Activation mechanisms of three types of industrial by-product gypsums on steel slag–granulated blast furnace slag-based binders

Abstract

Desulphurisation gypsum (DG), desulphurisation ash (DA) and fluor gypsum (FG) are three types of industrial by-product gypsum. The production and stockpiling of these types of gypsum may cause waste of resources and environmental problems. In this study, we focus on the activation mechanisms of these materials on steel slag (SS)–granulated blast furnace slag (GBFS)-based binders and their hydration mechanisms. Results showed that the binder with DA had a lower early strength and higher long-term strength than the other two binders. DG and FG provided Ca2+ and SO42− to generate C–S–H gels with SiO44− and ettringite with AlO45−. The attached spherical C–S–H gel particles and aciculate ettringite formed a reticular structure to achieve improvements in strength. The portlandite in DA promoted the dissolution of AlO45− and SiO44− in GBFS during the production C–S–H gels. However, the generation of ettringite was resisted by the less gypsum content in DA, thereby providing space for C–S–H gels to generate the network structure. The C–S–H gels in the binders containing DA exhibit a low Ca/Si atom ratio and enhanced mechanical properties. Further, the SO2− could be observed after 28 days, and hannebachite was consumed and gypsum was observed to increase. The conversion of SO32− to SO42− in binder with DA may occur at 20 ℃. DA and FG have a similar activation effect to that of DG on SS–GBFS-based binders, offering an alternative utilisation for solid wastes.