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The optional limit on the Na2O equivalent of portland cement, 0.60% maximum, originated in the early 1940s following recognition of concrete distress caused by alkali-silica reaction by the California Division of Highways and the U.S. Bureau of Reclamation. Over the years, it has been effective in preventing distress from alkalisilica reaction in a great many, but not all cases. Aggregates have since been identified that require additional mitigating measures, such as inclusion of pozzolans. The need for different methods of aggregate evaluation has also been shown. Limits on the total alkali content of concrete have also been found useful. It is now apparent that a single alkali limit is impractical for all cases. The wide variety of natural aggregates requires that the cementitious materials be matched to the aggregates.
The intent of this paper is to present some of the highlights in the development of methods to avoid deleterious alkali-silica reaction. No attempt has been made to present a complete review.
Associate, Openaka Corporation, Inc., Denver, CO
Stock #: CCA10305J