Control of urease activity in enzyme-induced carbonate precipitation method for soil improvement at high temperatures

Enzymatically induced carbonate precipitation (EICP) is widely studied as a promising technique for soil stabilization and cementation. The solidification inhomogeneity resulted from higher urease activities always hampers the wide application of EICP. To date, several methods have been developed to effectively improve the solidification homogeneity at temperatures below 60 °C; however, several practical application fields have a higher environmental temperature over 60, even reaching 75 °C. The higher urease activity and quick decay at these temperatures easily result in solidification inhomogeneity and eventually lower strengths. In this study, the combined addition of garlic extract (GE) and dithiothreitol (DTT) was proposed to solve the problem. The influence of the proposed method on urease activities and production rates for calcium carbonate (CaCO3) was investigated and the sand solidification test was conducted to further study the influence of the method on treatment effects. Results showed that the urease activity significantly decreased with the GE addition, while the urease activity increased after the DTT addition, regardless of temperatures. With a higher content of DTT, both the increasing ranges of urease activities and production rates for CaCO3 were larger. In the sand solidification test, the GE addition decreased the precipitation rate of CaCO3 at high temperatures, which was beneficial to obtain smaller differences in sonic time values and CaCO3 contents at different parts of sand columns. Subsequently, the DTT would recover urease activity to ensure a sufficient produced amount of CaCO3 and to achieve higher strength. The optimum contents of GE and DTT were different for the samples solidified at different temperatures. The proposed method had significant application potential in the fields of geotechnical and materials engineering.