High-performance phosphogypsum slag cement based on anhydrous phosphogypsum: mechanical enhancement and environmental assessment

To address the challenge of low phosphogypsum (PG) utilization in phosphogypsum slag cement (PSC) due to impurity-related performance issues, this study introduces a novel approach by incorporating calcined anhydrous phosphogypsum (APG) to develop a high-APG-content PSC system. The innovation lies in leveraging a synergistic activation mechanism using calcium carbide residue (CCR) and ground blast furnace slag (GBFS) to enhance the low reactivity and environmental friendliness of APG. The hydration process, microstructure, and pore structure were analyzed by Hydration heat, X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), thermogravimetry (TG), scanning electron microscope (SEM), and mercury intrusion porosimeter (MIP), and the environmental behavior was evaluated. Results showed that: An optimized mix proportion (58 % APG, 40 % GBFS, 2 % CCR) that achieved high APG incorporation (58 %) while providing excellent mechanical and water resistance, with 28-day compressive strength of 76.50 MPa, 1.71 % water absorption, and a 0.93 softening coefficient; CCR-induced alkalinity promoted GBFS dissociation, generating abundant C-S-H gel and ettringite to refine pore structure and densify the matrix, significantly improving water resistance; Adding 1 %-2 % CCR increased the alkalinity of the system, which was beneficial for hydration reaction. Improving the pH value of PSC effectively increases the leaching risk of heavy metals and phosphorus. Moreover, the carbon emissions of PSC were <1/7 of ordinary Portland cement. The research results can enrich the PSC system and improve the utilization rate of solid waste.