Reutilization of gangue wastes in phosphogypsum-based excess-sulphate cementitious materials: Effects of wet co-milling on the rheology, hydration and strength development

Abstract

This paper presents an experimental study on the effects of calcined gangue and wet co-milling on the properties of phosphogypsum-based excess-sulphate cementitious materials (PESCMs), including setting time, rheology, heavy metal solidification and strength development. For PESCMs containing 0%-50% calcined gangue, with and without wet co-milling, we examined hydration and microstructural evolution. Results indicate that the addition of calcined gangue shortens the initial and final setting time of fresh PESCM pastes, and impairs stability, fluidity and strength development. After wet co-milling, the rheological and mechanical properties of PESCM pastes are improved, where the binders with 10–20% calcined gangue show a 40% increase in 28-d compressive strength. Hydration of calcined gangue is rapid and weakens the retarding effect of impurities, providing more active aluminates and silicates for further hydration. Wet co-milling promotes physical dispersion, chemical dissolution and thus hydration, which helps refine microstructure for a better development of strength and heavy metal solidification capability.