a state of the art review of high performance concrete structures built in canada

A State-of-the-Art Review of High Performance Concrete Structures

Built in Canada: 1990-2000

John A. Bickley Denis Mitchell

ii

John A. Bickley, P.Eng. is a Consulting Engineer in Concrete Technology and a Principal Investigator with Concrete Canada. Denis Mitchell is a Professor of Civil Engineering at McGill University and is Scientific Director and a Principal Investigator with Concrete Canada. This publication is intended for the use of professional personnel competent to evaluate the significance and limitations of its content and who will accept responsibility for the application of the material it contains. The Cement Association of Canada and the authors disclaim any and all responsibility for application of the stated principles or for the accuracy of the sources. May 2001

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State-of-the-Art Review of the Durability, Economics and Constructability of High Performance Concrete Structures Built in Canada: 1990-2000. Executive Summary In the search for durability, researchers in Canada and in other countries sought for higher performance materials. Technology from other countries, notably France, Norway, Japan and Germany, was incorporated into developments in Canada in the 1980s. High Performance Concrete (HPC) was included in this research. With the establishment of Concrete Canada (CC) in 1990, a co-ordinated and concentrated programme of research commenced. In 1994, this programme expanded to include demonstration projects to implement HPC technology on construction sites. Technology Transfer was a primary goal of CC. Many seminars, workshops and technology transfer days were held across Canada, by CC alone, in co-operation with American Concrete Institute (ACI) Chapters, the Cement Association of Canada (CAC) and its member companies, and for specific entities such as Provincial Highway Departments and Cities. Between 1990 and 2000, CC researchers published over 400 Papers in scientific journals. It seemed appropriate, as the old millennium ended, to assess the practice in the use of HPC in Canada over the past 10 years. The extent of its use, the varying specifications, results, economics and problems encountered have been reviewed. Looking ahead, areas for ongoing research and development have been identified. The study demonstrates that, for those who have correctly implemented this technology, HPC is the high quality concrete of choice for high strength, durability and optimum life-cycle costs.

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Preface In 1990, as a Principal Investigator in the newly established and funded Network of Centres of Excellence on High Performance Concrete, one of my main activities was to lecture on this research programme and its objectives. At the time, the term High Performance Concrete was virtually unknown. Now, ten years later, I am no longer asked, "What is HPC?" A perception that the use of HPC is now widespread led to the decision to produce this review. It seemed timely, after a decade of the intensive development, promotion and implementation of HPC, to step back and survey the extent of the use of this material across Canada, the achievements, the problems encountered, and to suggest directions for future practice. The task turned out to be greater than I had envisaged. Despite my close involvement with the implementation of this technology, I was surprised to find the extent and variety of uses for this quality of concrete. As the pieces of the puzzle fell into place, a comprehensive picture formed. There are some inconsistencies in my classification of projects. For instance, the Confederation Bridge is detailed in Chapter 4 on Precast Concrete Products. This structure must be considered to be one of the most outstanding precast concrete projects in the world. It seemed more appropriate to place it in Chapter 4 than in Chapter 3. Similarly, some projects have incorporated more than one technology, i.e. Conventional HPC and HPC using a Ternary cement. In such cases, the project is reported in the chapter covering the more innovative technology. With the help of Rico Fung of the Cement Association of Canada and Kevin Cail of Lafarge Canada Inc., both of whom helped co-ordinate input from the cement companies and monitored the progress of this report, a nation-wide net was cast for information. As shown by the acknowledgements, many across the country provided me with information. To all of them, I extend my sincere thanks. This report is based on my own library and experience, and the input I received from the many who helped. No doubt I have missed many projects, but the end result does demonstrate that HPC is now a widely accepted construction material. I hope that this review will contribute to the correct use of HPC, and that, overall, the durability and serviceability of our structures will be improved. John A. Bickley Toronto, Spring 2001

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Acknowledgements Particular thanks are due to Denis Mitchell for his chapter on design, Rico Fung and Kevin Cail for their guidance and support, Don Hopkins and Joan Dawson for the preparation of the manuscript for publication, my wife, Jean, for proof-reading; and to the many, listed below, who supplied me with information. Pierre-Claude Aïtcin, Université de Sherbrooke; Vic Anderson, DELCAN; Herve

Bachelu, Saskatchewan Highways and Transportation; Beata Berszakiewicz, Ontario Ministry of Transportation; Ken Bontius, Hatch Mott MacDonald; Don Brennan,

Department of Works, Services and Transportation Newfoundland and Labrador; Paul Carter, Reid Crowther; Barry Charnish, Yolles Partnership Inc.; Mike Chung, City of

Toronto; Louis-Georges Coulomb, Ministère des Transports, Québec; Martin Darby,

Lafarge Construction Materials; Savio DeSouza, AMEC; Walter Dilger, University of Calgary; Sal Fasullo, DAVROC Testing Laboratories Inc.; James Fletcher, Nova Scotia

Power Inc.; Richard Gagné, Université de Sherbrooke; Richard Golec, Pre-Con; Malcolm Gray, AECL; Gilbert Haddad, Terratec; John Hart, Consultant; Jack Holley, Lafarge

Construction Materials; Dale Hollingsworth, Lafarge Construction Materials; Henri

Isabelle, Consultant; Harry Jagasia, UMA; Jan Jofriet, University of Guelph; Kamal Khayat, Université de Sherbrooke; Jana Konecny, Ontario Ministry of Transportation;

Ulrich Kuebler, Sky Cast Inc.; Francois Lacroix, Cement Association of Canada; Gord Leaman, Jacques Whitford; Bill LeBlanc, Con-Force; Gene Lecuyer, Lafarge Canada

Inc.; Michel Lessard, Euclid Admixtures Canada; Wib Langley, Consultant; Bob Loov,

University of Calgary; Paul Lowe, Lafarge Construction Materials; Ron Lowther, BC Ministry of Transportation and Highways; Yves Malier, ENPC, Paris and ENS Cachan;

P.K. Mehta, University of California, Berkeley; Mike Meschino, Yolles Partnership; Grant Milligan, Quinn Dressel Associates; Rusty Morgan, AMEC; Richard Morin, Ville

de Montréal; Robert Munro, Lafarge Canada Inc.; K Nasser, University of Saskatchewan;

Nikola Petrov, Université de Sherbrooke; Michel Pigeon, Université Laval; Tony Purdon, SAR Transit JV; Gary Pyke, Nova Scotia Transportation and Public Works; Bob

Ramsay, UMA Group; Elizabeth Read, SEM; John Ryell, Trow Consulting Engineers Ltd.; Phil Seabrook, Levelton Associates; Hannah Schell, Ontario Ministry of

Transportation; Fred Strang, Department of Transport, New Brunswick; Michael

Thomas, University of Toronto; Jean-Francois Trottier, Dalhousie University; Jim Turnham, SAR Transit; Daniel Vezina, Ministere des Transport, Québec; Gary Winch,

Lafarge Canada Inc.; Steve Zupko, Lafarge Canada Inc.

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CONTENTS

Executive Summary………..……………………….……………….... Preface………………………………………………………………… Acknowledgements……………………………………………………

iii vi v

CHAPTER 1

Introductions

Introduction……………………………………………………... Background and History………………………………………...

1 1

CHAPTER 2

Standards

National Standards for Structural Design………………………. CSA A23.3 and CSA S6 Bridge Code………………….

National Standards for Materials……………………………….. CSA A23.1 & 23.2………………………………………

CSA A 3000…………………………………………….. CSA A 413……………………………………………… CSA S 438………………………………………………

4 4

19 19 19 20 20

CHAPTER 3

Review of Bridges

General………………………………………………………….. Alberta………………………………………………………….. British Columbia……………………………………………….. Manitoba……………………………………………………….. New Brunswick………………………………………………… Newfoundland and Labrador……………………………………

Northwest Territories…………………………………………… Nova Scotia…………………………………………………….. Ontario………………………………………………………….. Prince Edward Island…………………………………………… Quebec………………………………………………………….. Saskatchewan……………………………………………………

21 21 27 30 31 33 34 34 37 45 47 51

CHAPTER 4

Precast Concrete Products Confederation Bridge…………………………………………… Bridges………………………………………………………….. Concrete Pipe…………………………………………………… Precast Concrete Slabs………………………………………….. Hollowcore Slabs………………………………………………..

Tunnel Segments……………………………………………….. Spun Concrete Poles……………………………………………. Parking Structures………………………………………………. Precaster Experience…………………………………………….

58 60 63 63 64 64 65 67 67

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CHAPTER 5 Buildings and Parking Structures Buildings……………………………………………………….. Parking Structures……………………………………………….

70 71

CHAPTER 6

Marine Applications Hibernia Offshore Platform…………………………………….. Grand Manan Wharf…………………………………………….

75 76

CHAPTER 7

Agricultural Applications…………………………………….……..

79

CHAPTER 8

Shotcrete……………………………………………………………..

82

CHAPTER 9

Emerging Technologies

Self-Consolidating Concrete……………………………………. Reactive Powder Concrete……………………………………… Use of Ternary Cements………………………………………… High Performance Roller Compacted Concrete………………....

88 91 92 93

CHAPTER 10

Discussion and Recommendations

Discussion………………………………………………………. Cementitious Materials………………………………… Supplementary Cementing Materials………………….. Admixtures…………………………………………….. Mix Design……………….……………………………. Testing…………………………………………………..

Constructability………………….…...…………………. Monitoring………..…..…………………………………

Conclusions and Recommendations……………………………. Cementitious Materials….…..…………………………... Admixtures….……………….………………………….. Testing…………………….…….………………………. Specifications…….……….………………….…………. Constructability…….……….…………………………... Curing…………..………………………………………. Service Life Predictions……...…...…………………….. Summary……………………………………………..….

98 98 98 98 98 99

103 105 108 108 108 108 108 108 109 109 109

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Chapter 1 Introductions Introduction Mehta (1994) stated that his holistic model of concrete deterioration "provides a clear justification why impermeability of concrete should be the first line of defence against any of the physico-chemical deterioration processes described earlier. If adequate attention in concrete making and processing is paid to hold the first line of defense, why would one need epoxy-coated reinforcement for protection against corrosion, ASTM Type V cement for protection against sulfate attack, and low-alkali cement or non-reactive aggregates for protection against expansion associated with the alkali-silica reaction?" He went on to say "From the standpoint of life-cycle costs and conservation of resources, the ecological implications of the foregoing proposition cannot be ignored for too long". In Canada, experience with concrete durability problems has led to a similar conclusion: that the impermeability of the cover concrete is paramount. With ternary mixes and available admixtures, high strength is relatively easy to achieve. The current fixation in research and practice is the construction of durable structures. Owners are demanding an extended service life and want reassurance prior to construction, that it will be achieved. As a consequence, increasing effort is focusing on the development of predictive life-cycle models that can provide assurance of the specified service life, and can be used to calculate life-cycle costs. This approach is particularly relevant since first costs for the use of HPC are often higher than for conventional concrete. It is widely accepted that life-cycle costs for HPC structures will be lower than those of similar structures using conventional concrete. It is now commonplace for construction contract specifications to require some form of permeability test, and the trend is to carry out this test on samples taken from the finished structure. The need to provide assurance of contract quality and the increasing use of performance or end-result specifications highlights the need for quicker and more reliable test procedures. Continuing research and site implementation of the correct procedures are ongoing construction industry objectives. Background and History Credit for the term "High Performance Concrete" must go to the French. It was coined in 1980 by Roger Lacroix and Yves Malier (Aïtcin, 1998). In 1986, the French project "New Ways for Concrete" brought together 36 researchers from France, Switzerland and Canada. Leading the Canadian group was Pierre-Claude Aïtcin. The research, findings and field applications of all the members of this group formed the contents of the first book published that was solely devoted to High Performance Concrete (Malier, 1990).

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Towards the end of 1988, Pierre-Claude Aïtcin, assisted by Denis Mitchell and Michael Collins, wrote the successful proposal for the Network of Centres of Excellence on High Performance Concrete, funded under the Federal Government "Centres of Excellence Programme". This research programme started in 1990, and, in its second phase, starting in 1994, the Network became known as Concrete Canada. The researchers who comprised Concrete Canada were not the only Canadians researching and using HPC, however, they were the pre-eminent and most active group in this field. By virtue of many publications in scientific journals, a Newsletter sent to 7,000 persons world-wide, the organization of technology transfer days and seminars, and the construction of demonstration projects, Concrete Canada played the major role in establishing HPC as a widely accepted construction material in Canada. In the United States, the Strategic Highway Research Programme (SHRP) sponsored a project on High Performance Concrete. In 1990, "High Performance Concretes", an annotated bibliography, 1974-1989, was published as SHRP-C/WP-90-001. The definition used by SHRP for HPC was as follows: 1. "It should meet one of the following criteria

a) A 3-hour strength not less than 3,000 psi b) A 24-hour strength not less than 5,000 psi c) A 28-day strength of not less than 10,000 psi d) A water-cement ratio (including pozzolans) less than 0.36

2. It should also have a durability factor not less than 80 after 300 cycles of freezing and

thawing". Many of the entries in this bibliography met the above criteria, but the authors of only two of the 2204 publications included in this document used the term High Performance in the titles of their Papers, and these were dated 1986 and 1987. Since then the term has become a popular buzzword. In 1993, the American Concrete Institute published the following definition: "High-performance concrete (HPC) is defined as concrete which meets special performance and uniformity requirements that cannot always be achieved by using only the conventional materials and mixing, placing and curing practices. The performance requirements may involve enhancements of placement and compaction without segregation, long-term mechanical properties, early-age strength, toughness, volume stability, or service life in severe environments".

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In most applications, the water-cementing materials ratio will not exceed 0.40, but, as will be noted later in this report, some truly high performance concretes do not meet any of the above definitions. Cast-in-place HPC will normally contain silica fume. Precast concrete may not, particularly where the main parameter needed is high strength. In the decade 1990-2000, there has been an enormous amount of research on this subject, and thousands of Papers have been published (Zia, 1997). Major research programmes have been carried out in many countries in Europe, Asia, Australasia, Japan and North America. A unique feature of the Concrete Canada programme has been the use of demonstration projects to effect the implementation of the correct use of HPC on construction projects. Since 1990, many such projects have been carried out across Canada. The use of HPC has recently spread rapidly. Most Provincial Highway Departments and some major cities have adopted its use, or are in the process of doing so. As a result, many consultants are specifying it, and, consequently, many contractors are winning contracts which contain innovative features. This is resulting in some potential teething problems that are discussed later. REFERENCES Mehta, P.K., "Concrete Technology at the Crossroads-Problems and Opportunities", Concrete Technology Past, Present, and Future, ACI SP 144, 1994, pp. 1-30. Aïtcin, P-C., " High-Performance Concrete", E & FN Spon, 1998, pp. 591. Zia, P., "State-of-the-Art of HPC: An International Perspective", Proceedings PCI/FHWA International Symposium on High Performance Concrete, New Orleans, October 1997, pp. 49-59. Malier, Y., "Les Bétons à Haute Performance", Presse de L'Ecole National des Ponts et Chaussées, 1990. English Edition E & FN Spon, 1992.

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Chapter 2 Standards National Standards for Structural Design

CSA A 23.3-94 Design of Concrete Structures and CSA S6-00 Canadian Highway Bridge Design Code INTRODUCTION

This section presents the design requirements for high-strength concrete in the 1994 Canadian Standards Association (CSA) Standard A23.3-94 "Design of Concrete Structures" (CSA 1994). The differences between the provisions of the 1994 CSA Standard and those in the 1999 ACI Code are discussed. In addition, the requirements for high-strength concrete in the Canadian Standards Association (CSA) Standard S6, “Canadian Highway Bridge Design Code” are also discussed. LIMITS ON SPECIFIED COMPRESSIVE STRENGTH OF CONCRETE

The provisions in the 1994 CSA Standard are applicable for designs having a specified concrete compressive strength not less than 20 MPa nor more than 80 MPa. The upper limit for the compressive strength of the concrete was chosen because of the insufficient amount of test data on the response of structural elements constructed with very high-strength concrete. The Standard permits designs with concrete compressive strengths greater than 80 MPa, provided that the structural properties and detailing requirements for these higher strength concretes are established for concretes similar to those to be used. Furthermore, it is pointed out that high-strength concretes vary in their brittleness and need for confinement. The Standard cautions designers planning to use high-strength concretes to determine whether such concretes are available in their region and it also points out that it may be necessary to undergo prequalification of concrete suppliers and contractors. The 2000 Canadian Highway Bridge Design Code (CSA S6, 2000) provides limits on the concrete compressive strength “unless otherwise approved”. These concrete compressive strength limits are:

• a minimum strength of 30 MPa for non-prestressed members; • a minimum strength of 35 MPa for prestressed concrete; and • a maximum strength of 85 MPa unless approved. The Commentary to CSA S6 indicates that the minimum concrete strength limit of 30 MPa was chosen to provide a minimum level of durability. The Commentary also cautions designers about using concrete strengths greater than 85 MPa since “special consideration of the structural response of this material may be warranted”.

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MODULUS OF ELASTICITY OF CONCRETE The 1994 CSA Standard provides three methods for determining the modulus of elasticity, Ec, at the design stage, as follows: • by testing cylinders of similar concrete.

• by determining the modulus of elasticity, Ec, for concrete with ãc between 1500

and 2500 kg/m3 as

where ãc is the density of concrete in kg/m3. This equation is based on the work of (Carrasquillo et al, 1984) and gives a more appropriate expression for the modulus of elasticity, Ec, for concrete compressive strengths greater than 40 MPa.

• by determining the modulus of elasticity, Ec, of normal density concrete with

compressive strength between 20 and 40 MPa as

This simpler expression is suitable for use with lower strength concretes and is about 5% lower than that given in the 1999 ACI Code.

The CSA Standard also cautions designers that the modulus of elasticity of high-strength concrete is highly dependent on the properties of the aggregates used and hence can vary in different regions of the country (Baalbaki et al, 1991). If the modulus of elasticity is critical to the design, then a minimum value of Ec shall be specified and shown on the drawings. SPECIAL CONFINEMENT REQUIREMENTS FOR HIGH-STRENGTH CONCRETE COLUMNS

Studies on high-strength concrete columns (by Yong et al, 1988, Cusson and Paultre, 1994, Ibrahaim and MacGregor, and Polat, 1992), have indicated the need to provide a greater degree of confinement to improve the ductility of high-strength concrete columns. Furthermore, there is a tendency for splitting cracks to form in high-strength concrete columns, resulting in premature spalling of the concrete cover and a reduction in the capacity as discussed by (Collins et al, 1993).

( )

′

2300 6900 + 3300 = c

1.5γcc fE (1)

cc fE ′ 4500 = (2)

8

Tie Spacing Limits The 1994 CSA Standard requirements for maximum tie spacings in columns made with normal strength concrete are the same as those in the 1999 ACI Code. However, the tie spacing requirements for columns made with concrete, having a specified compressive strength greater than 50 MPa, are reduced by multiplying the tie spacing limits of the ACI Code by 0.75. Thus, for higher strength concrete columns, the tie spacing shall not exceed the smallest of:

• 12 times the diameter of the smallest longitudinal bars or the smallest bar in a bundle;

• 36 tie diameters; • 0.75 times the least dimension of the compression member; and • 225 mm in compression members containing bundled bars.

The additional confinement for high-strength concrete columns is aimed at providing greater confinement and improved ductility.

Anchorage Details for Ties

The 1994 CSA Standard also requires that ties in columns made with specified concrete compressive strengths greater than 50 MPa have standard tie hooks with a bend of at least 135o. The typical 90o bend anchorages are replaced with 135o bend anchorages for the ties in high-strength concrete columns in order that the ties remain effective, even if some concrete cover spalling takes place. Confinement for Fire Resistance

While there are a number of ongoing research projects aimed at developing a better understanding of the influence of high-strength concrete on the fire resistance of columns, a number of important observations have been made (Phan). It has been found that high-strength concrete can experience "explosive spalling" when subjected to rapid heating. The rate of temperature increase, the type of aggregates, the details of reinforcement, the moisture content and the porosity of the concrete are all important factors which affect the spalling of the concrete. Due to the low permeability of high-strength concrete, it tends to retain moisture and, hence, rapid heating leads to the development of large internal vapour pressures, which results in explosive "spalling". Since the fire resistance is affected by loss of cover, it is hoped that the 1994 CSA Standard with more closely spaced ties with 135o bend anchorages should improve the fire resistance of high-strength concrete columns. Research is currently under way to study the effects of these new details and the influence of steel fibres on the fire resistance of high-strength concrete columns.

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FLEXURAL AND AXIAL LOAD RESISTANCES OF HIGH-STRENGTH CONCRETE ELEMENTS In determining the factored resistance for flexure and axial loads the 1994 CSA Standard prescribes a plane-sections approach using one of the following two methods:

Using Realistic Stress-Strain Relationships The position and magnitude of the resultant compression in the concrete may be found by first assuming a realistic stress-strain relationship between the compressive stress and concrete strain and then integrating these stresses. This relationship must account for the fact that as the concrete strength increases the compressive stress-strain curves exhibit greater initial stiffness, greater linearity and decreased ductility. Fig. 1 shows plots of stress-strain relationships which illustrate these features (Collins and Mitchell, 1997). In using this approach it is necessary to account for differences between the in-place strength and the strength of standard cylinders. In this regard, the CSA Standard requires that the compressive stress-strain curve for the in-place concrete be based on stress-strain curves with a peak stress no greater than 0.9f’c.

Using Stress Block Factors The 1994 Standard provides an alternate approach using an "equivalent rectangular concrete stress distribution", together with a maximum strain at the extreme concrete compression fibre of 0.0035. A value of 0.0035 was chosen to better reflect the extreme concrete compressive fibre strain at flexural ultimate for a large range of concrete compressive strengths. The equivalent rectangular concrete stress distribution is defined by the following:

• a concrete stress of á1öcf shall be assumed uniformly distributed over an equivalent compression zone bounded by edges of the cross section and a straight line located parallel to the neutral axis at a distance a = ß1c from the fibre of maximum compressive strain;

• the distance c shall be measured in a direction perpendicular to that axis; and • the factors á1 and ß1 shall be taken as:

These new stress block factors are more suitable for a wider range of concrete strengths than those in the previous 1984 CSA Standard (CSA A23.3-84). The stress block factors are intended to account for both the significant change in shape of the stress-strain curves as the concrete strength increases and the difference between the concrete cylinder strength and the in-situ strength of the column concrete.

0.67 0.0015 - 0.85 = ≥′cf1α (3)

0.67 0.0025 - 0.97 = ≥′cf1β (4)

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Fig. 2 illustrates the two analysis procedures for determining the factored flexural resistance of members. Fig. 3 compares the factored moment resistances, Mr, using the new stress block factors of the 1994 Standard, with those determined using stress block factors of the 1984 CSA Standard, for a 400 mm by 600 mm deep beam singly reinforced with 3 No. 30 bars. The two approaches are very similar for the case of pure moment. This figure also illustrates that for this example, doubling the concrete compressive strength results in only about a 6% increase in pure moment capacity.

Maximum Axial Load Resistance The maximum factored axial load resistance Prmax of compression members is determined from the following expressions:

(a) for spirally reinforced columns:

Prmax = 0.85 Pro (5)

(b) for tied columns:

Prmax = 0.80 Pro (6) where Pro is the factored axial load resistance at zero eccentricity defined as:

where

öc = resistance factor for concrete, equal to 0.60 Ag = gross area of section Ast = total area of longitudinal reinforcement At = area of structural steel shape Ap = area of prestressing tendons ös = resistance factor for reinforcing bars, equal to 0.85 öa = resistance factor for structural steel, equal to 0.90 öp = resistance factor for prestressing tendons, equal to 0.90 fpr = stress in prestressing tendons when concrete reaches limiting compressive strain fy = specified yield strength of reinforcement yield Fy = specified yield strength of structural steel section

The value of Prmax in the 1994 CSA Standard is a function of the stress block factor, á1, which varies with the concrete compressive strength. Fig. 4 compares the Prmax values calculated using the 1984 (similar to the 1999 ACI Code approach) and 1994 CSA Standards for a 450 mm by 450 mm column containing 8 No. 20 bars. For this column, containing 1.2% steel, the new provisions give about 4%, 9% and 13% lower capacities for concrete strengths of 30, 60 and 80 MPa, respectively.

pprtystysptstgccro AfAFAfAAAAfP - + + ) - - - ( = aφφφα ′1 (7)

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Limit of c/d Due to the change in the maximum strain at the extreme concrete compression fibre from 0.003 to 0.0035 in the 1994 CSA Standard, the tension reinforcement in flexural members shall not be assumed to reach yield unless:

where c is the depth of compression and d is the effective depth of the member. When c/d exceeds this limit, the stress in the tension reinforcement must be computed based on strain compatibility.

MINIMUM AMOUNT OF FLEXURAL REINFORCEMENT

The purpose of providing a minimum amount of flexural reinforcement is to ensure a ductile flexural response. An insufficient amount of flexural reinforcement can result in the flexural capacity being lower than the cracking moment, resulting in a brittle response after cracking. The 1994 CSA Standard gives three alternative approaches for satisfying the requirements for minimum reinforcement as given below:

(1) At every section of a flexural member where tensile reinforcement is required

by analysis, minimum reinforcement shall be proportioned so that:

where the cracking moment, Mcr, is calculated using the modulus of rupture, fr.

(2) In lieu of (1) above, minimum reinforcement may be determined from:

where bt is the width of the tension zone of the section considered. However, for slabs and footings only the minimum amounts for "temperature and shrinkage" need to be provided.

(3) The requirements (1) and (2) above may be waived if the factored moment

resistance, Mr, is at least one-third greater than the factored moment, Mf.

yf + 700

700

d

c ≤ (8)

crr MM 1.2 ≥ (9)

h f

0.2 =

ymin t

cs b

fA

′ (10)

12

Older codes (CSA A23.3-84 and ACI 318-83) typically required a minimum reinforcement ratio that was a function of the yield strength of the reinforcement, but was not a function of the concrete strength. The 1994 CSA Standard and the 1995 ACI Code make the minimum amount of reinforcement a function of not only fy, but also f’c to account for the higher cracking moment as the specified concrete strength is increased. Fig. 5 shows the variation of the reinforcement ratio, ñ, with increasing compressive strength. With the 1994 CSA provisions, a smaller amount of minimum reinforcement is required than previous code provisions for concrete strengths below about 40 MPa. Larger amounts of minimum reinforcement are required by the 1994 Standard for flexural members with concrete compressive strengths above 40 MPa.

MINIMUM AMOUNT OF SHEAR REINFORCEMENT The purpose of minimum shear reinforcement is to prevent brittle shear failures and to provide adequate control of shear cracks at service load levels (Collins et al, 1993). The 1984 CSA Standard (CSA A23.3-84), like the 1983 ACI Code (ACI 318-83), required a minimum area of shear reinforcement equal to 0.35bws/fy (i.e., stirrups to carry 50 psi) which is independent of the concrete strength. As the concrete compressive and tensile strengths increase, the cracking shear also increases. This increase in cracking shear requires an increase in minimum shear reinforcement such that a brittle shear failure does not occur upon cracking. The 1994 CSA Standard (CSA A23.3-94) makes the minimum amount of shear reinforcement a function of not only fy, but also f’c to account for the higher cracking shear as the specified concrete strength is increased. Where shear reinforcement is required, the minimum area of shear reinforcement shall be such that:

Figure 6 compares the 1994 CSA and the 1999 ACI required amounts of minimum shear reinforcement. The CSA requirements provide a more gradual increase in the required amount of minimum shear reinforcement as the concrete strength increases. Tests carried out by (Yoon et al, 1996) on large beams with concrete strengths varying from 36 MPa to 87 MPa indicated that the amount of minimum shear reinforcement prescribed by the 1994 CSA Standard provides adequate control of diagonal cracks at service load levels and provides reasonable levels of ductility. CRACK CONTROL REQUIREMENTS FOR HIGH-STRENGTH CONCRETE ELEMENTS

As discussed above, the amount of minimum reinforcement required for both flexure and shear is a function of the concrete compressive strength, f’c. An important design issue is whether or not the amount of uniformly distributed reinforcement required in

y

wcv f

bfA

s 0.06 = ′ (11)

13

disturbed regions is also a function of the concrete strength. These disturbed regions include deep beams, corbels and regions near supports. The 1984 CSA Standard A23.3 introduced the strut-and tie design procedure for these disturbed regions and these requirements remain unchanged in the 1994 Standard. In the strut-and-tie design procedure the tension ties and compressive struts are first designed and then uniformly distributed horizontal and vertical reinforcement is added to control cracking at service load levels. The CSA Standard requires a minimum amount of uniformly distributed reinforcement corresponding to a reinforcement ratio of 0.002 in both the horizontal and vertical directions. This maximum spacing of this crack control reinforcement is 300 mm. For bridge design (CSA S6, 2000 and AASHTO, 1994 and 2000), this minimum reinforcement ratio has been increased from 0.002 to 0.003. An important question to be answered is whether or not this minimum reinforcement ratio should be a function of f’c, in keeping with the philosophy for minimum amounts of flexural reinforcement and shear reinforcement. Preliminary experimental evidence from testing carried out in full-scale bridge pier caps (Macleod et al, 1996) indicated the following:

• a reinforcement ratio of 0.0018 was sufficient to control service load cracking for the specimens having a concrete compressive strength of 38 MPa.

• a reinforcement ratio of 0.003 was adequate in controlling the service load cracking for the specimens having a concrete compressive strength of 79 MPa.

TRANSMISSION OF COLUMN LOADS THROUGH FLOOR SLABS When the specified compressive strength of concrete in a column is greater than that specified for a floor system, transmission of the column load through the floor system needs to be investigated. There are three methods of dealing with this issue in the 1994 CSA Standard as described below: (1) "Puddled" High-Strength Concrete in Slab - One method is to provide concrete

of the strength specified for the column, f’cc, "puddled" in the floor slab at and around the column locations. The top surface of the column concrete placed in the floor shall extend at least 500 mm into the floor from the face of the column to be considered effective (see Fig. 7(a)). This usually requires that the higher strength concrete in the floor in the region of the columns be placed before the lower strength slab concrete is placed to avoid accidental placement of the lower strength concrete in the column area. In addition, the lower strength concrete must be placed while the higher strength concrete is still plastic and must be vibrated to ensure integration of the two concretes.

(2) Accounting for Confinement Effects - Another approach is to take account of

the confining effect of the floor slab surrounding the column (see Fig. 7(b). The 1994 Standard prescribes an effective concrete compressive strength, f’e, which differentiates between the different amounts confinement at interior, edge and corner columns as shown in Fig. 7(b).

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(3) Use of Vertical Dowels - The third approach is to supplement the strength of the weaker concrete, "sandwiched" between the upper and lower column, by adding sufficient vertical dowels to enhance the capacity locally (see Fig. 7(c)), or by adding spirals or hoops in this critical region to increase the confinement and effective strength of the concrete in the slab region.

DEVELOPMENT LENGTHS OF REINFORCEMENT The 1994 CSA Standard (CSA A23.3-94) has adopted the same approach as the 1995 ACI Code by limiting the maximum permissible value of the square root of f’c to 8 MPa when calculating development lengths. More research is needed on this important topic since there is a tendency for more brittle bond failures in high-strength concrete members unless an adequate amount of transverse reinforcement is provided (Azizinamini et al, 1993, Abrishami et al, 1995). CONCRETE CAST IN CSA CERTIFIED PRECAST PLANTS The 1994 CSA Standard employs material resistance factors rather than capacity reduction factors when calculating the factored member resistance. For elements produced in certified manufacturing plants, the concrete material resistance factor, öc, may be taken as 0.65, rather than 0.60. This increased value of öc, reflects the better quality control achieved in certified precast plants. SEISMIC DESIGN The "Special Provisions for Seismic Design" in the 1994 CSA Standard (CSA A23.3-94) limits the specified compressive strength, f’c, used in design to 55 MPa. These special provisions contain the seismic design and detailing requirements for ductile and nominally-ductile structural elements. This conservative approach was deemed necessary by the code committee because of the lack of test results of high-strength concrete elements subjected to reversed cyclic loading. The 1995 New Zealand Standard (NZS 3101:1995) limits the specified concrete compressive strength to 70 MPa for ductile elements and elements of limited ductility. The 1999 ACI Code (ACI 318-95) does not have an upper limit on the specified concrete strength for the design of ductile elements. CONCLUSIONS The 1994 CSA Standard (CSA A23.3-94) introduced special provisions for the structural design of high-strength concrete members which have some significant differences with the ACI Code (ACI 318-95). It is clear that more research is required in many different areas in order to develop codes for the future. The Canadian Highway Bridge Design Code (CSA S6, 2000) currently does not give any additional benefit for the use of high-performance concrete in determining cover requirements for different types of construction (prestressed and non-prestressed) and for different exposure conditions. It is hoped that future research will take account of the improved durability of high-performance concrete.

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REFERENCES Canadian Standards Association, "CSA A23.3-94 Design of Concrete Structures", Rexdale, 1994, pp. 199. American Concrete Institute, Building Code Requirements for Structural Concrete (ACI 318-95) and

Commentary, Detroit, MI, 1999, pp. 391. Canadian Standards Association, CSA S6, “Canadian Highway Bridge Design Code”, Rexdale, 2000, pp. 724. Carrasquillo, R.L., Nilson, A.H., and Slate, F.O., "Properties of High Strength Concrete Subject to Short-Term

Loads", ACI Journal, V. 78, No. 3, May-June 1981, American Concrete Institute, Detroit, pp. 171-178. Baalbaki, W., Benmokrane, B., Chaallal, O. and Aï tcin, P.-C., "Influence of Coarse Aggregate on Elastic

Properties of High-Performance Concrete", ACI Materials Journal, Vol. 88, No. 5, Sept.-Oct. 1991, pp. 499-503.

Yong, Y.K., Nour, M.G., and Nawy, E.G., "Behavior of Laterally Confined High Strength Concrete Under Axial Loads", Journal of Structural Engineering, Vol. 114, No. 2, Feb. 1988, ASCE, pp. 332-351.

Cusson, D. and Paultre, P., "High Strength Concrete Columns Confined by Rectangular Ties", Journal of Structural Engineering, Vol. 120, No. 3, Mar. 1994, ASCE, pp. 783-804.

Ibrahaim, H.H.H. and MacGregor, J.G., "Flexural Behaviour of High Strength Concrete Columns", Structural Engineering Report No. 196, Dept. of Civil Engineering, University of Alberta, pp. 197.

Polat, M.B., "Behavior of Normal and High Strength Concrete Under Axial Compression", Master's thesis, Department of Civil Engineering, University of Toronto, 1992, pp. 175.

Collins, M.P., Mitchell, D., and MacGregor, J.G., "Structural Design Considerations for High-Strength Concrete", Concrete International, Vol. 15, No. 5, May 1993, American Concrete Institute, Detroit, pp. 27-34.

Phan, L.T., "Fire Performance of High-Strength Concrete: A Report of the State-of-the-Art", NISTR 5934, National Institute of Standards and Technology, Gaithersburg, Maryland.

Collins, M.P. and Mitchell, D., "Prestressed Concrete Structures", Response Publications, Montreal/Toronto, 1997, pp. 766.

Canadian Standards Association, "CSA A23.3-84 Design of Concrete Structures for Buildings", Rexdale, 1984. American Concrete Institute, Building Code Requirements for Reinforced Concrete (ACI 318-83), Detroit, MI,

1983, pp. 111. Yoon, Y.-S., Cook, W.D. and Mitchell, D., "Minimum Shear Reinforcement in Normal, Medium and High-

Strength Concrete Beams", ACI Structural Journal, V. 93, N. 5, Sept/Oct, 1996, pp. 576-584. “AASHTO LRFD Bridge Design Specifications and Commentary”, American Association of State and

Highway Transportation Officials, Washington, D.C. 1994 with updates in 2000, pp. 109. MacLeod, G.D., Cook, W.D. and Mitchell, D., “Full-Scale Tests of Bridge Pier Caps”, Proceedings of

Graduate Student Seminars, Concrete Canada, Moncton, 1996, pp. 10. Azizinamini, A., Stark, A., Roller, J.J. and Ghosh, S.K., "Bond Performance of Reinforcing Bars Embedded in

High-Strength Concrete", ACI Structural Journal, V. 90, No. 5, Sept-Oct 1993, pp. 554-561. Abrishami, H.H., Cook, W.D. and Mitchell, D., "Influence of Epoxy-Coated Reinforcement on the Response of

Normal and High-Strength Concrete Beams", ACI Structural J., V92, N2, Mar/Apr. 1995, pp. 157-166. 16. New Zealand Standard, NZS 3101:1995, "Concrete Structures Standard", Standards Council of New

Zealand, Wellington, New Zealand, pp. 264.

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Figure 1 Variation of compressive stress-strain curves with increasing compressive strength. Adapted from Collins and Mitchell, 1997.

17

Figure 2 Assumptions for determining flexural resistance (1994 CSA Standard).

18

Figure 3 Variation of Mr with increasing concrete compressive strength.

Figure 4 Variation of Prmax with increasing concrete compressive strength.

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Figure 5 Variation of ñ with increasing concrete compressive strength.

Figure 6 CSA 1994 and ACI minimum amounts of shear reinforcement (note that the 1989 ACI requirements remain unchanged in the 1999ACI Code.

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Figure 7 Transmission of column loads through floor slabs

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National Standards for Materials

CSA A 23.1-00 Concrete Materials and Methods of Concrete Construction and A23.2-00 Methods of Test for Concrete

The main text of the latest edition of this standard has been reviewed to ensure that it is compatible with the material and construction needs of HPC. This edition also includes an Appendix J that provides guidance on the use of HPC. Subjects on which guidance is provided are:

Introduction General Cement and Supplementary Cementing Materials (SCMs) Water Aggregates Admixtures Reinforcement Formwork Fabrication and Placement of Reinforcement Mix Proportions Durability Requirements Concrete Quality Production of Concrete Placing of Concrete Curing References

CSA A 3000-98 Compendium of Cementitious Materials

This document brings together the latest editions of all the CSA standards for cementitious materials, viz.:

A 5 Portland Cement A 8 Masonry Cement A 23.5 Supplementary Cementing Materials A 362 Blended Hydraulic Cement A 363 Cementitious Hydraulic Slag A 456.1, A 456.2 and A 456.3 which cover all physical and chemical testing of the materials in the above five standards

The new edition of A 362 provides for a large range of binary and ternary blended cements, incorporating blast furnace slag, fly ash and silica fume in various percentages and combinations. This new concept offers the buyer a wide range of potential choices. For example, it is possible to buy blended cement containing Portland Cement, Slag and Silica Fume interground or blended in specific proportions. Already this option has been exercised on a number of contracts – see Chapter 9 Emerging Technologies.

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CSA S 413-94 Parking Structures In the current edition, HPC is not allowed in cast-in-place floors and roofs. In precast prestressed roofs and floors, low-permeability concrete is allowed. This concrete is specified to have a maximum water-cementitious ratio of 0.40 and a maximum coulomb rating (ASTM 1202)* of 1500 at 28 days. Later ages, up to 91 days, may be specified for these tests where fly ash or slag is used. * ASTM C 1202-97 "Test Method for Electrical indication of Concrete's ability to

resist Chloride Ion Penetration". This test is commonly called the Rapid Chloride Permeability Test (RCP).

CSA A 438-00 Concrete Construction for Housing and Small Buildings The new edition contains an Appendix R: Premium Quality Residential Basements. This appendix is intended for use where new basements are designed for residential use. Desirable properties for the concrete forming the walls of these basements are:

Minimal evaporative water to reduce noxious and harmful mould growth High impermeability to water and gas Reduced shrinkage High-quality finish

Criteria are provided for the use of self-consolidating concrete in these structures to meet the above properties. A demonstration building and other projects using this technology are described later in Chapter 9 Emerging Technologies.

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Chapter 3 Review of Bridges by Province General It is in the bridge field that HPC has found the widest and earliest use. The following are summaries of HPC use in the Provinces, in alphabetical order. Alberta As in other Provinces, durability problems with normal quality concrete led to efforts to improve the serviceability of bridges. Alberta Transportation and Utilities (ATU) enlisted the assistance of the University of Calgary to research a number of materials improvements, some of which would meet today's criteria for HPC (Carter, 1998). An excerpt from this reference summarizes well the philosophy driving changes in Alberta practice:

"Analysis of primary highway bridge rehabilitation costs showed that after a certain bridge condition level was reached, the rehabilitation costs increased exponentially in relation to time. Bridge decks that were in poor condition consumed more money than if they had been repaired a few years earlier. It was concluded that most of the existing major bridges would benefit economically from protection systems, and that new and less expensive protection systems that were applied at the right time, and that were intended to keep the condition of the bridges good, would be less expensive, produce better repair service life, and result in a higher number of annual repairs than the current policy of focusing repairs to bridges in bad condition”.

During the 1980s some of the bridge management changes used high performance materials. These included the use of fibres and supplementary cementing materials. Some milestones of innovation were as follows:

• Silica fume shotcrete in a culvert repair, 1983 • Steel fibres in three bridge deck repairs and eight shotcrete repairs, 1984 • Superplasticized steel fibre reinforced overlays, 1984 • Silica fume steel fibre shotcrete in prebagged proprietary mixes for ten bridge

repairs, 1985. Five more in 1986 • Fly ash in overlays, 1985 • Silica fume superplasticized overlay, 1985 • Proprietary overlays without superplasticizer, 1987 • Proprietary 12% silica fume superplasticized overlay, 1988

In the 1990s research at the U of C investigated the use of superplasticizers and SCMs with local materials to improve durability (Johnston, 1993).

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During the 1990s, silica fume overlays became the preferred protection system. They replaced membranes below asphalt paving on bridges. Recently, most overlays have incorporated steel fibres. The lessons learned in the use of these high performance overlays were summed up as follows (Carter, 1998):

• "It is possible and practical to produce a consistent mix for silica fume concrete on a large scale,

• Superplasticizer is a must with silica fume mixes, • In general only compatible admixtures should be used, • Avoid cement/admixture compatibility problems by trial batching, • Silica fume concrete with its lack of bleed water and susceptibility to surface

crusting from evaporation should be placed and finished in low evaporation conditions,

• Prevention of cracking is a major concern in Alberta's climate, • Mild weather conditions are essential to preventing cracking, • Mix temperature is best in the range of 12°C (ATU specifications call for

rejection if > 18°C), for prevention of cracking and for keeping slump and air retention properties to manageable levels,

• Ice is needed for temperature control on many ATU pours, • Best time to pour is at night because hot decks absorb water from mix, making

finishing hard, night time pours do not conflict with the mix supplier’s other customers’ jobs,

• Use of compatible retarder/superplasticizer combination has benefits, • Transit mix HPC can be used acceptably for pours within 1 hour travel time, and

this means most Alberta sites; dry truck batching is not as good as plant mixing, • Pre-bagged mixes are harder to work with than transit mix, partly because oven

dried aggregates create slump variability from batch to batch, • Today's pours are done with a workable, 120 mm slump, • Mono-monecular curing compound is recommended for use immediately after

texturing and prior to wet burlap placement to reduce surface cracking, • A second generation superplasticizer, when properly matched with an air

entraining agent, can meet the recognized requirements for air void spacing factor (<0.23 mm),

• Add superplasticizer after batching and mixing for 5 minutes; adding the superplasticizer during batching can result in unmixed balls in the mix,

• HPC can be used for bridge deck construction and replacement".

Developments were also made in the use of HPC for precast bridge girders, and these are described in chapter 4 - Precast Concrete Products. The following specification was used in a number of bridges:

• Specified 28-day strength: 55 MPa • Type 10 cement plus 7.5-10.0% silica fume • Minimum cement content: 380 kg/m³ • Maximum water-cement ratio: 0.35 • Delivered temperature: 10-18°C • Maximum coulomb value: 600 • Air: 5-8%

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Bridges constructed to this specification include the Fish Creek and Canyon Meadows 1995, Stoney Trail CPR 1997 and Ogden Road Overpass, Elevated Roadway at Calgary Airport and Center Street in 1998. Details of some other recent HPC bridges are as follow:

Bridge

Date

Specified 28 Day Strength

Maximum RCP Value

Components

MPa Coulombs Stoney Trail 1997 55 600 C-I-p box girders Centre Street rehabilitation 1999 45 600 C-I-p deck

35 600 C-I-p barrier walls Anderson/McLeod 2000 50 1000 C-I-p decks Interchange 40 1000 C-I-p barrier walls Deerfoot Trail/ 22X 2000 50 1000 C-I-p decks Interchange 40 1000 C-I-p barrier walls Fish Creek LRT 2000 50 1000 C-I-p decks

40 1000 C-I-p barrier walls Some recently rehabilitated or reconstructed bridges have incorporated stainless steel reinforcement: Cadotte River Bridge and Marten River Bridge These two bridges were rehabilitated in 1999. Each bridge consisted of three 10.7 m spans of prestressed concrete box girders (no deck). The spans were made continuous for live loads through the addition of a 130 mm thick silica fume concrete overlay reinforced with stainless steel reinforcing. A total of 14.4 tonnes of stainless steel reinforcing was used. It was supplied in stainless steel grade 316N and strength grade 420 MPa. Bar sizes used were Imperial #4, #5 and #6. Sturgeon River Bridge This bridge replacement project was constructed in the Fall of 2000. It is a 40 m simple span "Bulb-Tee" girder bridge (25.4 span/depth ratio) with a HPC deck. The girders have an ultimate concrete strength of 65 MPa and release strength of 45 MPa. A total of 9 tonnes of stainless steel clad reinforcing was used in the top mat of the deck and in the curbs. The stainless steel cladding was stainless steel grade 316L and strength grade 420 MPa. In 1999, the Province of Alberta adopted a specification for HPC in the form of Special Provisions. In 1999, these provisions were used for two bridge deck overlays and for the

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top slab of a box culvert. In 2000, they were used for three bridge deck overlays and for the deck of the Sturgeon River Bridge. HPC is designated as Concrete-Class SF (Modified). Key criteria for this concrete are as follows:

• Minimum 28 day compressive strength: 50 MPa • Maximum water/cementing material ratio: 0.36 • Minimum cement content (excluding SCMs): 350 kg/m³ • Silica fume: 7.7% to 9.5% • Sum of silica fume and fly ash: 25% of cement content • Slump at discharge: 120 +/-30 mm • RCP at 28 days: <1000 coulombs • Slump of trial mix 45 minutes after batching to be at least 50% of initial slump • Determine air void system of hardened concrete • For 7 days after casting, the temperature differential between the centre and

surface of the concrete shall not exceed 20°C • Fog misting to be applied from time of screeding until concrete is covered with

white filter fabric or burlap. • Cracks to be measured in width and length. Those over 0.3 mm in width to be

repaired. • Penalties are charged for understrength concrete down to 42 MPa, below which

the concrete is unacceptable, as follows:

Test results: MPa Penalty: $/m³ 50 or over Nil 49 to 50 20 48 to 49 40 47 to 48 60 46 to 47 80 45 to 46 100 44 to 45 130 43 to 44 180 42 to 43 240

Below 42 rejected

Trial batches are to be made at least 35 days before concrete placement. A trial batch placement of at least 3 m³ is required to simulate anticipated placing procedures. Where stainless steel is used as reinforcement, it is specified to meet the requirements of ASTM A955M-96 "Deformed and Plain Stainless Steel Bars for Concrete Reinforcement" and shall be deformed, stainless steel Grade 316LN or 2205 Duplex and strength Grade 420. Chairs or bar supports shall be non-metallic. Tie wire shall be Grade 316L stainless steel.

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Comprehensive specifications were recently adopted for HPC by the Cities of Calgary and Edmonton, and by Reid Crowther. Key criteria are listed in the following table: Calgary Reid Crowther Edmonton

Date January 2000 August 2000 November 1999 Cement: kg/m³ Min 360 Min 340 Min 340 Silica fume: % Max 8 Max 8 Max 8 W/c ratio: Max 0.37 Max 0.37 Max 0.37 Air: % 5-8 5-8 5-8 RCP: coulombs Max 600† 700 +/- 35 % Max 1000¶ Air void system CSA A23.1* CSA A23.1 - 28-day strength Decks/girders 50 MPa 50 MPa # Barrier walls 40 MPa

50 MPa with corrosion inhibitor‡ 40 MPa #

Scaling test 0.4kg/m²/30 cycles 0.4 kg/m²/30 cycles 0.4 kg/m²/30 cycles † Decks and girders ‡ 40 MPa with fibres and either corrosion inhibitor or shrinkage reducing admixture. ¶ For 50 MPa concrete. # 50 MPa for decks, abutment deck slabs and approach slabs; 40 MPa for Barrier walls and medians. * Air void system limits can be relaxed if 300 cycles of freezing and thawing tests to ASTM C 666 produce a durability factor greater than 90%. Curing with fog mist or evaporation retarder to start immediately after finishing. Curing to continue for at least 5 days (3 days for overlays) with wet burlap covered with vapour proof sheeting. The City of Calgary requires tests in advance of construction to determine the cracking potential of the proposed mix. Cracks over 0.2 mm in width in the structure are repaired. A number of penalties are imposed for failures to meet specification requirements: Unit Penalty: $/m³

3.5-4.5 MPa below specification 70 Strength > 4.5 MPa below specification 150 or remove

0.2 % outside limits 60 Air content > 0.2 % outside limits 150 or remove

RCP 601-1200 coulombs 40 >1200 coulombs 250 or remove For overlays, a corrosion inhibitor is specified. The RCP value is given as 600 coulombs plus a 20% tolerance. Consequently, the penalties shown in the above table are different, only for RCP values, as follows: 750 - 1000 coulombs: $ 40/ m³. > 1000 coulombs: $ 250 or remove.

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The City of Edmonton adopted a specification for HPC in November 1999. Key criteria are as follows:

Min Cement

W/C Ratio

Max Slump

28 Day Strength: MPa

RCP: Coulombs

Mix

Element

Air%

Kg/m³ Max mm* mm† Min Max HPC

1 All decks and slabs

5-8 340 0.37 70 150 50 1000

HPC 2

Barriers and medians

5-8 340 0.37 70 150 40 NA

All mixes contain 8% silica fume and a corrosion inhibitor. *Before superplasticizer, † after superplasticizer. HPC cannot be placed if the anticipated air temperature is expected to exceed 22°C. Temperature of concrete at discharge must be between 10°C and 18°C, using ice or liquid nitrogen if needed to not exceed 18°C. Immediately after finishing fog misting, evaporation retarder or special curing compounds shall be applied to the concrete surface. Penalties are the same as the Calgary specification except for compliance with maximum RCP values for which the penalties are as follows: 1001- 4000 coulombs: $40/m³, > 4000 coulombs: $250/m³ or remove. The Read Crowther specification contains the following key criteria:

Slump Mix

Element

Admixtures

Air %

Cement Minimum

Kg/m³

W/C Ratio Max

mm mm

HPC 1 Deck, superstructure, barriers, toppings

CI 5-8 340 0.37 70 150

HPC 2 Barriers, toppings Fibres, SRA 5-8 340 0.37 70 150 HPC 3 Barriers, toppings Fibres, CI 5-8 340 0.37 70 150

CI: Corrosion inhibitor, SRA: Shrinkage reducing admixture.

Mix 28 Day Strength: MPa

Tendency to crack: Width (mm) x Length (m) per m² of Surface Area*

RCP: Max Coulombs

HPC 1 50 Comparative evaluation: 0.25-0.35 700 +/- 35 % HPC 2 40 Comparative evaluation: 0.25-0.35 700 +/- 35 % HPC 3 40 Comparative evaluation: 0.25-0,35 700 +/- 35 %

*Cracking for the area under consideration will be determined by measuring the estimated total crack length of cracks greater than 0.2 mm wide multiplied by the average crack width of each crack and then divided by the area under consideration in square metres, as defined by a perimeter 500 mm beyond the nearest crack under consideration.

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HPC will not be placed if the air temperature is anticipated to exceed 22°C. Concrete temperature, as delivered, shall be between 10°C and 18°C, and ice or liquid nitrogen shall be used to ensure that the concrete temperature does not exceed 18°C. Curing with pre-wetted burlap shall begin no more than 30 minutes after final finishing, and be continued for at least 7 days. Penalties in this specification are as follows:

3.5 MPa to 4.5 MPa below $ 50/ m³ Strength > 4.5 MPa below $ 100/m³or remove Up to 0.2 % outside range $ 60/m³ Air Entrainment > 0.2 % outside range $ 150/m³or replace 1001-2500 coulombs $ 250/m³ Permeability > 2501 coulombs No payment, plus acceptable

protection or replace For cracking, as measured by the definition shown above, the penalties are as follows: 0 to 0.30 No deduction 0.31 to 0.6 $ 100/m³ plus specified repair 0.61 to 1.0 $ 200/m³ plus specified repair > 1.0 No payment plus acceptable protection system or replace British Columbia As in other provinces, there was not suddenly a day when all concrete became HPC. Requirements for high strength and durability became imperatives before 1990. The Annacis Bridge is a case in point (Taylor et al, 1986). In order to meet strength, weight and durability criteria, the deck was cast in a High-Strength HPC, it just was not called HPC. The precast panels used the following mix:

Type 10 cement: 425 kg/m3 Water-cement ratio: 0.19-0.24 Air content: 4-6 % Compressive strength: MPa At 16 hours: 40-50

At 56 days: > 75 The cast-in-place deck topping contained fly ash, had a water-cement ratio of 0.28, and contained a superplasticizer. Compressive strength at 56 days averaged 63 MPa with a standard deviation of 3.3 MPa. Both these concretes would qualify as HPC but were not designated as such at the time.

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A major rehabilitation project in 1999 was the deck overlay replacement on the Columbia River Bridge at Revelstoke (Morgan, 2000) using a steel fibre reinforced HPC. The original construction in 1959 was concrete infill to a metal T-grid deck surfaced with asphalt. By the 1990's, the bonded concrete overlay that replaced the asphalt in the 1970's had delaminated and spalled, resulting in potholes. The existing concrete was removed to within 10 mm of the T-grid using high-pressure water jets. The concrete mix was dry batched in Vancouver in 1600 kg bulk bin bags, discharged into transit mixers near the site, water and admixtures added and the concrete delivered after 30 minutes batching and mixing time. Travel and discharge time was 45 minutes to 1.5 hours. Just prior to placement, a sand-cement bonding agent was scrubbed into the T-grid cells. A Bidwell machine compacted and finished the overlay. The concrete was placed at night, fog sprayed prior to covering with wet burlap and plastic sheeting for 3 days followed by 4 days of wet curing. The concrete mix design was as follows:

Material Proportions Kg/m³ Type 10 cement Silica fume

375 30

Coarse aggregate Fine aggregate

1010 750

Water 135 Steel fibres 50 Water-reducing admixture Superplasticizer Corrosion inhibitor Air-entraining agent

1.2 l 4.0 l 10.0 l 0.2 l

Air content of the fresh concrete was 5-8%, slump 70 +/- 20 mm, water-cement ratio 0.35 and steel fibre content 0.64 % by volume. The properties of the hardened concrete were as follow:

Compressive strength: MPa 3 days 35 7 days 55 28 days 68 Flexural strength and toughness at 7 days Flexural strength: MPa 4.8 Toughness (ASTM c 1018) Level III to level IV JSCE SF-4 Toughness factor: MPa 2.7 Round determinate panel test Absorbed energy at 40 mm

290 J

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In view of the results obtained on this project, a similar specification and procedure was used on the Laforme Creek Bridge in Revelstoke in 2000. The SkyTrain Millennium Line Project is a 20.4 km extension of the existing LRT line. The 16 km elevated guideway is comprised of 5,675 precast HPC segments, and used 135,000 m³ of HPC. It is the largest precast segmental construction contract undertaken in North America. The use of segmental construction allowed for different spans. The segments were cast in a facility in Port Moody established for the project. The 17 month construction time mandated a one day cycle for most segments resulting in a 14 hour strength requirement of 18 MPa. Where segments were to be erected within 48 hours of casting, a 35 MPa strength was required prior to stressing. The project specification was for a 100-year service life with "required maintenance no greater than ordinarily required for similar structures". The specification for the contract was independently evaluated. This review took a holistic view by asking two basic questions:

a) What are the mechanisms that could cause deterioration of the reinforced concrete

construction prior to the 100 year design service life? and b) How does the specification address these potential deterioration mechanisms, so

as to provide a structure which meets the required service life? Deterioration mechanisms evaluated and considered in the concrete mix designs included: frost damage, de-icing salt scaling, chloride ion and carbonation induced corrosion, alkali-aggregate reactivity, and cracking due to drying shrinkage and thermal stresses. The criteria adopted for the segment concrete were as follows: Specified 28-day strength: 40 MPa* Type 10 cement: 378 kg/m³ Flyash: 42 kg/m³ Air content: 6% Maximum aggregate size: 14 mm Target water-cementitious ratio: 0.32 Maximum water-cementitious ratio: 0.36 *60 MPa for some segments. Pre-construction tests were made to confirm air-void systems. Further analyses and modelling were made throughout the project to verify that "Time to Initiation of Corrosion" and "Time to Repair" were consistent with the 100 year service life specified. Tests were made on samples from the 20 year old existing LRT structure, as representative of the exposure to chlorides expected for the new structure.

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A build-up rate of 0.032 kg/m³ was determined. RCP values of 2,600 coulombs were obtained from 28 day lab cured test cylinders, but 800 coulombs at 365 days were obtained from cores taken from a discarded concrete segment which had been field cured. Quality control was excellent with coefficients of variation generally between 4 and 6% and as low as 3%. Of 13,000 loads of concrete delivered, only two had to be rejected. Temperature probes in each segment form monitored the temperature of the hydrating concrete. These data, converted to maturity values, correlated closely to compressive strength, enabling form removal times to be determined accurately. The data also facilitated the fine-tuning of the mix designs. Manitoba Up to 1998, the following bridges used HPC:

Manitoba Highways

Bridge Component Plum River 75 mm overlay Assiniboine River Floodway 75 mm overlay Little Saskatchewan River Superstructure Assiniboine River Bridge 75 mm overlay Boine River 100 mm overlay

All concrete contained 8% silica fume and met a 35 MPa 28 day strength requirement. City of Winnipeg

Bridge Component Norwood Bridges, North & South

140 mm deck lift

Charleswood 75 mm overlay LaSalle River, North & South 75 mm overlay

All concrete contained 8% silica fume and met a 35 MPa 28 day strength requirement. Key criteria in the current Manitoba concrete specifications are as follow:

Manitoba Cement 10 SF Cement content: kg/m³ 340 Silica fume content: % 8 Water-cement ratio 0.37 max Rapid chloride permeability 1000 coulombs max Air: % 5-8 28-day strength: MPa 45 Allowable cracking width (mm) x length (m) per square metre of surface area: 0.25 to 0.35

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New Brunswick During the last five years, over 150 HPC structures have been constructed in New Brunswick. A review of test data from 25 HPC projects showed average coulomb values were 730 while for 4 projects using normal strength concrete with Type 10 cement, the average coulomb value was 4024. No value is specified, but values less than 1000 are expected for the specified concrete prior to the addition of a corrosion inhibitor. A value of 1500 coulombs is expected after the addition of the corrosion inhibitor. The reinforcement is uncoated and the decks are waterproofed and paved. The following summary of New Brunswick experience is based almost verbatim on a presentation made by Fred Strang of the New Brunswick Department of Transportation at the ACI Convention in Toronto in October 2000 (Strang, 2000). High Performance Concrete - Specifications and Mix Design The Department specifications are method based. The specifications are as follows:

• 28 day compressive strength of 45 MPa • Type 10 SF (low alkali) cement • 420 kg/m³ cement content • 0.37 water-cementitious ratio • Plastic air content of 5-8% after final discharge • Slump is 125 +/- 50 mm after final discharge • Maximum concrete temperature (at delivery) 25°C • Corrosion Inhibitor • The deck is then waterproofed and paved

Construction Methods Goals

The goals this department is striving to meet are as follows:

• Eliminate plastic shrinkage cracking and crazing • Minimize transverse cracking • Produce a surface texture suitable to receive waterproofing • Meet specified surface tolerances

The department has had success meeting these goals following the practices described below:

Placing

• Place the concrete at night. At night there is less evaporation of water from the surface of the concrete because the relative humidity is higher and there is less wind. The temperature is also lower at night. This prevents rapid drying of the surface. The concrete properties such as air and slump remain more consistent.

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• The newer superplasticizers EO/PO combination polymer (Ethylene oxide/Polyethylene oxide) gives better consistency on site. Less time is spent on site testing. Control of the water content at the plant is critical for consistency of plastic concrete properties on site.

• The sooner the screeding operation is performed after the concrete is placed, the easier the concrete will be to work with and to finish.

Finishing

• Success with a bullfloat has been limited. This concrete is sticky and will pull and tear. The bullfloat can be used but additional hand finishing is usually necessary.

• The newer superplasticizers EO/PO comb polymer (Ethylene oxide/Polyethylene oxide) finish better.

• Concrete with slumps between 125 mm and 150 mm seem to finish the best. Concrete with slumps over 150 mm does not produce such a good finish. New Brunswick decks have a 3% crown.

• The majority of surface imperfections such as aggregate tears and ridges are finished with the hand trowel. The closer the finisher is behind the screed machine the easier it is to finish.

• The area beyond the screed rails that is finished entirely by hand is more prone to problems with meeting the surface tolerance requirements.

• It is easier to finish the concrete under the screed rails when the rails are raised. The screed rails are removed when the concrete is still plastic and the voids are filled with fresh concrete. The use of shorter lengths of screed rail pipe allows the filling and finishing of the voids in a timely manner.

Misting

• The timing of when to mist and how much to mist is important. It will change with the time of day and other weather conditions.

• If concrete is placed at night, early morning, or on a cool day, the misting system will be used sparingly.

• As the placing operation progresses, the misting is heavier and becomes the transition to water curing (which is continued for a minimum of 7 days using a burlap or non-woven geotextile fabric).

Surface Finish

• The surface finish needs to meet the requirements of the waterproofing manufacturer.

• Surface projections are to be ground.

• A delay in finishing the plastic concrete will result in voids in the surface. Trying to remove these voids, by working water into the top surface, is unacceptable.

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Newfoundland and Labrador About 15 bridges have been constructed in HPC since the introduction of an HPC

specification in 1998. The change to HPC is considered a success. Plastic and other cracking is no more than in bridges cast with normal concrete. Finishing, as elsewhere,

has been more difficult than with normal concrete, but, with experience, the finishers have become accustomed to the challenge. Meeting the 1000 coulomb requirement has

not proven to be difficult.

Criteria for HPC are included in the Department of Works, Services, and Transportation

specification Section 904 of January 1999. Key criteria are as follows:

Superstructure 45 MPa at 28 Days 40 MPa at 28 Days

Water/Cement Ratio 0.36 max 0.37 max Slump as per mix design* as per mix design* RCP: coulombs 1000 max 1000 max Air content: % 6+/- 1 % 6+/-1 % Air void system: Spacing factor: µm 230 max 230 max Specific surface: mm²/mm³ 25 min 25 min

* Maximum slump after addition of superplasticizer shall be 230 mm. The mix design

shall state the slump before and after the addition of superplasticizer and appropriate tolerances.

Type 10E-SF cement or Type 10 plus silica fume is specified, and the silica fume content must be 7-10% by mass of cement. Cementitious content for all superstructure concrete is

420 kg/m³. Air content for severe exposure (decks, curbs, endblocks, barriers and grade separation columns) shall be 7+/-1%.

With regard to curing, decks are floated, straight edge and broom finished, and then coated with evaporation retardant. The concrete is then kept moist for at least 7 days at a

temperature of at least 10°C.

The penalty for failure to meet strength requirements is: $ (Adjusted concrete price) = $

(Bid price) - $ (10 (Specified strength-Tested strength)).

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Northwest Territories The department of Transportation specification for cast-in-place concrete was revised in

January 2000. Class SF concrete contains 7.5% silica fume and meets a specified 28 day strength of 35 MPa. Minimum cement content is 350 kg/m³ and maximum water-cement

ratio 0.38. Where fibre is added, the requirements are the same. Air void system requirements are as per CSA A23.1. Temperature at the time of discharge must be

between 10 and 18°C. Curing is by the placing of filter fabric or burlap on the finished

surface as soon as the surface will not be marred as a result. A fine water spray is then applied and the concrete wet cured for at least 7 days.

For bridge deck repairs, requirements are similar with the following exceptions: cement

content: minimum 360 kg/m³, 10% silica fume, 60 kg/m³ steel fibres. Curing by wet

burlap is carried out for a minimum of 3 days.

Penalties for lower than specified strengths are as follow: New construction:

28 Day Compressive Strength Penalty: $/m³ 35 MPa and above Nil

34 to 35 MPa 15 33 to 34 MPa 30 32 to 33 MPa 45 31 to 32 MPa 60 30 to 31 MPa 80 29 to 30 MPa 110 28 to 29 MPa 150 27 to 28 MPa 200

Below 28 MPa Reject Repairs:

28 Day Compressive Strength Penalty: $/m³ 35 MPa and over Nil

32.5-35 MPa 25 30-32.5 MPa 50 27.5-30 MPa 100

Below 27.5 MPa Reject

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Nova Scotia In 1996, Concrete Canada received a request from the Deputy Minister of the Department of Transportation and Public Works (NS TPW) for assistance in the design and construction of a bridge in HPC. Separate meetings were held to discuss design and construction, and a pre-tender workshop was held for bidders. An industry committee consisting of representatives from NS TPW, Dalhousie University, CPCA, the Atlantic Provinces Ready Mixed Concrete Association, Concrete Canada, Jacques Whitford and Lafarge developed the special provisions for HPC (Bickley, 1998). A preconstruction test programme was carried out at Dalhousie University, (Trottier, 1997). Extensive tests were made on suitable locally available aggregates. Six trial mixes were then made, and tested for strength at ages up to 91 days, modulus of elasticity, air void system, scaling resistance and rapid chloride permeability. The early creep of one mix was determined. The bridge is a two span 215 mm thick continuous deck 70.59 m long and 8.85 m wide on three 1900 mm bulb tee girders per span. Uncoated reinforcing steel was 400 MPa grade to CSA G30.12-78. Prestressing strand was 16 mm nominal 1860 MPa grade to ASTM 415 or CSA G279. The specified strength for all cast-in-place concrete in the bridge was 60 MPa, and 65 MPa for the girders. The design in HPC allowed a wider spacing of girders with a consequent reduction in cost. The use of HPC resulted in the elimination of waterproofing and paving and the use of uncoated reinforcing steel. Prior to construction, an economic analysis was made to compare costs for alternative designs (Fletcher, 1997). The results were as follows:

Construction Costs Life Cycle Costs Normal strength bridge $484,697 $578,827 HPC bridge-paved $470,317 $525,070 HPC bridge- exposed deck $444,815 $454,587

As a result of the extensive pre-construction testing, the contract document gave the bidders the option of using the mix developed at Dalhousie or, after carrying out equivalent testing, proposing an alternative mix. The successful contractor chose to use the proven mix, which was as follows:

kg/m³

Type 10E-SF cement (low alkali) 450 Class F fly ash 30 Will-Kare fine aggregate 690 Will-Kare coarse aggregate 1045 Water 144 mL/100 kg of cement Micro-Air 350* Daratard 17 and/or WRDA-82 250*mL/m3 WRDA 19 5000*

*To be adjusted as necessary

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Specification criteria for the concrete were as follows:

• Slump: before superplasticizer: 60 mm, after superplasticizer: 190 +/- 30 mm • Air content at discharge from truck: 7 +/- 1 % • Minimum compressive strength at 28 days: 60 MPa • Spacing factor: average not greater than 230 µm, no value to exceed 260 µm • Rapid chloride permeability at 91 days: 600 coulombs maximum • Maximum delivered concrete temperature: > 2m: 18°C, < 2m: 25ºC • Maximum concrete temperature in situ: 70ºC, maximum gradient: 20ºC

"Curing: Apply an evaporation retarder immediately after initial screeding and/or between finishing operations as needed to aid in bullfloating and final texturing. Curing compound shall be applied at twice the manufacturer's suggested rate immediately after texturing, within 20 minutes of initial screeding and prior to covering with burlap. The second application of curing compound shall be applied at 90º to the first. Two layers of burlap, pre-soaked for 24 hours, shall be placed over the curing compound immediately after initial set of the concrete, kept continuously wet for 7 days, and covered with a layer of moisture vapour barrier immediately following the placement of the burlap". Shortly after the bridge was completed, the construction team met to review the project. With respect to design, the expectations had been that the use of HPC would lead to significant increases in girder spans. In fact, the potential increase was found to be one metre. The reduction in the number of girders, the elimination of the waterproofing and paving, and the use of uncoated steel resulted in cost savings. The service life study confirmed this and contract prices confirmed the study figures. Because a pre-tested mix was specified and time constraints did not allow for the development of an alternative, the specified mix was used. It was felt that, in future, the contractor should propose the mix. It was agreed that testing laboratories retained by the contractor could provide adequate proof of compliance with the specification criteria. The specified mix was used initially by the precaster. Difficulties with the grading of the 20 mm aggregate led to a change to 13 mm aggregate. To meet the release strength of 54 MPa, the water-cement ratio had to be reduced from 0.30 to 0.26. It was agreed that, on future contracts, pre-cast concrete contractors should be allowed to propose mixes based on their experience. It was considered that compressive strengths up to 80 MPa could be specified for girders. The restriction that girders could not be shipped until 28 days after casting should be changed to a lesser delay, taking into account the high early strengths achieved. The cast-in-place concrete was easy to place, but finishing took longer. The longer curing period and other first time requirements affected costs.

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The specified slump of 190 +/- 30 mm for the deck was found to be too high, about 150 mm being more suitable. In future, slump would be determined by site trials. As all superplasticizer was added on site, control of slump was considered possible. The deck was placed in mild weather. The temperature, 24 hours after placing, was 8-12 ºC, and it was 40 hours before the hydration induced temperature rise started. Peak temperature was 23ºC. Neither fog misting, nor evaporation retarder, was used for curing. Curing compound was applied immediately after finishing at twice the rate suggested by the manufacturer. The second application was at 90º to the first. Saturated burlap sheets were applied as soon as the surface could withstand their application. If a catwalk is required in future for fog misting, an extra man will also be needed. Insulation was used on the deck for curing. A 9 m long 0.25 mm wide crack occurred over one pier. There was slight separation at the expansion joints. These cracks were filled by gravity with a low viscosity epoxy. The trial slab was thought to be helpful for contractors handling HPC decks for the first time, and this provision should be kept for two years. On this contract, the trial slab cost $8,000, considerably less than the $18,000 reported for a bridge in Ontario. The pre-bid workshop was considered useful for bidders and their suppliers to become aware of new and non-standard clauses. The deck pour, planned for 6 hours, took 11-12 hours due to reduced loads and the time taken for travel and testing. Overall variation of strength test results was, according to ACI 214 criteria, poor. Air void systems and RCP results were excellent. The owner was satisfied that a durable structure had been achieved. At the time of construction, four corrosion probes were installed in the deck and two in the parapet. Initial readings of corrosion, current densities, and half-cell potentials, taken six months after the deck was cast, showed the steel to be passive (Hansson and Marcotte, 1998). Further readings will be taken in 2002. Annual half-cell surveys by the owner have shown no corrosion activity. Ontario As early as 1992, at least one transportation project with special durability requirements used HPC (Hart et al, 1997), but this was a special use in tunnel segments which did not affect the general acceptance of HPC. In 1994, as part of Concrete Canada's implementation mandate, a combined MTO/CC committee developed the design changes and special provisions needed for the construction of the first bridge in Ontario to incorporate HPC. Prior to this, MTO had investigated the use of HPC as a means of improving structural performance and service life (Schell et al, 1997). In 1992 and 1993, MTO had used HPC in a bridge deck overlay and a thin slab replacement. In 1995, two bridge decks were rehabilitated using HPC overlays.

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The first bridge built by MTO using HPC throughout most of the structure was on Highway 20 over 20 Mile Creek (Bickley, 1996, Schell and Konecny, 2000). This single span bridge, which had a cast-in-place deck on precast prestressed girders, used HPC in the deck and barrier walls, abutments and wing walls. The design was not changed to reflect the 60 MPa concrete used, the object being to investigate the durability of HPC and its potential for use under routine contract conditions. To this end, the deck was not waterproofed or paved and the reinforcement was uncoated. Three types of probes were cast into the deck to measure corrosion activity of the reinforcing steel and corrosion resistance. A number of innovative constructability issues were dealt with in the construction of this project. A mandatory pre-bid meeting for all potential bidders was held at which the differences in the contract resulting from the decision to use HPC were presented and discussed. Trial batches were required prior to submission of a proposed mix design. A trial slab was constructed using the materials, plant and personnel intended for the deck. Tests included in-place measurement of air void systems, temperature monitoring of the deck, provision for insulating the deck to control temperature gradients and RCP tests on cores from the deck. The specified 28 day compressive strength was 60 MPa and Type 10E-SF cement content 450 kg/m³. Some finish problems occurred, but the test results on the hardened concrete were excellent and the project was considered a success. A summary of test data is as follows: Compressive Strength 28 Days MPa

All Tests Deck

Number of tests: N 23 12 Mean strength: X 77.5 80.1 Standard deviation: s 4.77 4.20 Coefficient of variation: V 6.15 5.70 Rapid Chloride Permeability tests: Coulombs

N 28 12 X 823 758 s 191 135

Range (average of 2 tests) 632 - 1365 605 - 995 Air void data; Spacing factor: Before pumping: all data 0.144 mm, deck 0.142 mm After pumping: all data 0.204 mm, deck 0.206 mm Cover to top steel: mean 72.6 mm, standard deviation 7.2 mm. The next prototype bridges were constructed during Phase 1 of Highway 407. This was a 69 km concrete highway with 127 bridges. In 1994, CC made presentations to the design

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and construction team on the potential benefits of HPC for bridge construction. Innovation committees were set up, including one to consider innovative bridge construction. As a result, two of the bridges incorporated HPC (Bickley et al, 1997, Jagasia, 1997). The first used HPC in the deck and barrier walls and the second also used HPC in the precast prestressed CPCI 1900 girders. The reinforcement was uncoated, and corrosion probes were cast into the exposed decks. The specification requirements were similar to those on the Highway 20 bridge, except that a lower cement content was specified and slag was incorporated into the mix to facilitate finishing. Test data for the two decks were as follows:

28-day compressive strength: N = 7 mean 72.8 MPa standard deviation 6.2 MPa Rapid chloride permeability: mean 514 coulombs, range 403-672 coulombs Spacing factor: mean 170 µm, range 106-225 µm It was considered, by those involved, that these trial projects were successful. Subsequently a CC/CAC committee developed input to an HPC specification that formed the basis for the acceptance by MTO of HPC as an alternative material for bridge construction. In May 1998, MTO issued Special Provision No. HPC May 1998. Since then, approximately 60 MTO bridges have been constructed with HPC or are currently under construction. The adoption of this technology by the MTO has led to some consultants and cities following suit. Based on the experience gained on trial and demonstration projects between 1992 and 1998, the 1998 specification introduced by MTO was an end result specification.. In this specification, HPC was defined as follows:

• Minimum 28 day compressive strength: 50 MPa • Must contain silica fume (in Type 10E-SF cement) and may contain other

supplementary cementing materials • Maximum RCP value of 1000 coulombs at 28 days • Minimum air content: 3%, mean spacing factor not to exceed 250 µm, maximum

spacing factor not to exceed 300 µm • Slag or fly ash or slag plus fly ash not to exceed 25% of total cementitious • Superplasticizer added at plant or site • Slump immediately prior to placing or pumping not to exceed 230 mm • Trial mix and trial slab required. Trial slab will be waived if contractor has prior

experience • Fog misting followed by 7 days moist curing.

Based on criteria established by Concrete Canada, delivery temperature was restricted to a maximum of 25°C, and the contractor is required to control the temperature of the

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concrete and the temperature difference within the concrete. The temperature of the centre of the concrete must not fall below 10°C or exceed 70°C and the difference between the centre and the surface must not exceed 20°C. As the presence of significant cracks would compromise the protection provided by the HPC, they must be repaired as follows:

Decks waterproofed and paved: cracks wider than 1 mm Exposed concrete decks: cracks wider than 0.3 mm On the three prototype bridges (Highways 20 and 407), no cracks occurred during the construction that were wide enough to need repair. This is attributed to the fog misting after placing followed by 7 days wet curing, and control of temperature as described above. In keeping with other MTO end result specifications, bonuses and penalties are applied based on the consistency of results. For compressive strength, the mean and standard deviation are used to calculate the percent of results within permissible limits. A bonus payment up to $5/m³ or penalties as great as $40/m³ may apply. Cracks are repaired at the contractor’s expense and criteria for rejection of the work are detailed. Air void determinations on cores are required to meet the following criteria:

Minimum air content: 3% Average spacing factor: 250 µm max Maximum spacing factor: 300 µm In the event these criteria are not met, the concrete is removed or a remediation scheme proposed by the contractor, may be accepted. The Ministry has worked with industry to develop a payment adjustment formula for air void parameters that fail to meet the specification requirements. This will be introduced in the near future. For rapid chloride permeability results, a value of between 1000 and 2000 coulombs results in a penalty of up to $25/m³ of concrete. MTO has continued monitoring these three prototype bridges. Results to date show no deterioration and the absence of any significant corrosion. Recent cracking described later is the cause of some concern and will be watched. The monitoring is covered in more detail in the section on Monitoring in Chapter 10.

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The results obtained using the 1998 specification can be summarized as follows:

• Strength: mean strengths from 51.8 MPa to 64.9 MPa. Standard Deviations from about 3.5 MPa to 6 MPa

• Air void parameters: Average air content: 5.9%, average spacing factor 0.150

mm. The specification requirements were met 98% of the time.

• Rapid Chloride Permeability: averages 380 to 1267, with typical averages being less than 600. High values were found to be due to improper testing. Mixes containing slag averaged 380 to 557 coulombs at 28 days.

MTO experience to 2000 was summarized as follows (Schell and Konecny, 2000): “Field Issues Curing - Although there was resistance, both from contractors and from MTO field staff responsible for enforcement, to the introduction of fog misting and extended wet curing of HPC, this appears to have been largely overcome. A number of contractors have modified their deck finishing equipment to provide machine-mounted fogging systems for deck placements. In some cases and, where it appears to work most effectively, these are augmented by hand-held equipment. With this arrangement, stoppages of the automatic equipment, or redirection of the mist by wind, can be compensated for, and fogging maintained by the hand-held equipment. Consideration is being given to making the presence of a hand-held fogging wand mandatory on site. Finishing - Finishing of bridge deck surfaces has been an issue on several jobs, with grinding of a rough or uneven deck surface necessary, in some cases, to produce a surface smooth enough to receive the normal hot-applied waterproofing treatment. The Ministry's current specification for finishing is aimed more at elimination of high and low areas than dealing with roughness issues, and attention to this area is required. To some extent, this appears to be a function of contractor experience as well as mix design. There appears to be little transfer of experience from one job to the next, as the contractor moves from one concrete supplier to the next. The use of trial slabs has, unfortunately, not provided the intended effect of allowing the contractor to work out his finishing problems prior to starting work on a structure. Appropriateness of Mixes - Although the specification responded to industry's desire for increased allowable replacement of cement by supplementary cementing materials, and greater flexibility in types and amount of cement used, this does not appear to have been exploited to any degree to date. Mixes are conservative, some more so than the original trial work, with extremely high cement contents (450 to 480 kg/m³) typical. Slag at the 25% replacement level, commonly used in conventional MTO concrete, is being used in an increasing number of mixes, about half of those under the current specification, with good results. No contractors have elected to utilize fly ash, or add additional Portland cement, although the specification allows this.

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It is hoped that as contractors and suppliers become more familiar with HPC and with the performance characteristics of their mixes, that there will be more "customizing" and thus optimization of mix designs. For example, there appears to have been no deliberate attempt, to date, to develop mixes with superior finishing characteristics, although it is certainly possible and is desirable from the contractor's viewpoint as well as the ministry's. Appearance - The appearance of MTO's HPC installations is not attractive. Colour of the concrete is dark and blotchy in appearance. Decks are not visible because of waterproofing and paving, but barrier walls and other components are. While this is not expected to be detrimental to performance in any way, it is a factor in terms of overall acceptance of the material. Costs - Based on recent contract figures, a premium of between 0 and 20% of normal costs is being paid for HPC. This is slightly less than the anticipated $60/m³ premium based on assessment of costs related to special features such as trial batches and slabs, and additional curing requirements”. City of Toronto Since 1995, the City of Toronto has used HPC for concrete overlays and deck replacements. Type 10E-SF cement is used. The following are some of the key criteria from the City specification:

• Silica fume content: 8-9.5% by mass • Type 10E-SF cement: 355 kg/m³ min • Aggregate: 13 mm limestone • On exposed concrete decks, the aggregate shall be 12 mm trap rock • Slump at discharge: maximum 75 mm without superplasticizer • Minimum strength at 7 days: 35 MPa • Air entrainment: 7% ± 1% • Maximum concrete temperature as delivered: 25°C

Slag is not used in rehabilitation contracts as there is a need to return the deck to service within a few hours. Fog mist is applied to the concrete during finishing. Pre-soaked burlap with a moisture vapour barrier is placed on the overlay within 2 m of the finishing operation and kept wet for a minimum of 7 days. For bridge decks, a 19 mm limestone aggregate is used. Black reinforcing steel is used and cover is specified as 80 mm ± 10 mm. It is reported that these stringent cover limits have proven to be attainable. All decks are waterproofed and paved. The modest increase in first cost is considered more than offset by better durability leading to a lower service life cost. To date, about 50 bridge decks and 20 overlays have been constructed with HPC.

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A major City project involved seven new bridges over the Humber River at a cost of $100 million. One was a pedestrian and cycle bridge forming part of the waterfront trail. This elegant steel arch bridge has won acclaim for architectural merit. The post-tensioned deck, comprised of only 200 m³ of silica fume concrete, was the only HPC used on this project. The other six bridges carry high volume traffic in and out of Toronto on the Gardiner Expressway. The first of these bridges used traditional bridge deck concrete. Subsequently a change to HPC was made for the remaining five bridges. Key criteria from the specifications for the last five bridges were as follows: Reinforcing steel: uncoated. A trial slab 13 m wide by 10 m long by 250 mm thick was specified. This was to be placed using the mix, plant, methods and personnel to be used on the bridge. Tests on fresh and hardened concrete included cores taken from the trial slab to check compliance with the specification. At the time of the first HPC contract, the degradation of the in-situ air void system of pumped mixes was a concern and the following clause was included in the contract specification:

"Contractors should note that the site transportation and placing of high workability mixes, particularly when pumps are used, can degrade the air void system of the concrete. Contractors should ensure that the potential effects of the site transportation and placing system proposed by them be taken into account by them and their concrete supplier when designing mixes for this project".

Concrete properties were specified as follows:

• Cement: 10E-SF • Silica fume content: 6-8% • 28-day compressive strength: 45 MPa • Cementitious content: 355 kg/m³ minimum • Water-cement ratio: 0.40 maximum • RCP: 1000 coulombs maximum • Air content at end of pump: 6-8% • Air void system (on cores drilled from the structure)

Air content: 3% minimum Average spacing factor: 230 µm maximum No individual test greater than: 260 µm

• Slump: 50 +/- 20 mm before addition of superplasticizer 180 +/- 40 mm after addition of superplasticizer • Maximum temperature of concrete as delivered: 25°C

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Typical compressive strengths for these projects averaged 60 MPa.

Immediate curing was by fog misting until burlap was applied. The contract provided for a penalty of 5% of the value of the day's production of concrete if curing was not started within 10 minutes of the passage of the finishing machine. Final curing was by two layers of pre-soaked burlap covered by white plastic vapour barrier. The burlap was kept continuously moist for 7 days.

A landmark project on which HPC is being used in bridges is the expansion of Toronto's International Airport. As will be seen from this report, the compressive strength specified has varied from project to project. The trend has been from the initial use of 70 MPa in the early Quebec bridges, to 60 MPa in the prototype Ontario bridges, to the adoption of 50 MPa by MTO. The downward trend in specified strength results from a desire to improve the finishability of HPC containing silica fume, and a realization that, if there are no design advantages to the use of high strength, then durability can be assured at lower strength levels. This is provided the specification requires the concrete to meet durability parameters and the specification is enforced. For bridge 201 in the Toronto International Airport expansion, the designer specified a compressive strength requirement of 35 MPa at 28 days. In order to assure durability, the quality of the air void system and chloride permeability of the concrete in-place were specified, a trial slab was mandated, stringent water and thermal curing criteria were used, as provided by the MTO specification, and, through a discussion process that brought all parties on board, a high level of quality control was achieved (Bickley and Fung, 2000). In order to meet the durability criteria, silica fume was used in the mix, together with a maximum water-cementitious ratio of 0.40. Statistical analysis of the compressive strength test results determined that the mix met a specified strength level of 45 MPa. Bearing in mind the high level of QA/QC achieved on this contract, it was suggested that a strength requirement of 40 MPa might be the optimum for general use where a higher strength was not a design benefit, provided that the durability characteristics of the concrete were met. At this strength level economics, durability and finishability could be said to be optimized. A summary of deck concrete test data is as follows:

28-day compressive strength:

N = 20 Mean: 50.5 MPa Standard deviation: 3.5 MPa Rapid chloride permeability: mean: 588 coulombs, range: 411-829 coulombs Spacing factor: mean 203 µm, range: 173-232 µm

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As a result of experience gained on bridge 201, over 40 bridges in the GTAA expansion will be built with HPC, with many already underway or completed. Another project at the GTAA incorporating HPC is the elevated roadway accessing the new terminal. The specification is basically the MTO specification and pours of up to 3000 m³ of the 1 m. thick, post-tensioned deck were made starting in hot weather in the summer of 1999. In order to meet the 70°C maximum temperature, the 20°C maximum temperature gradient, and the maximum delivered temperature of 25°C, a number of steps were taken. In the concrete mix 24% of the 10E-SF cement was replaced with slag, a retarder was used, the coarse aggregate was soaked with cold water and concreting took place at night. In the first pour in June, a maximum temperature of 57-58°C was reached. In-situ test data were as follows:

Mean Standard Range No of Deviation Results Air content: % 6.7 1.4 3.6-9.7 28 Spacing factor: µm 134 19 98-173 28 RCP: coulombs 512 172 263-1053 28

Compression test results at 28 days were analyzed with the following results:

No of results: 100 Mean: 55.14 MPa Standard deviation: 5.43 MPa Coefficient of variation: 9.8% Data from some other bridge projects were as follows:

28-day strength: MPa

Year Component

Specified Achieved

RCP: Coulombs

1997 Deck 35 45.9 575 1997 Overlay 50 60.3 423 1997 Deck 45 49 720 1997 Overlay 45 54.4 - 1998 Deck 50 67.5 378

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Prince Edward Island Hillsborough River Bridge (1996 to 1997) This project consisted of the expansion of an existing steel structure from two lanes to four lanes. This work was undertaken by Strait Crossing Limited as part of the arrangement to construct the Confederation Bridge. The existing abutments and piers were widened to accommodate the increased width and concrete buttresses were added to the existing structural steel frame to support each new lane upstream and downstream on the structure. The project used three different concrete strengths, but for certain elements concrete with a specified compressive strength of 45 MPa was specified. Originally, all concrete was specified with Type 10 cement, however, for the higher strength, the concrete was proportioned with Type 10E-SF (low alkali) cement and Class F fly ash. The mixture had a specified slump of 175 to 200 mm after the addition of superplasticizer, and a total air content of 5 to 8 percent. Results (based on 105 sets of compressive strength specimens) were: Average 28 day compressive strength 54.2 MPa, standard deviation 8.2 MPa Range of 28 day compressive strength 37.2 to 78.6 MPa Average air content 7.6 percent, standard deviation 1.0 percent Range of air content 5.2 to 11.0 percent Average slump 170 mm, standard deviation 35 mm Range of slump 80 to 240 mm In the case of low 28 day results, additional strength specimens held for later age testing at 56 days and, in the majority of cases, met the specified strength of 45 MPa. Some of the low compressive strength results at 28 days were associated with elevated air contents. Pinette River Bridge (1996 to 1997) An existing structure over the mouth of the Pinette River was replaced to correct horizontal and vertical alignment of the bridge and roadway. The cast-in-place concrete specifications for the project were generally based on those used for the Confederation Bridge. All concrete was specified with a minimum 28 day compressive strength of 50 MPa using Type 10E-SF (low alkali) cement and Class F fly ash, 5 to 8 percent total air content, and a slump after the addition of superplasticizer of 190 ± 30 mm. The structure consisted of two spans (versus the original three spans) of New Brunswick DOT Type 1 prestressed precast girders using conventional concrete having a specified 28 day compressive strength of 40 MPa. The abutments and centre pier were founded on 500 mm diameter concrete pipe piles filled with 50 MPa cast-in-place concrete.

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Results (based on 23 sets of compressive strength specimens): Average 28 day compressive strength 56.9 MPa, standard deviation 6.3 MPa Range of 28 day compressive strength 45.8 to 70.2 MPa Average air content 7.2 percent, standard deviation 0.64 percent Range of air content 5.5 to 8.0 percent Average slump 180 mm, standard deviation 33 mm Range of slump 110 to 220 mm For two sets of compressive strength specimens failing to meet the 28 day specified strength, additional specimens cast and tested at 91 days exceeded the specified strength. Québec Taking advantage of the pioneering research on HPC at Sherbrooke University and also at the University of Laval, the Province of Québec has been a leader in the use of HPC in Canada. Organized by the Montreal office of the Canadian Portland Cement Association (CPCA), the "Projet Voies Nouvelles du Béton (Project on New Directions for Concrete)", launched in October 1990 and supported by Concrete Canada, CPCA, MTQ, The City of Montreal, cement producers and structural engineers, provided a framework for HPC projects. As a result, the first bridges in Canada using concrete designated as HPC were built in Québec (Lessard et al, 1993, Malier and Larrard, 1993, Aitcin et al, 1998, Mitchell et al, 1993, Lessard, 1994, and Lachemi et al, 1994). The extensive data obtained, evaluated and publicized, provided invaluable encouragement to others. The first was a 17 m single span bridge at St Eustache, replaced in 1992. Due to the advanced state of deterioration, it was replaced with 70 MPa HPC pretensioned channel girders, placed side by side to eliminate the need for deck slab formwork. The deck was cast in 30 MPa concrete. The 70 MPa was not needed structurally but was used to assure long term durability. The second replacement bridge, also in 1992, was a pedestrian bridge over a 6 lane highway in Laval. The Z-shaped precast pretensioned girders were cast with 70 MPa air entrained HPC. The girders were erected during one night to avoid traffic delays. The girders were connected structurally by precast deck slabs with a latex concrete topping. The third bridge was at Portneuf, in fall 1992 (Aitcin and Lessard, 1994). This was a single span rigid frame comprising precast post-tensioned beams, a thin cast-in-place deck and external prestress cables. The specified 28 day compressive strength was 60 MPa. Test results averaged 75.3 MPa with a standard deviation of 3.5 MPa and a coefficient of variation of 4.6%. The average air content in-place was 5.4% with a standard deviation of 0.8% and a coefficient of variation of 15%. The average spacing factor of the air void system in the hardened concrete was 190 µm with a standard deviation of 33 µm. and a coefficient of variation of 4.6%.

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The fourth bridge was built in 1993 over Highway 50 near Mirabel. It was a two span continuous structure comprising precast beams and a cast-in-place deck and external prestress cables. Compared to a bridge of the same design made with conventional bridge concrete, the cost was 5% less (Coulombe and Ouellet, 1995). The mean compressive strength at 28 days was 80.7 MPa and the air content 6.3%. By the end of 1997, a total of 12,065 cubic metres of HPC had been used by the MTQ in 14 bridges (Coulombe and Vezina, 1998). Most bridges used 60 MPa cast-in-place decks on 60 MPa AASHTO precast, prestressed girders. Pumping concrete was not allowed, so as to avoid degradation of the air void system. On all contracts, the specification requirements for compressive strength, air content, slump and spacing factor were met. A survey of two bare decks subjected to the direct action of de-icing salts were as follows: Chloride ion content in the bare decks after 5 years: % by weight of concrete

Depth: mm 0-12.5 12.5-25 25-50 50-75 75-100 Portneuf 0.164 0.017 0.008 0.009 0.008 Mirabel 0.035 0.008 0.009 0.008 0.008

Test data from the first 13 bridges built by the MTQ from 1992 to 1998 were as follows (Vézina,1997):

Test MPa Mean s Min Max n Slump: mm 60 168 28 130 210 6 50 150 34 90 200 7 Air: % 60 5.8 0.8 4.5 6.8 6 50 5.7 1.1 4.5 7.6 7

Compressive 60 73.6 8.4 56 83 6 Strength: MPa 50 62.5 5.6 50 74 7 Spacing factor: µm 60 208 54 157 319 6 50 177 25 125 218 7 Specific surface: in-1 60 24.8 3.0 19.9 30.7 6 50 27.5 3.5 21.1 33.6 7 Scaling: kg/m² 60 0.071 0.03 0.16 6 50 0.102 0.019 0.18 5

RCP: coulombs 60 393 165 1237 5 50 666 205 1319 8

Notes: MPa is the 28 day strength specified, s is the standard deviation, n is the number of bridges to which the data relate.

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Criteria for HPC mixes from the MTQ Standard 3101 are as follows:

TYPE XIIIA XIIIB

Compressive strength at 28 days: MPa 50 60

Minimum cement content: kg/m³* 360 380 Water-cement ratio 0.37 0.35 Coarse aggregate size: mm 5-14 5-14 Air content: % 4-7 4-7 Slump: mm +/- 40 180 180 Scaling: 0.5 kg/m²/50 cycles yes yes

* For cast-in-place concrete Type 10E-SF, for prestressed precast beams Type 30 + 7 -

10% silica fume or Type 30E-SF. Water-cement ratio includes silica fume as cement. In 1995, the deck of the Jacques-Cartier Bridge in Sherbrooke was reconstructed between August and November with 1,800 m³ of 60 MPa air entrained HPC (Blais et al, 1996). In hot weather, ice was used and, in cold weather, hot water to maintain delivery temperatures of 18ºC maximum in hot weather, and 22ºC in cold weather. The high early development of strength accelerated the construction and it was estimated that this saved $150,000 just in the reduced times that drivers had to use a 3 km detour. This does not include significant savings in user delay costs. During the rehabilitation of the Benjamin-Moreau Bridge in 1996 (Aï tcin, 1998), the opportunity was taken to investigate whether or not the degradation of air void systems during pumping could be mitigated. High-slump HPC was used in the reconstruction of the parapet wall. The wall was divided into four sections and different pumpline configurations and pressures were used in each section (See figures 1-4). The results were as follows:

1 2 3 4 A B A B A B A B

Fresh concrete Slump: mm 165 100 195 170 200 170 220 130 Air content: % 5.0 4.0 5.5 2.6 4.2 2.8 5.1 2.1 Hardened concrete Compressive strength: MPa 76.4 78.7 70.3 81.9 76.4 82.5 73.3 78.6 Spacing factor: µm 205 395 195 485 220 450 215 470 Air content: % 4.8 3.6 5.3 2.3 3.7 2.8 4.6 2.3 Scaling: kg/m² 0.01 0.01 0.01 0.01 0.01 0.02 0.02 0.02 Length change: mm 0.025 0.025 0.025 0.025 0.025 0.025 0.010 0.030 Durability factor: % 99 100 99 98 100 99 98 98 Notes: A: Before pumping B: After pumping Scaling: ASTM C 672 Length change: ASTM C 666 Durability factor: ASTM C 666, procedure A

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It was not possible, from the above data, to determine a systematic way of reducing the degradation of the air void system during pumping. Despite the degradation of the air void system in all configurations, the durability of all the resulting concrete was excellent. The City of Montreal is a leader in the optimum utilization of HPC. In 1994, a mix containing silica fume and specified to meet a 40 MPa strength was used on the Wellington Bridge. The test results were approximately 50 MPa at 28 days. Between 1996 and 1997, three projects used HPC based on specifications developed jointly by the City of Montreal and Sherbrooke University. The Henri-Bourassa-Albert-Hudon and Henri-Bourassa-Merien overpasses used 50 MPa HPC in the structural sidewalks, gradient walls, columns, parapet and central wall. The Rodolphe-Forget overpass was made entirely with 50 and 60 MPa HPC. Subsequently, HPC was used on the Chabanal and Peel-de la Commune enclosed passageways. To date, HPC has been used in the repair of about 25 structures. On some, a Ternary cement has been used and these are described in Chapter 9. During the above period, the City staff worked with concrete experts from industry, suppliers and MTQ to develop a specification for HPC. A first edition was produced in June 1998 and a second edition in January 2000 (Morin and Campeau, 2000). This specification is a stand-alone document covering materials and methods of construction. It is one of the most developed City specifications for HPC in Canada to date. Some requirements of interest are as follows:

• Notes are provided for guidance on the effects of pumping on temperature, slump and air content.

• Cement is Type 10E-SF except where concrete dimensions are large enough to cause problems due to heat of hydration. In such cases, Type 20 cement with a maximum heat of hydration of 350 J/g at 7 days is specified.

• Maximum temperature of concrete on delivery: 5-22°C for components less than 750 mm thick, 5-20°C for components greater than 750 mm thick.

• Maximum internal temperature: 70°C. • Maximum spacing factor determined on standard test specimens: 230 µm before

pumping, 325 µm after pumping. • Maximum RCP value: 1000 coulombs at 28 days unless a later age is specified. • Maximum scaling loss: 500 g/m² after 56 cycles using BNQ test 2621-90.

Immediately after initial finishing, an evaporation retarder is sprayed on flatwork. Curing by pre-soaked burlap or synthetic fibre mats is started as soon as the surface can support workers without damage. Wet curing is continued for an uninterrupted period of 7 days and at a temperature of at least 10°C.

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An important aspect of the use of HPC is the control of shrinkage cracking. Autogenous shrinkage is of particular concern in HPC, but most data available to date have been generated by laboratory experiments. The opportunity was taken by the City, in co-operation with the University of Sherbrooke, to instrument two components of a CNR viaduct in Montreal during construction (Nikola et al, 2000). Thermocouple equipped vibrating strain gauges were placed in a column and in the deck. The column was 5m high and 1.2 m in diameter. The deck was 1.3 m thick and contained 1370 m³ of concrete. Concrete composition and data were as follows: Component W/B Binder Entrained f1

c Curing Conditions Ratio Type kg/m3 Air %2 MPa

Column 0.38 10SF 390 8.4 50/52³ Sealed quasi adiabatic conditions

Deck 0.38 10BA 450 5.9 40/40³ 7 days wet curing Notes: 1: Low-Alkali, 2: Before pumping, 3: Targeted/Obtained. It was reported that, in the column during the first 3.5 days, autogenous shrinkage opposed thermal expansion. For the next 3.5 days, autogenous shrinkage acted in the same way as thermal contraction, but was less significant than in the first three days. In the deck, after 7 days, thermal gradients and water curing resulted in shrinkage in the surface of 90 µm/m and expansion at the bottom surface of 100 µm/m. Saskatchewan During the last four years, the Department of Highways and Transportation has used HPC in the superstructure (decks and barrier walls) of about six new bridges. The concrete mix used contained 22.7 kg of silica fume per cubic metre (approximately 7% of cementitious content) for durability purposes. Silica fume has been incorporated into the concrete for standard precast prestressed box girders for modular bridges constructed on the highway system by SDHT forces. Approximately 15 bridges with girders incorporating silica fume have been constructed since 1994. While most of these bridges are simply paved with hot mix asphalt, one structure was constructed with a concrete overlay containing silica fume. Concrete containing silica fume has also been used on deck rehabilitation projects since 1994. To date testing for in-situ air void systems and rapid chloride permeability has not been specified.

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REFERENCES Carter, P.D., "Use of High Performance Concrete for Construction and Restoration of Alberta Bridges",

Proceedings University of Calgary Symposium on High Performance Concrete, Calgary, November 1998.

Johnston, C.D., "Superplasticizers for Concrete Bridge Construction", Alberta Transportation and Utilities, ABTR/RD/PAP-93/08.

Taylor, P., Torrejon, J.E.and Manniche, K., "Use of Concrete in the Annacis Bridge Main Span", Proceedings International Conference on Concrete in Transportation, Vancouver, September 1986, ACI SP 93, pp. 695-720.

Morgan, D.R., "Columbia River Suspension Bridge: Deck Overlay Replacement", Presented at the ACI Convention, Toronto, October 2000.

Strang, F.A., "Present Developments in the Construction of High Performance Concrete Bridge Decks", Presented at the ACI Fall Convention, Toronto, October 2000.

Bickley, J.A., "Design, Construction Testing and Monitoring of West River East Side Road High Performance Concrete Bridge", Concrete Canada Report, May 1998.

Trottier, J.F., "High-Performance Concrete Bridge Structure", Mixture Design and Testing, Department of Civil Engineering, Dalhousie University, December 1997.

Fletcher, J, "Project Outline and Economic analysis: West River East Side Bridge, Pictou County, Nova Scotia", Presented at Concrete Canada meeting, October 1st, 1997.

Hart, A.J.R., Ryell, J. and Thomas, M.D.A., "High Performance Concrete in Precast Tunnel Linings: Meeting Chloride Diffusion and Permeability Requirements", PCA/FHWA International Symposium on High Performance Concrete, New Orleans, October, 1997, proceedings, pp. 294-307.

Schell, H.C., Berszakiewicz, B.and Ip, A.K.C.,"Developing High Performance Concrete Specifications for Highway Bridge Construction-Experience of the Ontario Ministry of Transportation", Proceedings PCI/FHWA International Symposium on High Performance Concrete, New Orleans, October 1997, pp. 328-342.

Bickley, J.A.,"The Use of High-Performance Concrete in the Construction of Highway 20 Bridge Over 20 Mile Creek", Concrete Canada Report, October 1996.

Schell, H.C. and Konecny, J., "Ontario's Approach to Ensuring Quality of High Performance Concrete", Presented at the ACI Convention, Toronto, October 2000.

Bickley, J.A., Berzakiewicz, B., Carter, K., Pianca, F. and Raven, R. "Construction, Testing and Monitoring of Highway 407 High-Performance Concrete Structures B22A and B22C at Levi's Creek in Mississauga", Concrete Canada Report, August 1997.

Jagasia, H. K., "Design and Construction of High Performance Concrete Bridges on 407 Express Toll Route", Proceedings PCI/FHWA International Symposium on High Performance Concrete, New Orleans, October 1997, pp. 533-542.

High Performance Concrete, Special Provision 904HPC, Ontario Ministry of Transportation, May 1998, pp. 13.

"Humber Pedestrian Bridge", Delcan Report, undated. "The Gardiner Expressway Bridges, Summary", Delcan Report, undated Crabb, J.M., Meyboom, A.and Anderson, W.V., "The Gardiner Expressway Bridges", Presented at the

Sixteenth Congress of the International Association for Bridge and Structural Engineering, "Structural

Engineering for Meeting Urban Transportation Challenges", Lucerne, September 2000. Bickley, J.A. and Fung, R.," Optimizing the Economics of High-Performance Concrete", Cement

Association of Canada publication, Summer 2000.

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Lessard, M., Gendreau, M.and Gagné, R., "Statistical Analysis of the Production of a 75 MPa Air Entrained Concrete", Symposium on the Utilization of High Strength Concrete, Lillehammer, Norway, June 1993, pp. 793-800.

Malier, Y. and de Larrard, F., "French Bridges in High-Performance Concrete",Symposium on the Utilization of High Strength Concrete, Lillehammer, Norway, June 1993, pp. 534-544.

Aï tcin, P-C., Ballivy, G., Mitchell, D., Pigeon, M. and Coulombe, L-G., "The Use of High-Performance Air Entrained Concrete for the Construction of the Portneuf Bridge", Symposium on High Performance Concrete in Severe Environments, ACI SP-140, pp. 53-72.

Mitchell, D., Pigeon, M., Zaki, A.R .and Coulombe, L-G., "Experimental Use of High-Performance Concrete in Bridges in Quebec", Structural Concrete Conference, CPCA/CSCE, Toronto, May 1993, pp. 63-72.

Lessard, M., "Statistical Analyses of the Results from the Highway 50 Viaduct in Mirabel", Concrescere, Newsletter of Concrete Canada, no 11, March 1994.

Malier, Y. and de Larrard, F., "French Bridges in High-Performance Concrete", Symposium on the Utilization of High Strength Concrete, Lillehammer, Norway, June 1993, pp. 534-544.

Aï tcin, P-C., Ballivy, G., Mitchell, D., Pigeon, M. and Coulombe, L-G., "The Use of High-Performance Air Entrained Concrete for the Construction of the Portneuf Bridge", Symposium on High Performance Concrete in Severe Environments, ACI SP-140, pp. 53-72.

Mitchell, D., Pigeon, M., Zaki, A.R. and Coulombe, L-G., "Experimental Use of High-Performance Concrete in Bridges in Quebec", Structural Concrete Conference, CPCA/CSCE, Toronto, May 1993, pp. 63-72.

Lessard, M., "Statistical Analyses of the Results from the Highway 50 Viaduct in Mirabel", Concrescere, Newsletter of Concrete Canada, no 11, March 1994.

Lachemi, M., Bois, A-P, Miao, B., Lessard, M. and Aï tcin, P-C., "First year Monitoring of the First Air Entrained High Performance Bridge in North America", ACI Structural Journal, July-August 1996, pp. 379-386.

Aitcin, P-C., and Lessard, M. 1994. "Canadian Experience With Air-Entrained High-Performance Concrete", Concrete International, Vol 16, No 10, pp. 35-38.

Coulombe, L-G. and Ouellet, C., "Construction of Two Experimental Bridges Using High-Performance Air-Entrained Concrete", presented at the Transportation Research Board 74th Annual Meeting, Washington, January 1995.

Coulombe, L-G. and Vezina, D., "Utilization of High Performance Concrete in Bridge Construction by the Québec Ministry of Transportation ", Proceedings International Symposium on High-Performance and Reactive Powder Concretes, Sherbrooke, August 1998, Vol 4, pp. 81-90.

Vezina, D., "Experience du Ministere des Transports du Quebec Avec le Beton Haute Performance (1992 A 1997)", Proceedings ACI Quebec and Eastern Ontario Chapter seminar, December 1997, pp. 89-98.

Blais, F.A., Dallaire, E., Lessard, M. and Aï tcin, P-C., "The Reconstruction of the Bridge Deck of the Jacques-Cartier Bridge in Sherbrooke (Québec) Using High-Performance Concrete", Proceedings CSCE Annual Conference, Edmonton, May/June 1996, Vol llb, pp. 501-508.

Aitcin, P-C, "Yamaska Bridge: Air-Void Stability and Finishing Field Trials for Pumped HPC", Concrete Canada Report, 1995.

Morin, R. and Campeau, A., "Devis Technique Normalisé Pour Le Béton À Haute Performance (BHP), 3VM-20, Ville de Montréal, Janvier 2000.

Petrov, N., Morin, R., Bonneau, O. and Aï tcin, P-C., "In-Situ Shrinkage in High-Performance Concrete Structures", Proceedings RILEM International Workshop on Shrinkage of Concrete-Shrinkage 2000, Paris, October 2000.

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Sturgeon Bridge - stainless steel reinforcement

Bob Ramsay, UMA Group

58

Deck Prepared for Waterproofing

Fred Strang, NBDOT

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General view of Columbia River Bridge at Revelstoke, B.C.General view of Columbia River Bridge at Revelstoke, B.C.

Rusty Morgan, AMEC

SkyTrain Extension Vancouver, BC

Jack Clark

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Chapter 4 Precast Concrete Confederation Bridge The pre-eminent example of the use of precast HPC is the Confederation Bridge (Holley et al, 1999 and Langley et al, 1997). At 13 km, it is one of the longest multi-span bridges in the world. With spans up to 250 m and girders weighing 7500 tonnes, it is an outstanding example of the potential for the use of precast concrete. Designed for a service life of 100 years in a freeze-thaw marine environment, protection of the uncoated steel in the superstructure is provided solely by the concrete. The following are extracts from the first referenced paper:

"Most of the bridge components, including the main girders and support piers, were fabricated on land at one of two precast facilities situated either side of the bridge. Seven different types of concrete were required to provide various combinations of the following properties:

• low permeability to chloride ions • high early strength (for post-tensioning) • high resistance to ice abrasion • low heat rise in massive sections • underwater placement (tremie concrete) • slipforming • high density for ballast • resistant to freezing and thawing, and saltwater attack (all exposed concrete) • pumping (most concrete) • high flow in congested areas • controlled set"

A blended low-alkali 10E-SF cement ground to significantly finer limits (89.7% passing a 45 µm sieve) than required by CSA A 362 was used. An extensive preconstruction testing programme included the following tests:

• 500 cycles of rapid freezing and thawing, ASTM C666 procedure A • 100 cycles of de-icer salt scaling tests, ASTM C672 • 90-day chloride penetration ponding tests, AASHTO T259 • Abrasion resistance, ASTM C1138 • Water permeability • Creep and shrinkage at various ages of loading, ASTM C512

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Specified concrete properties.

Concrete Class Class A Class C Class F

Strength: Mpa 18 hrs 30 28 days 55 30 91 days 60 40 28 days cast in air 35 28 days cast in water 28 10SF cement: min kg/m³ 450 300 400 Fly ash: max kg/m³ 130 W/cm: max 0.34 0.4 Chloride Permeability: max coulombs 1000 1000 Water permeability: max m/s 14-10 Air content: % 5 to 8 5 to 8 4 to 7 Spacing factor: µm Mean 230 230 - Individual max 260 260 - Slump: mm 180+/-40 180+/-40 Slump flow: mm - 500 to 600 Chloride content: max % of cement 0.06 0.06

Mix proportions for the main classes of concrete and typical trial mix test results were as follows:

Concrete Class A1 A1-F5 C3-2 Ice-Shield F

Mixture proportions (kg/m³) Type 10SF 453 435 329 507 309 Fly ash - 46 130 58 103 w/cm 0.33 0.31 0.31 0.25 0.4 Slump (mm) Initial 220 210 220 200 220 After 30 min 170 150 190 200 200 Air content (%) 6 6.2 7 7 6 Spacing factor (µm) 158 191 162 163 N/A Compressive strength (MPa) 1 day 26.3 25.7 7.7 38.9 3 day 19 7 day 34 28 day 68.3 68.5 56 79.4 52 91 day 73.5 76.7 64.7 92.1

Note: A1-F5 was mix A1 modified with 10% fly ash to reduce the loss of air during pumping.

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Properties of the mixes were as follows:

Concrete Class A1 A1-F5 C3-2 Ice-Shield

Freezing and Thawing: RDF% 300 cycles 99 99 100 100 500 cycles 100 100 100 100 Salt scaling: mass loss g/m² 50 cycles 36 34 278 66 100 cycles 112 448 591 102 Rapid chloride permeability: coulombs 28 days 450 475 780 315 91 days 300 225 260 235 Chloride ion penetration: 91 days - mm 0-13mm 0.082 0.166 0.2 0.068 13-25mm <0.002 <0.002 0.013 <0.002

The maximum concrete temperature allowed during hydration was 70°C and the maximum temperature gradient was 20°C/m. The factors resulting in the successful placement of 450,000 m³ of HPC on this project were described as follows:

"This exceptional performance was made possible by applied concrete technology, rigorous material testing, high standards and quality control, and solid partnering between the producer and the general contractor working together to solve unexpected problems encountered during the placement of large quantities of high performance concrete".

Bridges The use of HPC in precast prestressed concrete bridge girders has been shown to result in technical and economic benefits. In Alberta, it has been shown that the 20 hour transfer strength can be met and a 60 MPa 28 day strength achieved at lower material cost and without the traditional use of accelerated curing (Johnston, 1989). On the Highway 407 project, two bridges were constructed of HPC. For the second, the CPCI 1900 precast prestressed girders were cast with 60 MPa HPC. The transfer strength was 48 MPa and oversize 0.5 inch strand (13.08 mm diameter) was used to reduce the number of strands. By these means, the number of girders required were reduced from 4 to 3, a saving of about $30,000 (Jagasia, 1997, Bickley et al, 1997). A study of HPC girder costs (Hassanain and Loov, 1998) for a two span continuous slab on girder 3 lane bridge using CPCI 1400 girders showed that, as the concrete strength was increased, the total superstructure costs decreased. Each span was 28 m. For instance, an increase in the compressive strength of the girders from 43.4 MPa to 72.1

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MPa decreased the superstructure cost from $163/m² to $130/m² where low trans-portation and erection costs prevailed. Where transportation and erection costs were high, the costs were, respectively, $252/m² and $183/m². As on Highway 407, the reduced cost resulted from the need to use fewer girders with the HPC alternative. A study of the economics of high strength concrete in spliced prestressed girders (Lounis and Mirza, 1998) showed similar trends. A study of AASHTO-PCI bulb-tee 72 girders with spans of 45, 50 and 55 m, and concrete strengths of 40, 50, 60 and 70 MPa showed increases in maximum permissible girder spacings. Again, this permits the use of fewer girders. In both of the last two studies cited, there was a maximum concrete strength beyond which no additional benefit accrued, or at which the strength was unattainable or release strengths could not be achieved. Test data for precast components for four bridges in Ontario were as follows:

Martingrove MTO 98-39 Dundas Street Specified strength at 28 days: MPa 60 50 45 Type of cement 10SF 30 30 Pelletized silica fume yes Yes Fly ash yes No of results 9 3 7 Slump:mm Mean 202 50 203 Standard deviation 26.8 nil 25.5 Air content: % Mean 5.3 5.7 4.6 Standard deviation 0.4 1.2 0.3 Compressive strength at 28 days: MPa mean 71 60.2 63.4 standard deviation 5.2 1.8 1.9 RCP:Coulombs (average) - - 711 Spacing factor: um (average) - - 151 On the fourth bridge project, the initial mix used tended to flash set. This problem was solved by the use of retarders. The test data for the double tees were as follows:

Number of Mean 28 day Standard results strength: MPa Deviation: MPa

Before retarder 60 58.3 5.4 After retarder 103 75 7.3

The coefficient of variation of the results before and after adding a retarder were similar, showing that the mix was the problem, not the level of quality control.

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In 1998, bulb tees were used on Highway 14 and Whitemud Freeway overpass. Release strength was 35 MPa at 12 hours. Type 30SF cement was used. Bulb tees were also used on the Highway 3 bridge over Local Road G/S near Monarch. Release strength was 38 MPa and 28 day strength was 65 MPa. Span was 33.5 m. The concrete contained 10% silica fume. Data from two recent Alberta projects were as follows:

Anderson Road Calgary Airport Interchange Parkade Trapezoidal 3660 wide Double Tees Girders 100 mm thick flange

Type 30 cement: kg/m³ 450 380 Silica fume: kg/m³ 22.5 31 W/cm ratio: 0.28 0.32 Accelerated cure yes yes Finishing aid no yes

Performance Average 28 day strength: MPa 80 65 Average 16 hour strength: MPa 40 30 Average air content: % 6 6 Slump: mm 150 130 RCP at 28 days: coulombs 600 505

Prestressed precast girders were used in the following bridges in Manitoba: Rural Municipalities

Bridge No Type Span: Metres Northern Affairs 24 Channel 12 Cooks Creek 18 " 12 Boyne River 24 " 8 La Salle River 24 " 12

All contained 8% silica fume, and met a 40 MPa 28 day strength requirement. For the Main Street Bridge over the Assiniboine River, the City of Winnipeg used 26 post-tensioned precast trapezoidal box girders in phases 1 and 2. Specified strength at 28 days was 60 MPa. The concrete contained 8% silica fume. Type 10E-SF cement has been used in the manufacture of prestressed bridge girders in New Brunswick and Nova Scotia since 1995 (Thomas et al, 1998).

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Because of concerns with the potential alkali-aggregate reactivity characteristics of Nova Scotia and New Brunswick aggregates, low-alkali 10E-SF cement is used. Approximately 900 HPC girders have been produced for bridges in New Brunswick. Typical properties of these girders are as follows:

Type 30 Low-Alkali Type 10SF Low-Alkali Type 10SF No corrosion inhibitor Corrosion inhibitor

Cement: kg/m³ 430 433 433 Water 172 151 151 W/CM 0.40 0.35 0.35 Slump: mm 125 155 135 Air: % 4.0 6.0 6.0 Strength: MPa 12 hours 36.8 24 hours 37.9 30.2 28 days 61.4 65.4 58.0 Absorption: % 4.23 2.76 Concrete Pipe Type 10E-SF cement is used in the production of concrete pipe, storm drains, box culverts and concrete manholes for use in aggressive environments. In 1997, silica fume concrete pipe was used in the Mixed Cargo Terminal Project at Belledune, New Brunswick. It was also used in the Cave Creek Collector Upgrade Sewer in Ottawa, in a high chloride environment. A 50-year life was specified, and the use of 10E-SF cement proved to be the most cost-effective alternative. The pipe was dry cast with 455 kg/m³ Type 10E-SF cement containing 7.5% silica fume, a w/cm ratio of 0.23 and an air content of 5-7%. Typical properties of this pipe were as follows (Smith, 1996):

Specified Type 10SF Type 10 Max absorption: % 2.5 2.0 5.0 Max RCP: coulombs 2500 450 2500 28-day strength: MPa 62 50

Apart from the improved physical properties, the surfaces of the pipe were smoother than normal production pipe.

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Precast Concrete Slabs Prestressed precast slabs were cast in New Brunswick for wharf projects in Eastport, Maine and Halifax, Nova Scotia. Target release strengths of 32 MPa were achieved in 22 hours without the use of heat. Compressive strengths at 28 days exceeded 90 MPa using 450 kg/m³ of 10E-SF cement. Hollowcore Slabs Hollowcore slabs were made with 10E-SF cement where Type 20 was specified. A better finish was obtained than that normally achieved using the regular production mix of Type 30 cement plus fly ash. Tunnel Segments Two major tunnel projects in Ontario have been lined with precast HPC tunnel segments designed to have a 100-year service life (Hart et al, 1997). These contracts are believed to be the first in North America to have chloride diffusion and water permeability criteria specified as contract requirements. The first was the CN St Clair River Rail Tunnel, constructed from 1992-1994. The tunnel had an internal diameter of 8.4 m resulting in unusually large segments. Each of the six segments forming a tunnel ring was 5 m long, 1.5 m wide and weighed 7.5 tons. Key requirements from the concrete specification were as follows:

• Cementitious content: 400-550 kg/m³ • Compressive strength at 28 days: 60 MPa • Maximum water-cementitious ratio: 0.38 • Non air entrained concrete • Maximum chloride diffusion at 120 days: 600 x 10 15 m²/sec • Maximum water permeability at 40 days: 25 x 10-15 m/sec • Minimum proportions of fly ash or slag and maximum proportions of silica fume

Groundwater chlorides of up to 4000 ppm, sulphates up to 155 ppm and a hydrostatic head of 35 m mandated a very low permeability concrete to meet a 100-year service life requirement. The initial use of a mix containing 30% fly ash and 6% silica fume met the diffusion criterion, but hairline cracking, attributed to the use of silica fume, led to the elimination of silica fume in the mix. Subsequently, few diffusion tests met the specification criterion, but a water permeability test did. Based on a paper by Thomas and Matthews (1996), a significant long-term improvement in the diffusion coefficient was predicated under the saturated conditions existing in service. Compressive strength tests on 381 sets of standard cylinders averaged 76.3 MPa with low standard deviation. RCP test on cores removed from a trial segment gave values of 284 - 366 coulombs for the extrados and 190 - 212 for the centre of the segment.

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The second contract was the segments for the Sheppard Line Subway in Toronto. These segments for a 5.2 m diameter tunnel were more typical in size than those of the St Clair tunnel. Key requirements from the contract specification were as follows:

• Cementitious content: 400-550 kg/m³ • Compressive strength at 28 days: 60 MPa • Maximum water/cementitious ratio: 0.35 • Minimum supplementary cementing materials content: 25% • Air entrainment to meet freeze-thaw criteria according to ASTM C 666,

procedure A • Chloride diffusion values at 120 days: Target: 1000 x 10-15 m²/sec

Maximum: 1500 x 10-15 m²/sec • Water permeability: maximum: 100 x 10-15 m/sec

Production values were as follows:

• Chloride diffusion (x 10-15 m²/sec): Mean: 554, maximum: 1300 • Water permeability (x 10-15 m/sec): mean: 1.34, maximum: 4.77 • Compressive strength (791 tests): 74.9 MPa

The results of 6 comparative diffusion and RCP tests were as follows:

• Mean of diffusion tests: 662 x 10-15 m²/sec • Mean of RCP tests: 390 coulombs

The specification of diffusion and water permeability as acceptance criteria was a strategy to ensure long service life in severe exposure conditions. In practical terms, a 120 day test is unacceptable to contractors at both the bidding stage and as a QC test during production. The opportunity was taken on the Sheppard Line contract to make trials of a faster test more suited to production QC ( DeSouza et al, 2000). A sorptivity test was used on the extrados of segments after initial accelerated steam curing followed by 5 days curing in a fog room and a further 8 days in stockpiles. The 14 day test age was adopted as the earliest at which reasonably consistent moisture equilibrium would be achieved. The results were combined with an established mean diffusion value for the segment concrete and the predicted service life read of a graph. A 14 day test is not ideal, but is an improvement on a 120 day test. Further development in this area is desirable.

Spun Concrete Poles The durability of concrete utility poles, including those spun-cast, has not been satisfactory. The exposure to de-icing chemicals and freeze-thaw attack is severe. Cover is inevitably small to keep the dimensions and weight of the poles within acceptable limits. Further, past production procedures induced cracking due to internal shrinkage of the concrete. Poles are produced in large numbers resulting in the potential for economies of scale if overall weight could be reduced.

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Research at the University of Calgary (Dilger and Rao, 1996) established principles for the design of suitable mixes and spinning and curing regimes. These principles allow the design of concrete mixes with high strength, lower weight and very good durability. Building on this research, a test programme was carried out by The University of Calgary and Sky Cast Inc. of Guelph (Dilger et al, 1998). The research demonstrated that a properly proportioned mix could be fully consolidated without segregation and prestressed within 6 to 8 hours. The durability and strength characteristics of the optimized concrete mixes were determined for all critical parameters. Subsequently, tests were initiated by Sky Cast Inc. and carried out by an independent laboratory in 1999 to confirm the strength and durability of production poles. Some of the properties of a production pole were as follows:

Test Result Specified Resistance to Freeze-thaw ASTM C 666, Procedure A Relative Dynamic Modulus: % 92.2 90 min Length Change: % 0.002 0.035 max

Salt Scaling Resistance Mass loss: kg/m² 0.72 0.80 max

Resistance to Chloride Ion Penetration Coulombs Passed in 6 hours 231 1000 max

Chloride Diffusion at 120 days x 10-12 m²/sec 0.65 no limit

Air Void Parameters Air content: % 2.2 3.0 min Spacing factor: mm 0.185 0.3 max

Compressive Strength: MPa 7 days 65.8 28 days 72.1 50 56 days 73.5

All of the above acceptance criteria are Ontario specified, except strength which is the requirement in the CSA Standard A 14-00 Concrete Poles. The above results characterize a high strength very durable pole with an expected service life of more than 35 years. The study showed that twice as much cover would be needed if HPC were not used.

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Parking Structures Test data for a parking structure in Brampton, Ontario using precast beams and double tees was as follows:

Plant 1 Plant 2 Specified 28-day strength: MPa 40 40 Type of cement 30 10SF Pelletized silica fume yes Fly ash yes No of test results 33 16 Slump: mm Mean 178 209 standard deviation 15.2 6.2 Air content: % Mean 5.5 5.4 standard deviation 0.35 0.7 Strength Mean 64 60 standard deviation 3.4 3.9 RCP: coulombs (average) 623 1148 Spacing factor: µm (average) 180 197

Precaster Experience A precaster with plants in British Columbia, Alberta, Saskatchewan and Manitoba summarizes experience with HPC for precast concrete as follows:

• No problems with plastic shrinkage cracking, thermal shock or microcracking during a decade of experience with precast bridge girders using HPC containing silica fume up to 9 %. Girders were mainly bulb-tee sections, with some trapezoidal sections and box and channel sections. All were poured inside a plant under controlled conditions.

• Finishing problems and/or minor cracking have been encountered with flatwork type panels and double tees poured with higher dosages of silica fume. A limit to a 5% silica fume content is recommended for these types of units. Finishing aids have proven to be helpful in minimizing problems on flatwork utilizing silica fume.

• RCP testing has produced fairly variable results. More correlation testing or a correlation of this and chloride ponding type tests is recommended.

• Research should be undertaken on the performance of HPC structures as they age. The effects of construction practices and cracking should be investigated.

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REFERENCES Holley, J.J., Thomas, M.D.A., Hopkins, D.S., Cail, K.M. and Lanctot, M-C., "Custom HPC Mixtures for

Challenging Bridge Design", Concrete International, Vol 21, no 9, September 1999, pp. 43-49. Langley, W.S., Gilmour, R.A., Turnham, J., Forbes, G. and Mostert, T., "Quality Management Plan for the

Confederation Bridge", ACI SP 171, pp. 73-96. Johnston, C.D., "Silica Fume Concrete for High-Strength Precast Prestressed Highway Bridge Girders",

Proceedings of The Third International Conference on Fly Ash, Silica Fume Slag and Natural Pozzolans in Concrete, Norway, 1989, ACI SP 114, pp. 1077-1100.

Jagasia, H.K., "Design and Construction of High Performance Concrete Bridges on 407 Express Toll Route", Proceedings PCI/FHWA International Symposium on High Performance Concrete, New Orleans, October 1997, pp. 533-542.

Hassanain, M.A. and Loov, R.E., "Design Optimization of Precast Girder Bridges Made With High-Performance Concrete", Proceedings PCI/FHWA Symposium on High Performance Concrete, New Orleans, August 1998, pp. 1-12.

Lounis, Z. and Mirza, M.S., "High Strength Concrete in Spliced Prestessed Concrete Bridge Girders", Proceedings PCI/FHWA Symposium on High Performance Concrete, New Orleans, August 1998, pp. 39-48.

Bickley, J.A., Berzakiewicz, B., Carter, K., Pianca, F. and Raven, R. "Construction, Testing and Monitoring of Highway 407 High-Performance Concrete Structures B22A and B22C at Levi's Creek in Mississauga", Concrete Canada Report, August 1997.

Smith, M.,"Silica Fume Used to Extend Service Life of Pipe", Concrete Pipe Journal, Vol II, October 1996, pp. 8-9.

Hart, A.J.R., Ryell, J. and Thomas, M.D.A., "High Performance Concrete in Precast Tunnel Linings: Meeting Chloride Diffusion and Permeability Requirements", PCA/FHWA International Symposium on High Performance Concrete, New Orleans, October, 1997, proceedings, pp. 294-307.

Thomas, M.D.A. and Matthews, J.D., "Chloride Penetration and Reinforcement Corrosion in Fly Ash Concrete Exposed to a Marine Environment", Third CANMET/ACI International Conference on Performance of Concrete in a Marine Environment, ACI SP-163, 1996, pp. 317-338.

DeSouza, S.J., Hooton, R.D. and Bickley, J.A., "A Practical QC test Programme for HPC in Precast Tunnel Liners", ACI SP 191, 2000, pp. 99-114.

Dilger, W.H. and Rao, S.V.M.K., "Design of High Performance Concrete Mixtures for the Commercial Production of Spun-Cast Poles", Proceedings CSCA 1st Structural Specialty Conference, Edmonton, June 1996, pp. 509-521.

Dilger, W.H., Kuebler, U. and Wang, M., "High Performance Concrete for Spun-Cast Utilities Poles", In Publication

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Confederation Bridge, P.E.I.

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Chapter 5 Buildings and Parking Structures Buildings High Strength HPC has found favour in the construction of tall buildings and structures. In Toronto and Calgary, a number of large high-rise buildings have been built with 70 and 85 MPa concrete. Recent Buildings with High-Strength Concrete (Bickley, 1999 and Lafarge 2000) are:

Building Location Year Stories Design Strength MPa

Scotia Plaza Toronto 1988 68 70 Bay Adelaide Center Toronto 1991 57 85 BCE Place Phase 1 Toronto 1992 52 70 BCE Place Phase 2 Toronto 1993 48 85 Simcoe Place Toronto 1994 33 85 Millenium Tower Calgary 1998 24 85 Bankers Hall 2 Calgary 1999 53 80 TCPL Tower Calgary 2000 35 85 Pantages Place Toronto 2000 46 85

Starting with Scotia Plaza, a logical approach was developed to ensure the achievement of the specified high strengths by these HPC mixes (Ryell and Bickley, 1987). Ternary mixes were used in all the Toronto buildings. Initially, undensified silica fume was added separately. This proved to be difficult to mix uniformly, and a special batching sequence had to be developed to overcome the mixing problem. Subsequently, Type 10E-SF cement was available for the later projects. Innovative procedures employed on these projects included nitrogen cooling of concrete in hot weather, in-place testing for early form removal, as early as 11 hours after casting, and pre-construction mockups to investigate thermal problems with large sections. A high degree of quality control was achieved on all these projects as shown in the following tables (Ryell and Fasullo, 1993):

Projects using 70 MPa Concrete

Scotia Plaza

BCE Place Phase 1

BCE Place Phase 2

Bay Adelaide

No of tests 143 287 294 93 Mean strength: MPa 92.5 86.8 93.9 95.2 Standard deviation: MPa 6.8 8.1 6.0 5.8 Coefficient of variation: % 7.3 9.3 6.4 6.1

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Projects using 85 MPa Concrete BCE Place Bay Adelaide Simcoe Place Phase 2 No of tests 281 137 102 Mean strength: MPa 98.7 98.7 104.7 Standard deviation: MPa 5.6 5.3 5.7 Coefficient of variation: % 5.7 5.4 5.4

At the time Scotia Plaza was under construction, the use of silica fume in Canada on tall buildings was in its infancy. There was also concern to establish the long term properties of silica fume concrete. Cores were taken from a typical column at ages of 1, 2 and 7 years to confirm the mechanical properties of the concrete in situ (Bickley et al, 1991 and 1994). Further long-term in-situ data was obtained by casting and instrumenting an experimental column in a high-rise concrete building in Montreal (Aitcin et al, 1985 and Aitcin et al, 1990). The high early strength properties of HPC have also been utilized to reconstruct busy entrances to a fast food restaurant overnight and have them back in service next morning (Lessard et al, 1994). Parking Structures The current edition of CSA S 413-94 does not allow for the use of HPC in nonprestressed components. Where prestressed concrete is used, there are options to use "low permeability concrete". For cast-in-place components, this type of concrete can be used in conjunction with a membrane for bonded tendons, with a membrane or epoxy-coated bars or corrosion inhibitor for unbonded tendons or bonded tendons in non-metallic ducts. For precast concrete, low permeability concrete can be used with epoxy coated top bars, with corrosion inhibitor and with a sealer. All the last three systems listed can be used with uncoated welded steel wire fabric. Low permeability concrete is defined as concrete having a maximum water-cement ratio of 0.40 and an average coulomb rating of 1500 after standard curing for 28 days. (Where slag or fly ash are incorporated in the mix, the test may be made at ages up to 91 days.) This type of concrete would qualify as HPC. Despite the limitations of CSA S 413, HPC, meeting more stringent specifications, has been used in the construction of cast-in-place concrete parking structures. One example is the parking structure built as part of the Sheppard subway line project at the Don Mills Station and Fairview Mall. The relevant TTC specification requirements for this project were as follows:

• Compressive Strength at 28 day’s 45 MPa • Cementitious content: minimum 395 kg/m3 (65 % Type 10, 30 % slag, 5 % silica) • Maximum water-cementitious ratio: 0.40 • Air: 6 % +/- 1 % • Temperature at time of placing: maximum: 27 °C, minimum: 10°C • Maximum internal temperature: 43°C

Fog curing was specified prior to finishing and applying saturated burlap for 7 days.

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The contractor expressed concern about fog misting because the deck area at each level was 54 m x 54 m, and the practicality of doing it during the winter. The opportunity was taken to carry out comparative trials on the upper level during construction. The contractor was advised to use a commercial power washer with a misting hose. By elevating this hose on the upwind side of the structure, a fog mist was reasonably applied to the whole surface. Three adjacent areas of the placement were chosen for tests:

Zone 1: Fog misting only Zone 2: Fog misting plus evaporation retarder Zone 3: Evaporation retarder only The placing and finishing was witnessed, and a representative of the supplier instructed the placing crew on the use of the evaporation retarder. After the surface had hardened, sorptivity tests were made and cores taken from each of the test areas. A summary of test results is as follows:

Sorptivity Tests

RCP tests: coulombs

Densities: kg/m³

mm/min 0.5 Top Middle Top Middle

Fog misting 0.032 185 240 2410 2415 0.031 185 240 2400 2415

0.032 190 250 2400 2400

Fog misting + 0.029 185 235 2400 2400 Evaporation retarder 0.031 170 215 2430 2405

0.029 190 215 2395 2420

Evaporation retarder 0.036 175 200 2395 2380 0.036 195 245 2385 2380 0.039 190 230 2385 2375

Test cylinders 280 2415 230 2450 265 2455

There is very little difference between the test results for sorptivity or RCP for any of the three curing regimes. Sorptivity tests on the three lower levels, which it is understood were not fog cured, gave values of 0.061 mm/min0.5. Based on these few results, it would appear that fog curing and evaporation retarder produce similar sorptivity results, while the absence of either results in significantly higher sorptivity.

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Other cores tested at the University of Toronto gave an average resistivity of 87,467 ohm cm, with a range of 75,337 to 104003. Diffusion values ranged from 0.53-3.08 x 10-12 with an average of 1.48 x 10-12. Bulk diffusion values at 90 and 365 days, respectively, were 1.65 and 0.96 x 10-12. RCP values were similar to those in the above table. HPC was used in the repair of a parking garage in Kitchener in 1998. The specified 28 day strength was 35 MPa and test results exceeded 40 MPa. The RCP value obtained was 565 coulombs. REFERENCES Bickley, J.A., "North American Trends in the Development of High-Strength Concrete", Proceedings 5 th

International Symposium on High Strength/High Performance Concrete, Sandefjord, Norway, June 1999, pp. 1-13.

Lafarge, Private communication. Ryell, J. and Bickley, J.A., "Scotia Plaza: High Strength Concrete for Tall Buildings", Proceedings

Utilization of High Strength Concrete, Stavanger, Norway, June 1987, pp. 641-654. Bickley, J.A., Ryell, J., Rogers C. and Hooton, R.D., Some Characteristics of High Strength Concrete:

Canadian Journal of Civil Engineering, Vol. 18, No. 5, 1991, pp. 885-889. Bickley, J.A., Ryell, J., Rogers C. and Hooton, R.D., Some Characteristics of High Strength Concrete: Part

2, Canadian Journal of Civil Engineering, December 1994, Vol. 21, No. 6, pp. 1084-1087. Aï tcin, P-C, Laplante, P. and Bedard, C. "Development and Experimental Use of a 90 MPa (13,000 psi)

Field Concrete", ACI SP 87, 1985, pp. 51-70. Aï tcin, P-C, Sarkar, S.L. and Laplante, P. "Long Term Characteristics of a Very High Strength Field

Concrete", Concrete International, Vol 12, no 1, January 1990, pp. 40-44. Lessard, M., Dallaire, E., Blouin, D. and Aitcin, P-C., "High-Performance Concrete Speeds Reconstruction

for McDonalds", Concrete International, September, 1994.

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Scotia Plaza, Toronto, ON

Fairview Mall Parking Garage

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Chapter 6 Marine Applications Hibernia Offshore Platform The Hibernia offshore concrete platform, built in Newfoundland, used 165,000 m³ of high performance concrete (Hoff, 1998). The platform now in service on the Grand Banks was designed to resist the impact of icebergs, and to be durable in a severe marine environment. The outside ice wall, 1400 mm thick, is joined to X and Y walls, which transmit loads to the interior tie wall. The topsides are supported on four circular shafts of 17 m i.d. connected to the base slab. These shafts are connected at the top by a corbel ring to provide bearing for the topside structure. The overall height is 111.2 m and diameter 108 m. The base was constructed in a dry dock and then floated to a deep water anchorage where the rest of the construction took place. The structure involved the slipforming of complex shapes. Some material quantities illustrate the magnitude of the project:

• Concrete: 165,000 m³ of pumped concrete, of which 27,000 m³ was air-entrained high-strength concrete and136, 000 m³ was reduced density concrete.

• 500 MPa high yield reinforcement: 93,000 tonnes. • T-headed bars for shear reinforcement: 2,200,000. • Dyform post-tensioning strand: 2,530 tonnes. • Vacuum grouting of 175 m long ducts. • Mechanical couplers to avoid lap splicing: 910,000. • Average density of reinforcement: 611 kg/m³.

After some initial concrete work with a temporary batch plant, a permanent plant was installed for the base concreting. This consisted of two 2 m³ twin axle high shear mixers with separate materials feed trains to each. Similar 2.5 m³ mixers were used in the batch plant for the deep water construction. Provision was made for the heating and cooling of concrete. Type 10 cement containing blended silica fume at 8.5 +/- 0.5% was used having an Na2O equivalent of 0.72%. High dosages of superplasticizer were used to produce concrete with slumps of 220-240 mm that was pumpable over large distances and placeable in reinforcement densities averaging 611 kg/m³. The one-year design compressive strength of the concrete was 69 MPa. An extensively equipped laboratory was built on site. Test cylinders 100 mm in diameter by 200 mm were used and ends were ground before testing.

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Typical test results for structural concrete were as follows:

Mean 28 Day Strength: MPa

Std. Deviation. MPa

Normal Density Concrete 81.7 3.1

Modified Normal Density Concrete 83.5 2.5 Tests were also made for creep, drying shrinkage, water permeability, in-situ strength, air void parameters, freeze-thaw resistance (ASTM 666 Procedure A) and chloride ion permeability. All test data confirmed the high quality of the concrete reflecting the high level of quality control exercised throughout the project. Grand Manan Wharf As no suitable construction facilities existed on this small island, the new wharf was formed from four massive concrete caissons cast in Saint John and towed 100 km to Grand Manan (Hopkins et al 2000). Three of the caissons were 30 m long by 14.6 m wide by 15.5 m high. The fourth was slightly smaller. Exterior walls were 500 mm thick and the cells were separated by 300 mm thick walls. After the casting of the bases the walls were slipformed, at rates of 160 to 185 mm/hr. all the concrete was placed by pump. The almost 6000 m³ of concrete was placed in just over four weeks in 1999. Key specification criteria were as follows:

• Type 10E-SF low-alkali cement: minimum 420 kg/m³ • Water-cementitious ratio: 0.39 maximum • Coarse aggregate: 20 mm • Sand content: 48-50% of total aggregate • Air content 5-8% • Slump: 100 -15 mm • Unit weight: 2302 kg/m³ • Air and slump limits were specified at the discharge end of the pump • Curing by water or steam • Service life: 75 years

The use of silica fume had, in the past, caused finish problems in slipformed concrete, and the contractor for this project had concerns in this regard. The use of a non-chloride accelerator in the mix lubricated the concrete interface with the slipform. The mix was slipformable at about 3.5 hours.

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To meet the New Brunswick DOT's cold weather and curing requirements, the caissons were enclosed in insulated tarpaulins. Low-pressure steam provided a 100% humidity for 7 days of curing and kept the concrete above the 10°C minimum temperature specified. Compressive strengths were 53.5 MPa. REFERENCES Hoff, G.C., "The Hibernia Offshore Platform-A Major Canadian Use of High Performance Concrete",

Proceedings International Symposium on High-Performance and Reactive Powder Concretes, Sherbrooke, August 1998, Vol 4, pp. 29-56.

Hopkins, D.S., Strang, F., Woytowich, W., Ballantyne, T. and Thomas, M.D.A., "The Wharf That Floated", ACI Atlantic Chapter Conference, St. John’s, Nfld. 2000.

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Grand Manan Wharf, New Brunswick

Wharf Repairs at Port of Saint John Saint John, New Brunswick

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Chapter 7 Agricultural Applications HPC has been used in agricultural buildings where the impermeability of HPC provides durability against the aggressive agents from the animals and feed. Used in swine nurseries, HPC reduced infections by inhibiting the growth of harmful bacteria, which normally breed in the pores of conventional concrete. The result was heavier pigs and higher profits to the breeder (Gagné et al, 1994). 60 MPa HPC was also used for the floor slab of a poultry smokehouse. In recent years there have been many large pig-breeding factories established on farmland. In these facilities, the pigs live on precast slats above a lower level where wastes are collected. Previously the precast slats were made with conventional concretes and these had a short service life in the aggressive environment. Research has been carried out which confirms that precast slats made with HPC provide significantly longer service life than the quality of concrete usually used (Idriss et al, 2001). Two series of tests were made to determine the time to corrosion of steel reinforcement in mortar specimens exposed to hydrogen sulphide. In the first series, the specimens were subjected to impressed voltage and electrochemical potential tests. For the impressed voltage tests, 95.5 mm diameter cylinders 200 mm long were cast with a 11.3 mm diameter 400 MPa reinforcing bar in the middle. After 28 days wet curing, the specimens (three replicates) were immersed in a solution of 2000 ppm of H2S for a year. The reinforcement was then connected to a 40-volt direct current to make it anodic with respect to an external cathode, which was connected to the negative pole of the DC source. The time to develop a longitudinal crack was noted. For the electrochemical potential tests, specimens 100 mm by 100 mm by 30 mm thick were cast with an 11.3 mm diameter reinforcing bar in the middle. Five stainless steel wires were attached to the reinforcing bar, three of which protruded from the specimen. The other two were attached at the ends of the bar outside the test specimen. The specimens were wet cured for 28 days. The specimens (three replicates) were immersed in H2S for 650 days and half-cell readings taken every 10 days starting at day 60. Once the readings indicated active corrosion, the specimens were tested to determine the concentration of sulphides that initiated corrosion.

Failure time Susceptibility to Mix Tc min Corrosion, µA-1min-2

Type 10 w/c ratio 0.55 165 62.5

Type 10SF w/c ratio 0.35 36,000 86.3 x 10-6

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In the second series of tests, diffusion tests were made on specimens immersed in H2S and epoxy coated on all but one surface. The time to reach the threshold value for corrosion in the Type 10E-SF 0.35 w/c ratio mix was more than eight times as long as in the Type 10 0.55 w/c ratio mix. From these tests, it was concluded that the life of slats made with the Type 10E-SF mix would be double that of slats made with conventional concrete. In Ontario, all the precast concrete producers use HPC for farm applications. In addition to slats, other HPC products are manger feeder bottoms, kennel floors and bunker silos. REFERENCES Gagné, R., Chagnon, D. and Parizeau, R., "Utilization of High-Strength Concrete in the Agricultural

Industry", Concrete Canada Technology Transfer Workshop, Sherbrooke University, October 1994. Idriss, A.F., Negi, S.C., Jofriet, J.C. and Hayward, G.L., "Corrosion of Steel Reinforcement in Mortar

Specimens Exposed to Hydrogen Sulphide, Part 1: Impressed Voltage and Electrochemical Potential Tests", In publication, Journal of Agricultural Engineering Research.

Idriss, A.F., Negi, S.C., Jofriet, J.C. and Hayward, G.L., " "Corrosion of Reinforcing Steel in Mortar Specimens Exposed to Hydrogen Sulphide, Part 2: Diffusion Tests", In publication, Journal of Agricultural Engineering Research.

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Chapter 8 Shotcrete The development, in 1910, of a double-chambered gun enabled a sand-cement mortar called Gunite to be sprayed onto structures. This process, with coarse aggregate added in the 1950s, became known as dry-mix shotcrete. By 1960, the development of pneumatic equipment made wet-mix shotcrete practicable. Widely used for repairs, the shotcrete process exhibited practical deficiencies such as excessive rebound, and, even with the addition of polymers, was not durable. During the 1980s, many improvements were made to material science, plant and procedures, which made the use of high performance shotcretes possible. These were summarized as follows (Morgan, 1992): Materials:

• “The use of steel and polypropylene fibre reinforcement in lieu of conventional mesh reinforcement;

• The use of special high early-strength cements, in lieu of accelerated shotcretes, in projects requiring early-strength development;

• The use of supplementary cementing materials, such as fly ash and silica fume, as additions or partial replacements, for the special benefits that these materials impart to shotcrete.

Plant and Procedures:

• The use of dry-batched, premix materials, supplied in either small (typically 30 kg) paper bags or large (typically 1600 kg) synthetic cloth, bulk bin bags;

• The use of mobile volumetric batching equipment with special dispensers for materials such as steel fibre reinforcement and silica fume;

• The use of robotic placement equipment, particularly for repair in road, rail, sewer and water tunnels;

• Improvements in wet-mix pumps and dry-mix guns; • Improvements in ancillary shotcrete equipment, such as shotcrete nozzles and

predampening units for use with dry, premixed shotcretes; • Special dispensing units for addition of silica fume slurry at the nozzle, with or

without accelerators, in the dry-mix shotcrete process”. In 1993, a study was made of four dams in British Columbia, which had previously been repaired with shotcrete (Heere et al, 1996). Recommendations for repair were made based on current high performance shotcrete technology. In 1995, the multiple arches Littlerock Dam in California was repaired using silica fume steel fibre reinforced air-entrained shotcrete (Forrest et al, 1995), and Canadian technology. The shotcrete was used, as part of a seismic upgrading, to stiffen the arches of the dam.

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The good practice measures taken to ensure a competent repair were as follows:

• Surface preparation of an adequate roughness profile (which was measured), suitable moisture condition, cleanliness and hardness.

• Anchors were grouted in a 1.2 m grid. • A 28 day compressive strength of 41 MPa, 60 kg/m³ of steel fibres, 400 kg/m³ of

cementitious material with 10 5 of the total silica fume, and an air content of 10-12% at the pump to ensure about 5 +/- 1% in place.

An extensive preconstruction programme was carried out covering surface preparation, bond testing, core grading, shotcrete testing for physical properties including toughness, and anchor testing. Intensive construction monitoring included bond tests and coring to examine shotcrete thickness and compressive strength. The bond test requirement of 1 MPa was met at all locations except two. At these locations adjacent retests passed. Compressive strengths of cores ranged from 40 MPa to 67 MPa, and all cores met grading requirements. A total of 4500 m² of shotcrete overlay were placed. Berth faces in the Port of Montreal were repaired using steel fibre and polyolefin fibre shotcretes (Morgan et al, 1998). A total of 866 m2 were repaired. The object of the trial repairs was to compare performance and costs with the cast-in-place concrete repairs used before. The berth faces were built early in the 20th century and were in a seriously deteriorated condition despite previous repairs. An extensive preconstruction testing programme was carried out, which included the qualification of all the nozzlemen allocated to the project. The compressive strength of cores taken from the finished work had compressive strengths from 50.6 to 61.4 MPa. The cost of the shotcrete repair was $515/m² compared to $550/m² for the cast-in-place repairs previously made. An inspection after one winter showed no deleterious defects. Berth faces at the Port of Saint John were also repaired with high performance shotcrete (Morgan et al, 1996). The berths had been constructed at various times from the 1900s to the 1950s. In 1986, a 10-year repair programme started using air-entrained, wet-mix, steel fibre reinforced, silica fume shotcrete. In 1995, 9 years later, and after 2000 freezing and thawing cycles in a saturated condition, the shotcrete repair was inspected. No significant deterioration was found. Cores extracted from the repairs had compressive strengths from 53.5 to 60.1 MPa, slightly higher than cores from test panels nine years previous. Costs for these repairs during the period 1989 to 1995 ranged from $126 to $270 per m² and averaged $172 per m².

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HPC Shotcrete has been used in the repair of many marine structures including an oil-drilling platform (Morgan, 1997). Wet-mix shotcrete with a specified 28-day strength of 80 MPa and a direct tensile bond strength of 2 MPa was used. In BC, the Ministry of Transportation and Highways has used fibre-reinforced HPC shotcrete to stabilize creek beds and protect bridge piers and abutments from scour. In BC, an historic building, the Vancouver Block, was rehabilitated using HPC shotcrete (Chan and Morgan, 2000). Wind-driven rain had penetrated the walls and caused severe deterioration of the masonry walls and corrosion of the structural steel. In 1997/98, at a cement plant in Bath, Ontario, a cement storage silo with a capacity of 68,000 tonnes was constructed of high performance shotcrete. The dome is 55 m in diameter and 29 m high. An inflatable form was attached to the foundation ring beam. After inflation, the interior was sprayed with polyurethane insulation and reinforcing steel fixed. The concrete was then sprayed on the inside in a single layer. Wall thickness varies from 0.51 m at the base to 0.15 m at the top of the dome. The inflatable form remains in place as permanent waterproofing. The wet mix shotcrete used had the following proportions:

• Type 10E-SF cement: 480 kg/m³ • Coarse aggregate: 200 kg/m³ • Fine aggregate: 1340 kg/m³ • Water: 215 kg/m³

Water reducing and air entraining admixtures produced the desired set characteristics, a slump of 100 to 125 mm and an air content of 5-8%. The low rebound of 12% was attributed to the use of silica fume and a low coarse aggregate content in the mix. Test panels were made and cored. A summary of test data is as follows:

Concrete Cylinders Concrete Cores 7 days 28 days 7 days 28 days

No of tests 89 89 12 24 Mean strength: MPa 43.1 55.8 32.9 43.9 Standard deviation: MPa 3.43 4.68 6.85 5.35 Coefficient of variation: % 8.0 8.4 21.0 12.0

A major use of high performance shotcrete is the support of rock in tunnels, particularly in mines. A comprehensive review of this application was produced by an admixture supplier's underground construction group (Melbye, 1996). The need for the correct specification and application of specifications for shotcrete resulted from conflict between specifiers and contractors (Wood, 1992). The need for preconstruction qualification testing and ongoing QC testing during construction was emphasized. Two case histories are given in detail.

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Details of typical high-performance mixes and performance specifications are reproduced in the following tables:

Components Dry Mix Wet Mix kg/m³ % of dry kg/m³ % of dry Materials Materials

Cement 420 19 420 18.1 Silica fume 50 2.2 40 1.7 Aggregate (blended) 1670 75.5 1600 68.9 Steel fibres 60 2.7 60 2.6 Accelerator 13 0.6 13 0.6 Superplasticizer 6 litres 0.3 Water reducer 2 litres 0.1 Air entraining agent if required Water 180 7.7

Characteristic Test Method Minimum Required

ASTM C42 5

Uniaxial compressive strength: MPa 8 hr (accl.) 1 day " 10 3 day " 20

" 30 7 day 28 day " 40

ASTM C1018 4

Flexural strength: MPa 7 day 28 day " 6

ASTM C1018 3.5

Toughness index I5 I10 " 5 Boiled absorption: % ASTM C 642 8 max

Voids volume: % " 17 max Accelerated set: min ASTM C 403 Initial: 10

" Final : 30 Aggregate gradation ACI 506R-90 1,2 or 3

Note: The standards quoted in the above table have all been updated since 1992. The paper concluded that the complex installation of brittle layers of shotcrete and wire mesh could be replaced with a single pass of steel fibre reinforced silica fume shotcrete. An outstanding example of the application of high performance shotcrete in the mining industry is Inco’s Stobie mine in Sudbury (O'Hearn et al, 1998). A number of extensive

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in-situ trials were made to confirm that steel fibre reinforced silica fume shotcrete could safely replace the use of traditional shotcrete plus wire mesh reinforcement and rock bolts. The trials also served to optimize the wet mix that was used. The final proportions per m³ were as follow:

• Type 10 cement: 400 kg • Silica fume: 40 kg • Water: 180 kg • Superplasticizer: 850 ml/100 kg of cement • Coarse aggregate: 350 kg • Fine aggregate: 1,275 kg • Steel fibre: 50 kg

A high degree of quality control was exercised during construction. Analysis of the results showed not only that the high performance shotcrete system was cheaper and easier to install than traditional shotcrete systems, but the safety margin of the finished installation was better.

REFERENCES Morgan, D.M., "New Developments in Shotcrete for Repairs and Rehabilitation", Proceedings, Advances

in Concrete Technology, Athens, May 1992, pp. 699-739. Heere, R., Morgan, D., Banthia, N. and Yogendran, Y., "Evaluation of Shotcrete Repaired Dams In British

Columbia", Concrete International, Vol 18, no 3, March 1996, pp. 24-29. Forrest, M.P., Morgan, D.R., Obermeyer, J.R., Parker, P.L. and LaMoreaux, D.D., "Seismic Retrofit of

Littlerock Dam", Concrete International, Vol 17, no 11, November 1995, pp. 30-36. Morgan, D.R., Rich, L. and Lobo, A., "About Face-Repair at Port of Montreal", Concrete International,

Vol 20, no 9, Septenber 1998, pp. 66-73. Morgan, D.R., Bremner, T.W. and Gilbride, P., "Repair of Berth Faces at the Port of Saint John, New

Brunswick", Concrete Canada Technology Transfer Day, University of Moncton, August 1996, pp.61-72.

Morgan, D.R., "Shotcrete Repair of Infrastructure in North America", Beton-Instandsetzung '97, Igls, Austria, January 1997, pp. 21-37.

Chan, C. and Morgan, D.R., "Infrastructure Repair and Rehab: Shotcrete: Spraying on the Solution", CE News, March 2000, pp. 66-71.

Hopkins, D.S., Cail, K., Robert, N. and Thomas, M.D.A., "World's Largest Dome for Cement Storage Silica Fume Shotcrete", Canadian Society for Civil Engineering, Proceedings Annual Conference, Regina, June, 1999, pp. 117-133.

Melbye, T.A., "Sprayed Concrete for Rock Support", MBT International Underground Construction group, Switzerland, 1994.

Wood, D.F.,"Specification and application of fibre reinforced shotcrete", Rock Support in Mining and Underground Construction, Kaiser and McCreath, Editors, Balkerma, Rotterdam, 1992, pp. 149-156.

O’Hearn, B., Buksa, H. and Walker, S., "Stobie signals shotcrete success", Engineering and Mining Journal, August 1998.

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Bath Cement Storage Silo

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Chapter 9 Emerging Technologies Self-Consolidating Concrete This type of concrete, originally invented in Japan, was developed in Canada at the University of Sherbrooke and has been used in a number of new and rehabilitation projects in Canada (Khayat, 2000). Self-consolidating concrete (SCC) is a class of HPC based primarily on the properties of the concrete during placement. Properly proportioned and controlled, this concrete will flow significant distances inside formwork, consolidate to normal density without the application of compactive effort, resist the segregation of coarse aggregate from the paste and produce high quality finishes. Experience has shown that a high degree of QC is required, but there are benefits, especially where access is difficult, where the noise of vibration is undesirable and where labour savings for placing, compacting and finishing can be achieved. The high quality finish possible, with virtually no "bug holes" makes it particularly suitable for architectural quality exposed finishes. The first full-scale application of this technology in a new building was at the Canadian Centre for Technology at the National Research Council campus in Ottawa in 1999. The basement walls for a three-unit residence were cast using this technique (Khayat et al, 2000). After a laboratory development programme at Sherbrooke University and the casting of two prototype walls in Toronto, the installation in Ottawa was made without any problems with the concrete. The following were the test results on the fresh and hardened concrete. Concrete Mix Design and Fresh Concrete Properties

kg/m³ Cement 215 Silica Fume 16 Slag 215 Water 203 Sand 665 Coarse Aggregate 855 VMA 3.5 l/m³ Superplasticizer 3.0-4.0 Set retarder 1.04 Air entrainer 0.65

Slump flow: mm 630-650 Fresh air content % 5.2 Unit weight: kg/m³ 2245 Concrete temp: °C 22

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Concrete Test Results:

Truck Load 1 2 3 4 5 6

Slump flow: mm 640 +/- 10 Fresh air content: % 4.9 5.4 5.2 Filling capacity: % 85 90 Compressive strength: MPa 7 days 34.2 34.8 36.2 34.6 33.2 28 days 46.7 43.1 43.2 45.9 50.7 RCP at 56 days: Coulombs 540 560 Air void system Air content: % 5.4 4.7 Spacing factor: µm 300 265 SCC has been used in a number of rehabilitation contracts. On the Webster parking structure in Sherbrooke, the soffit and sides of a reinforced concrete beam supporting a slab was repaired with SCC. Holes 100 mm in diameter were drilled through the slab on one side of the beam and the concrete was placed through these. The concrete had to flow down the entry side of the beam formwork, under the soffit and up the other side, as well as along the length of the beam. Small holes were drilled on the opposite side of the beam to allow air to escape as the form filled. An additional innovation was the use of a ternary cement. At the Beauharnois Dam, an L-shaped slab and beam element with restricted access was rehabilitated with SCC. A mobile mixer was used for the production of the concrete. This necessitated special modifications to both the batching sequence and mixing. A reaction wall built at the University of Sherbrooke used 240 m³ of SCC. An underground drainage conduit in Shawinigan was successfully repaired using 130 m³ of SCC. The Quebec Ministry of Transport has completed eight repair projects, and the City of Montreal and the Montreal Metro have each completed one. An example of the use of self-consolidating concrete in Montreal is the repair to 200 m of parapet walls on McDougall Road on Decarie Blvd. Access was only possible from the side to be repaired. The cross-section of the repair is shown on page 96. A total of 200 m³ of 50 MPa SCC was used, and all test results exceeded 50 MPa. Research carried out by the City over the last two years indicates greater tensile creep for SCC, resulting in a reduced tendency to crack. A project at the Toronto International Airport expansion that used a self-consolidating HPC was the New Passenger Terminal (Meschino and Ryell, 2000). The pipe columns supporting the roof are 31 m high. They had to be filled with concrete and contained significant reinforcement. Evaluation of the various options for filling these columns

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resulted in a decision to fill them from the bottom, provided a suitable mix could be developed which could be pumped at a pressure the pump could handle. A mix was developed based on the technology used for self-compacting concrete. The mix contained 450 kg/m³ of cementitious material, 10 mm of uncrushed pea gravel. a superplasticizer and a self-levelling admixture. A slump flow of 650-700 mm was used as the acceptable range of workability. After field trials of the proposed mix, the first column was successfully used as a trial. The filling process for the 12 m³ of concrete takes about 15 minutes and pumping is smooth without high pressures. Four cores were taken from the trial column at the top, bottom and two intermediate levels. Mean strength was 44.0 MPa and the cores were seen to be uniform in quality with no segregation or voids. Lafarge has developed a proprietary version of this type of concrete with the name "Agilia®". The first use of this concrete was in the massive columns to the first four floors of the Wall Centre in Vancouver, a 48 storey building (Concrete Products, 2000). The decision was based on the successful demonstration casting of five columns in the underground parking area. The 8 ft. square columns, which were stripped after as little as 18 hours, attained compressive strengths in excess of 70 MPa. Prior to proposing the use of SCC, an extensive test programme was carried out for Lafarge by AMEC. In this programme, the mechanical properties of SCC were compared to those of a conventional 50 MPa mix. The results were summarised as follows: From the test results, it can be concluded that Lafarge's Agilia® self-compacting concrete demonstrates the following characteristics:

• Satisfactory air-void system for freeze-thaw durability, • Similar shrinkage properties compared to an ordinary 50 MPa concrete mix, • Significantly reduced creep strain compared to an ordinary 50 MPa concrete

mix, • Slightly lower but comparable modulus of elasticity values to an ordinary 50

MPa concrete mix, • Compressive strengths that exceed a 28 day nominal compressive strength

requirement of 50 MPa, • Similar cold joint bonding characteristics to an ordinary 50 MPa concrete mix.

Agilia® has also been used on projects at the ICT building at the University of Calgary using 50 MPa concrete in columns, core walls and stairways, and at the Calgary Eaton Centre.

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Reactive Powder Concrete This is an ultra high-strength HPC patented by the French construction firm, Bouygues, in 1994. It is usually heavily dosed with special steel fibres and contains no coarse aggregate. The cement, silica fume and fine aggregate are graded to achieve optimum packing. Typical mechanical properties compared to an 80 MPa concrete are as shown in the following table (Perry,1998):

Property Unit 80 MPa RPC

Compressive strength MPa 80 200 Flexural strength MPa 7 40 Modulus of Elasticity GPa 40 60 Fracture Toughness 10³ J/m² <1 30 Freeze-thaw, ASTM C 666 A RDF 90 100 Salt Scaling g/cm² 80 <10 Carbonation depth: 36 d in CO2 mm 2 0 Abrasion 10-12 m²/s 275 1.2

In 1994, small-scale feasibility trials in the use of RPC were conducted at the University of Sherbrooke and at a precast plant (Bonneau et al, 1996). The successful completion of these trials resulted in a decision to build a pedestrian and bicycle bridge in the City of Sherbrooke in 1996 (Aitcin and Richard, 1996). The design is a lightweight space truss consisting of precast segments assembled on site. The bridge has a span of 70 m and a deck width of 4.2 m. The deck is 30 mm thick, stiffened with 70 mm high transverse ribs 1.7 m apart, and was cast in RPC with fibre. A low-heat type of reactive powder concrete has been developed at the laboratories of the Atomic Energy of Canada Limited (Gray and Shelton, 1998) to meet needs for mass pours for nuclear reactor foundation mats and for underground containment of nuclear wastes.

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Three high performance mixes were compared. Mix proportions were as follows:

High Volume Fly Ash Standard HPC Low Heat HPC kg/m³ kg/m³ kg/m³

Portland Cement 194 Type 10 497 Type 50 97 Type 50 Silica fume - 49.7 97 Fly ash 194 - - Silica fume - - 194 Superplasticizer 1.5 7.1 10.3 Fine aggregate 895 703 895 Coarse aggregate 1040 1100 1040 Water 128 124 97 W/CM 0.33 0.23 0.5 Temperature: °C rise 40 43 23 maximum 70 66 53 100 day strength MPa 58 128 96 It was concluded from the test programme that:

• The low temperature rise would reduce temperature gradients. Cooling costs would be reduced.

• This HPC should be more durable than standard HPC. • Workability is good. • Early age curing needs careful attention. • Inert filler replaces cement that would not hydrate in practice. • The use of less cement is environmentally beneficial.

The Use of Ternary Cements As discussed above, CSA 3000-98 Cementitious Materials Compendium provides criteria for ternary cement blends in which Portland cement is blended with any two of silica fume, fly ash or slag. A range of combinations can be specified providing for the use of one cement powder tailor-made to meet specific contract requirements. The following tables give summary details of some contracts in Nova Scotia on which this option has already been exercized (Langley, 2000).

Project Criteria Mix Characteristics 80-year design life Cement: 450 kg/m³ Beaverbank Bridge low permeability w/c: 0.34 f1

c: 60 MPa Caterpillar Tractor High Resistance to Cement: 430 kg/m³ Equipment Yard surface abrasion w/c 0.37

f1c: 56 MPa

Howe Avenue Heavy traffic Cement: 410 kg/m³ Street Paving durability w/c: 0.38

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In Montreal, repairs to the Notre Dame - St Augustin overpass and the Saint Michel Quarry snow dumping pier used a ternary cement based on the successful use of this cement in sidewalk construction in 1998 (Bissonette and Morin, 2000). The ternary cement consisted of Type 10 cement with 6% silica fume and 25% fly ash. On the overpass, the columns were made of 35 MPa HPC and the deck of 50 MPa HPC. On one side, the sidewalks and parapets were made with conventional 50 MPa HPC and on the other side with 50 MPa HPC using the ternary cement. By using closely spaced joints, a crack free structure was obtained. A similar ternary cement was used to repair 9 kilometres of Autoroute 13. The new reinforced concrete pavement used 48,000 m³ of concrete. High Performance Roller Compacted Concrete Until recently, RCC paving was a relatively low-grade material used for the construction of logging roads and storage areas not subjected to high impact or abrasion loading. Research at Laval University has established improved concrete mix design procedures (Marchand, et al, 1997). These are based on obtaining the optimum packing of the various sizes of particles, and the addition of silica fume to the mix in a binary 10E-SF cement. In the Province of Quebec approximately one hundred projects have been completed using High Performance Roller Compacted Concrete (HPRCC). The first, in 1995, was a 25,000 m² storage yard for Noranda Minerals in Rouyn-Noranda. Up to October 1997 more than 240,000 m² of HPRCC pavement had been constructed, using over 67,000 m³ of this concrete. In 1996, the largest project till then was a 87,000 m² log yard at Domtar Papers in Windsor, Quebec. Built in 7 weeks using a pug-mill mixer, the contractor produced 26,000 m3 of concrete at a rate of 90 m3/hour. Compaction was by an ABG Titan high-density paver for top lift and a conventional Cedar Rapids asphalt paver for the bottom lift. The pavement thickness was 300 mm. In order to cope with 75 tonne log handlers, the specification required minimum 7 day strengths of 40 MPa in compression and 5 MPa in flexure. The mix designed to meet these requirements is shown in the following table.

Mixture Composition Type 10SF

Cement Water Fine

Aggregate Coarse

Aggregate Water

Reducer kg/m³ kg/m³ kg/m³ kg/m³ ml/kg* 295 103 774 1347 4

* Per kg of binder

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Laboratory tests made prior to construction and field tests made during construction are shown in the following table.

Compressive Strength MPa

Flexural Strength MPa

3 days 7 days 28 days 3 days 7 days 28 days Laboratory 39.2 45 52.8 6.2 6.7 78.1 No of specimens 2 2 2 2 2 2

Field 34.6 40.1 - 6.1 7.1 8.7 No. of specimens 114 110 - 77 93 4

A chemical compound was used for curing using double coverage in two directions and the amount recommended by the manufacturer was doubled. Experience has shown that premature drying of HPRCC will reduce its resistance to abrasion and scaling. In 1995, a 25,000 m2 slag dumping area was built for Noranda mines in Rouyn-Noranda. Slag transporters weighed 90 tonnes and contained molten slag at 800°C. After cooling, the slag was dumped onto the RCC area. In addition, the area was traversed all day by a D-9 bulldozer. The specification for this project called for compressive strengths of 50 MPa at 7 days and 62 MPa at 28 days. Minimum flexural strengths 5.1 MPa at 7 days and 9.4 MPa at 28 days were called for. Field test specimens reached 55 MPa at 7 days. The mix used was as shown in the following table:

kg/m³ Type 10SF Coarse Fine Water Cement: Aggregate Aggregate

359 1270 846 127 Using a continuous flow pugmill, the paving was completed in 10 days. The 8,000 m³ of RCC was placed at rates up to 1,800 m³ per day. Compaction was by ABG Titan Pavers, and the two lifts totalled 360 and 450 mm. Because of the increasing interest by the City of Montreal in the potential use of RCC in their road system, a programme was carried out to optimize mixes (Reid et al, 2000). The use of lower binder content was investigated to reduce drying shrinkage and the incidence of cracking. Since the RCC would be paved with asphalt, a high quality finish was unnecessary. A test section was built in Montreal in 1998. As a result of the success of this trial, a 9000 m² section of boulevard was built in 1999, followed in 2000 by a 23,000 m² snow depot.

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REFERENES Khayat, K.H., Private Communication, November, 2000. Trudel, G.A., Bergeron, G. and Khayat, K.H., "Use of Self-Consolidating Concrete in Highly Restricted

Areas for Rehabilitation of Underground Drainage Conduit", Presented at ACI Fall Convention, Toronto, October 2000.

Khayat, K.H., Bickley, J.A. and Lessard, M., "Performance of Self-Consolidating Concrete for casting Basement and Foundation walls", ACI Materials Journal, May-June 2000, Vol.97 no 3, pp. 374-380.

Meschino, M.and Ryell, J., "Bottom-Up Construction of 31 Meter High Reinforced Concrete-Filled Steel Columns for the Greater Toronto Airports Authority New Terminal Building", Presented at the ACI Convention, Toronto, October 2000.

Perry, V., "Industrialization of Ultra-High Performance Ductile Concrete", Symposium on High-Strength/High-Performance Concrete, University of Calgary, November, 1998.

Bonneau,O., Poulin, C., Dugat, J., Richard, P. and Aitcin, P.C., "Reactive Powder Concrete: From Theory to Practice", Concrete International, Vol 18, no 4, April 1996, pp. 47-49.

Aitcin, P.C. and Richard, P., "The Pedestrian/Bikeway Bridge of Sherbrooke", Proceedings 4th International Symposium on Utilization of High-Strength/High-Performance Concrete, Paris, 1996, pp. 1399-1406.

Adeline, R., Lachemi, M. and Blais, P., "Design and Behaviour of the Sherbrooke Footbridge", Proceedings International Symposium on High-Performance and Reactive Powder Concretes, Sherbrooke, August 1998, Volume 3, pp. 89-97.

Gray, M.N.and Shelton, B.S., "Design and Development of Low-Heat, High-Performance Reactive Powder Concrete", Proceedings, International Symposium on High-Performance and Reactive Powder Concretes, Sherbrooke, August 1998, pp. 203-230.

Langley, W.S., Private Communication, November 2000. Bissonette, B. and Morin, R., "Expérimentation d'un ciment ternaire pour la reconstruction du passage

supérieur Notre-Dame/St Augustin à Mon tréal", 7e Colloque sur la progression de la recherche québécoise sur les ouvrages d'art, Université Laval, Quebec, Mai 2000.

Marchand, J., Gagne, R., Ouellet, E. and Lepage, S., "Mixture Proportioning of Roller Compacted Concrete-A Review", Proceedings Third CANMET/ACI International Conference, Auckland, New Zealand: Advances in Concrete Technology, ACI SP 171, 1997, pp. 457-486.

Reid, E. and Marchand, J., "High-Performance Roller Compacted Concrete Pavements: Applications and Recent Developments", Proceedings Canadian Society for Civil engineering 1998 Annual Conference, Halifax.

Reid, E., Marchand, J. and Ouellet, E., "Mechanical Behaviour and Frost Durability of Low Binder Content Roller-Compacted Concrete", US Army, Air Force and Navy Transportation Systems Workshop, San Diego, February 2000.

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HPC

Self-Consolidating Concrete

Roller Compacted Concrete Noranda, Quebec

102

One Wall Centre Vancouver, BC

Pedestrian-Bikeway Bridge Sherbrooke, PQ

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Chapter 10 Discussion and Recommendations Discussion Cementitious Materials Cement - There is now almost universal use of blended cements for cast-in-place HPC. The most common type is 10E-SF, a type 10 cement plus silica fume. Recently a number of projects have used a ternary cement blended from a Type 10 cement, silica fume and fly ash. For precast concrete Type 30 and Type 10E-SF are in use. In areas of extensive alkali-aggregate reactivity, a Type 10E-SF low alkali cement has been used. Supplementary Cementing Materials Silica Fume - Silica fume has been used commercially in Canada since 1982 (Isabelle, 1987). A Canadian standard for this material was published in June 1986 as part of CSA A 23.5-86. Since then, it has become widely used in the production of HPC (Thomas et al, 1998). The achievement of very low RCP values is impractical without the inclusion of silica fume. All current specifications for cast-in-place HPC require the use of silica fume in the mix. Current specifications for precast concrete requiring a maximum RCP value of 1500 coulombs do not require the inclusion of silica fume. Slag and Fly Ash - Both supplementary cementing materials are widely used in HPC. Benefits are better finishing, improvements in impermeability and resistance to chemical attack, and economy. Admixtures Superplasticizers - Obtaining satisfactory workability with mixes containing silica fume is impractical without the inclusion of superplasticizers. Practice with regard to the place of addition varies. Proponents of addition at the concrete plant claim greater admixture efficiency. There is reluctance on the part of some authorities to allow this fearing a lack of control on how much of the liquid added to the concrete is water and how much is admixture. In such cases, the slump before and after superplasticizer is specified. There may be a trend to allow addition at the plant. Most engineers allow re-dosing with admixture, if necessary, at the site. Typically, water-reducing admixtures are used in combination with superplasticizers, and concretes for bridge decks are often retarded. Mix Design Some specifiers use a prescription specification and none use a completely performance or end result specification. There is almost universal prescription of cement content, supplementary cementing materials content, slump and air content limits.

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On most contracts, the concrete supplier or precast concrete company takes responsibility for the mixture design. Where the Owner takes this responsibility, it can limit the supplier's ability to use his expertise, and may, on occasion, result in the imposition of a less than optimum mix. Many specifications require trial mixes and often specify the lead time by which the data are to be available. Generally insufficient time is allowed for trial mixes. Testing Slump - Practice with regard to specifying slump varies, with most specifiers stating limits. In the field it has been found that the use of superplasticizers empowers the contractor to use whatever slump is optimum for the placing conditions. (Cross falls and gradients on bridges determine what slump is practical.) The choice of slump is best left to be decided in the field. This would be in line with the requirements of CSA A 23.1-2000. Air Content - In the earlier part of the decade, 1990-2000, the degradation of air void systems in these very workable mixes between the discharge of the concrete by the supplier and final compaction in place was a major concern. This was particularly true of pumped concrete. It gradually became fairly wide practice to require confirmation of the in-situ air void system. This created liability concerns between the supplier and contractor. Some specifications had a clause added to try to ensure that the contractor discussed this issue with the concrete supplier prior to finalizing a contract for the supply of concrete. Two responses resulted. The air void systems at the point of discharge were improved to allow for degradation, and admixture companies developed air-entraining agents that produced more stable air voids. Today, the specification of in-situ air void parameters should not be a cause of concern to either the supplier or the contractor. Philosophically, all tests to determine the quality of concrete should be made on samples taken from the structure. It is the structure that the Owner buys. There remain concerns on the part of concrete suppliers in particular that the standard of reliability of testing for these parameters needs to be more reliable, with less variability between test laboratories. Restricting testing to named technicians with proven skill would be one desirable measure. In addition, the 2000 edition of CSA A 23.1 has tightened the limits on the magnification used in the test. This must now be between 100 and 125. Rapid Chloride Permeability - This is the most widely used test to confirm that a concrete mix has low permeability to chloride ions. While it is not a direct measure of permeability, it has been shown to be a reliable index of the permeability and diffusion coefficients of concrete made with slag, fly ash and silica fume (Bridge Views, November/December 2000). Adding calcium nitrite raises the conductivity of the pore solution. It is practice to test such mixes before the calcium nitrite is added. Ingredients that are conductive, such as steel fibres or aggregates containing iron, will also negate the test results.

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On many contracts the test has been made on specimens cast from samples fabricated from the concrete at the point of discharge. There is an increasing practice to test cores taken from new construction to confirm in-situ quality. Where this is done early in the life of the concrete, and before it is contaminated, the results can be compared to pre-concreting tests. Like air void determinations on cores taken from the structure, this approach provides assurance that the concrete in place meets the owner's durability requirements. The usual test age is 28 days after casting. Where the concrete contains SCMs, specifications increasingly recognize the possible need to test specimens at later ages, instead of or in addition to, tests at 28 days. An important issue in the test procedure is the curing history of the test specimens. The permeability of HPC containing SCMs improves with age, particularly if the concrete is saturated throughout the pre-test period. If the test specimens are cured in water or in a fog room until the test age, the improvement in impermeability may not reflect that of the structure. With silica fume mixes, the difference may be insignificant, but this is an area that warrants further research and standardization. As this survey shows, the predominant coulomb value specified is 1000. Some jurisdictions that initially specified 600 have changed to 1000. Some others specify 700 +/- 35%. This survey shows that very few test results have exceeded 1000. At this value it is felt that the concrete is very durable. Where test results have exceeded the 1000 coulomb value, the result has been attributed to poor testing or the choice of an unsuitable mix. From extensive published test data from many contracts, it is clear that the concrete industry can consistently meet a 1000 coulomb maximum requirement for cast-in-place concrete. It is possible that a lower value could be specified for particularly severe exposure conditions, but a raison d'étre would be needed to justify a lower value. Where this parameter is a performance issue, penalties are levied by some Provincial Highway Departments and Cities for failure to meet the maximum value specified. The MTO, for instance, applies the following penalties:

Pa = (C-1000) /40 where Pa = price reduction in $ per m³ per lot and C = average RPC of a lot.

Some other Highway Departments and Cities also impose penalties as detailed above in this report.

Some specifications are silent on any adjustment of price due to failure to meet the maximum value specified. It is possible that, as more experience is gained in the use of this test, other mechanisms will be developed to deal with a failure to meet this aspect of the specification.

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In practice, there is some evidence that the variability of the test is significantly less than ASTM C 1202 would suggest. On Bridge 201 at Pearson Airport (Bickley and Fung, 2000) the difference between the results of two laboratories testing cores from the deck was as follows:

Parameter Lab 1 Lab 2 Number of tests 4 8 Range 546 to 829 411 to 697 Average 658 553 Average of all tests 588

Despite the widespread use of this test without apparent difficulty in applying it, a faster test is considered desirable. The age at which the test is started is at least 28 days and sometimes later if slag or fly ash is included in the mix. The test takes about two days to condition the specimens and determine the coulomb value. Results are thus not available until at least 30 days after the concrete, to which the test specimens relate, has been placed. As the trend to performance specifications spreads, the need for faster and more reliable tests will increase. This need is being addressed by an FHWA contract (Stanish et al. 2000). As a result, it is likely that a new test will be proposed for standardization in the near future. It will require considerable promotion to change practice from the current widespread use of the RCP test. Diffusion - The permeability of concrete to chloride ions can be determined by diffusion tests. Using current techniques, this test takes 120 days from the time the test specimens are 28 days old. It is an expensive test. It is not really a practical quality control test. Recent attempts to replace it have focussed on the use of a modified ISAT test combined with established diffusion values. In one application, usable quality control test results were obtained at an age of 14 days (DeSouza et al, 2000). Scaling - A minority of authorities specifies testing for scaling resistance. The scaling resistance of HPC is good (Aï tcin, 1998). Where significant percentages of supplementary cementing materials are used, there are reservations about the reliability of standard scaling tests to predict in-service performance, which has been better than would be predicted by the test. Compressive Strength - Most specifications evaluate test results for compliance in accordance with CSA A 23.1. A number of jurisdictions have mechanisms to penalize contractors based on the consistency with which the specified strength is met, but no bonus for good performance. The MTO in end-result, or performance, specifications provides for a bonus for the production of concrete meeting strength requirements with good consistency. A comparison of the level of quality control of prescription and end-result contracts was made in 1991 (Bickley, 1991). The performance of the concrete on end-result contracts,

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where bonuses could be won, was superior to that on prescription contracts. Perhaps, there is a moral here. For high-strength concretes to be consistently delivered, an extensive and detailed pre-concreting programme is necessary (Ryell and Bickley, 1987). Where the recommended procedures have been followed, the results have been a high level of QA and QC and excellent compliance with specified requirements (Ryell and Fasullo, 1993). ACI Committee 363 "High-Strength Concrete" has produced a document (ACI 363, 1998) which provides guidance on quality control and testing for high-strength concrete projects. There have recently been two projects where the advice in the above three references was not followed. The result was extensive failure of test results to reach the specified high strengths, with significant costs as a result. While most high-strength concrete buildings have used the concrete in the inside of buildings, high strength is sometimes used in structures exposed to the elements. Where this results in a requirement for air-entrained high-strength concrete, the effect of entrained air on strength must be considered. Each 1% of air will reduce the strength of a concrete by about 5% (Aitcin, 1998), so a 6% air content will result in a loss of strength of about 20% allowing 2% for entrapped air. It may be impractical to achieve a very high strength air entrained concrete. In such instances, it is even more essential to follow the best advice on preconstruction testing and QC during construction. Advice on mix design for such critical mixes is available (Aitcin, 1998). Two approaches have been used to address the need for air entrainment in HPC exposed to freezing and thawing. Research at the University of Sherbrooke established that the air void system required to make HPC resistant to freezing and thawing can be significantly inferior to the criteria in our National Standards (Aitcin, 1998). Most specifications cite or copy the provisions in CSA A 23.1-94, Section 14. In the MTO Special Provisions for HPC, issued in 1998, the requirements for the air void system, and the revised provisions in Section 14 of CSA A 23.1-00 are summarized below.

CSA A 23.1-00 Parameter MTO Special Provisions, May 98 Conventional Concrete HPC

Spacing factor: average µm 250 230 250 Spacing factor: max µm 300 260 300 Hardened air content: % 3 3 -*

* Where specified in HPC specifications, the number has been 3%. On a recent contract requiring very high strength concrete, the requirement for air-entrainment made it impractical to achieve the specified strength. Current belief is that

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mixes with water-cementitious ratios of 0.30 and above require air entrainment, and those under 0.25 do not. In between these two values, the need is uncertain. In the case described, the mix had a water-cementitious ratio of 0.27. Tests were made on the mix without air-entrainment and after over 400 cycles of freeze-thaw tests to ASTM C 666 procedure A, the relative durability factor was over 90%. The contract proceeded using the non air-entrained mix. It is noted that the specifications of several of the Highway Departments and Cities reviewed above allow acceptance on the basis of ASTM C 666 tests where the specified air void systems cannot be met. This approach is generally approved on HPC bridge contracts in the USA. Constructability Trial Slabs - The use of trial slabs, as specified in the MTO special provisions for HPC, has proven to be useful. Constructing a length of deck with the materials, plant and personnel that are to be used in the contract, often highlights potential problems. These trial slabs are expensive to construct, possibly in the range of $10,000 to $20,000. It is reasonable, in accordance with MTO policy, to waive this requirement where a contractor has recent prior experience of HPC. Placing and Compacting - HPC is usually placed at high or relatively high slumps. Vibration is still needed to ensure full compaction. When the deck of Bridge 201 at Pearson Airport was finished, the finishing machine left a narrow strip at each side of the deck, which had to be hand finished. This is the normal situation when finishing bridge decks. The only way to avoid this is to mount the finishing machine on rails supported outside the edges of the deck. This is expensive and may present structural problems. After the finishing of the deck, sorptivity tests were made on the deck. These tests showed that the sorptivity of the hand-finished edges was significantly higher than the rest of the deck. This raises the concern that these edges may be more permeable to chloride intrusion than the rest of the deck. It was suggested in the report on Bridge 201 (Bickley and Fung, 2000), that the use of a hand held plate vibrator to compact and finish the upper layer of the edges might be a solution to this problem. Finishing – Probably, the most controversial aspect of the use of HPC is in the finishing of bridge decks. The use of superplasticizers enables high quality to be achieved with high slumps. On occasion, where a range is specified, the slump may be too high for the crossfalls and gradients that occur on some bridges. A wide range of slumps can be achieved by the use of superplasticizers without compromising the quality or strength of the concrete. Therefore, the contractor should choose the appropriate slump for the job conditions. Mixes containing silica fume are more difficult to finish than conventional bridge deck concrete. Finishing can be improved by the use of slag or fly ash. The greater the

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percentage of these supplementary cementing materials, the easier the concrete is to finish, but still not as easy as conventional concrete. Experience is that the finishers become more successful with increasing experience, but there is still concern amongst the finishers with the difficulties that they face. There is also concern with owners with regard to surfaces that are not of the finished quality they want, and which, sometimes, have to be ground to meet criteria for smoothness. Absent is a systematic effort to optimize mixes for finishability, and considered modifications to the equipment and operating mode of deck finishing machines. These machines were developed for conventional deck concrete. It is understood that some advice is available from the manufacturers of deck finishing machines. It may be that with the rapidly increasing use of HPC in both Canada and the United States a more fundamental study of possible modifications by the manufacturers is warranted. Curing - It is trite to say that curing is the most neglected aspect of concreting. It is well known that all concrete would be immeasurably better if properly cured; but, so often, it is not. With HPC, poor curing is not an option. Unless the loss of moisture is prevented by fog curing (or immersion in water), HPC shrinks autogenously (Aitcin, 1998, Tazawa, 1999). This shrinkage starts with the com-mencement of hydration and before the concrete has set. The amount of shrinkage that can occur autogenously can be of the same order as drying shrinkage. Thus, if effective curing is not started as soon as concrete in a deck is finished, severe cracking is inevitable. This is why most specifications for HPC require fog curing to start after initial finishing. Some specifications mandate evaporation retarders as an alternative to fog curing or as the only specified cure prior to the extended period of wet curing commonly required. It seems logical to understand why fog curing should be the preferred method of initial curing. That an evaporation retarder may be effective is less easy to understand. Tests made during the construction of the TTC Sheppard Line Parking Structure described above showed no difference between the RCP values for fog curing, fog plus evaporation retarder and evaporation retarder alone. The extent of the testing was limited. There would seem to be merit in investigating this material further. In practice, the curing specification adopted by MTO has proven to be effective. Until a well-proven alternative is established, it would seem imprudent to reduce the amount of curing that is so important to the quality of HPC. When combined with control of the thermal history of the concrete, this procedure has produced crack free bridge decks. It has been shown that, for severe exposures, curing HPC until the strength reaches 70% of the specified 28-day strength is adequate (Wang et al, 1997). Depending on whether or not accelerated curing is applied to the concrete, the curing period to meet this criterion may be less than 7 days. For concrete cured at normal temperatures, 70% of the 28-day strength will need about 7 days of curing.

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Monitoring The prime imperative for the use of HPC is the assumption that structures constructed with it will have an enhanced service life. Durability will be better, life cycle costs less, intervals between rehabilitation longer, and repairs less costly. These assumptions are based mainly on the rational testing of HPC durability parameters and extrapolations using life cycle prediction models. All current life cycle prediction models use assumptions that are, in the main, educated guesses. What is missing are long term field performance data to support these assumptions. Perceived performance to date confirms the assumptions, but the volume and duration of the supporting data is not yet adequate. The prime barrier to more extensive monitoring is a real difficulty in obtaining funding. As a result, the amount of data available is not extensive. Corrosion Monitoring - The use of HPC in structures exposed to the elements is based on the assumption that corrosion of the reinforcement will not be initiated for a long time. On some of these projects, a probe with elements at increasing cover depths has been used (Hansson et al, 2000). This configuration allows the ingress of chlorides to be monitored by the development of corrosion activity at different levels. The owner is thus given advance warning of impending corrosion and the data can be used to predict time to corrosion for the reinforcement in the structure. Hereunder is a compilation of Concrete Canada corrosion monitoring projects reported: Exposure Structure Installed Nature of the Structure and Environment Marine UGG Dock, Vancouver, BC 1994 Prisms with range of concrete quality in

splash zone UGG Pile, V UCG Pile,Vancouver, BC 1996 Pile replacement pile jacket Deltaport, Delta, BC 1997 Prisms with range of concrete quality inside caissons and on breakwater

Industrial Vancouver Wharves Sulphur Dumper Pit

1999 Concrete in railcar dumper pit; hghly corrosive sulphur exposure

Harmac Pulp and Paper Mill, BC

1994 Prisms (both cast-in-place and precast) with range of concrete quality in effluent tank

Iona Sewage Outfall 1997 Concrete corrosion state in existing Richmond, BC outfall

Bridges Oak Street Bridge, 1997 Replacement overlay Vancouver, BC Fraser River, Hope, BC 1997 Replacement deck Tsable River, Courtenay, BC 1998 Deck of new HPC segmental structure

Nova Scotia Bridge 1998 Deck

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The Highway 20 bridge and one of the two Highway 407 demonstration bridges were instrumented by MTO. Access to the latter has precluded a full monitoring programme. For the Highway 20 bridge, annual surveys have been made in the five years since completion. During the construction of this bridge, four clusters of three types of corrosion probes were installed in the deck:

• Graphite reference electrode • Ag/AgC1 reference electrode, and • 3EP three element probe consisting of an MnO2 reference electrode and two

carbon steel and stainless steel electrodes Monitoring included the following procedures:

• Visual Inspection • Delamination survey • Cover survey • Half-cell survey • Linear polarization, by 3LP and GECOR procedures • Resistivity, by four-point resistivity probe • Chloride ion profiles • Review of data from the embedded probes

The full results will shortly be published by the MTO. To date, the results of the survey show that the structure has performed very well. There are some recently developed long fine cracks, but the steel has remained in a passive state. No physical damage is apparent. Thermal Effects - The dimensions of the components of the Confederation Bridge were such that thermal studies were undertaken before and during construction (Dilger, 2000). Data included temperature measurements across a cold joint of two segments of a box girder. The data showed a temperature difference between the two segments at the time of hardening of 18ºC. This difference would result in tensile stresses in the concrete as the temperature between the segments equalized.

The structure was instrumented with over 250 temperature sensors located at six sections. Movement at expansion joints and strains are monitored as is solar radiation using pyrometers. Freeze-thaw cycles occurred almost every day during February and March 1998, confirming the severe nature of the environment at the bridge location. This monitoring is expected to continue for ten years after the completion of the bridge.

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For non-massive structures, such as most bridge decks, a maximum concrete temperature of 70°C and a maximum gradient between the centre and surface of the concrete of 20°C have been found to be effective in avoiding significant cracking. While temperature-stress relationships can be investigated using a number of available computer programmes, the practical advice given in Table 18 of CSA A23.1-2000 has been found to be reliable on most typical construction contracts. REFERENCES Isabelle, H.L., "Development of Canadian and American Specifications for Silica Fume", International

Workshop on Condensed Silica Fume, Montreal, 1987, CANMET Compilation of Papers.

Thomas, M.D.A., Cail, K. and Hooton, R.D., "Development and Field Applications of Silica Fume Concrete

in Canada: A Retrospective", Canadian Journal of Civil Engineering, Vol. 25, No. 3, June 1998, pp.

391-400.

Bickley, J.A. and Fung, R., "Optimizing the Economics of High-Performance Concrete", Cement

Association of Canada, 2000.

Bickley, J.A.,"Directions in Concrete Research", MTO research and development branch, report MAT-91-

09, September 1991.

Ryell, J. and Bickley, J.A.,"Scotia Plaza: High Strength Concrete for Tall Buildings" Proceedings:

Utilization of High Strength Concrete, Stavanger, Norway, June 1987, pp. 641-654.

Ryell, J. and Fasullo, S., "The Characteristics of Commercial High Strength Concrete in the Toronto

Area", Presented at the 1993 CPCA/CSCE Structural Conference, Toronto, May 1993.

ACI 363.2R-98, "Guide to Quality Control and Testing of High-Strength Concrete".

Aï tcin, P-C, "High-Performance Concrete", E & FN Spon, 1998, pp. 591.

Tazawa, E.,Ed, "Autogenous Shrinkage of Concrete", Proceedings of the International Workshop,

Hiroshima, June, 1998, E & FN Spon, 1999, pp. 411.

HPC Bridge Views, Issue no 12, November/December 2000, pp. 2-4.

DeSouza, S.J., Hooton, R.D. and Bickley, J.A., "A Practical QC Test Programme for HPC in Precast

Tunnel Liners", ACI SP-191, 2000, pp. 99-114.

Hansson, C.M., Seabrook, P.T. and Marcotte, T.D., "In Situ Corrosion Monitoring Using Embedded

Probes: Why? What? How? And-so what?" Presented at the ACI Convention, Toronto, October 2000.

Wang, M., Dilger, W.H. and Langley, W.S., "Curing of High Performance Concrete-An Overview",

Proceedings PCI/FHWA Symposium on High Performance Concrete, New Orleans, August 1997, pp.

283-293.

Dilger, W.H., "Temperature Effects in Concrete and Composite Bridges", Keynote paper, Proceedings of

the Workshop on Research and Monitoring of Long Span Bridges, Hong Kong, April 2000, pp. 1 -13.

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Conclusions and Recommendations Cementitious Materials Portland and a wide range of blended cements are available. The design of durable and/or strong concrete is facilitated by these choices. Admixtures Available admixture combinations allow the choice of optimum workability while maintaining low water-cement ratios. Testing Tests to determine durability parameters should be made on test specimens drilled from the finished structure. The RCP test has proven to be a reliable index of durability. It is almost universally specified. The most common requirement is a maximum of 1000 coulombs, at 28 days or, sometimes, later if supplementary cementing materials are involved. Stable air void systems can routinely be achieved in-situ if suitable air-entraining agents are chosen and the mixes are designed to allow for significant testing variations. Where high-strength concrete (70 MPa or stronger) is specified, the preconstruction laboratory and field testing procedures, described in ACI 363.2R-98, are essential. Specifications Specifications should be end result or performance specifications as far as is practicable. Consistency as well as compliance with minimum requirements is highly desirable. To encourage consistency, bonuses should be offered. It is essential that HPC specifications include durability criteria including RCP and air-void system limits. Durability parameters must be enforced. Specifying strength alone, even with potentially durable concrete, is inadequate assurance of durability. Constructability The chances of the successful use of HPC on a contract depend largely on pre-construction and pre-concreting meetings with all those responsible for the supply, installation and supervision of concreting. Adequate lead-time should be allowed for trial mixes. Trials slabs are of significant value on bridge contracts where a contractor has no prior experience of HPC.

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The finishability of HPC for bridge decks needs to be improved. The manufacturers of finishing machines should undertake a new look at this issue. Designers of concrete mixes should optimize mixes for finishability. Curing The three rules for successful HPC are curing, curing and curing. Curing must be done by the book, and supervision must enforce curing specifications. Fog curing after finishing, followed by 7 days wet curing, has proven to be effective. The effectiveness of evaporation retarders as an alternative to fog curing warrants further research. Service Life Predictions The accuracy of the service life and cost life-cycle predictive models available would be much enhanced by data obtained by monitoring new structures. For reliable and accurate predictions of service life and life cycle costs much more monitoring data are needed. Summary The last 10 years have seen an increasing use of HPC. Many authorities are convinced that long term durability and lower life cycle costs result. Certainly, these are the benefits to be expected. If they are to be realized consistently, the enforcement of state-of-the-art specifications is essential. Printed in Canada

a state of the art review of high performance concrete structures built in canada

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