Preventing Alkali-Silica Reaction

Alkali silica reaction (ASR) mitigation techniques from various states in the United States, and from various countries and international organizations, were assessed and summarized. A set of recommended mitigation procedures was developed, which requires not only the use of low alkali cement, but replacement of part of it by Class F fly ash (or Class N pozzolan) (25% to 40% by weight), or ground granulated blast furnace slag (GGBFS) Grade 100 or 120 (40% to 50% by weight), or a combination of both. The Class F fly ash (or Class N pozzolan) should also have a maximum of 1.5% available alkali, a maximum 6% loss on ignition, and a maximum of 8% CaO (lime). Some recent applications following these guidelines are presented. In addition to mitigating ASR, these recommendations are expected to: (1) reduce concrete costs, (2) enhance the durability of concrete, (3) increase fly ash and GGBFS recycling, and (4) support the 1997 Kyoto protocol by significantly reducing CO₂ production. If 25% of all cement were to be replaced (in addition to current replacements), total yearly savings to the United States economy could be in excess of $1 billion.