M. Rivest’s research while affiliated with Université Laval and other places

This study follows another experimental study where different types of sealers were applied on plain and air-entrained large concrete cylinders made with high-alkali contents and highly alkali–silica reactive limestone aggregates. The main objective was to determine the effectiveness of these sealers in counteracting concrete expansion and surface deterioration due to alkali–silica reaction under various exposure conditions. This study indicated that all three sealers tested, the silane-, oligosiloxane-, and polysiloxane-based sealers, could stop concrete expansion due to ASR and even produced contraction, even for concrete cylinders subjected to wetting and drying, freezing and thawing, and sodium chloride solutions. In 1991, the same silane, oligosiloxane, and polysiloxane were applied on sections of median barriers showing various degrees of deterioration due to ASR. These sections were subjected to wetting and drying, freezing and thawing, and, during winter, to deicing salt. The silane was also applied on other sections of the same barriers in 1994. Observations and measurements over 10 years indicate that the aesthetic appearance of these median barriers, particularly those sealed with the silane, was greatly improved, while internal humidity was significantly reduced, and concrete expansion as well, when not arrested. The period of time during which the above three sealers were capable to stop ASR expansion varies with the sealer used and the degree of concrete deterioration at the time of sealing. For instance, the silane, which was the best among all products tested, caused concrete contraction for at least 6 years in median barriers that were severely affected by ASR, and likely for more than 10 years in moderately affected barriers. The overall results confirm the conclusions obtained previously in the laboratory: a good sealer such as the silane tested may greatly improve the aesthetic appearance and stop the expansion of non-massive ASR-affected concrete members, at least up to about 300 mm in thickness, and subjected to wetting and drying, freezing and thawing, and salt water. However, the poor result obtained in the field with another silane-based sealer indicates that a sealer cannot be selected based on its composition only.Key words: alkali–silica reaction, concrete; cracking, expansion, internal humidity, median barrier, sealer, silane, siloxane.

Low- and high-alkali, plain and air-entrained large concrete cylinders, 255 mm in diameter by 310 mm in length, were made with a highly alkali–silica reactive limestone. After curing, a number of cylinders were sealed with silane, oligosiloxane, polysiloxane, linseed oil, or epoxy, with others subjected to 179 freezing and thawing cycles in humid air (one cycle per day). All cylinders were then subjected to 14-day exposure cycles, including in the most severe case periods of humid storage in air, drying, wetting in salt water, and freezing and thawing cycles. All low-alkali specimens did not either expand or develop surface cracking, even those with a deficient air void system and exposed to freezing and thawing cycles. All unsealed high-alkali cylinders subjected early to a series of freezing and thawing cycles did not significantly expand during these cycles, but presented high expansion afterwards. Wetting and drying significantly reduced alkali–silica reaction (ASR) expansion compared with constant humid storage; however, it promoted map-cracking. Regardless of the air content, freezing and thawing increased greatly the concrete expansion in the presence of ASR, even after ASR was almost complete; freezing and thawing also greatly promoted surface cracking. On the other hand, all cylinders early sealed with silane, oligosilixane, or polysiloxane did not either significantly expand or show map-cracking, whatever the exposure conditions and the air content; these cylinders progressively lost mass with time. On the other hand, the epoxy resin was not effective. The linseed oil prevented map-cracking while significantly reducing expansion, however not sufficiently. After one or 1.5 years, some expanding cylinders were sealed with silane, oligosiloxane, or polysiloxane; they started to loose mass and contracted immediately after being sealed, whatever the exposure conditions. The results obtained thus indicate that a good sealer may greatly improve the aesthetic appearance (e.g., map-cracking) and stop expansion of ASR-affected concrete elements of 255 mm or less in thickness, made with a water-to-cement ratio in the range of 0.50, and exposed to wetting and drying, freezing and thawing, and salt water.Key words: air entrained, alkali–silica reaction, concrete, cracking, expansion, freezing and thawing, sealer, silane, siloxane, wetting and drying.

The determination of available alkalis from aggregates is very important for design of durable concrete. This brief article answers comments on the authors original research study in which the researchers used 0.7 M NaOH or KOH solution to extract K or Na in a variety of aggregates at a solution-to-aggregate ratio of 1; the study found that the alkalis released by the aggregates in these alkali solutions can be up to 12.7 kilograms per meter cubed Na2Oe depending on the nature of the aggregate. In the commentary, Mr. Shu contended that the alkali solution extraction procedure presented in the paper is an ion-exchange test in nature and seems incorrect to be used to evaluate the available alkalis from aggregate for alkali-aggregate reaction in concrete. In this reply, Mr. Berube et al explain why their study utilized appropriate tests that measured not only ion exchange but other chemical reactions as well. The researchers discuss the reliability of immersion tests in NAOH and KOH solutions and consider the role of solution-to-aggregate ratio.

In Phase I, particles from 17 different aggregates, 1.25-5 mm in size, were immersed in continuously agitated solutions at 38 degreesC: distilled water, Ca(OH)(2)-saturated solution, 0.7 M NaOH (measurement of K supply), and 0.7 M KOH (measurement of Na supply). These solutions were periodically analysed for K and/or Na up to 578 days. More alkalies were released in alkaline solutions than in lime-saturated solution, with lower values in water. After 578 days, the aggregates released between <0.01% and 0.19% Na(2)O(e), excluding the nepheline-rich aggregate tested (0.68%). This would correspond to a contribution to concrete from <0.1 to 3.4 kg/m(3) Na(2)O(e) (12.7 for the phonolite), based on an aggregate content of 1850 kg/m(3). In general, the feldspar-rich aggregates released significantly more alkalies. In Phase II, the water-soluble alkali content of mass concrete elements from many dams was measured using a hot water extraction method. The values obtained often largely exceed the soluble alkali content expected to be released by the cement used. These results thus also suggest that large amounts of alkalies were supplied with time by the aggregates, particularly by feldspar-rich ones.

In-situ monitoring of concrete deformations and movements is the best way to assess the current expansion of concrete members affected by alkali-silica reactivity (ASR). However, laboratory tests on cores are less expensive and more rapid, and are commonly used to assess the potential for further expansion due to ASR. The risk of expansion and damage due to ASR can be reasonably assessed in the laboratory from: (1), the inherent expansivity of the concrete under study, which is determined by testing core samples in air at 100% RH and 38°C; (2), the residual absolute reactivity of the aggregates present in the concrete under study, which can be determined by testing core samples in IN NaOH solution at 38°C or, even better for coarse aggregates, by testing aggregates extracted from cores through the concrete prism test CSA A23.2-14A or ASTM C 1293; (3), the amount of alkalies that are still active in the concrete, i.e. in the pore solution, which is estimated by a hot-water extraction method on ground concrete, and (4), humidity, (5), temperature, and (6), stress conditions (confinement, reinforcement, pretensioning, postensioning) in service. The individual risk indices corresponding to each of the above parameters are combined to determine the potential rate of ASR expansion of concrete members in service, either already affected by ASR or not.

The knowledge of the active-or soluble-alkali content of concrete is useful in the diagnosis and prognosis of alkali-aggregate reactivity (AAR). A method often used for determining this content is hot-water extraction from ground concrete samples. This method was applied to 17 aggregates and 8 concretes incorporating aggregates presenting different degrees of alkali-silica or alkali-carbonate reactivity. The following conclusions can be drawn: (1) a correction must be made to take account for the alkalies released by the aggregates in the test; (2) using cold water rather than hot water has no significant effect on the results; (3) grinding to <160 μm appears more appropriate than <80μm (lower amount of alkalies released by the aggregates); (4) the soluble-alkali content progressively decreases as alkali-silica reaction (ASR) progresses, which indicates that a significant part of alkalies, progressively incorporated in the reaction products from ASR, is not leached in the test: (5) the repeatability from one series of tests to another and the reproducibility from one laboratory to another appear relatively poor; (6) the use of a control concrete with a known soluble-alkali content may greatly improve the repeatability and the reproducibility of the method.