Enhancing the volumetric stability of phosphogypsum base course materials by MICP treatment

Phosphogypsum (PG), a by-product of wet-process phosphoric acid production, remains underutilized due to its hygroscopic nature, susceptibility to expansion, and high impurity content. Cementitious stabilization is a practical approach for producing PG-based materials; however, its application is constrained by limited strength, volumetric stability, and hazardous-element. In this study, microbially induced carbonate precipitation (MICP) was coupled with a supersulfated cement (50% PG, 44% slag, and 6% cement), enabling the PG content to be increased to 80%. The effects of MICP on mechanical performance and microstructural evolution were investigated. MICP partially neutralized PG acidity and increased compressive strength to 9.49 MPa at 14 d and 13.98 MPa at 28 d. The strain range decreased from (-3300–6500) × 10 -6 to (100–3000) × 10 -6 . Leachate concentrations of P, F, As, and four heavy metals decreased by an average of 92.00%, and the overall performance satisfied expressway base-course specifications. Microstructural evidence indicates that microbially mediated nucleation alters the spatial distribution of ettringite, thereby mitigating crystallization-pressure-induced damage. Peptide metabolites are inferred to as strengthen hydrogen-bond interactions at the CaSO 4 ·2H 2 O–CaCO 3 interface, contributing to enhanced late-age strength and volumetric stability. Overall, this strategy offers a scalable route for high-volume PG utilization and broadens the engineering applicability of MICP.