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.

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.

The Accelerated Mortar Bar Method (AMBM) ASTM C 1260 (or CSA A23.2-25A) is used with success for evaluating the effectiveness of supplementary cementing materials (SCMs) in suppressing expansion due to alkali-silica reactivity in concrete (ASR). This study attempts to answer the question of why this method gives good results with SCMs. The most beneficial effects of SCMs against ASR is thought to be alkali decrease in the pore solution while the bars are immersed in 1N NaOH at 80°C. Mortar bars made with different SCMs were tested in normal conditions as well as in pure water and in air at 100% RH. The expansion results were compared with the chemistry of the mortar pore solution expressed under high pressure. The results confirmed that in the presence of an SCM, the alkali decrease in the pore solution remains the most critical mechanism involved in the AMBM. The results also confirmed that alkali equilibrium between the pore solution and the NaOH immersion solution is not achieved in the presence of an SCM at the end of the testing period of 14 days.

La réussite des élèves est le résultat de multiples facteurs auxquels tous les partenaires et intervenants éducatifs sont appelés à contribuer. L’engagement des parents, tout au long du cursus scolaire, s’avère un facteur déterminant pour cette réussite d’où la préoccupation d’un rapprochement école-famille. Cet article a pour objet d’expliciter et d’exemplifier diverses modalités de soutien et d’accompagnement offertes aux personnels scolaires, par le programme Une école montréalaise pour tous (UÉMPT), dans le cadre plus spécifique de la collaboration école-famille et ce, plus précisément en littératie. Le texte débute en présentant la préoccupation d’UÉMPT envers les familles et leur implication pour l’actualisation du plein potentiel de chaque élève. Il aborde ensuite quelques éléments qui permettent de situer l’action d’UÉMPT puis la méthodologie qui a présidé à la mise sur pied des interventions à UÉMPT. Une discussion conclusive permet de souligner les potentiels et les limites de ces interventions.