Preparation and characterization of quaternary clinker-free cementitious materials containing phosphorus slag, calcium carbide slag, desulfurization gypsum, and metakaolin

The extensive accumulation of phosphorus slag (PS) not only occupies land but also pollutes the environment. In the present study, calcium carbide slag (CS) and desulfurization gypsum (DG) were used to synergistically activate PS, and metakaolin (MK) was added to provide additional Al₂O₃ for the cementitious system. The setting time, pH development, compressive strength and hydration mechanism of the composite cementitious system were investigated. The results show that CS can activate the pozzolanic activity of PS to generate C-S-H, but the PS-CS binary system has a longer setting time. Adding DG and MK in the binary system promotes the formation of abundant AFt, C-S-H, and gismondine, shortens the setting time, and improves the compressive strength at 7 days and 28 days. The cementitious system prepared with 40% PS, 25% CS, 15% DG, and 20% MK exhibits the best compressive strength at all ages, with a compressive strength of 32.8 MPa at 28 days, and the leaching concentration of heavy metals complies with the relevant regulatory requirements. The results of this study provide an approach for the large-scale utilization of PS.