Soil improvement by microbially induced calcite precipitation (MICP): a review about mineralization mechanism, factors, and soil properties

Cement and chemical materials are common methods for soil reinforcement, but they are limited because of environmental pollution. Therefore, it is very important to find a way of soil reinforcement that can save energy, reduce emissions, and protect the ecological environment. Microbially induced calcite precipitation (MICP) technology is an energy-saving, environmentally friendly, and sustainable reinforcement method. It has a good effect on sand reinforcement as well as on strength improvement, stiffness, erosion resistance, and permeability of sand. This paper, based on key issues such as the mineralization mechanism of microorganisms and the influential factors of MICP, considers that the MICP process involves a series of biochemical reactions. The principle of MICP mineralization was discussed from the perspective of bacterial metabolism from methanogenesis, photosynthesis, sulfate reduction, denitrification, ammonification, and ureolysis. Factors related to the microbial activity (including bacterial strain and medium, bacterial solution concentration, cementation solution and calcium source, temperature and pH, auxiliary additives), factors related to the fabrication of biocemented soils (including grouting methods, number of cycles and retention time), and soil types and properties on MICP cementation effect were analyzed. It has important scientific significance for future-related research and has an important reference value for further optimization of MICP parameters.