Strength enhancement of alkaline activated fly ash cured at ambient temperature by delayed activation of substituted OPC

Despite the considerable attention being paid to geopolymer concrete, its application has been limited due to its requirement of high temperature curing. In this study, we aim to increase the reactivity of fly ash at ambient condition by substituting OPC in high-alkaline medium. A series of experiments of compressive strength test, heat flow measurement, XRF, XRD, and SEM analysis is conducted to understand the mineralogical and microstructural impacts of the substituted OPC. The XRD experiments reveal that abundant Ca source in fly ash and OPC transforms to katoite and amorphous phases of C-A-S-H and C-S-H. The formation of zeolite precursors was also influenced by the OPC substitution. Furthermore, the delayed dissolution and activation of OPC in high-alkaline medium that observed by reaction heat measurement, play a positive role of filling existing voids which can efficiently enhance mechanical strength of complex system.