Experimental Study of MICP-Solidified Calcareous Sand Based on Ambient Temperature Variation in the South China Sea

Abstract

With the continuous advancement of the construction of the Hainan Free Trade Port and Island Reef Project, deploying Microbial Induced Calcium Carbonate Precipitation (MICP technology) for related research on the temperature range in this area would be of great significance. MICP technology is an innovative and sustainable new soil reinforcement technology that uses the metabolic activity of specific bacteria to produce calcium carbonate precipitation (CaCO3) to connect loose soil. A few previous studies reporting on the applications of MICP technology in different temperature environments drew different conclusions. Therefore, this study involved MICP sand column reinforcement tests at ambient temperatures of 20 °C, room temperature, 30 °C, and 40 °C. The reinforcement effect was evaluated using indicators such as CaCO3 generation rate, Ca2+ conversion rate, bacterial adhesion rate, water absorption rate, and unconfined compressive strength, providing a reference basis for the future applications of MICP technology to island and reef engineering construction. The results showed that, with an increase of temperature from 20 °C to 40 °C, the CaCO3 production rate, Ca2+ conversion rate, and unconfined compressive strength showed a trend of first increasing and then decreasing; the UCS was 548 KPa at 20 °C and 2276.67 KPa at 30 °C; the water absorption rate at 20 °C was 25.32, which decreased continuously with increasing temperature, and reached 21.49 at 40 °C; and the bacterial adhesion rate also continued to rise in the range of 20 °C to 40 °C, from 10.91 to 28.44. The increase in temperature had an impact on the physiological state of bacterial cells. A scanning electron microscope test shows that CaCO3 crystal forms generated under different temperature environments were different, and the CaCO3 mineral deposits generated during MICP reinforcement at 30 °C were denser. Fewer gaps were present between adjacent sand particles, and the bond was tight, which served better as a bridge. The strength of the solidified sample was also higher. The annual average temperature of the South China Sea is about 30 °C. The findings of this experiment provide feasibility and sustainable development for MICP project reinforcement in the South China Sea.