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

碱硅反应（ASR）是引起混凝土膨胀和破坏的一种常见劣化方式。在野外条件下，这种退化需要数年才能显现出来。然而，实验室测试可以加速反应并在更短的时间内获得结果。加拿大和美国标准CSA A23.2-09 14A和ASTM C1293中描述的混凝土棱镜试验（CPT）被认为是评估集料碱反应性和预防措施有效性的最可靠的实验室试验。事实上，包括加拿大标准在内的许多标准中针对ASR建议的预防措施水平都是基于CPT的结果。然而，最近发表的研究表明，一些预防措施限制了CPT的2年扩张，当在现场暴露的大区块中进行测试时，扩展时间为15年。确定这一观察结果背后的原因，并提出一种增强的方法来确定补充固井材料（SCM）的水平或预防措施，以减轻长期膨胀，这是很有意义的。该方法是本提案的目标之一，将考虑到CPT的2年扩展，以及长期现场暴露下材料性能与CPT条件下材料性能之间的差异。这项研究的结果将为标准开发人员提供数据，使他们在指定预防措施的级别时更加舒适。此外，对于在相对较短的时间内提供可靠结果的加速测试方法，业界的兴趣也越来越大。欧洲标准（RILEM）采用的混凝土微棒试验（CMBT）由于其各种优点，是一种很有前途的测试方法。然而，需要进行全面的研究，以确认该试验适用于广泛的加拿大骨料和SCM，并推荐合适的骨料粒径、试验周期和试验的膨胀极限。这是本建议的内容。

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.