Effect of Activator on Strength and Microstructure of Alkali Activated Concrete with Class C Fly Ash

In this research work, the effect of the alkaline solution to fly ash ratio, the concentration of activator solution, and curing conditions on class C fly ash- (CFA) based geopolymer concrete (GPC) were studied. The alkaline solution to fly ash ratio was varied from 0.50 to 1.20. The concentration of the sodium hydroxide solution was varied from 4 to 14 M. Geopolymer concrete specimens were exposed to various curing conditions, viz. ambient, oven, and external exposure curing. The compressive strength of GPC was determined at various ages. Microstructural properties were studied by SEM and XRD analysis. From the test results, it was found that (1) alkaline solution to fly ash ratio has a marginal effect on compressive strength (2) sodium hydroxide solution concentration below 6 M results in very low compressive strength of about 14 MPa in geopolymer concrete.