Improvement of characteristics and freeze-thaw durability of solidified loess based on microbially induced carbonate precipitation

Bio-cementation is currently applied to solidify sandy soils, but only few studies use it to cement loess soil particles. In this study, the microbially induced carbonate precipitation (MICP) method was used to solidify loess soils. In addition, loess is widely distributed in the regions of northwest of China, where repeated seasonal freeze-thaw results in the structural damages in loess. Therefore, the freeze-thaw cycle test was conducted to study the durability of bio-treated loess soils. Results showed that the permeability coefficients of all samples decreased during the solidification, but the change pattern varied greatly because of different densities. Calcium carbonate (CaCO₃) in samples with smaller densities distributed relatively uniformly. After solidification, the content of large aggregates and small pores increased, and the content of small aggregates and large pores decreased. For samples with a density of 1.5 g/cm³, the content of large aggregates was the largest and the content of small aggregates was the smallest. Moreover, compared with untreated samples, increasing freeze-thaw cycles resulted in a larger increase in sonic time values of treated samples, but their mass and strengths significantly decreased. The increase in freeze-thaw cycles decreased the difference between sonic time values in solidified samples, while porosity and contents of large pores increased regardless of density. Overall, after bio-cementation, the solidified samples with a density of 1.5 g/cm³ had better aggregate effect and resistance for freeze-thaw cycles, and a uniform solidification effect, which present promising potential for application of MICP in the field.