Study on Effect of GGBS, Molarity of NaOH Solution and Curing Regime on Compressive Strength and Microstructure of Fly Ash-GGBS Based Geopolymer Concrete

Abstract

In this study, the effects of ground granulated blast furnace slag (GGBS) and molarity of NaOH solution on compressive strength (CS) and microstructure of fly ash-GGBS based geopolymer concrete (GPC) have been investigated under different curing regimes. Class F fly ash and GGBS were used as aluminosilicate source materials where fly ash was replaced with 20, and 40% GGBS. A combination of varying concentrations of NaOH solution (8, 10, and 12 M) and Na2SiO3 solution was used as the alkaline solution. Cube specimens of 150 mm size were cast for determining CS of GPC at the ages of 7 and 28 days. The curing regimes adopted for fly ash-GGBS based GPC specimens were ambient curing and water curing. The microstructure of GPC was studied by X-ray diffraction (XRD) and Field emission scanning electron microscopy (FESEM) analyses. From the results, it is observed that the workability of GPC mixes reduced when GGBS content and molarity of NaOH solution was increased. The CS of GPC mixes increased as the amount of fly ash replaced by GGBS and the molarity of NaOH solution increased, under both curing regime. GPC cube specimens subjected to water curing achieved higher CS as compared to ambient curing at both the ages. Results of XRD and FESEM analyses confirmed the presence of N–A–S–H and N–(C)–A–S–H gel, which are responsible for the development of CS of geopolymer concrete.