A Sustainable Hybrid Stabilization Approach for Expansive Soils: Integrating Enzyme-Induced Carbonate Precipitation with Sodium Alginate Biopolymer

Expansive soils undergo severe shrink–swell behavior under moisture fluctuations, often leading to structural damage and costly maintenance. This study presents a sustainable hybrid stabilization technique combining enzyme-induced carbonate precipitation (EICP) with sodium alginate biopolymer. In the EICP process, urease-catalyzed hydrolysis of urea in the presence of calcium ions promoted calcium carbonate precipitation, while sodium alginate improved solution retention and cohesion. Laboratory tests showed notable improvements in soil performance, with unconfined compressive strength increasing over 300% and split tensile strength nearly sixfold compared to untreated soil. Swelling potential and pressure were reduced by more than 90%, and the free swell index declined below 5%. Microstructural and chemical analyses confirmed uniform calcite precipitation and effective biopolymer integration within the soil matrix. These results highlight the hybrid technique as a promising alternative to conventional stabilizers, though further research on cost, sustainability, and field-scale feasibility is required to ensure broader applicability.