ACI 225.1T-20

Alkali-silica reactivity (ASR) is a potentially deleterious expansive reaction between alkalies in the pore solution of concrete and certain reactive aggregates. When ASR was first identified as a distress mechanism in the 1940s, cements with equivalent alkali contents below 0.60 percent by mass were shown to reduce the risk of this reaction. Subsequent research has shown that limiting the cement alkali content to 0.60 percent is not always sufficient to control deleterious ASR with every aggregate nor in all concrete mixtures. It is now well accepted that the reactivity of the aggregate and the amount of alkalies available in the concrete are more important in predicting deleterious ASR than cement alkali content alone.