A Possible Method for Identifying Fly Ashes That Will Improve the Sulfate Resistance of Concretes

Abstract

Abstract Current methods for determining sulfate resistance of fly ash concrete often require several years of testing. An accepted method that can be used to predict sulfate resistance in a few days does not exist. A hypothesis is submitted as a possible step towards development of a comprehensive theory. The sulfate reactivity of fly ash is characterized by its chemical composition. One high calcium fly ash was shown to react similarly to blast-furnace slags. Sulfate resistance of comparable fly ash concretes is shown to correlate with ash composition; therefore, based on chemical composition of fly ash, a sulfate resistance factor R is proposed. The factor is the ratio (C-5)/F, where C is calcium oxide and F is ferric oxide in percent. When R is less than 1.5, a fly ash should improve the sulfate resistance.