Thermo-mechanical characteristics of geopolymer mortar

Abstract

Abstract This paper presents the effect of ground granulated blast furnace slag (GGBFS) on partial replacement of fly ash (FA) in the manufacture of ambient cured Geopolymer Mortar (GPM). Geopolymer mortars were manufactured by using a combination of sodium hydroxide and sodium silicate as the alkaline activator solution. The production of FA/GGBFS based geopolymer mortar was studied by using 8 M, 10 M, 12 M and 14 M concentrations of NaOH; and by 0%, 10%, 20%, 30% and 40% partial replacement of fly ash by GGBFS to study the compressive strength of geopolymer mortar at 3, 7 and 28 days of maturity. For GPM with 100% fly ash as the sole binder, heat curing in oven with varying temperatures from 60 °C to 100 °C at an interval of 10 °C was considered. The results on GPM with 100% fly ash having 12 M NaOH concentration cured at 90 °C achieved maximum compressive strength of 51.55 N/mm2. The compressive strength has increased and yielded a maximum of 59.2 N/mm2 with the increase in NaOH concentration up to 12 M after partial replacement of fly ash by 30% GGBFS. Further, GPM samples were also subjected to elevated temperature varying from 200 °C to 1000 °C at every 200 °C interval in muffle furnace and the change in compressive strength and its corresponding weight loss was studied. It has been observed that the effect of elevated temperature on the compressive strength of GPM had a direct relation of weight loss with the increase in temperature. X-ray Diffraction (XRD) analysis on Geopolymer Mortar indicates that GGBFS played a vital role in the geopolymerization mechanism for strength development of ambient cured geopolymer mortar. Scanning Electron Microscope (SEM) analysis of Geopolymer mortar revealed formation of dense structure with early age setting and strength gain.