Mineralogy of Calcium Carbonate in MICP-Treated Soil Using Soaking and Injection Treatment Methods

Treatment method can have a significant influence on the mineralogy of the precipitated calcium carbonate (CaCO₃) in soil treated by microbially-induced carbonate precipitation (MICP). Rhombohedral calcite crystals are the most desirable form of CaCO₃ for geotechnical applications due to their thermodynamically stable nature. However, not all treatment methods produce this form of CaCO₃. Soaking and injection are two methods for MICP treatment of soil commonly used in the laboratory. The injection method was found to be more efficient for obtaining rhombohedral calcite crystals. It appears that rhombohedral calcite crystal growth is hindered in the soaking treatment method due to high concentration of organic matter in the treatment solution. These results indicate that mineralogical considerations should be included when determining an appropriate method for MICP-treatment of soil in the laboratory such that the resulting specimen is representative of the in situ mechanical behavior of MICP-treated soil.