Effects of the physicochemical properties of fly ash on the compressive strength of high-volume fly ash mortar

•The effect of fly ash properties on compressive strength of fly ash mortars was investigated.•The development of pozzolanic strength can be divided into two stages.•The SAI and the pozzolanic strength index were linearly correlated.•The pozzolanic strength was dominated by a combination of physical and chemical properties of fly ash. This study investigated the effect of the physicochemical properties of fly ash, including the particle sizes and chemical composition of the amorphous phase, on the compressive strength of high-volume fly ash mortars in which 50vol.% of ordinary Portland cement was replaced with fly ash. The enhancement in the compressive strength of the high-volume fly ash mortars was observed due to the pozzolanic reaction after 7days of hydration. This was found to depend on a combination of factors, including the content of amorphous SiO2 and Al2O3, amorphous alkalinity, and surface area per volume of fly ash.