Utilizing local coal fly ash as a low-cost secondary cementitious material for improved physicochemical and mechanical performance of mortars

Abstract This study aims to evaluate the physicochemical properties of local coal fly ash (CFA) as a secondary cementitious material (SCM) with a focus on improving the strength activity index (SAI) on final mortar strength. Ordinary Portland cement (OPC) was partially replaced with CFA, i.e. 5–30 % by weight and mixed with sand and water to form mortar and tested for setting time, consistency, workability, heat of hydration and compressive strength, focusing on the strength activity index for 3, 7 and 28 days under standard conditions. The investigations revealed that both initial and final setting times and workability of CFA-blended OPC increase, which is beneficial for desirable construction applications. However, the consistency decreases slightly, which could be due to the decrease in demand of water for hydrated mortar. The initial and final hydration temperature of CFA-blended OPC decreases, whereas the time to reach maximum hydration temperature increases. The results showed that after 28 days of curing, OPC blends with CFA improve the compressive strength of the mortar. This highlights the effective reutilization of local CFA as a low-cost and viable SCM with enhanced compressive strength. The formulation allows to develop construction materials with improved properties and also to mitigate environmental problems due to coal burning.