One-Phase EICP Biotreatment of Sand Exposed to Various Environmental Conditions

Enzyme-induced carbonate precipitation (EICP) has been described as a bioinspired solution for ameliorating the mechanical properties of soil by precipitating calcium carbonate to bond sand particles. This study investigates the use of EICP utilizing a cost-effective jack bean meal as a source of enzyme to cement sand. Three different EICP cementing solutions were used to treat sand specimens in this study. The performance of biocemented sand was investigated under several key environmental conditions. These conditions include the effect of the EICP cementing solution concentration, curing time, temperature, wetting and drying cycles, exposure to sulfate contamination, and exposure to seawater. Increasing the concentration of the EICP solution facilitates dense calcite precipitation, which leads to higher soil strength. Scanning electron microscopy was used to observe the carbonate precipitation pattern. The images showed that increasing the curing temperature up to 40°C has led to more calcite and dense aragonite than vaterite, which means the enzyme has greater efficiency. A substantial increase in the unconfined compressive strength after one cycle of treatment with jack bean meal as the source of the enzyme was achieved, which tolerated the high salinity of the EICP cementing solution. The unconfined compressive strength of treated soils with a high-molarity EICP cementing solution was around 2.9 MPa at 5.6% ${\mathrm{CaCO}}_3$. Finally, the EICP-treated sand specimens showed higher resistance against seawater and wetting/drying cycles of freshwater, whereas less resistance was observed for the case of immersion in a 5% sulfate solution.