Is the Available Alkalitest A Good Durability Predictor for Fly Ash Concrete Incorporating Reactive Aggregate?

Abstract

ABSTRACTThe available alkali test has been used for years as a method for preventing the use of a high-alkali fly ash in concrete containing reactive aggregate. This report presents data on fifteen good-quality Western ashes, both Class C and Class F, that are currently used in readymixed concrete. All fifteen ashes were effective in reducing the expansion due to the alkaliaggregate reaction. The reduction in mortar bar expansion (ASTM C 441) varied from 16% to 81%. Correlation of the percent reduction was made with available alkalies as Na2O, silica content, lime content, sulfur content, and the sum of silica, alumina and iron oxide. Surprisingly, the best correlation to percent reduction was with sulfur and the least was with available alkalies. This data indicates that most, if not all, fly ashes are effective in reducing the alkali aggregate reaction and that the available alkali test is not the best method for predicting the effectiveness of a fly ash in controlling this reaction.