Soil Stabilization Against Water Erosion via Calcite Precipitation by Plant-Derived Urease

Stabilization is often necessary to improve the stiffness, strength and durability of both natural and compacted soils. Soils are typically stabilized via the addition of hydraulic binders, such as cement and lime, which present however relatively high carbon and energy footprints. Alternative stabilization techniques are therefore explored to minimize environmental impact while preserving good material properties. Among these techniques, enzyme induced calcite precipitation (EICP) has gained prominence in recent years. EICP exploits the action of the urease enzyme to catalyze the hydrolysis of urea and to produce carbonate ions, which then react with calcium ions inside the pore water to cause precipitation of calcium carbonate (i.e. calcite). The precipitated mineral bonds particles together, thus improving the hydro-mechanical characteristics of the soil. This paper presents a preliminary investigation on the use of plant-derived urease, instead of pure reagent-grade urease, to minimize environmental and financial costs. The urease enzyme is obtained from a liquid soybeans extract, inside which urea and calcium chloride are dissolved. This stabilizing solution is then mixed with a silty clay to produce stabilized samples, which are subjected to water erosion tests.