5.1 This guide provides recommendations for identifying the potential for deleterious AAR and selecting appropriate preventive measures, based on a prescriptive-based or performance approach, to minimize the risk of deleterious reaction. In regions where occurrences of AAR are rare or the aggregate sources in use have a satisfactory field performance record verified by following the guidance in this standard, it is reasonable to continue to rely on the previous field history without subjecting the aggregates to laboratory tests for AAR. In regions where AAR problems have occurred or the reactivity of aggregates is known to vary from source to source, it may be necessary to follow a testing program to determine potential reactivity and evaluate preventive measures. In this guide, the level of prevention required is a function of the reactivity of the aggregate, the nature of the exposure conditions (especially availability of moisture), the criticality of the structure, and the availability of alkali in the concrete.

5.2 Risk Evaluation—To use this guide effectively, it is necessary to define the level of risk that is acceptable, as this will determine the type and complexity of testing (Note 1). The risk of deleterious expansion occurring as a result of a failure to detect deleteriously reactive aggregates can be reduced by routine testing using petrography, or laboratory expansion tests, or both.

5.3 For conventional structures, preventive measures determined by either performance testing or the prescriptive approach described in this guide can be expected to generally reduce the risk of expansion as a result of ASR to an acceptable level. For certain critical structures, such as those exposed to continuous moisture (for example, hydraulic dams or power plants), in which ASR-related expansion cannot be tolerated, more conservative mitigation measures may be warranted.

5.4 There are no proven measures for effectively preventing damaging expansion with alkali carbonate reactive rocks in concrete and such materials need to be avoided.

5.5 If an aggregate is identified as potentially deleteriously reactive as a result of ASR, and the structure size, class, and exposure condition requires preventive measures, the aggregate may be accepted for use together with appropriate preventive measures following the prescriptive or performance methods outlined in this guide.