Composition and pozzolanic properties of pulverised fuel ashes. II. Pozzolanic properties of fly ashes, as determined by crushing strength tests on lime mortars

Abstract

Abstract The pozzolanic activities of 14 representative British fly ashes have been compared by determining the crushing strengths of their lime mortars cured for periods of 7–730 days. The mortars differed considerably both in the crushing strengths attained and in the rates at which these strengths were developed. The relations between the crushing strengths and the carbon content, glass content, silica and alumina content, density, and specific surface of the ashes have been examined, as such factors have been suggested in the literature as parameters of pozzolanic activity. For short periods of cure, none of these factors was found to correlate closely with crushing strength; the best correlation was that given by the specific surface of the ashes, as determined from the particle size analysis. For long periods of cure, the best correlation was given by the SiO 2 or the (SiO 2 + Al 2 O 3 ) content of the ashes. The activity of an ash was found to reside in its siliceous particles and was determined by their particle size characteristics. The chemical compositions of these particles lay within a fairly narrow range and differences in composition within this range were found to have no significant influence on activity.