Sodium alginate-regulated biomineralization with polyacrylamide for sustainable stabilization of expansive soils: Optimization, hydro-climatic durability, and erosion resistance.

Sodium alginate (SA) is a natural biological macromolecule with unique potential for regulating biomineralization through ionic coordination and hydrogel network formation. In this study, an SA-mediated mineralized hydrogel system was constructed with polyacrylamide (PAM) to regulate microbially induced calcium carbonate precipitation (MICP) for the durable stabilization of expansive soil. A Box-Behnken response surface design was used to optimize the cementation solution concentration and the dosages of SA and PAM, with unconfined compressive strength (UCS) and shear strength as response targets. Under the optimized conditions, the 3-day UCS and shear strength reached 417.5 and 165.5 kPa, respectively, and the 28-day UCS increased to 2150 kPa, exceeding that of the conventional MICP-treated soil by more than twofold. In addition, the optimized system exhibited markedly improved hydro-climatic durability, with a mass loss ratio of only 22.6% after five rainfall erosion cycles, compared with 74.36% for untreated soil. Microstructural characterization revealed that SA-mediated ionic confinement regulated calcium ion migration and carbonate deposition, whereas PAM enhanced interparticle bonding through polymer bridging, jointly promoting the formation of a continuous organic-inorganic composite matrix with reduced pore connectivity and restrained crack development. The enhanced stabilization performance was mainly attributed to the combined improvement in cohesion, structural continuity, and resistance to cyclic environmental disturbance. These findings highlight the key role of sodium alginate in regulating biomineralization and demonstrate the potential of biological macromolecule-mediated mineralized hydrogels for sustainable geotechnical stabilization.