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Mortar bar expansion tests for evaluating alkali-silica reactive aggregates are not always reliable. Containers with efficient wick systems may cause excessive leaching of alkalies out of mortar bars, thus reducing the expansion. This problem has become more apparent since the introduction in 1987 of a new recommended container for the ASTM C 227 mortar bar test. It is believed that the use of this container can result in deleteriously expansive aggregates appearing to be innocuous in laboratory testing. Similar effects were found with concrete prisms made with alkali-carbonate reactive aggregate. If laboratory expansion tests are to be reliable, it is necessary to calibrate the severity of the storage condition by conducting calibration tests with known alkali-reactive aggregates as reference materials. The use of Pyrex glass is not satisfactory for calibrating storage conditions because it contributes alkalies to the reaction.
Petrographer, Engineering Materials Office, Ministry of Transportation, Downsview, Ontario
Associate professor, University of Toronto, Ontario
Stock #: CCA10548J