Blending of Fly Ashes to Reduce Variability in the Heat of Hydration and Compressive Strength

Abstract

Since fly ash is an industrial by-product, its properties are not controlled and, as such, are highly variable, leading to a high degree of variability in the performance of concrete. The feasibility of the blending of fly ashes in order to homogenize their properties was investigated by studying the variability in the heat of hydration and compressive strength of mortar mixes. All the mixes, including control mixes as well as blends, were prepared by replacing 30% ordinary portland cement (OPC) with either one fly ash or a blend of fly ashes. Blends of various fly ashes were prepared to homogenize their Blaine fineness, reactive silica content, and alumina content, the main parameters that influence the properties of concrete. It was found that blending the fly ashes, obtained from different sources, reduces the variability in the heat of hydration and the compressive strength. Single and double parameter blends were prepared to homogenize either a single or two parameters of fly ash by blending two or more fly ashes. It was observed that all the blends effectively reduced the variations in the hydration of cement and strength of cement mortars. Additionally, it was also found that homogenizing the Blaine fineness was the most effective means to reduce the variation in the performance of the mortars.