Multi-objective optimization of anhydrous phosphogypsum-based composite cementitious materials

Phosphogypsum, a waste residue generated during the production of phosphoric acid, currently suffers from low utilization rates. To address this issue, this study utilized response surface methodology (RSM) to develop an anhydrous phosphogypsum-based composite cementitious material (APCCM) enhanced with blast furnace slag (BFS) and carbide slag (CS). The incorporation of BFS and CS aimed to improve the setting time, fluidity, bleeding rate, and strength of the APCCM. Additionally, the hydration mechanism was analyzed, achieving multi-objective optimization of the APCCM. The results showed: that BFS and CS exhibited significant activating effects on anhydrous phosphogypsum, with the formation of C-S(A)-H and ettringite enhancing the workability and strength characteristics of the material. A regression model was established using RSM to determine the optimal composition, which consisted of 57.5% anhydrous phosphogypsum, 39.5% BFS, 3% CS, and a water-to-binder ratio of 32.4%. The APCCM exhibited an initial setting time of 369 min and a final setting time of 895 min, with a fluidity of 159.2 mm, a bleeding rate of 6.91%, a 7-day flexural strength of 4.54 MPa, a 7-day compressive strength of 26.6 MPa, a 28-day flexural strength of 6.67 MPa, and a 28-day compressive strength of 44.18 MPa. The research findings present a viable alternative to cement binders, contributing to the sustainable development of building materials.