Rheological behavior of biogenic calcium carbonate from high-concentration enzyme-induced calcium carbonate precipitation and the mechanical properties of treated soil

The application of traditional enzyme-induced calcium carbonate precipitation (EICP) technology for rock and soil reinforcement, wind and sand control, and concrete crack repair is limited. These limitations are caused by the high water content in low-concentration reaction solutions and the low efficiency of calcium carbonate generation. In this study, a high-concentration optimization method is proposed. Through orthogonal experiments, the effects of highly active urease and high-concentration cementation solutions (composed of calcium chloride and urea) on the pH and viscosity of the reactant solution and the strength properties and microstructure of biogenic calcium carbonate were systematically investigated. Compared with the traditional EICP method using a soybean urease concentration of 100 g/L, the urease activity increased by approximately 78% to 313%. Moreover, a calcium carbonate conversion efficiency above 80% was maintained with a 2.25 M cementation solution. The use of highly active urease significantly enhanced the calcium carbonate production, mechanical strength, and crystal size, thereby greatly improving the shear rheological behavior of the system. With the optimized cementation solution, the 7 d unconfined compressive strength of the fine-grained soils increased by approximately 485%, and substantial precipitation of spherical, rod-shaped, and rhombic calcium carbonate crystals filled and bonded the soil particles. A comprehensive evaluation using the TOPSIS entropy weight method was conducted to assess the efficiency, mechanical performance, environmental impact, and cost effectiveness of the high-concentration cementation solution. The findings showed that the high-concentration EICP technique was a rapid, efficient, and environmentally sustainable method for stabilizing fine-grained soils.