International Concrete Abstracts Portal

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.

This paper reports the results of a study on the resistance of lightweight aggregate concrete to the penetration of chloride ions. Concrete specimens were fabricated with a blended silica fume cement at a water-cementitious materials ratio of W/CM = 0.40 or 0.30 and with combinations of aggregate as follows: (i) limestone coarse aggregate and river sand, (ii) expanded slate coarse aggregate and river sand, or (iii) expanded slate coarse and fine aggregate. A further series of mixes was made using the latter combination of aggregates with the blended cement being partially replaced with 25, 40 or 56% fly ash. Concrete specimens were subjected to a series of tests including “rapid chloride permeability” (ASTM C 1202), and non-steady-state diffusion (bulk diffusion test). Tests were conducted at 28 and 56 days, and 1 and 3 years. The results up to one year clearly show the benefits of incorporating expanded slate in the concrete, with permeability and diffusion coefficients being reduced significantly. The improvements attributed to the presence of the lightweight aggregate appeared to increase with the maturity of the concrete and, after 3 years continuous curing, the reduction in the apparent chloride diffusion coefficient was observed to be as much as 70%. As expected, the addition of fly ash produced further reductions in permeability and diffusion. The data developed in this study were used as input parameters for service life predictions. Although, there are insufficient data to allow firm conclusions to be drawn from these analyses, it is clear that the incorporation of lightweight aggregate will lead to a significant extension of the service of life.

This paper deals with a numerical modeling of concrete carbonation, based upon durability indicators (DIs), within the framework of a durability approach. Firstly, the methodology and the selected panel of universal DIs concerning carbonation are presented. Secondly, with the purpose of protecting structures against carbonation-induced corrosion, a model accounting for the coupled CO2-H2O-ionic transports, the carbonation reactions of Ca(OH)2 and C-S-H, the pH decrease, and the microstructure evolution is described. In this model, the DIs porosity, initial Ca(OH)2 content, and liquid water permeability are introduced as major input data. Complementary parameters are also used: Ca(OH)2 crystal size, C-S-H content and capillary pressure curve. The main numerical outputs are the carbonation kinetics, the residual Ca(OH)2 and newly formed CaCO3 content profiles, and the pH value. As a first step, the model is validated with accelerated carbonation data obtained on a cement paste and on three porous concretes. The carbonation depth and profiles, measured by means of phenolphthalein spray test and thermal analysis respectively, are in good agreement with the numerical simulations. The study is completed by a sensitivity analysis. The model, together with the test methods required for the assessment of the relevant DIs, could be included in a toolkit for durability evaluation and prediction of carbonation-induced corrosion of real structures.

The dimensional stability of cement based materials (mortar or concrete) may be improved through the use of shrinkage reducers or expansive agents. In this study the combined use of a propylene glycol ether based shrinkage reducer (SRA) and a calcium oxide based expansive admixture has been investigated. Mortar and concrete specimens (prepared without admixtures or with SRA or EXP or SRA and EXP) has been compared through compressive strength determinations, free drying shrinkage, restrained shrinkage and restrained expansion measurements. A synergistic effect on the shrinkage reduction has been observed when the shrinkage reducing admixture and the expansive agent have been used together. In order to elucidate such phenomenon, the hydration of cement pastes containing these kinds of admixtures has been followed by ESEM-FEG (Environmental Scanning Electron Microscopy – Field Emission Gun) and specific surface area measurements.

In the dry shake hardeners (60% of quartz-based sand and 40% of portland cement), applied on the top of concrete industrial floors to improve their abrasion resistance, the alkali-content in terms of Na2O eq. can be as high as 6 g/L corresponding to 6 kg per cubic meter against 1.5-2.0 kg/m3 of Na2O considered to be the threshold value for the alkali-silica reaction. Due to this situation, coarse aggregates of the concrete substratum, in direct contact with the top layer of the cement-based hardener, are exposed to a higher risk of alkali-silica reaction at the transition zone due to the very high content of alkali in the hardener top layer. In order to prevent this type of ASR in concrete industrial floors, a special binder, containing 50% of ground slag or fly ash and 50% of portland cement, was used in combination with a quartz-based crushed sand on the top layer (40% weight of binder and 60% of quartz). Due to the presence of GGBFS or fly ash in the cement-based hardener, the ASR of the coarse aggregate of the sub-strate in direct contact with the top-layer was really prevented. However, this technique of manufacturing durable concrete industrial floors, was not accepted by the workers because they should wait too much more time for the hardening of the surface. A special mix was adopted with improved performance in terms of setting properties: a very fine ground slag, with a specific surface area of about 650 m2/kg, was combined with an accelerating admixture, and was succesfully adopted for both a durable concrete industrial floor and a trouble-free for the workers.