Aggregate Reactions in Concrete: Addressing the Needs for test Methods, Preventive Measures, and Mitigation

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Aggregate reactions in concrete have been reported to cause major damages to structures. Alkali-silica reaction (ASR) and oxidation of sulphide phases in some aggregates are two major aggregate reactions that have been associated with severe damages to concrete. The scarcity of aggregates in many locations in Canada may push for the use of aggregates from new sources which need to be prequalified. Quick and reliable prequalifying test methods are therefore in need. If the aggregate under consideration is found reactive, the availability of ways to identify adequate preventive measures will be essential. This is because the economic and environmental feasibility may require the use of such aggregate rather than hauling non-reactive aggregates from distant locations. Since its discovery in the 1940's, ASR has been the focus of many research projects that produced test methods, preventive measures, and ways to manage affected structures. However, there are still some unresolved issues pertaining to ASR testing. Specifically, the most reliable lab test Concrete Prism Test (CPT) was found to overestimate the efficacy of some preventive measures. In addition to the need for improvement in current test methods, researchers and practitioners can benefit from a better way to prescribe the type and level of preventive measures based on a more precise way of identifying the reactivity of aggregates. Another type of aggregate reaction is the oxidation of sulphide phases found in some types of aggregates. Damages due to this type of reaction have been reported in a number of locations all over the world since the early 1900's. The relatively recent cases of Trois-Rivières, Québec, and Connecticut, USA have attracted considerable attention due to the level of damage and economic loss. While tests to screen aggregates have been recently proposed, a concrete test is yet to be developed. This test can be utilized to evaluate the efficacy of possible preventive measures. This proposal addresses the above technical needs. In terms ASR, a new innovative strategy to identify aggregate reactivity will be investigated. This will help achieving a more precise determination of the levels of Supplementary Cementing Materials (SCMs) common preventive measures for ASR required to mitigate the expansion. In addition, an enhanced method of testing will be evaluated. The new method reduces the loss of alkalis from the sample during the test resulting in more accurate expansion values. For the oxidation of sulphide phases in aggregate, the activities in this proposal will focus on developing a concrete test. Recent work by the applicant has shed light on testing regimes that can produces expansion under lab conditions. In addition, a new approach will be investigated which entails exposing the concrete samples to oxygen-rich environment under a relative humidity that sustains oxidation.