Durable phosphogypsum-based composite binders with ground-granulated blast furnace slag and carbide slag: Performance optimization and environmental assessment

The global industrial challenges of massive phosphogypsum (PG) stockpiles, persistent underutilization, and inferior water resistance of conventional gypsum-based materials necessite innovative recycling strategies. Herein, we engineered a phosphogypsum-based composite binders (PBCB) by coupling ground-granulated blast furnace slag (GGBS) and carbide slag (CS) with anhydrous PG (APG) and β-hemihydrate PG (β-HPG). The compressive strength and water resistance of PBCB under air curing and water curing were investigated at 180d. Its phase composition, hydration process, pore structure, and microstructure were explored, followed by an evaluation of its environmental and economic benefits. Results showed that the combination of APG and β-HPG can significantly shortened the setting time of PBCB. Under the synergistic effect of hydration products, the mixture of 70 % APG/10 % β-HPG and 18 % GGBS/2 % CS shows the best performance. After 180d of air curing and water curing, the compressive strength and softening coefficient are 44.5 MPa, 0.83 and 41.9 MPa, 0.89, respectively. Notably, under water curing, the compressive strength decreases by only 4.17 %–10.32 %, while the softening coefficient increases by 6.74 %–12.64 %. In addition, the carbon emissions per unit strength and cost per unit strength are only 21.0 % and 35.7 % of those of ordinary Portland cement, respectively. This work establishes a viable technical pathway for transforming hazardous PG stockpiles (>80 million tons/year globally) into low-carbon sustainable binders. • An innovative approach combines APG and β-HPG as a composite binder. • The combination of APG and β-HPG can significantly improve the setting time of PBCB. • PBCB achieves a compressive strength of 41.9 MPa and a softening coefficient of 0.89 after 180d of water curing. • PBCB demonstrates significant environmental and economic benefits.