Experience with alkali-aggregate reaction in the Canadian prairie region

Abstract

This paper summarizes alkali-aggregate reaction (AAR) experience in the prairie region to date. Information is presented on reactive rock types and their geological significance, laboratory test data, field evidence of affected structures, and industry practices for preventive measures and management of affected structures. The frequency and severity of documented AAR-affected structures in Manitoba, Saskatchewan, and Alberta is low, Alberta having the highest incidence. A significant number of aggregate sources in the region show potential for excessive expansion when subjected to laboratory testing. The lack of field evidence is generally attributed to the lower alkali contents of cements that have historically been produced and used in the region. Limited number and extent of searches for affected structures, inadequate diagnosis of the phenomenon, and client confidentiality are also factors. It is imperative that specifiers, owners, researchers, suppliers, and producers be aware of the potential reactivity of local aggregates. The occurrences of AAR-related deterioration in the field demonstrates that the phenomenon is not limited to the laboratory. The effectiveness of low to moderate alkali contents of concrete mixtures in controlling the AAR phenomenon demonstrates the need to specify low-alkali cement and the importance of measuring the effectiveness of supplementary cementing materials in preventing AAR. There is a need to conduct extensive field searches for affected structures and it is important that suspected cases of AAR be properly diagnosed.Key words: alkali-aggregate reaction, concrete, Manitoba, Saskatchewan, Alberta, laboratory testing, field evidence, pattern cracking, prisms, mortar bars, prevention, management.