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SP-234 The Canada Centre for Mineral and Energy Technology (CANMET) of Natural Resources, Ottawa, Canada, has played a significant role in Canada for over 40 years in the area of durability of concrete. CANMET, in association with the American Concrete Institute and the Institute for Research in Construction/National Research Council, Ottawa, sponsored the First CANMET/ACI International Conference on Concrete Durability held in Atlanta, Georgia, April 27-May 1, 1987. The refereed proceedings of the Atlanta conference and Montreal conference (the Second CANMET/ACI International Conference on Concrete Durability, held August 4-9, 1991) were published as ACI SP-100 and ACI SP-126, respectively. Unlike the first conference, this second conference was not named after any individual(s), and the future conferences in this series would follow this precedent. In 2006, CANMET, in association with several other organizations in Canada and the U.S., sponsored the Seventh CANMET/ACI International Conference on Durability of Concrete. The conference was held in Montreal, Canada, on May 28-June 3, 2006. More than 75 papers were peer reviewed in accordance with the policies of the American Concrete Institute. The proceedings of the conference, consisting of 50 refereed papers, were published by the American Concrete Institute as ACI SP-234. In addition to the papers that have been published in the refereed proceedings, more than 50 other papers were presented at the conference. A number of these were published as supplementary papers in a special volume. During the conference, special sessions were held on subjects with sulfate attack on concrete and high-performance lightweight concrete. Some of the papers related to these subjects were published in the supplementary volume. Thanks are extended to more than 15 review panel members who met in Budapest, Hungary, in 2002 to review the papers. Without the dedicated efforts of the reviewers, it would not have been possible to have the proceedings ready for distribution at the conference. The cooperation of the authors in accepting reviewers’ suggestions and in revising their manuscripts accordingly is greatly appreciated. The authors are also to be commended for their prompt return of their finalized manuscripts. The assistance of A. Bilodeau, Chair of the audio-visual review panel, is gratefully acknowledged. Thanks are also extended to P. Gupta and C. Mansfield-Joiner for their help in processing the manuscripts. The contributions of the ACI staff for their help in publishing the proceedings on time is also recognized. As an integral part of the conference, a special symposium was held to honor Professor K. Sakata of Japan for his outstanding contributions in the broad area of concrete design and technology over the past 20 years. The proceedings of the symposium were published as a separate volume.

Recycling of demolished concrete is an effective method for reducing construction waste. Recycled fine aggregate includes a large quantity of hydrated cement paste. The cement paste influences qualities of recycled fine aggregate, and, in turn, the properties of concrete containing recycled fine aggregate. As a result, concrete containing recycled fine aggregate has lower strength and durability than concrete with natural aggregate. However, the manner in which the quality of recycled fine aggregate influences the properties of concrete remains unclear. When considering the use of recycled concrete for construction, the durability of concrete with recycled fine aggregate must be investigated. The purpose of this study is to determine the influence of the quality of recycled aggregate on the properties of concrete at W/C ranging from 0.25 to 0.7. The parameters investigated to evaluate durability are strength, pore volume, shrinkage, carbonation, and resistance to frost damage. The results show that water absorbed by the aggregate migrates to paste around particles of aggregate, and influences the volume of water and pores in paste. Therefore, when recycled fine aggregate with high water absorption is used in concrete, shrinkage and volume of gas permeating into concrete increase, and durability lowers.

The development of cement-based screeds unbound to their support is still limited because of the curling which occurs at the corners and perimeter of the screed. This phenomenon is mainly due to the moisture gradient that appears within the thickness of the screed: the upper surface dries and shrinks, while the lower one remains humid. One possible solution limiting this phenomenon is using calcium sulfoaluminate cement instead of normal portland cement. Experiments utilizing an original device show that the curling is three times lower when using calcium sulfoaluminate cement. Moreover, when polyol is added to the mixture (0.63% of the cementitious material content), curling is still reduced by 23%. Polyol reduces drying shrinkage by 40%, but does not affect the mass loss of the screed and the porous distribution. The results obtained show that polyol can be considered as an efficient shrinkage reducing admixture (SRA) for calcium sulfoaluminate-based mortar and concrete.

Different testing methodologies exist for the diagnosis of Alkali-Silica Reaction (ASR) in concrete. But the problem is to quantify the reaction because some methods are qualitative (petrographic method) and not always specific (accelerated swelling test could be biased by other expansive reaction as DEF).The aim of this study is to improve the diagnosis in concrete by following new parameters. This application supplements other methods. These new parameters are porous and absolute mass volume giving apparent mass volume which increase for the ASR. To obtain these parameters, the extraction of silica of the aggregate skeleton contained in concrete matrix is needed. The increase of apparent mass volume of silica from aggregate skeleton related the alteration of reactive silica which has for consequence the increase in swelling of concrete. These physical parameters are specific to ASR. They may be used for quantitative assessment of the alteration of reactive silica from aggregate which permit to follow ASR reaction degree responsible for the degradation of concrete. Encouraging results have been obtained on laboratory concrete for two different aggregates (flint aggregate or siliceous limestone) and also on field concrete.

The determination of the starting point of autogenous shrinkage strains is still a point of discussion within the scientific community. Several approaches, each one more or less easy to implement, have been proposed to determine this important point when dealing with low water to binder ratio (W/B) concrete. It is at this moment that external water curing must be applied to control the detrimental effects of the development of early autogenous shrinkage strains because the development of early cracking can be very detrimental for concrete durability. Concrete is continuously subjected to volumetric changes, particularly at an early age, when hydration heat and autogenous shrinkage evolve very fast. It is difficult to separate thermal and plastic shrinkage from shrinkage due to chemical contraction. In large concrete elements, it is appropriate to calculate isothermal shrinkage to reach the starting point of autogenous shrinkage. Neither the temperature criterion alone, nor the penetration resistance test can predict the starting point of autogenous shrinkage, and therefore, the risk of early-age cracking. In this research, the concept of threshold of solidification was coupled with that of temperature rise to more accurately determine the starting point of autogenous shrinkage. An experimental study on the development of isothermal shrinkage of large concrete elements made with different binders was carried out. In order to clarify the effect of the W/B on the importance of the determination of the starting point of autogenous shrinkage, concrete mixtures were made at three W/B: 0.45, 0.35 and 0.26.Isothermal shrinkage was measured using vibrating wire gauges imbedded in a large concrete element. Experimental results show the importance of the correct determination of the starting point of autogenous shrinkage when the W/B is low.