Enzyme-induced Carbonate Precipitation Using Soybean Urease in Coal char-treated Sandy Soil

Enzyme-Induced Carbonate Precipitation (EICP) has emerged as a sustainable and efficient bio-cementation technique to improve the mechanical properties of sandy soils by promoting the formation of calcium carbonate. However, the effectiveness of EICP is often constrained by environmental factors affecting urease activity and the limited availability of nucleation sites. This study investigates the incorporation of coal char as an additive to EICP-treated sandy soil to enhance its mechanical strength. Soybean-derived urease was used to catalyze the EICP process, with coal char added at varying concentrations (0%, 5%, 10%, and 20% by weight of soil). The treated samples were evaluated through unconfined compressive strength (UCS), triaxial compression tests, calcium carbonate content analysis, thermal conductivity measurements, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results indicate that highest compressive strength and calcite precipitation were observed at the soil with 10% coal char content. The inclusion of 10% coal char significantly improved the compressive strength of EICP-treated soil by 35.65%, 33.58%, 22.5%, and 16.50% at 3, 7, 14, and 28 days, respectively. Similarly, their calcium carbonate precipitations increased by 8.33%, 21.87%, 21.70%, and 31.81% over the same time intervals compared to the EICP-treated samples without coal char. This increase in calcium carbonate also led to a corresponding rise in the density of the coal char-treated mixtures. These enhancements are attributed to the porous structure of coal char, which provides additional nucleation sites for mineralization. These findings demonstrate that EICP-coal char mixture forms a novel, low-carbon bio-cementation system that can be deployed in situ as a sustainable alternative to conventional cementitious stabilizers. This technique not only strengthens weak sandy soils but also offers broader engineering value by providing an environmentally friendly ground-improvement strategy and future sustainable soil-stabilization practices.