Another Look at Test Methods for Alkali-Aggregate Reaction and their Capacity to Evaluate Preventive Measures

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Alkali silica reaction (ASR) is a common deterioration mode that causes expansion and disruption in concrete. The deterioration takes years to manifest itself under field conditions. However, laboratory tests are available to accelerate the reaction and obtain results within a shorter time. The Concrete Prism Test (CPT) described in the Canadian and American Standards, CSA A23.2-09 14A and ASTM C1293, has been known as the most reliable laboratory test to evaluate alkali reactivity of aggregates and the efficacy of preventive measures. Indeed, the level of preventive measures recommended to counteract ASR in many standards including the Canadian Standards are based on results from the CPT. However, recent published work showed some preventive measures that limited the 2-year expansion in the CPT to develop expansions at 15 years when tested in large blocks under field exposure. It is of interest to identify the reason(s) behind this observation and come up with an enhanced approach to identify the levels of supplementary cementing materials (SCM) or preventive measures required to mitigate long-term expansion. This approach, which is one of the objectives of this proposal, will take into consideration the 2-year expansion from CPT as well as the differences between the material performance under long-term field exposure and that under CPT conditions. The outcomes of this research will provide standard developers with data that make them more comfortable in specifying levels of preventive measures. In addition, there has been a growing interest in the profession to find accelerated test methods that provide reliable results within a relatively short period of time. The Concrete Microbar Test (CMBT) adopted by the European Standards (RILEM) is a promising test for this purpose due to various advantages. However, comprehensive research is needed to confirm that the test is suitable for a wide range of Canadian aggregates and SCM, and recommend the suitable aggregate size, testing period, and expansion limit for the test. This is covered under this proposal.