Influence of fly ash characteristics on the strength of portland-fly ash mixtures

Abstract

Modern thermal power plants are producing large amounts of fly ash that is generally quite suitable for use as a supplementary cementitious material in concrete. However, for this purpose the fly ash utilization in the United States continues to remain low, mainly on account of lack of quality control. This is because the current standards on fly ash do not contain specifications and test methods that are able to assess adequately the performance of a fly ash in concrete. Based on tests on 11 different fly ashes and direct determination of compressive strength of test mortars made with a fixed proportion of fly ash by weight of the cementitious materials, and a fixed ratio between water and the cementitious material, it seems that the calcium content and particle size distribution of the fly ash are the most important parameters governing the strength development rate in normally cured portland cement-fly ash mixtures.