concrete rehabilitation

8/6/2019 Concrete Rehabilitation

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Concrete Rehabilitation

Reinforced Concrete Structures: Condition Surveying, Rehabilitation and Establishment of Corrosion Protection Measures

Introduction:MATCO has extensive experience as corrosion consultants for reinforced concrete structures.When approaching the problem of a deteriorating reinforced concrete structure, it is necessary tovisually observe and make measurements of the corrosion activity, geometry, concrete and steelmaterials, associated construction materials, etc., in addition to the state of corrosion which thestructure has already suffered. After such observations and measurements, assessment of potential rehabilitation techniques and, as required, corrosion analysis, MATCO can recommendmeasures and materials to consider which will help to mitigate further corrosion deterioration of the structure for its expected life using cathodic protection and/or coatings. The methodologyemployed is described below.

On-Site Condition Evaluation Survey:The on-site condition evaluation survey includes a detailed investigation of all areas of thereinforced concrete structure and may require several hours to several days, depending upon thesize of the structure. Several analysis techniques are implemented during this on-site evaluationsurvey, including but not limited to the following.

Visual examination - to identify surface defects.

Petrography - to determine concrete condition.

Hammer/chain- to detect delaminations.

Phenolphthalein - to determine carbonation depth.

Chloride content - to identify chloride corrosion.


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Half cell potential mapping - to determine corrosion risk (map corrosion hot areas).

Linear polarization - to determine corrosion rate.

Continuity - to determine continuity/connectedness of rebar.

Stray current identification - to determine stray current corrosion risk.

Resistivity - to determine concrete resistivity and corrosion risk.

Concrete core samples are marked and retrieved for petrographic analysis. At least one will befrom an area of rusting of the rebar reinforcement or concrete. At least one will be from an

undamaged and un-corroded area of the concrete structure.Laboratory Petrographic and Corrosion Analysis:Laboratory analysis of petrographic and corrosion product samples are conducted byexperienced petrographic and corrosion specialists. Petrographic evaluation will determineaggregate type and size, depth of carbonation, air void content and mode of deterioration if present. These will determine integrity of concrete and the best means of rehabilitation andcorrosion protection.

Determination of Extent of Damage and Remaining Service Life:Based upon on-site surveying and laboratory analysis result, and employing sound materials andstructural engineering principles, determination of extent of damage and remaining service life are

undertaken. Critical questions to be answered here are the following. Is the reinforced concrete structurally sound?

Does the reinforced concrete require repair or replacement?

Materials Selection and Coatings Application:Consideration is given to materials selection for repair and/or replacement of the components of the reinforced concrete structure. In addition to concrete repair materials, this will includealternative materials to non-concrete auxiliary materials and maintenance coatings which may beapplied to mitigate corrosion.

Assessment of Repair and Cathodic Protection Systems:Assessment is undertaken of suitable repair systems, and of suitable cathodic protection systemsfor the reinforced concrete structure. Cathodic protection (CP) is a method wherein a sufficientamount of electric or impressed current (DC) is continuously supplied to a submerged or buriedmetallic structure to mitigate, slow down or stop altogether the natural corrosion processes fromoccurring. This technique is routinely used in service of submerged units or structures in brineand seawater environments.

The galvanic anode cathodic protection system generates DC as a result of the natural electricalpotential difference (electrochemical reaction) between the metal to be protected (cathode) and


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another metal to be sacrificed (anode). The sacrificing metals such as zinc (Zn) or aluminum (Al)all have a lower more negative electrical potential. The current output of this system is affected byfactors such as the driving voltage difference between the anode and the cathode, the resistivityof the electrolyte (concrete), pH, and salinity.

The Next Step... While MATCO has the expertise and the technology to unravel even the most difficultmaterial failures, your input is vital for a complete analysis. By filling out the service request form andgiving us a description of the problem, you can be sure that all aspects of your problem will be considered.Well send you a proposal for your work, including methods and costs. Solutions are just around thecorner!

MATCO Contacts for Main & Florida Offices:Toll-Free: 1-800-221-9090MATCO Main: (412) 788-1263MATCO Florida: (954) 563-6440Emergency Contact: (412) 952-9441

email: [email protected]

Main Office Address:MATCO Services, Inc.4640 Campbells Run Road

Pittsburgh, PA 15205

An Overview of Some Development in CONCRETE TECHNOLOGY

Dr. S.S. Rehsi , Consultant (Building Materials' Former United Nations Expert on Building Materials, Chandigarh

IntroductionThere has been rapid advances in concrete technology during the past three decades or so. The improvement in strength and otherstructural properties achieved earlier through the use of steel reinforcement are now accepted as routine and the reinforced cement

concrete and prestressed concrete have become conventional materials. Later work led to the development of a variety of concretes in the form of, among others, fibre reinforced concrete, polymer concrete, Ferrocement, sulphur concrete, lightweightaggregate concrete, autoclaved cellular concrete, high-density concrete, ready-mixed concrete, self-compacting concrete,rollercompacted concrete, high strength concrete, super high-strength concrete, high performance concrete, high-volume fly ashconcrete, self-curing concrete, floating concrete and smart concrete (1-27). Some of these concretes are briefly discussed here.

Fibre Reinforced Concrete
mailto:[email protected]:[email protected]


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Different types of mineral, organic and metallic fibres have been used. Among the mineral fibres, use of asbestos in the productionof asbestos cement products is well known. Since, water absorption of the asbestos fibre is high, its use in concrete increases waterrequirement. Consequently, there is reduction in strength of the concrete. Organic fibres such as, coir, jute, rayon and polyester areattacked by the highly alkaline condition in concrete. As a result, concrete containing these fibres loses strength with time. Otherorganic fibres namely, nylon, polypropylene and polyethylene are alkali-resistant. But, due to their lower modulus of elasticity, theincorporation of these fibres do not increase strength. Concrete containing nylon or polypropylene fibres, however is reported to

develop higher impact resistance. Virgin Poly-Propylene fibers of structural grades, such as Forta Ferro Fibres, having high strengthand moduls of elasticity are now available from FORTA Corpn USA. These are being extensively used all over world forPavement/highways/Runway construction, Fibreshotcreting of tunnels, Repair and Rehab jobs and Bridge deck construction inclIndia. Among all fibres the use of steel fibre in concrete has received far greater attention, in the past but because of the corrosionproblem structural grade poly propylene and other synth fibers are taking over now.

The compressive strength, tensile strength, fatique strength, modulus of elasticity, abrasion resistance, skid resistance and thermalconductivity of steel fibre reinforced concrete has been found to be slightly higher than the corresponding plain concrete. Whilecreep and shrinkage are more or less unaffected, there is over 100 percent increase in the flexural strength and impact toughnessof plain concrete when reinforced with steel fibre, 2 percent by volume. At the same fibre content, use of a blend of fibres havingdifferent aspect ratio, in place of single aspect ratio fibre, gives greater structural benefits. It has also been found more beneficialas well as economical to use steel fibres only in the tensile zone of the flexural member. Unlike plain concrete, steel, fibrereinforced concrete is not brittle and offers far greater resistance to cracking. The fibres act as crack arrestors and restrict the

growth of flaws in concrete from enlarging under stress into visible cracks. The ultimate failure is reached only when some of thefibres get pulled out of the matrix. As compared to plain concrete, the resistance of steel fibre reinforced concrete to thermal shockand heat spalling is also far superior.

The major applications of steel fibre reinforced concrete are in pavements (both for new construction and overlays), precastconcrete units, concrete reactor pressure vessels, blast resistant structures, machine foundations, tunnel linings and structuresrequiring resistance to thermal shocks, such as refractory linings.

Polymer ConcreteDepending upon the method of monomer incorporation into the concrete, the polymer concrete is termed as

i. polymer impregnated concrete, when dried precast concrete is impregnated with monomer and polymerized in-situ,

ii. polymer cement concrete, when cement, aggregate, water and monomer are mixed together and polymerized afterlaying and,

iii. polymer concrete, when aggregate and monomer are mixed together and polymerized after laying.

A number of factors such as distance to be penetrated, degree of drying, total porosity and pore size in concrete, monomerviscosity, whether or not vacuum and/or pressure is applied, influence the extent of monomer filling in polymer impregnatedconcrete. The widely used monomers are methly methacrylate, styrene, acrylonitrile and chlorostyrene. The monomerpolymerization is done either by thermal catalytic process or by radiation.

As compared to plain concrete, the strength and other properties of polymer concrete are considerably higher. At 6 per cent


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polymer loading, the mechanical properties of polymer impregnated concrete vis--vis corresponding plain concrete were found tobe as follows:

Compressive strength, 2 to 4 times higher

Tensile strength, about 4 times higher

Modulus or Elasticity, About 4 times higher

Creep and Permeability, Almost Nil

With almost nil permeability, the polymer impregnated concrete has much greater resistance to the attack of acidic and/or sulphatecontaining waters

Economics permitting, applications of polymer concrete having good scope are: concrete pipe manufacture, concrete piles, concretetiles, tunnel supports and linings, precast concrete decks, precast concrete building units for use in aggressive conditions, desaltingstructures, lightweight concrete constructions and providing surface protection to cast in-Situ concrete.

Ferrocement

Ferrocement is a kind of reinforced concrete in which the matrix is cement mortar, microconcrete and the reinforcement is in theform of layers of wire mesh or similar small diameter steel mesh closely bound together to produce a stiff structural form. The mixproportions of the cement mortar usually are: cement 1 part, sand 1.5 to 2.5 parts and water 0.35 to 0.5 part, by weight.Admixtures are added in the mix for improving to properties. The maximum size of sand grains depends upon the mesh openingand reinforcing system to ensure proper penetration. Different types of wire mesh such as, hexagonal wire mesh (commonly knownas chicken wire mesh), welded wire mesh, woven mesh, expanded metal mesh, are used. Use of Hexagonal Mesh is not preferreddue to its poor resistance to loads. The mechanical behavior of Ferrocement is greatly influenced by the type, quantity, orientationand strength properties of the mesh. The thickness of ferrocement elements range from 2 to 3 cm with 2 to 3 mm external cover.When additional strength is required, one or more layers of steel bars are inserted between the inner layers of the mesh. Use of short random fibres in Ferrocement elements at the same steel content has been found to greatly increase the modulus of elasticityand strength. Polymer impregnation of the Ferrocement elements, with and without short random fibres is reported to considerablyimprove upon these properties.

Ferrocement has a variety of applications. The important among these are: construction of fishing and cargo boats, grain storagebins, water storage tanks, biogas holders and digesters, fermentation tanks, precast roofing and walling units, cooling towers,sewage troughs, septic tanks, irrigation channels, drying pans for agricultural products, shutters and formwork for use in concreteconstructions, lining for tunnels and mines, and providing waterproofing treatment over RCC or RB roofs, lining of surface of tanks


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or swimming pools. Ferrocement has been successfully used in india by SERC (G)'s Material Science Group for construction of domes, large tanks, manhole covers, Drainage units and for repair and rehab of structures. the new techniques and applicationsdeveloped by this group are being used on large scale on commercial basis.

High Strength ConcreteIS: 456-2000 designates concrete having 28-day compressive strength of 60 to 80 N/mm2 corresponding to grades M60 to M80 ashigh strength concrete (HSC).

The production of HSC requires stringent control on the quality of materials used. The Portland cement should, preferrably, be of 53grade conforming to IS: 12269- 1987. Crushed stone coarse aggregates produced from trap, quartzite or granite give higherstrength and are more suitable than rounded gravel for use in making HSC, particularly when the desired concrete strength is 70 N/mm2 or more. Studies on the effect of the size of coarse aggregate on the strength of concrete showed that smaller size producedhigher strength. A maximum coarse aggregate size of 10 mm is considered suitable for use in HSC. The use of mineral admixturessuch as fly ash, silica fume, metakaoline in combination with suparplasticizers in HSC matrix greatly enhances impermeability,durability and strength.

The use of HSC in construction offers the advantages of

i. reduction in the size of concrete members with resultant reduction in self-weight,

i i. greater s ti ffness,

iii. early stripping of formwork and

iv. lowering of construction cost due to reduction in the concrete member size and self-weight.

It has, therefore, been widely used in the construction of highrise buildings and bridges in many countries including India. A superhigh-strength concrete, called reactive powder concrete (RPC) is produced by eliminating the use of coarse aggregate. The concretematrix consists of cement, finely ground sand with particle size close to that of cement, silica fume and short steel fibres. Thewater/cement ratio is kept very low, around 0.15. The desired workability is obtained by using higher amounts of super plasticizers.The RPC does not require reinforcement bars. It is suitable for use in building very thin structures meeting different architecturalneeds.

High Performance ConcreteHigh performance concrete is defined as concrete that meets special Performance and durability requirements in terms of mechanical properties, volume stability and longer life in severe environmental conditions to which the concrete is exposed duringits service life. High performance of concrete is generally linked to strength of the concrete; higher the strength, better theperformance. Therefore, in the first place high performance concrete has to be a high strength concrete. Besides high strength, lowpermeability of concrete is an essential requirement to prevent ingress of corrosive waters containing chlorides, sulphates and /orother deleterious salts. Low permeability is achieved by using higher cement content, mineral admixtures such as fly ash, Silicafumes, metakaoline or granulated blast furnace slag, and keeping water/cement ratio low at 0.35 or less. Higher amounts of superplasticizers are used to obtain the desired workability in the concrete matrix. Workmanship has to be excellent to ensure fullcompaction and proper concrete cover over embedded steel reinforcement. All these and subsequent adequate curing of concreteafter laying and regular maintenance of concrete construction ensure high performance.

High-volume Flyash Concrete


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High-volume fly ash concrete technology was developed at the Canada Centre for Mineral and Energy Technology (CANMET),Ottawa, Canada in 1980s. It enables minimizing the amount of cement required to produce high quality concrete for different typesof applications by incorporating upto 50 to 60 percent fly ash in the concrete mix. The concrete is prepared using a lowwater/cement ratio of 0.30, and the desired workability is obtained by using super plasticizers. While highvolume fly ash concretewas initially developed for mass concrete construction where low heat of hydration and just enough early strength were required,later work showed that this concrete developed excellent long-term structural properties, namely compressive strength, flexuralstrength, splitting tensile strength, and Youngs modulus of elasticity. Its durability measured in terms of its low water permeability,resistance to carbonation, alkaliaggregate reactions and penetration of chlorides and sulphates, was also found to be excellent. Inview of this, highvolume fly ash concrete is eminently suitable for structural applications, in addition to its use for building of roadsand pavements. It is being used for such constructions in Canada, U.S.A. and other countries. In India, Ambuja Cements Ltd, hasmade a beginning by building two fly ash concrete roads, one at Ropar (Punjab) and another at Ambujanagar (Gujarat) in 2002,using 50 per cent fly ash in the concrete mix. Both these roads are reported to be performing very well.

Self-compacting ConcreteA concrete that gets compacted by itself totally covering reinforcement in the formwork is called self-compacting concrete (SCC). Itis highly flowable, selflevelling, self-defoaming and coahesive and can be handled without segregation. Like any other superplasticized concrete, the ingredients in SCC mix consists of cement, coarse and fine aggregates, mineral and chemical admixtures.A limiting value of coarse aggregate as 50 per cent of the solid volume of the concrete, and of fine aggregate as 40 per cent of thesolid volume of the mortar fraction in the SCC mix proportion is suggested for achieving good self-compact ability. Commonly usedmineral admixtures are fly ash, silica fume, ground blast furnace slag Chemical admixtures consists of a super plasticizer and aviscosity modifying admixture. The use of one or more mineral admixtures having different morphology and particle-sizedistribution improves deformability, self-compact ability and stability of the SCC. While the super plasticizer helps achieving highdegree of flow ability at low water/ Cementing material ratio, the viscosity modifying admixture increases viscosity of the freshconcrete matrix and reduces bleeding.

The SCC has the advantages of easy placement in thin - walled elements densely reinforced concrete structure, quality, durabilityand reliability of concrete structures, faster construction and reduced construction cost.

Self-curing Concrete

Curing of concrete by which the concrete, after laying, is kept moist for some days, is essential for the development of properstrength and durability. IS 456-2000 recommends a curing period of 7 days for ordinary Portland cement concrete, and 10 to 14days for concrete prepared using mineral admixtures or blended cements. But, being the last act in the concreting operations, it isoften neglected or not fully done. Consequently, the quality of hardened concrete suffers, more so, if the freshly laid concrete gets


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exposed to the environmental conditions of low humidity, high Wind velocity and high ambient temperature.

To avoid the adverse effects of neglected or insufficient curing, which is considered a universal phenomenon, concrete technologistand research scientists in various countries including India, are working on the development of self-curing concrete. Different linesof action are being pursued. These include

i. use of water-soaked, surface dry lightweight aggregates which release water when the concrete starts getting dry and

losing water,

ii. develop high early strength concrete, which attains a strength of 20N/mm2 in 30 minutes and so may not require furthercuring, and

iii. develop a system by which some enteric coated particles or capsules containing membrane-forming curing compound(or a substance that reacts with water to do so) is distributed over the surface of the concrete slab in the final stages of finishing. The particles will open if the surface becomes dry and a membrane will form while the concrete is still water-saturated upto its top but has no free water on the surface.

Smart ConcreteSmart concrete is a concrete that can take care of its own shortcomings or that can act as a senser to help detecting internal flawsin it. It is produced by incorporating some changes in the ingredients of the concrete mix. For instance,

i. due to its high density, the high strength concrete does not permit water vapours to go out during fire, leading to spallingoff concrete cover and damage to concrete members. Addition of 2kg polypropylene fibres per m3 of high strengthconcrete mix increases fire resistance. At high temperature during fire, these fibres melt and leave pores for watervapours to escape from the concrete surface, thus preventing spalling and damage,

ii. incorporation of 0.5 per cent specially treated carbon fibre in the concrete mix increases the electrical conductivity of theconcrete. Under load, the conductivity decreases but returns to original on removal of the load. The concrete could thusact as a senser to

a. measure the number, speed and weight of the vehicles moving on concrete highways, and

b. detect tiny flaws regarding internal condition of concrete construction after an earthquake, and

iii. Use of porous carbon aggregate, available in the form of coke at the steel plant, in the concrete mix imparts goodelectrical conductivity which can help in room heating, melting of ice on concrete highway and runways by passing lowvoltage current.

ConclusionAs other areas of research and development (R&D) in concrete technology has been a continuing process, Different types of concretes, as described above, have been developed from time to time, to meet the needs of the construction industry.Technologies for self-curing and smart concrete are still in the development stage, but are expected to be fully developed soon andavailable for use in constructions.

References

Stateoftheart Report on Fibre Reinforced Concrete, ACI Committee 544, ACI journal, November 1973, pp-729-743

Neville, Adam, End, Proceeding: RILEM Symposium on Fibre Reinforced Cement Ltd. Lancaster(U.K.)


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Parameswaran, V.S., and Krishnamoorthy, T.S., Eds., Proceedings Fibre Reinforced Concrete, Madras, December 16- 19-

1987, Vol.11, Oxford TBH Publishing Co. Pvt. Ltd., New Delhi(India)

Shah, S.P., Ed., Proceedings: Conference on new Materials in Concrete construction, University of iiiinoisat Chicago Circle,

Chicage, Iiiinois (U.S.A.), 15-17 December 1972

Proceedings International Symposium on Fibre Reinforced Concrete, ACI Special Publication, SP-44,American concrete

Institute, Detroit (U.S.A.). 1974. Swamy, R.N. Concrete Technology & Design, Vol 1 :New Concrete Materials, Vol.2: New Reinforced Concretes, Vol. 3:

Cement Replacement Materials, Vol.4: Ferro cement Current and potential Applications, Blackie and Sons Ltd.(Publishers). London (U.K.), 1988

Expansive Cement Concrete, ACI Special Publication, SP- 38,American Concrete Institute, Detroit, 1973

Ferrocement: Materials & Applications, ACI Special Publication, SP-61, American Concrete Institute, Detroit (U.S.A.),1979

Sharma, P.C., Ferro cement Segmental Shell Multipurpose Unit, Proceedings: Asia-Pacific Symposium on Ferrocement

Applications for Rural Development, University of Roorkee, Roorkee (India), 23-25 April, 1984,PP. 113- 124

Sharma,P.C., A Mechanized Process for producing Ferro cement Roof and wall elements Journal of Ferro cement, January

1983, PP.13-18

P.C. Sharma & V S Gopalaratnam - 'Ferrocement Water Tank' - Published by International Ferrocement Information

Center bangkok (Thailand)

P.C. sharma, K. Shashi Kumar & P. nimityongskul 'ferrocement roofing Elements' published by International ferrocement

information Center Bangkok (Thailand)

P.C. sharma- 'ferrocement Lining for Waterproofing, Rehabilation and Retrofilling of RCC and masonary Structures' key

note addressInternational workshop on 'Repair Rehabilitation and Retrofitting of concrete and masonary structures Oct2004, Gedu Bhutan.

Malhotra, V.M., Super plasticizers: Their effect on Fresh and Hardened Concrete, Concrete International, May 98 1,

pp.66-81

State-of-the-art Report on High Strength Concrete, ACI Committee 363, ACI Journal, July-August, 1984, pp. 364-411

Kishore, Kaushal, High Strength Concrete, ICI Bulletin No. 51, April-June, 1995,pp.29-31

Sen,B., High performance Concrete: Development and Prospects, ICI Bulletin No. 55,April- June,1996,pp.14-19

Basu, Prabir C., High Performance Concrete: Mechanism and Application, ICI Journal, April- June,2001,pp.15-26

Malhotra, V.M., and Mehta, P.K., High-Performance, High-Volume Fly Ash Concrete, Supplementary Cementing Materials

for Sustainable Development Inc., Ottawa, Canada, Marquardt Printing Ltd. Ottawa, Canada, August, 2002

High-Volume Flyash Concrete, Green Business Opportunities, Confederation of India Industry, Quarterly, Oct.-Dec.,2003

Handbook on High-Volume Flyash Concrete, CII (India) and CIDA (Canada) Publication.

Apte, M.D., Innovative Concretes and Fibres, ICI Journal, July-September, 2003, pp.9-10

Surlaker, Samir, Self-Compacting Concrete, ICI Journal, January-March, 2002, pp.5-9

Kumar, Rakesh and Rao, M.V.B., Self-Compacting Concrete: An Emerging Technology in Construction Industry, ICI

Journal, July-September, 2002,pp.9-12

Srinivasan, D.,Will there be A Self-Curing Concrete? Concrete International, September 2000

Bryant, Mather, Self-Curing Concrete-why Not? Concrete International, January, 2001, Reproduced in ICI Journal,April-

June,2003,pp.7-8


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Subramanian, N. Curing-The Last and The least Considered Aspect in Concrete Making, ICI Journal, April-June,2002,pp.13-25

Srinivasan, D., Research Needs in Concrete, ICI Journal, July-September, 2006, pp.5-6

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Assessment During Static And Dynamic Loading, ACI Materials Journal, April, 1996, pp.341-350

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