Effect of crystal morphology on cementability and micromechanical properties of calcium carbonate precipitate induced by crude soybean enzyme

Abstract

Enzyme-induced carbonate precipitation (EICP) has emerged as an innovative soil stabilization technology to precipitate CaCO3 by catalyzing urea decomposition. Although extensive efforts have been made to increase the calcium carbonate content (CCC) formed in the EICP process for the better bio-cementation effect, the cementability and micromechanical properties of CaCO3 are rarely known. A study of the cementitious characteristics and micromechanical properties of CaCO3 precipitates with different mixing percentages of crystal morphology is essential for soil improvement. In the present study, ultrasonic oscillation tests and nanoindentation tests were performed to investigate the cementability and micromechanical properties of CaCO3 precipitate. The results show that the cementability and micromechanical properties of CaCO3 precipitate are related to the composition of the crystal morphology. A high content of calcite is beneficial to improve the adhesion of calcium carbonate precipitate. Calcite has better mechanical properties (elastic modulus, hardness and ductility) than vaterite, and the presence of vaterite can significantly affect the measured value of mechanical properties in nanoindentation tests. The ductility of CaCO3 precipitate induced by crude soybean urease (CSU) is higher than that of CaCO3 precipitate induced by commercially available pure enzyme, suggesting that commercially available pure enzyme can be replaced by CSU for cost-effective field-scale engineering applications. This work can provide insight into optimizing the properties of CaCO3 precipitate from the micro-scale.