Development of bioinspired low-carbon geomaterials through EICP stabilization of olive stone biochar

Olive stone biochar (OSB), a carbon-rich by-product of biomass gasification, offers potential for long-term carbon storage in infrastructure applications. This study investigated soybean-based enzyme-induced carbonate precipitation (EICP) as a bioinspired approach to lightly stabilize gasification-derived OSB used as the primary granular phase in a low-carbon material system. Crude urease was extracted from powdered soybeans to catalyze calcium carbonate (CaCO 3 ) precipitation within the OSB matrix. The effects of soybean powder concentration, equimolar urea and calcium chloride concentrations, and treatment cycles were examined. The EICP-stabilized OSB samples were assessed using unconfined compressive strength (UCS) tests, CaCO 3 content measurements, scanning electron microscopy (SEM), and X-ray diffraction (XRD) analyses. Within the present extraction and treatment framework, 80 g/L soybean powder provided the most favorable balance in terms of urease activity, while 1.5 M equimolar urea and calcium chloride solutions yielded the most effective cementation. Under these conditions, samples treated for 10 cycles at 4°C achieved a peak UCS of approximately 234 kPa. SEM observations indicated progressive CaCO 3 deposition and enhanced interparticle bonding, while XRD analysis identified calcite as the dominant CaCO 3 polymorph. Preliminary economic and environmental assessments suggested that crude soybean urease had a relative cost advantage over purified urease and indicated the potential for a net-negative carbon balance under the adopted system boundary and assumptions. Overall, the results support the feasibility of using soybean-based EICP as an exploratory approach to lightly stabilize gasification-derived OSB under controlled laboratory conditions. However, durability, long-term performance, and application-specific engineering properties remain to be verified.