Significance and Use
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.
Note 1: The level of risk of alkali-silica reaction will depend upon the nature of the project (criticality of the structure and anticipated exposure). The determination of the level of risk is generally associated with the responsible individual in charge of the design, commonly a representative of the owner, and for structures designed in accordance with ACI 318, the level of acceptable risk would be determined by the licensed design professional.
5.3 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 conventional structures. 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 by selective quarrying.
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.
Scope
1.1 This guide provides guidance on how to address the potential for deleterious alkali aggregate reaction (AAR) in concrete construction. This guide addresses the process of identifying both potentially alkali-silica reactive (ASR) and alkali-carbonate reactive (ACR) aggregates through standardized testing procedures and the selection of mitigation options to minimize the risk of expansion when ASR aggregates are used in concrete construction. Mitigation methods for ASR aggregates are selected using either prescriptive or performance-based alternatives. Preventive measures for ACR aggregates are limited to avoidance of use. Because the potential for deleterious reactions depends not only on the concrete mixture but also the in-service exposure, guidance is provided on the type of structures and exposure environments where AAR may be of concern.
1.2 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with the standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
