Effect of NaOH activation on sulphate resistance of GGBFS and binary blend pastes

This paper presents an investigation into the observed enhanced performance that alkali activated ground granulated blast furnace slag (GGBFS) and binary blends offer against sulphate attack. X-ray diffraction (XRD) was carried out to identify and quantify the crystalline phases formed in a wide range of GGBFS and GGBFS-OPC (ordinary Portland cement) blends. Furthermore, specimens were exposed to a sulphate solution to examine the evolution of compressive strength along with identification of activation and/or hydration products. XRD demonstrated that ettringite was completely decomposed into its constituents in the presence of NaOH while quantification ascertained the formation of considerable amounts of hydrotalcite in the activated GGBFS and binary blends. Alkali activated GGBFS and binary blends specimens with higher GGBFS content offered enhanced resistance against aggressive sulphate ions and no significant degradation products were observed in these specimens after 6 months of exposure to sulphate solution. The results demonstrated that hydrotalcite formation may be a major reason for the improved sulphate resistance of alkali activated GGBFS and binary blend pastes with higher GGBFS content.