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This paper outlines the philosophy behind the 1994 revision of the Canadian Standards Association guidelines for preventing the risk of damage due to alkali-aggregate reaction (AAR) in new construction. Aggregates may be selected based on documented previous field performance, petrographic examination, or satisfactory performance in a sequence of accelerated and long-term expansion tests. If the aggregate is deemed not deleteriously reactive by one of these methods, it may be used in concrete with no further precautions. Potentially alkali-silica reactive aggregates may be considered for use in concrete provided appropriate preventive measures are taken to reduce the risk of damaging expansion. Recommended measures are: (1) limiting the total alkali content of the concrete (from portland cement and other sources) and (2) the use of supplementary cementing materials (SCMs), such as fly ash or slag. Minimum replacement levels are given for fly ash (20 to 30% depending on composition) and slag (50%). If these SCMs are to be used at lower replacement levels or at high concrete alkali levels, concrete-prism testing is required to assure the efficacy of the reduced amount of SCM in controlling expansion with the proposed aggregate. As yet, there is no specific guidance for using silica fume with reactive aggregates. Advice regarding alkali-carbonate reactive aggregates is restricted to selective quarrying and beneficiation to exclude the reactive material.
Manager, Engineering Materials Office of the Ministry of Transportation, Ontario,
Assistant professor, University of Toronto, Toronto, Ontario
Professor, University of Toronto, Toronto, Ontario
Stock #: CCA10018J