New insights into the retardation mechanism of phosphorus slag on the early cement hydration

Abstract

Phosphorus slag (PS) is widely reported to retard the cement hydration due to the existence of phosphorus and fluorine in it. However, the key role and its corresponding mechanism have not been fully reported. In this study, the effects of PS on the early cement hydration were investigated from the insights of solid phases, aqueous species and microstructures evolution. Results show that PS remarkably prolongs the induction period and setting time, and delays the microstructure evolution of cement paste. PS retards the early hydration of C₃S, inhibiting the precipitation of C-S-H and portlandite, but promotes the hydration of C₃A. It is likely that the insoluble phosphorus-fluorine compound in PS plays a more important role in the retardation. The doping of calcium or silicon in the phosphorus-fluorine compound can restrict its retarding effect on the early cement hydration.