A Substitute for Portland Cement: Experiments on Ecofriendly Reinforcement of Large-Scale Calcareous Sand by Microbial-Induced Carbonate Precipitation Spraying Method

In order to respond to the greenhouse effect and achieve sustainable development, microbial-induced carbonate precipitation (MICP) technology based on the spraying method was used as a substitute for Portland cement to reinforce calcareous sand. In order to simulate the tide and determine the suitable concentration, the effects of the initial water level and cementing solution (CS) concentration on the reinforcement were analyzed. The results showed that the distributions of penetration resistance and equivalent calcium carbonate content mainly include two patterns: monotonically decreasing, and initially increasing and then decreasing. The fully saturated case only showed a dense, thin layer of calcium carbonate on the surface, and in the completely dry case, middle cementation was produced. When the initial water level was 0.5 m, the largest range of 60 cm of effective cementation appeared, and both the equivalent calcium carbonate content and penetration resistance were the highest because the microorganisms were more likely to migrate to the particle connection. The calcium carbonate generated by the MICP reaction played a role in increasing the water retention capacity of the sand. As the degree of cementation increased, the SWRC gradually moved up and the matrix suction corresponding to the same volume water content increased sequentially. Increasing the spraying times and the concentration of CS generated more calcium carbonate. The penetration resistance of higher CS concentrations was larger with the same calcium carbonate content. There was a linear relationship between the normalized penetration resistance and the normalized shear wave velocity.