Effect of chloride and blend of chloride and sulphate salts on workability, early strength and microstructure of FA-GGBS geopolymer concrete

Abstract

The objective of this investigation is to examine the effect of admixed chloride based salt, and blend of chloride and sulphate based salts on workability, compressive strength at seven days, and microstructure of fly ash (FA)-ground granulated blast furnace slag (GGBS) based geopolymer concrete (GPC). All the GPC mixes were made with FA and GGBS at a proportion of 45%:55% (by mass), and alkaline activator solution used was a blend of sodium hydroxide (NaOH) solution at 8 M and 14 M concentration along with the sodium silicate (Na2SiO3) solution. The FA-GGBS based GPC mixes were admixed with 0% (control mix), 3.5% sodium chloride (NaCl), and blend of 3.5% NaCl and 5% sodium sulphate (Na2SO4) during the time of preparation of GPC mixes. The XRD study was conducted on FA-GGBS based GPC for microstructure analysis. The results showed an increase in the workability of salt-admixed FA-GGBS based GPC mixes than control (0% admixed salt) GPC. The addition of salts during preparation resulted a decrease in compressive strength of FA-GGBS GPC mixes. Halite formation in salt-admixed FA-GGBS based GPC mixes as indicated from XRD patterns led to reduction in strength of salt-admixed GPC.