Retarding effect of cementation solution concentration on cementation ability of calcium carbonate crystal induced using crude soybean enzyme.

Enzyme-induced carbonate precipitation (EICP) is an emerging and environment-friendly geotechnical technique for soil improvement. Despite the extensive amount of previous studies focusing on the mechanical properties of biocemented samples with varying calcium carbonate content, less is known about the cementitious property of calcium carbonate crystals generated in the EICP process. This paper presents a systematic study on the effect of cementation solution concentration (CCS) on cementitious property of calcium carbonate crystals. Solution tests were conducted to ascertain the dominant factor causing the retarding effect of CCS. Glass slide tests and ultrasonic oscillation tests were performed to evaluate the cementitious property of calcium carbonate crystal. The results of solution tests indicated that the higher CCS would affect calcium carbonate production and calcium conversion efficiency, which is mainly caused by the concentration of CaCl2 rather than urea. The increase in CCS will cause calcium conversion efficiency to decrease significantly, and calcium carbonate production will also decrease once CCS exceeds a threshold value. The higher CCS contributes to formation of larger calcium carbonate crystals and has little effect on the morphological characteristics of the crystal. Glass slide tests showed that mineral composition is controlled by the CCS of EICP solution. Increasing the CCS results in the increased vaterite content, which affects the cementitious property of calcium carbonate crystal, especially for CCS is higher than 1.0 M. The results are expected to help identify the retarding effect of CCS and to provide a reference for optimizing the cementitious property of calcium carbonate crystals. [ABSTRACT FROM AUTHOR]