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Vaughan, Canada

Shehata M.H.,Ryerson University | Jagdat S.,Ryerson University | Lachemi M.,Ryerson University | Rogers C.,Post Office Box 185
Proceedings, Annual Conference - Canadian Society for Civil Engineering | Year: 2011

This study investigates the role of supplementary cementing materials (SCM's) on the alkali reactivity of carbonate aggregates that marginally meet the expansion limit for the concrete prism test (CSA A23.2-14A). With the increasing use of SCM's in concrete, it is of interest to investigate their role on the expansion of concrete containing marginally alkali- reactive carbonate aggregate. While it is understood that most SCM's reduce the alkalinity of concrete pore solution and are unlikely to trigger more expansion, some types of SCM, such as high-alkali and high-calcium fly ashes, could raise the alkalinity of pore solution's and promote expansion. The concrete prism expansion test was used to investigate the role of fly ashes of different composition, slag, and metakaolin on concrete expansion. The SCM's were used at different replacement levels that are likely to be used in concrete in North America. A highly reactive carbonate aggregate from Kingston, Ontario was blended with non-reactive carbonate aggregate at different ratios until a one-year expansion value slightly lower than the expansion limit of 0.040% was obtained. This was found at a blending ratio of 10% reactive and 90% non-reactive aggregate. This blend of coarse aggregates was used as a marginally alkali-reactive carbonate aggregate. The 2-year expansion results showed that, except for high-calcium fly ash with high-alkali content, SCM's do not trigger more expansion in concrete with marginally reactive aggregate. The concrete microbar test was found to underestimate the expansion of marginally and moderately reactive carbonate aggregate compared with expansion obtained in the concrete prism expansion test.

Shehata M.H.,Ryerson University | Mikhaeel W.,Ryerson University | Lachemi M.,Ryerson University | Rogers C.,Post Office Box 185
Proceedings, Annual Conference - Canadian Society for Civil Engineering | Year: 2011

The recycling of reclaimed concrete aggregate (RCA) in concrete fits well with the concept of construction sustainability. However, it is essential to study the effects of RCA on the performance and long-term durability of concrete. Without such study, the incorporation of RCA in concrete is unlikely to be adopted by the construction industry. RCA produced from demolished structures affected by alkali-silica reaction (ASR) was found to produce significant expansion when used in new concrete. The levels of supplementary cementing materials (SCM's) required to mitigate the expansion were higher than those required for concrete with natural alkali-reactive aggregates. This study looks at various methods to mitigate the expansion in concrete containing reactive RCA. The concrete prism test (CSA A23.2-14A) was used to investigate the efficacy of the different mitigation approaches. One of the investigated options was blending the reactive RCA with non-reactive natural aggregate at a blending ratio of 70% to 30%, respectively. While blending alone was not effective in maintaining the 2-year expansion below the 0.04% limit, the addition of moderate levels of common SCM's were found effective in mitigating the expansion. The study also developed the level and type of SCM blends that mitigated the expansion in concrete with 100% reactive RCA. Some ternary blends, including a blend containing 20% low-calcium fly ash and 30% slag, were effective in mitigating the expansion. A combination of lithium nitrate and moderate levels of SCM's reduced the expansion in concrete prisms with 100% RCA; however, the expansion was slightly above 0.04% at 2 years and thus not completely effective.

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