges used are small or weak. Broadly speaking, detonatingcharges of 1–30 g weight may be regarded as small charges, while deflagrating charges are regarded as weak charges. A charge of the Dynamex type of 100 g weight probablycauses a reduction in strength within a distance of 200 mm from the charge. It has beenshown by linear regression analysis, see Molin (1984 (A)), that there is a significantnegative relationship between the strength of the charge and compressive strength at adistance of 130 mm from the centre of the charge. It is, however, only in the case oflarger charges that this reduction is of practical significance. Charges up to about 30 g inweight can, therefore, probably be accepted from the point of view of strength withoutany checks.

7 The effect on the environment

7.1 Vibrations

Detonating charges give rise to high levels of vibration in the vicinity of blasting. On theother hand, deflagrating charges are stated to cause no vibration problems. At a distanceof 1 m from the charge, the vibration velocity may be of the order of 300 mm/s, seeMolin (1983 (C)). Fig. 11 shows the vibration velocities measured in conjunction withblasting a 0.8×0.8 m opening with sixteen 7 g interval coupled dynamex charges.

Vibration velocity drops off rapidly with distance. The vibrations do not normallydamage concrete structures near the explosion. Blasting in the vicinity of elements ofstructure and installations which are sensitive to vibrations, such as computers inoperation, should, however, be avoided. In blasting tests near normal windows, nodamage was caused to the glass. The minimum distance was about 1 m. Danish tests(Lauritzen) also show that vibration damage is of very limited extent provided thatblasting is not carried out in unsuitable positions. The vibration that can be permitted inconjunction with localized cutting and partial demolition is considerably greater than theground vibrations due to blasting, piling or heavy vehicular traffic. Ground vibrations are,in most cases, in the form of surface waves or Rayleigh waves. These have a low velocityof propagation, small wavelengths and large amplitudes. There is a risk of


Fig. 11. The vibration velocity decreases rapidly with distance,

relatively large deformations and only low levels of vibration can therefore be permitted.Permissible values vary from 3 to 50 mm/s. In contrast to the Rayleigh wave, the shockwave caused by blasting in concrete involves only the risk of local damage in normalcases.

7.2 Air blast and flyrock

Blasting with detonating charges gives rise to air blast, see e.g. Persson and Almgren(1971).

The pressure and duration of the air blast are a function of reflection, strength of charge, degree of constriction, interaction with other charges, etc. Subject to simpleprecautionary measures, the air blast effect of small drilled-in charges which are fired at intervals is harmless. The pressure may be relatively high. In interval blasting in a largewarehouse using charges of 60 g maximum size, 0.9 kPa has for instance been measuredat a distance of 2.5 m. However, the impulse which is the integral of pressure withrespect to time is small. On the other hand, lay-on charges can give rise to very extensivedamage; windows are broken, partitions are cracked open, etc. For small drilled-in charges it is relatively easy to reduce the pressure and impulse of the air blast. It is not necessary to use heavy protective materials such as sand and water.

The histogram in Fig. 12 shows various alternatives for attenuating the air blast due to a 10 g charge of high detonation velocity.


It is evident that even lightweight materials such as mineral wool can provide a high degree of attenuation. 70 mm mineral wool and a rubber mat, for instance, providedattenuation of 85–90%. From the point of view of workload, it is obviously advantageousto use lightweight materials. The risk of damage is greatest if pressure and impulse areboth relatively high. Very high pressures do not necessarily cause damage if the impulseis low. For a study of the effect of charges that explode in the air, see Granstrom (1956).

Fig. 12. Relative pressure and impulse from a 10 g charge on a sand base covered with various damping materials.

Blasting causes ejection of concrete fragments. These may have a high initial velocityand a large throw. Flyrock is normally caught up by some form of protective covering.Rubber mats and blasting blankets, see Fig. 13, are usual.

The mats retard most of the material that has been blasted off. The blanket catches the fragments that have escaped through the blasting mat. The protective cover is designed sothat it allows the air blast to escape, since too impervious a cover would be thrown off.For instance, a blasting mat comprising tyres held together by steel lines does not impedethe air blast. The blasting blanket is often made so large that, in spite of its expansion, itretains the fragments that have passed through the mat. A blanket consisting of a strongnet of fine mesh size is often a good solution.


7.3 Dust and gases

Blasting of concrete gives rise to a lot of dust. This is particularly noticeable whenblasting is carried out indoors.

Dust control measures should sometimes be taken. Flooding with water can completelybind visible dust. On horizontal surfaces joists and a plastics foil can be used. These mustbe carried on some kind of supporting structure such as sheets of plywood, joists andstruts. On vertical surfaces the water can be provided in plastic tubes suspended on thewall side by side; see Fig. 14.

Fig. 13. Protection of conventional type with rubber mats and blasting blankets on wall.

If the dust is not captured directly, then at least in sensitive environments the roomconcerned should be hermetically sealed off. Fans can also be used to put the room undera partial vacuum so as to prevent dispersion of the dust. In normal cases, however,opening of windows should be sufficient.

Problems due to oxides of nitrogen (NO+NO) can arise in small and confined spaces where a lot of blasting is carried out. In normal cases, however, these gases should notcause any difficulties since small quantities of exlosives are used. In this way, the gasconcentrations can be kept below the permitted threshold values.


Fig. 14. Dust protection of wall with water contained in plastic tubes on either side of the wall.


8 A brief comparison with other methods

A detailed description of different demolition methods is given in RILEM (1985). Atpresent there is no method which can be used as a matter of course for the demolition ofexisting concrete structures. The reason is that reinforced concrete is a strong compositematerial consisting of constituents of widely differing properties. There are no evidentpoints of weakness. All the methods available at present have technical, economic orworking environmental shortcomings. In order, therefore, that the best result may beachieved in a demolition situation, it is essential that the correct method or combinationof methods should be applied. In the literature, only limited attention has been given tothe possibility of combining different methods.

Blasting is of no interest until the thickness of a construction exceeds 200–300 mm. For smaller thickness, breaking or sawing is, in most cases, more appropriate. Sawing ispreferable if a straight and tidy cut is required and if no adhesion is needed between thenew and old concrete at some later stage. An impact hammer on a carrier is probably anadvantageous method in some conditions. Quite a large space is however required eventhough relatively small hammers are now available. The remaining reinforcement mustbe checked if this is to be used for anchorage, since surface cuts in the reinforcement andsmalling may occur.

As mentioned above, blasting does not damage the reinforcement. Concrete is howeverdamaged to a certain extent, which is of signigicance if the strength of the concrete is tobe fully utilized. In such cases, light breaking must be carried out to expose soundconcrete. In confined spaces it is difficult to use bulky equipment. Even if there is spacefor an impact hammer on a carrier or for other heavy equipment, there may betransportation problems, for instance if a lift of sufficient capacity is not available to thedifferent storeys of the building. Work environmental comparisons may favour the use ofexplosives since the environmental stress is of very short duration if the limited disturbance due to drilling of the drill-holes is disregarded. Blasting can be carried out at suitable times. A work environmental comparison has been made in an old concretebuilding, Molin (1983 (C)). Fig. 15 sets out working environment profiles for blasting and for some conventional methods. In very sensitive environments such as hospitals andcomputer centres, blasting is not suitable. In such cases diamond drilling with bursting, orcrusher equipment, may be employed.


9 Practical examples of blasting

9.1 Edge beams on bridges

A lot of older bridges have damages on edge beams. The damage has been mainly causedby frost and corrosion stresses. The edge beams which are seriously damaged may haveto be demolished. The edge beams of two bridges, Molin (1983 (B)) and Molin (1985(B)) have been removed by blasting. The second bridge was constructed in 1958 and itsinclusion in this report will be of interest. It had a span of 36.7 m and an overall width of10.5 m. According to the drawings, it consisted of K300 watertight concrete without airentrainment admixture. The type of charge chosen was Bonoplast which contains, interalia, flegmatized compressed Hexotol of 10,

Fig. 15. Working environment comparison between blasting and some conventional methods.

13 or 18 mm diameter. Some data relevant to this explosive, made by Bofors AB, are setout below.

Density 1650 kg/m3

Velocity of detonation 8000 m/s

Energy content 6.5 MJ/kg


13×50 mm charges weighing 10 g were mainly used. They were positioned centrally inthe vertical direction and 80 mm from the inner edge, as shown in Fig. 16.

The specific charge was 0.42 kg/m3. In simplified terms, this may be defined as the total weight of charge divided by the volume of material. Initiation was by detonatorswith 25 ms delay. From the production point of view, the method worked very well inspite of the fact that no major effort was made to facilitate the actual work. An edgebeam, 37 m long could be demolished in 3–4 hours. Complete closure of the bridge was necessary only for a few minutes during the actual blasting. With a charge weight of 10 gand spacing of 300 mm, the edge beam was satisfactorily demolished. Before the newconcrete was placed, the blasted edge was cut back to sound concrete. The appearance ofthe edge beam before and after is shown in Fig. 17.

Fig. 16. Location of charges in edge beam


Fig. 17. Edge beam before and after blasting and cleaning with 30 g Primex charge.

9.2 Balcony brackets

Balcony supports in the form of brackets showed signs of reinforcement corrosion. Theywere found to have high chloride contents. De-icing salts had been used on the balconies and found their way to the brackets through open joints. It was necessary to demolishthese brackets since their loadbearing capacity was becoming inadequate. Lauritzen(1986 (B)) gives a detailed description of the demolition. The 15 storey building ofprefabricated concrete units was constructed in 1967/68. There is no informationavailable as to concrete strength. A cross section through the balcony is given in Fig. 18. This also shows the positions of drill-holes. The diameter was 18 mm. The chargeconsisted of 6g powder and 3 g PETN, placed in 16 mm PVC tubes. Initiation was by 25ms delay. In order to reduce the effect on the facades, the inner portions of the bracketswere not blasted. Sheets of plywood were used for protecting the facade. Rubber matswere laid on the balconies and a


Fig. 18. Location of charges in balcony bracket

blasting blanket was erected on a simple scaffold around the bracket. The results ofblasting are shown in Fig. 19.

Blasting of 15 brackets including breaking out the remaining portions took 40 manhours. It is stated that manual breaking out would have taken three times as long and thismethod would also have created more inconvenience for the tenants than blasting.

Fig. 19. Balcony bracket after blasting. The remaining part near the wall was taken away with a handheld breaker.


9.3 Piles

Piles can seldom be driven so that the pile head is at the intended level. They must,therefore, often be cut. Breaking out is usual and sawing is also employed. Two caseswhere explosives have been used are reported in the literature, see Lauritzen (1986 (A))and Molin (1984 (B)). Drilled-in small charges have great effect, especially if they are positioned at the centre of the pile and are of small extent. Spalling of corners occurs400–500 mm from the charge. If several charges are used, particularly if they are made long and slender, spalling can be reduced and a fairly straight edge can be obtained, seeFig. 20.

The dimension of the pile shown is 350×350 mm. Subsequent breaking out is alsoreduced if several charges are used. Blasting methods are particularly suitable when thereis a need to provide continuity, i.e. when starter bars must be left for concrete to beplaced later. In Denmark the method is used extensively. Tailor-made cover material of special fibre (ROMEX blasting mat) has been produced by the firm DEMEX and thismakes it possible for the other trades on the site to continue working even during theactual blasting operation. The method is faster and much cheaper than chopping out. Thephotograph in Fig. 21 shows the results of blasting according to DEMEX. The piles of 300 ×300 mm cross section had been charged with 17g PETN in 18 mm drill-holes.

Fig. 20. Cutting of pile with several long and thin charges


Fig. 21. Cutting of pile according to DEMEX. The piles of 300×300 mm cross section had been charged with 17g PETN in 18 mm drill-holes.

9.4 Openings in walls and floors

Practical tests on walls and floors have been carried out in an older concrete building,Molin (1983 (C)). The object was to study the utility of the blasting method for localizedcutting and partial demolition. It was found that the suitability of the method is enhancedas the thickness of construction and reinforcement ratio increase. It was foundappropriate to start with a larger quantity of explosive for the cut shots and to finish withextra careful blasting around the contours cf the opening. The charges were placed


centrally in the structure along a grid. Table 3 sets out data relating to blasting for a liftshaft and a door opening. These have not been optimized with regard to the blastingeffect. The results of blasting for the door opening are shown in Fig. 22.

Fig. 22. Blasting of door opening, before and after

Interval blasting was used with 25 ms delay. Not more than five charges had the same interval number. About 50 charges were needed for an opening. The method is probablyof most interest for structures of greater than 250 mm thickness. This is particularly thecase if the structure is heavily reinforced. Blasting indoors often requires special carewith regard to air blast and dispersion of dust.

Table 3. Blasting for lift shaft and door opening

Structure Thick-ness mm

Strength MPa

Reinforcement Charge weight g (Dynamex)

Distance mm

Specific charge kg/m3

Floor 290 22 020, 022 c170, c150

60 300 3, 5

Wall 160 25 010 C300 central

15 240 2, 3


9.5 Stairs

In order that the mobility of the elderly and the disabled should be increased, Swedishauthorities specify the installation of lifts in buildings of three or more storeys. In manycases the existing stairway is large enough to accommodate a small lift. Installation iscommenced by making an opening through the stairs. According to Molin (1985 (A)),experimental blasting in existing tall buildings has shown that blasting may be anappropriate type of measure where the flights of stairs are solid and of large thickness,see Fig. 23.

Fig. 23. Blasting in a staircase from below

All blasting was carried out using 5 g Primex charges, made by Nitro Nobel AB, inplastic tubes. The diameter was 15 mm and the cut length 25 mm. Removal of the brokenconcrete is facilitated by dropping it through the hole provided in the stairway whenblasting proceeds from the bottom upwards.


9.6 Concrete pipes

Detonating cord is wound round the circumference of the pipe. The action of the cord,which has a high velocity of detonation, produces a clean and straight cut. Fig. 24 shows a large concrete pipe which is to be cut. A detail of the actual cut is shown in Fig. 25.

9.7 Exposure of reinforcement

In conjunction with the modernization of buildings, exposure of the reinforcement issometimes necessary so that it may be surrounded by fresh concrete for repairs or mayact as a starter bar for further work, see Fig. 26.

Blasting produces undamaged reinforcing bars free from concrete. The method can becombined to advantage with high pressure water jet treatment. In repair work, pieces ofconcrete attached to the reinforcement must sometimes be broken away. This can be doneby a few grammes of a detonating explosive such as PETN.

Fig. 24. Detonating cord applied for cutting of a concrete pipe


Fig. 25. Detail of the actual cut in the pipe

Fig. 26. Blasting of slab and beam for exposure of reinforcement


10 Fragmentation of reinforced concrete

10.1 General

A lot of the material derived from demolition can be reused. Frag- mented concrete, when properly graded, may be of interest for use as aggregate in concrete instead of stone orgravel. Fragmented concrete can be obtained directly from the demolition site or from acrusher plant. At present, concrete is mostly crushed mechanically. It should, however, bequite possible to use explosives for fragmentation purposes only. In Belgium a lot ofresearch has been done in a joint project between the Belgian Building ResearchOrganization CSTC and RRB Nobel Explosives. Work concentrated on fragmentationand separation from the concrete. Only a very brief description will be given in thisreport. For more detailed information, reference should be made to Pauw and Fosse(1984).

10.2 Fragmentation experiments

Tests were made on a number of series of reinforced concrete units.


The parameters varied in the tests were

– size of charge – charge spacing – depth and diameter of the drill-hole

In small beams and slabs 12–25 mm diameter holes of 180–220 mm depth were drilled. PETN was used. Effectiveness, cost, separation of the reinforcement and each particlewere recorded. The best results in beam blasting were obtained with two 15 mm holeswhich were 150 mm deep. The beam cross section was 250×250 mm. The weight of charge was 15 g.

In the slabs (150 mm thickness, reinforcement 10 mm diameter at 100 mm spacing in both directions at both faces) 13 g charge and a specific charge of 0.5 kg/m3 were needed.

Several tests demonstrated that the size of charge had a clear influence on particle size. Cost was affected to a lesser extent. It was found that a large proportion of the cost wasaccounted for by drilling.



A specially viscous type of charge with a detonation velocity of 3700 m/s was developed.The concrete units were arranged as shown in Fig. 27. This arrangement made it possible for two units to be fragmented with one charge. At a specific charge of 2.0 kg/m3reinforcement was completely separated from the concrete. The relative specific chargeas a function of particle size is set out in Fig. 28.

Follow-up tests of practical orientation have been carried out. The grading of the particles has also been studied for different types of explosive.

10.3 Some conclusions

The results of the extensive Belgian tests and also practical experience from Denmark,indicate that blasting can also be used for fragmentation. In order, however, that themethod may become feasible on an industrial scale, mechanical control systems andsafety devices are needed. The economic aspects must be studied in greater detail in amajor demolition and reuse context.

Fig. 27. Fragmentation of two reinforced concrete units with one charge.


Fig. 28. Relative specific charge as a function of particle size

11 Conclusions

Experimental and practical experience indicates that blasting with drilled-in charges is a feasible method. It is especially suitable for thicker structures.

The charges should be small interval initiated detonating charges or in special cases deflagrating charges. The use of these types of charge and the interval delay mean thatthe effects on the concrete structure and the surroundings become acceptable, if simpleprotective measures are taken. However, some research and development are neededbefore the method will be fully accepted.

12 The need for research and development

Theoretical knowledge of blasting in reinforced concrete is limited. Some researchwould, therefore, be desirable. It is primarily the very complicated and time dependentstress/strain relationship immediately after detonation in the reinforced concrete structure,which must be elucidated. The functional relationship between the material parameters


and the rate of strain should also be studied. Some research tasks of developmentalorientation are indicated below.

– Production of recommendations regarding blasting techniques, with the emphasis on safety and liability aspects.

– Development of small and practical charges of varying sizes and strengths. – Development of small and cheap detonators with appropriate delays and little scatter in

firing times. – Development of simple, light and cheap devices which appreciably reduce air blast and

dust production and prevent flyrock. – Development of lay-on charges which can be used on thin elements of construction.

This applies primarily to blasting cords, see Subsection 4.2.2. The shape and metal lining of the charge must be optimized with regard to cutting action. A means of air blast attenuation should be an integral part of the charge.

– Study of different types of explosive, both deflagrating and detonating ones and their suitability when the working environment, must satisfy stringent requirements and the remaining edge region must exhibit no damage.

– Development of industrial fragmentation methods.

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Försiktig och skonsam sprängning under jord. Diskussionsdagar i Lule(INLINE) 17–18


september 1980. (Careful and controlled blasting below ground. Workshop at Lule(INLINE)a, 17–18 September 1980). (In Swedish). Lule(ILN)a University of Technology, Department of Rock Engineering and Rock Mechanics, 1981. 289 p. Technical Report No 1980:80T.

Gercke, M J. Berechnungsansätze zur Abschätzung der Wirkung einer eingeschossenen und einer aufliegenden Sprengladung. Sprengtechnik nr 6, 1952.

Granström, S A. Loading characteristics of air blasts from detonating charges. Stockholm. Proceedings of the Royal Institute of Technology, Stockholm. No 100, 1956.

Gustafsson, Rune. Bergsprängningsboken. (Rock Blasting Manual). (In Swedish). Stockholm: Swedish Building Centre, 1979. 322 p.

Henrych, J. The dynamics of explosion and its use. Amsterdam (Elsevier) 1979. 558 p. Heron Vol 27 1982 No 3. Reinhardt, H W. Concrete under impact loading: tensile

strength and bond. Delft, Netherlands: Delft University of Technology, Department of Civil Engineering, Stevin Laboratory, 1982. 48 p.

Holmberg, Roger and Rustan, Agne. First International Symposium on Rock Fragmentation by Blasting. Lule(aINLINE): Lule(INLINE)a University of Technology, 1983. 431 p. ISBN 91–7260–851-x.

International symposium on storage in excavated rock caverns, 1. (Stockholm 1977). Storage in excavated rock caverns: Rockstore 77/ed by Magnus Bergman. Oxford: Pergamon Press, 1978–3 Vol. Svaneholm et al. Smooth blasting for reliable underground openings. pp 573–579.

Ito, I, Sassa, K, Katsuyama, K, Hamajima, N. How to Control the Direction of Radial Cracks Caused by an Explosion. Journal of the Mining and Metallurgical Institute of Japan, Vol. 87 No 1006, 1971, (In Japanese, English summary available).

Ito, I, Sassa, K and Tanimoto, C. Blasting by Specially Made Low Explosives for Urban Works. Proceedings of the Japan Society of Civil Engineers, No 199, March 1972. (English translation available).

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Johansson, C H, Persson, P A. Detonics of High Explosives. London (Academic Press), 1970. 330 p.

Lamnevik, Stefan. Explosivämneskemi. (The chemistry of explosives). (In Swedish). Stockholm: FOA, 1983. 110 p.

Lamnevik, Stefan. Explosiva förlopp. Grunder for konsekvens- och riskanalys. (Explosive processes. The principles of consequence and hazard analysis). (In Swedish). 1983. Stockholm; FOA, 40 p.

Langefors, U and Kihlström, B. The modern technique of rock blasting. 3rd Edition. Stockholm; (Almqvist & Wiksell), 1978. 438 p.

Lauritzen, E.K (A). Dynamiskt belastade betongkonstruktioner Miniseroinarium. (Dynamically loaded concrete constructions -Miniseminar). Eskilstuna: Fortifikationsförvaltningen, Forskningsbyra(INLINE)n, 1986. Rapport A4:86. s 94–95.

Lauritzen, E.K (B). Mini-blasting for repair work, a Danish rehab project using small explosive charges. Batiment International Building Research & Practice, September/October 1986.

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Molin, Christer (A) and Pettersson, Esbjörn. Försiktig sprängning av hisschaktöppning i befintligt trapphus. Förstudie i betong-plattor. (Careful blasting of lift shaft opening in an existing stairway. Preliminary study in concrete slabs). (In Swedish). Stockholm: Swedish Cement and Concrete Research Institute, 1983. p 35.

Molin, Christer, (B). Försiktig sprängning av kantbalk. Fullskaleförsök p(INLINE) äldre betongbro. (Careful blasting of edge beam. Full scale test on an old concrete bridge). (In Swedish). Stockholm: Swedish Cement and Concrete Research Institute. Commissioned Project Function, 1983. Report No 8368, 40 p.

Molin, Christer, (c). Localized cutting in concrete by careful blasting. Stockholm: Swedish Cement an Concrete Research Institute, 1983. CBI forskning/research. FO 2.83, 252 p.

Molin, Christer, (A). A methods development study of localized cutting in concrete by careful blasting. Stockholm: Swedish Cement and Concrete Research Institute, 1984. CBI forskning/research. Fo 1.84. 149 p.

Molin, Christer, (B). Kapning av betongp(INLINE)lar med försiktig sprängning—en förstudie. (Cutting of concrete poles with careful blasting—a prestudy). Stockholm: Cement—och Betong-institutet. Uppdragsfunktionen, 1984. Rapport nr 8439. 15 s.

Molin, Christer, (A). Försiktig sprängning av hisschaktöppning i befintligt trapphus. (Careful blasting of lift shaft opening in existing stairway). (In Swedish). Stockholm: Swedish National Testing Institute, Building Technology, 1985. Working Paper No SP-BT/S 85:01.

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Index

Abrasion resistance 205 Accoustic barriers 50 Acid neutralization 95 Aggregate

natural, shortage of 2, 107 original 6

recycled, see Crushed masonry rubble; Recycled concrete aggregates

Air blast 246, 264-3 Air classification 18 Air entrainment 70, 76, 87, 88, 180 Air sifting 15 Alkali-aggregate reactions 15–82,123 Alkali-reactive aggregate particle contaminants 48–9 Alkaline waste water recycling 119, 125 Almgren, Lars-Ake 265 Aluminium contamination 46 Angelo, J. 94 Aquamator 19, 158 Arnold, C.J. 158 Asphalt 72

in masonry rubble 146, 153, 175 see also Bitumen contaminant

Association for Quality Control of Recycled Building Materials 175 Attached mortar 31, 32, 121

Bauchard, M. 14, 38, 116 BCSJ 19, 23, 34, 39, 40, 41, 58, 61, 68, 76, 80, 288 Belgium recycling projects 117 Berger, R.L 95 Bergholt, K. 95 Bernier, G. 52, 56, 64 Binder

content of fresh crushed masonry rubble concrete 178 masonry rubble powder as 213–4 Bitumen contaminant

in crushed masonry rubble 146, 153, 175 in recycled concrete aggregate 41–2,71, 121

Blasting 243-286 air blast 246, 264-3

blasting blanket 266 burden 246, 259 charges

coupling ratio 257 drilled-in 245, 246, 281 constriction 260 effect of 250–3 hole size 260 methods 253–60 spacing 260

interaction between charges 257 lay-on 245, 246, 282

effect of 253 methods 260–1

quantity 246 size determination 253 small charges 246 spacing 246,260 strength of explosive 256

compressive wave 250, 262 coupling rate 256–7 cracking 261–2

crack propagation 251 crack zone 246

deflagration 245, 249, 251, 252, 262-80 detonation 245-1, 249, 250-7

velocity of 256 development needs 247 disintegration principles

effect of exploding charge 250–3 explosion 249 explosives data 249 rate of loading of structures 248–9

dust control 247, 267–8,274 effect on concrete 246 energy conservation 251 environment and 246

air blast 246, 264–5 dust 267,276 flyrock 247, 266 gases 247, 269 vibrations 247, 248, 264

examples balcony brackets 272 concrete pipes 277, 278 edge beams on bridges 270–1 openings in walls and floors 275-–4 piles 274

Index 285

stairs 277 steel reinforcments 277, 278

flyrock 247, 266 fragmentation of reinforced concrete 281–2

drilled-in charges 281 lay-on charges 282

gases 247, 269 gas expansion stage 246 gas pressure 256

Hopkinson’s scaling law 259 impedance 250 nearby concrete, effect of 261–3

cracking 261–2 strength 264

setting time 252 shock waves 246, 250, 256, 262 spalling 253 steel reinforcement 246, 256, 269, 278 stemming 251, 257 techniques 246,253–60

charge parameters 256–7 concrete parameters 254–6 drilled-in charges 252–60 geometrical parameters 258–60

velocity of detonation 256 vibrations 247, 248, 264

Bleeding 91 Boegh, E. 63, 67 Boesman, B. 11 Bond strength, reinforced concrete 70 Brandt, J. 164 Bricks, see Masonry rubble;

Walling materials and individual forms e.g. Sand-lime bricks British Standard crushing value 37–8,121 Buck, A.D. 48, 52, 55, 76, 84, 97 Building rubble, see Masonry rubble Bulk density, see Density Burden 246, 259 Busch, J. 73

Carbonation

crushed masonry concrete 210, 211, 221 hardening due to 92 recycled concrete aggregate concrete 80123

Carpenter, S.H. 95 Case histories

Belgium 118 Czechoslovakia 118

Index 286

Germany 117 Japan 117 Netherlands 116 United Kingdom 119 US 112–6 USSR 117

Cat litter 94 Cellular concrete 145 Cement content

crushed masonry rubble concrete 178, 180 recycled concrete aggregate concrete 86

Cement hydration 177 Cement paste 31, 33 Cements

from crushed concrete fines 93 from masonry rubble powder 213–4

Charges (explosive) coupling ratio 257 deflagration 245, 249, 251, 252, 262 detonation 245–6,249, 250–1

velocitiy of 256 drilled-in 245, 246

constriction 260 effect of 250–3 hole size 260 methods 253–60 spacing 260

interaction between charges 257 lay-on 245, 246

effect of 253 methods 260–1

quantity 246 shock wave 246, 250, 256, 262 size of charge 253 small charges 246 spacing 246,260 strength of explosive 256

Charges (for disposal) 2, 111, 112 masonry rubble 217, 219

Charisius, K. 178, 214 Charisius, K. et al 192–3 Chemical admixture contaminants 45 Chemical oxygen requirement 224 Chloride contaminants

in crushed masonry rubble 174-6 in recycled concrete aggregates 174–45, 121 threshold chloride concentration 44 winter concreting 44–5

Index 287

Classification air classification 18 cyclone classifier 158 dry sieving 18 masonry rubble 157 wet classification 18

Clay lumps 8, 45,121 Codes, see Standards Coefficient of variation of compressive strength 58–60,122 Compaction 179 Compressed air separation 157 Compressive crushing test

crushed masonry rubble 169–70 fineness value 170

Compressive strength crushed concrete fines, products from 92–3 crushed masonry concrete brick strength 189–90

cement content 191 dense concrete 182–93 under sustained loading 201 particle size distribution and 192 porous structure 203 strength development 193 water/cement ratio 183, 184, 192

crushed masonry rubble 169–71,174 lean concretes 70, 71 rebound value and 70 recycled concrete aggregate concrete 3, 50–8, 121

bitumen contamination and 41–2 coarse and fine aggregates 55–6 coarse and natural sand 51–5 coefficient of variation of 58–60,122 dry mixing of aggregate and 57–8

ultrasonic pulse velocity and 70 Concrete blasting, see Blasting Concrete rubble

definition 160 see also Recycled concrete aggregates

Concrete, see individual forms e.g. Crushed concrete; Crushed masonry concrete; Lean concretes; Recycled concrete aggregate concrete; Waste concrete

Cone crusher 15 Contaminants

crushed masonry rubble 221 asphalt 175 chlorides 175

Index 288

glass 175 gypsum 157, 158, 173–4 metals 175 organic material 173 removal by washing 172–3 sulphur compounds 173–4

elimination of Aquamator 158 dry process 157–8 thermal process 158 wet process 158

recycled concrete aggregates 4 , 40 - 49 , 121 alkali-reactive particles 48–9 bitumen 41–2,122 brick rubble 46-3 chemical admixtures 45 chlorides 45-45, 139 clay 45–6,122 control methods 4 dangerous 21, 224 filler materials 45 fire-damaged particles 47 general 40 glass 40, 46, 122 gypsum 42, 122 high alumina cement 49 industrial chemicals 49 Japanese proposed standard 40, 44 lightweight concrete 45–6 metals 46, 122 mineral admixtures 45 organic substances 43122 particles susceptible to frost damage 47–8 radioactive substances 49 soil 45,122 sulphate impurities 4 weather damaged particles 47

Conventional concrete, meaning 5 Copple, F. 19, 112 Coquillat, G. 59, 63, 66, 68, 76 Coupling rate 256–7 Cracking

blasting, in 246, 251, 261–2 D-cracking 79,114

Creep crushed masonry concrete 198, 199, 221 recycled concrete aggregate concrete 64–5,123

Crushed concrete 5 economics of use 72–3

Crushed concrete fines

Index 289

alternative cements produced from 93 compressive strength of products made from 92–3 setting and hardening of fines 92–3 uses 91–5,125

acid soil neutralizer 94 cat litter 94 fertilizer 94 filters 95 oil spill removal 94 poultry grits 95 road construction 95–4,125 soil stabilization 125–94 source of silica 95 stabilization of sewage sludge 95 in US 113

Crushed masonry concrete applications

concrete block production 213 –8 crushed brick products 211–3 problems in 214

carbonation 211, 222 deformation properties 232 dense concrete

properties 230 workability 179 see also Fresh and Hardened

durability 207–11 fire resistance 211 fresh

binder content 178 bulk density 180 cement content 178, 180 compaction 179 composition dense concrete 179–80 porous concrete 180 free or effective water/cement ratio 177–8 void content 181 water requirement 176–7 workability dense concrete 178–9 porous concrete 179

frost resistance 207–10,222 hardened

containing crushed masonry sand 205–7 dense concrete appearance of surface 200 bulk density 182, 185–9 cement content 191

Index 290

compressive strength 182–93 under sustained loading 201 creep 198, 200, 236 flexural strength 193, 194 modulus of elasticity 196–8,221 particle size distribution 192 shrinkage 200,221 tensile splitting strength 193, 196 tensile strength 193–6 water absorption 183 water/cement ratio 183, 184 watertightness 201 porous structure abrasion resistance 204–5 compressive strength 203 density 202 porosity 202 shrinkage 203–4 thermal conductivity 205

mix composition 231 porous structure

properties 233 workability 179 see also Fresh and Hardened

shrinkage 200,203-20, 213, 221 standards

Germany 215 Netherlands 216

steel reinforcement protection 211 thermal conductivity 212 water absorption 183, 209 water content 209

Crushed masonry rubble brick strength 189–90 composition 229 concrete using, see Crushed masonry concrete contaminants 221

asphalt 175 chlorides 175 glass 175 gypsum 173–4 metals 175 organic material 173 removal by washing 172–3

sulphur compounds 173–4 definitions 160 deleterious organisms 176 fines 162–3 grading 161–2,179–80

Index 291

loss on ignition 175 natural sand 163–4 nature of, compressive strength of concrete and 190–1 pre-soaking 166, 177, 178, 221 properties 230

compressive strength 169–72,174 density 164–5,167, 221 frost resistance 168–9 sand-lime bricks 164 water absorption 165–6,167, 168, 221

quality control 176 sand fraction 162 standards

Germany 215,237–8 Netherlands 216, 239–40

Crushers 15–7, 120 cone crusher 15 “crusher characteristics” 23–5 diesel hammers 7, 8, 9 efficiencies 16, 17 grading products 229–25, 28–30 grain-size 23, 120 hammer crushers 9, 155, 157 impact crushers 9, 15, 17, 120, 157 jaw crushers 8, 10, 15, 17, 120 reinforcements in 9 secondary crushing 8 swing hammers 15

Crushing value, BS 37–8,121 Culuknoise, G.A. 119 C.U.R. 58, 64, 66, 70 Cyclone classifier 158 Czechoslovakian recycling projects 117 D-cracking 79,114 Damping capacity 64 Deflagration 245, 249, 251, 252, 262-80 Demolished concrete 7 Demolition

concrete blasting, see Blasting machines 8–9 noise 9 original concrete 7–10 sorting during 17–8 total selective demolition 111 vibrations 9

Denmark, standards for recycled concrete aggregate 105 Density

crushed masonry concrete

Index 292

fresh 179 hardened dense concrete 182, 184–9 porous structure 201

crushed masonry rubble 164–5,167, 221 recycled concrete aggregate concrete 86-87, 88 recycled concrete aggregates 33-35, 120–1

Density separation 46 Detonation 245–6,249, 250–1

velocity of 256 Dierkes, J.H. 7, 19 Diesel hammers 7, 8, 9 Disposal, masonry rubble 217, 219 Disposal charges 2, 111, 112, 217, 220 Dohmann, M. 224 Drees, G. 11, 19, 107, 111–2 Dry mixing 58,90 Dry sieving 18 Dry sifting 18 Drying shrinkage

crushed masonry concrete 200 lean concretes 71 recycled concrete aggregate concrete 65-9, 123

Dumping 2 charges 2, 111, 112, 218, 220 fresh waste, of 119

Durability 4 crushed masonry concrete 207–11 lean concretes 70 permeability and 74-7, 124 recycled concrete aggregate concrete 73–82, 123–4 steel reinforcements 80 water absorption and 74–5,123 see also individual aspects e.g. Frost resistance

Dust 18, 19 blasting and 246, 266–9,276 dry separation and 18, 157–8

Economic aspects

concrete recycling 107–12,125 crushed concrete use 72–3 France 109, 110 Germany 111–2 masonry rubble 215–7

disposal charges 217, 220 economic appraisal 217–9

Netherlands 108, 109 siting of plant 107-4, 217

Economies of scale 107

Index 293

Elasticity modulus, see Modulus of elasticity Electromagnets 8, 10, 12, 18 Energy aspects of recycling 112 Environmental considerations

blasting effects 246 concrete recycling 18–224,120 dangerous contaminants 21, 229 dust 18, 19, 158-9, 247, 267–8,276 ground water contamination 225, 50 mobile plant 18–9 noise 19, 20, 120 plant location sites 18, 19 vibrations 19, 21, 247

E.R.L. 37 Esser, A. 79, 84 Explosive fractionation 10 Explosive fragmentation 281–2 Explosives, see Blasting; Charges (explosive)

Fatigue strength 69 Federal Republic of Germany, see Germany Fergus, J.S. 23, 31, 39, 41, 50-7 Fill 50 Filters 95 Fineness value 170 Fines

crushed masonry rubble 162–3 see also Crushed concrete fines

Fire resistance 211 Fire-damaged particular contaminants 47 Flexural strength 3

crushed masonry concrete 193,212 recycled concrete aggregate 68, 69 reinforced concrete 70

Flyrock 247, 266 Forest rejuvenation 95 Forster, S.W. 95 Fragmentation of reinforced concrete

drilled-in charges 281 lay-on charges 282

France, recycling in 108, 110 Free water-content ratio law 85 Freeze-thaw resistance, see Frost resistance Fresh concrete

waste recycling 119, 125 see also Crushed masonry concrete, Fresh;

Recycled concrete aggregate concrete, fresh Friesenborg, B. 119

Index 294

Frondistou-Yannas, S. 52, 61, 84, 107, 110 Frost resistance

contamination by particles susceptible to 47–8 crushed masonry concrete 207–10,221 crushed masonry rubble 168–9 lean concretes 71 recycled concrete aggregate concrete 75–9, 123

Fujii, T. 66 Fuller curves 23, 120 Fungi, in crushed masonry rubble 175

Gaede, K. 174 Gases, blasting and 246, 256, 269 Genenger, R. 119 Gerardu, J.J.A. 30, 42, 52, 56, 61, 65, 68, 69 Germany

economic aspects of recycling in 110–2 recycling projects 116–7 standards crushed masonry concrete 214–5,237–8 masonry rubble aggregates 214–5 recycled concrete aggregate 215

Glass in crushed masonry rubble 175 in recycled concrete aggregate 40, 45, 121

Goeb, E. 38 Goerle, D. 73 Grading

crushed masonry rubble 161-3, 179–80 crusher products 229-25, 27–30

Graf, O. 33a 174 Grain-size

Fuller curves 23, 120 ratio of fine to coarse aggregate 87, 124

Granström, S.A. 266 Grelk, B. 119 Ground water contamination 225, 50 Gypsum contaminants

in crushed masonry rubble 157, 158, 173–4 in recycled concrete aggregates 42, 121

Hafemeister, D. 10 Hammer crushers 9, 155, 157

diesel hammers 8, 9 Handling aggregate 26–7 Hansen, T.C. 31, 34, 36, 45, 53,

54, 55–6,59, 63, 67, 84, 86, 90, 92, 94 Harada, M. 17, 20

Index 295

Hasaba, S. 31, 34, 36, 38, 66, 76 Hedegaard, S. 31, 87 Hedegaard, S.E. 87, 45 Heimsoth, W. 18 Hendriks, C.F. 30, 42, 52, 56, 60, 61, 65, 68, 69, 76, 116 Henrichsen, A. 116, 66, 78, 83, 87, 92 Henrichsen, A. et al 63 Henryck, J. 251 High alumina cement contaminants 49 Hironaka, M.C. et a/ 8, 10, 69 Hisaka, M. 76 Hoffmeister, K. 158 Hopkinson's scaling law 259 Hummel, A. 169, 177, 204, 214 Hydraulic excavator 8

Ikeda, T. 52, 69 Impact breakers 9 Impact crusher 9, 15, 17, 120, 157 Impurities, see contaminants and individual materials Industrial chemical contaminants 49 Ishikawa, N. 85 Ito, I. 252 Ivanyi, G. 79, 84

Japan

proposed standards 40, 44, 98–100 recycling projects 117

Jaw crushers 8, 10, 15, 17, 120 Johansson, C.H. 251 Joynes, H. 14, 117

Kabayashi, S. 15, 78 Kaga, H. et al 39, 90 Kakizaki, M. 17, 20 Kakizaki, M. et a/ 51, 52, 61, 70, 85 Karaa, T. 31, 36, 55, 63, 67, 69, 76, 80, 84, 90 Kasai, Y. 39, 65, 74, 77, 84, 117, 119 Kasai, Y. et al 57–8 Kashino, N. 52, 78, 84, 90, 91 Kawai, T. 54, 85 Kawamura, M. 30, 31, 34, 52, 37, 65, 67, 68, 69, 71, 77, 85 Kawano, H. 15, 78-78 Khan, A. 54, 55, 56, 74-7, 80, 84 Kihlström, B. 255, 259 Kikuchi, M. 70, 84, 85 Kleiser, K. 78 Koizumi, H. 70, 84

Index 296

Kreijger, P.C. 84, 86 Krejcirik, M. 118 Krueger, O. 7

Lambotte, H. 84 Landscaping 50 Langefors, B. 255, 259 Lardi, R. 79,96 Lauritzen, E.K. 243-286 Lean concretes 70-5

air entraining ability 70 compressive strength 70, 71 drying shrinkage 71 durability 71 earth-moist consistency 71 field density tests 72 modified CBR-value 72 modulus of elasticity 71 –3 rolling compaction 71 use in US 113

“Lightweight aggregates” 165 Lightweight concrete

contaminants 45–6 manufacture and composition 146 see also Crushed

masonry concrete; Recycled concrete aggregate concrete

Lindsell, P. 95 Literature searches 3 Loo, Y.H. 61, 66, 70, 84, 85 Los Angeles abrasion loss 38,121

percentage 17 test 47, 72

McCarthy, G.J. 57, 76 MacCreery, W.J. 57, 76 Magnetic sorting, self-cleaning electromagnets 8, 9, 12, 18 Malhotra, V.M. 52, 55, 69, 76,

84 Malier, Y. 53, 56, 64 Marga, M. 64, 56,85 Masonry rubble 4

aggregates from, see Crushed masonry rubble brick rubble contamination in concrete 45–6 classifying 157 composition 146, 148–53

influence of composition 153

Index 297

concrete from, see Crushed masonry concrete contaminants 45–6

gypsum 157, 158 continuity of materials flow 217 crushing 155, 157 disposal of deleterious fines 217 economics of utilization 216–7 ground powder as binder 214

hydraulic effect 214 reactivity 215

impurities, see Contaminants materials, see Walling materials meaning 143 preparation

general 155 impurities elimination 157–8 mobile crushing machines 158–60 rentability 159–60 sorting 153, 155, 156

recycling 138–240 historical survey 142–3 prospects 143

screening 157 sorting 153, 155, 156

Mazars, J. 53, 56, 64 Metal contaminants

crushed masonry rubble 175 recycled concrete aggregates 45, 121

Mineral admixture contaminants 45 Mix composition

crushed masonry concrete 231 recycled concrete aggregate concrete 88–9,124

Mobile plants 18–9,158–60 Modulus of elasticity 4

crushed masonry concrete 196–8,221 lean concretes 70–1 recycled concrete aggregates 60-63, 122–3

Molin, C. 243–86 Morlion, D. 31, 45, 56, 85, 90, 118 Mortar

attached 31, 32, 121 density of 38 34 original, meaning of 6

Motoyasu, H. 17, 20 Mukai, T. 70, 84, 85 Mukai, T. et al 40, 86, 90 Mulheron, M. 50, 68, 70, 77, 81, 83, 95 Munro, R.R. 19

Index 298

Nagataki, S. 54, 84 Narud, H. 31, 34, 36, 53, 54, 59, 84, 87, 90, 92 Natural aggregate shortage 2, 107 Natural sand 163–4 Natural stone 146 Nelson, L.A. 48 Netherlands

economic aspects of recycling in 108, 109 recycling projects 116 standards

crushed masonry concrete 215 crushed masonry rubble 215, 239–40 recycled concrete aggregate 100–3

Ng, H.T.S. 107, 110 Nishibayashi, S. 64, 65, 66, 78, 83 Nix, H. 18 Nixon, P J. 3, 36, 51, 76 Noise 19, 120

demolition 9 see also Vibrations

O'Mahony, M. 77 Organic material contaminants

crushed masonry rubble 173 recycled concrete aggregate 42-9, 121

Original aggregates, meaning 6 Original concrete 5–6, 7–10

demolition 7–11 separation of different

qualities of 7 steel reinforcement removal 7–10, 120

Original mortar density of 38 34 meaning 6

Orlowski, F. 119

Particle density, see Density Particle shape 30 Particle size 4, 192 de Pauw, C. 59, 84 Pavement breakers 7, 8

diesel hammers 8, 9 impact breakers 9 leaf spring whiparm hammer breaker 8 resonant breakers 9 Wirtgen machines 8 wrecking balls 8

Index 299

Periclase 46 Permeability 74–5,124 Persson, Algot 265 Persson, P.A. 251 Peterson, C.A. 251 Phenols 224 Physical properties,

see individual properties e.g. Compressive strength; Modulus of elasticity

Pietrzeniuk, H J. 19 Polish resistance 69 Porosity 202 Porous structure, see Crushed masonry concrete Poultry grits 95 Pre-soaking

crushed masonry rubble 166, 177, 178, 221 recycled concrete aggregates 221-2, 84, 90

Production plants 10–5 air sifting 15 closed system 11 crushers, see Crushers first generation plants 12, 120 grading crusher products, see Crushers manual contamination removal 12 masonry rubble

mobile 160 rentability 159–60

mobile 19,160– open system 11 screening 19 second generation 12, 13, 120 siting

economic aspects 107,217– environmental aspects 19-2

third generation 12, 120 washing 15

Puckman, K. 15, 66, 78, 83, 87, 92

Quality control 176

Radioactive contaminants 49 Rasheeduzzafar, 54, 55, 56, 74–5,80, 84 Ravindrarajah, R.S. 35, 38, 52, 55, 56, 69, 84, 85 Ravindrarajah, S.H. 61, 63, 64, 66 Ray, G.K. 114 Rebound value 70 Recycled concrete aggregate concrete

alkali-aggregate reactions 70–82,123

Index 300

bleeding of 91 durability, see Durability fresh

cement content 86 density 87, 88 free water-content ratio law 85 mix design 88–9,124 ratio of fine to coarse aggregate 87, 124 water requirement 84,124

meaning 6 production of 90–1 properties, see individual properties e.g. Compressive strength, Modulus of elasticity reinforcements in 70 repeated recycling and quality 50 sulfate resistance 83

Recycled concrete aggregate products 95–7 suitability of aggregates for 97

Recycled concrete aggregates dry mixing 58,90 fill, as 50 fine, see Crushed

concrete fines grading crusher products 229-25, 27–30 lean concretes from, see Lean concretes meaning 6 particle shape 30 pre-soaking 30–7,84, 90 production plant, see Production plants properties, see individual properties e.g. Compress- ive strength;

Density; Modulus of elasticity

road construction requirements 50 sorting, see Sorting storage and handling 26–7 surface texture 30 uses other than new concrete 50

Recycling economic aspects, see Economic aspects energy aspects 112 environmental problems, see Environmental considerations fresh concrete wastes 119, 125 reasons for 2-3 repeated, quality and 50

Reduction factor R 24 Reinforced recycled concrete aggregate concrete 70 Reinforcements, see Steel reinforcement Reinhardt, H.W. 248 Repeated recycling, quality and 50

Index 301

Resistance to polishing 69 Resonant Pavement Breaker 8 “rhino-horn” 8 Ridout, G. 10 Riker, R. 119 Rinehart, J.S. 1959a 262 Road construction

crushed concrete fines useage 262–94,125 lean concretes, see Lean concretes material requirements 50

Rottler, G. 76 Rubble, see Masonry rubble

Sakamoto, A. 52, 68 Samarai, M.A. 43 Sand

crushed masonry sand 205–7 natural 163–4

Sand Equivalent Values 38 Sand fraction, crushed masonry rubble 162 Sand-lime bricks

bulk density of concrete from 179 manufacture and composition 146 properties of rubble from 164

Sassa, K. 252 Sassa, K. et al 256 Sayes, L. 73 Scaling, Hopkinson's scaling law 259 Schroeder, C.J. 17 Schulz, R. 62, 64, 66 Schulz, R.R. 15, 31, 36, 52, 64, 117 Schwartz, D.R. 79 Scott, F. 95 Screening

masonry rubble 157 see also Sorting

Selective stockpiling 18 Self-cleaning electromagnets 8, 9, 12,20 Shah, S.P. 248 Shear strength

recycled concrete aggregate 69 reinforced concrete 70

Shock waves 246, 250, 256, 262 Shotcrete, rebound from 119 Shrinkage

crushed masonry concrete 213 dense concrete 199–200,221 porous structure 203–4

Index 302

drying, see Drying shrinkage Sintering 159 Soil contaminants 8, 45,122 Soil stabilization 122–94 Sorting 17–8

air classification 18 Aquamator 19, 158 compressed air separation 157 density separation 46 dry process 157–8 dry sieving 18 dry sifting 18 dust control during 158 magnetic 8, 9, 12, 18 manual pre-sorting 12, 153 masonry rubble 153, 155, 156 thermal process 158 wet classification 18 wet process 158

Soshiroda, T. 56 Spalling 253 Specific gravity 17 Standards 125

crushed masonry concrete Germany 215 Netherlands 216

crushed masonry rubble Germany 215,237–8 Netherlands 216, 239–40

recycled concrete aggregate Denmark 105 Germany 105 Japan 98–100 Netherlands 101–3 United Kingdom 104 United States 97 USSR 97

State-of-the-art report 1945–1977 3–5 literature reviewed in 136

State-of-the-art reports 1978–1989 5 Steel reinforcement

blasting and 246, 256, 269, 277, 278 in crushed masonry concrete 210, 211 in crushed masonry rubble 174–5 in recycled concrete aggregate concrete 70, 80 removal 7-11, 120

explosive fractionation 10 mesh 8

Index 303

Stemming 251, 257 Storage of recycled concrete aggregates 26–7 Strand, D.L 39, 76 Strength, see individual types e.g. Compressive strength Stress-strain relationship 63 Suaris, W. 248 Sulfate, see Sulphate Sulphate impurities 4, 173–4 Sulphate soundness 39, 47, 121

recycled concrete aggregate concrete 82 recycled concrete aggregates 17

Surface appearance 201 Surface texture 30 Svenson, A. 17 Swing hammers 15

Takahashi, Y. 52, 78, 84, 90, 91 Takemoto, K et al 76 Tam, C.T. 35, 38, 52, 55, 56, 61, 63, 64, 66, 69, 84, 85 Tanimoto, C. 252 Tensile splitting strength 193, 196 Tensile strength

crushed masonry concrete 193–6 recycled concrete aggregate 68

Terminology 5–6 Thermal conductivity 205, 212 Thermal expansion coefficients 70 Thum, W. 250 Torii, K. 52, 67, 68, 69, 71, 77, 85 Toriik, K. 30, 31, 34, 128, 37, 65, 76 Total selective demolition 111 Trevorrow, A. 16. 118

Ultrasonic pulse velocity 70 United Kingdom

recycling projects 117 standards 125

United States recycling projects 112–6 standards 97–8

USSR recycling projects 117 standards 117

Venstermans, J. 30, 45, 56, 85, 90, 117 Vibrations

blasting and 246, 248, 263-2 demolition 9

Index 304

Vyncke, J. 30, 45, 56, 85, 90, 117

Wainwright, P.J. 14, 117 Walling materials

manufacture and composition 143–6 blastfurnace slag bricks and blocks 145 cellular concrete 145 lightweight concrete 145 masonry bricks 143–5 natural stone 146 ordinary concrete 143 sand-lime bricks 145

properties 146, 147 types of unit 143

Walz, K. 204 Washing 15 Waste concrete, meaning 5 Waste, recycling of 119, 125 Watanabe, M. 54, 84 Water absorption 3

crushed masonry concrete 183, 208 crushed masonry rubble 165–6,167, 168, 221 recycled concrete aggregate concrete 73–5,123 recycled concrete aggregates 17, 26, 35–7,120–1

Water content crushed masonry concrete 208 free water-content ratio law 85

Water requirement fresh crushed masonry concrete 176–7 fresh recycled concrete aggregate concrete 84,124

Water/cement ratio crushed masonry concrete

fresh 177–9 hardened 183, 184, 192

recycled concrete aggregate concrete 77 Watertightness 201 Wedler, B. 204 Weichelt, F. 255, 256, 259 Wesche, K. 62, 64, 66 Wet classification 18 Winter concreting 44–5 Wirtgen machine 9 Workability

crushed masonry concrete 178–9 recycled concrete aggregate concrete 84,124

Wrecking balls 8

Yamane, S. 52, 68

Index 305

Yamato, T. et a/ 52, 78 Yamura, K. 64, 65, 66, 78, 83 Yanaga, K 76 Yanagi, K. et a/ 40 Yoda, K. et al 54, 93 Yoshikane, T. 38, 69, 72,92 Yrjanson, W.A. 48, 116

Zagurskij, V.A. 10, 62, 67, 117 Zhadanovskij, B.V. 10-10, 62, 67, 117 Zielinski, A.J. 249 Zinc contamination 46

Index 306

recycling of demolished b

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