The release of alkalis from pulverised-fuel ashes and ground granulated blastfurnace slags in the presence of Portland cements

Abstract

Various methods have been proposed and adopted to establish the quantity of alkali which becomes available for potential alkali silica reaction when pulverized-fuel ashes and ground granulated blastfurnace slags are incorporated in concrete and mortar. These methods are examined, compared and related to the results obtained from tests which involved direct reaction of the latent hydraulic binders with Portland cements. The evidence presented suggests that after 28 days at 38°C, 70% of the total alkalis in ground granulated slags can be released whilst at 20°C the corresponding figure is 45%. With pulverized-fuel ashes the amount of alkali released is dependent on the ratio of ash: opc and also upon the temperature, and can vary between 10 and 50% of the total alkali present. In the case of both latent hydraulic binders there is evidence that alkali continues to be released after 28 days.