This study aimed to enhance the efficiency of microbial-induced carbonate precipitation (MICP) for reinforcing sandy soil by inspiring natural processes involving microbial-induced carbon cycling and carbonation. The experiment focused on enhancing MICP curing of sandy soil using carbonic anhydrase (CA), which significantly increases the reaction rate of CO2 hydration (10(8) times faster) and facilitates the rapid hydration of CO2 (produced by urease (UA) decomposition of urea) to form a substantial amount of carbonate. The effect of carbonic anhydrase on MICP-reinforced sandy soil and its underlying mechanism were systematically examined through a combination of macroscopic physical and mechanical tests and microfabrication tests. The results showed that: (1) CA significantly increases the production of cement during the microbial consolidation of sandy soils, and the optimum dose of carbonic anhydrase producing bacteria is reached at about 4%, which increases the production of cement by 105.3%, compared with conventional MICP. (2) The incorporation of CA improves the compressive strength and resistance of the cured body. In the range 0.25-4.00%, the unconfined compressive strength of the solidified soil sample increases with the increase of the CA bacteria content. The strength of the cured soil sample reaches 1.915 MPa when the content is 4%, which is 8.54 times the strength of the conventional MICP cured sample. (3) CA does not change the product of the MICP process, it is still calcite, but after adding CA, the grain size of the calcite is larger, the shape of the hexahedron is more standardised, and the mechanical properties are improved. (4) In the process of MICP, urease and CA co-precipitate calcium carbonate-cured sandy soil. CA can significantly accelerate the rate of urea-generated CO2 hydrate and form HCO3- and CO32-, providing more favourable conditions for mineralisation.

Microbial induced carbonate precipitation (MICP) has the potential to have less hazardous impacts on the environment compared with traditional reinforcement technologies. In this paper, the mechanical property and cementing mechanism of MICP-treated mortar (MTM) are studied, and the double-layer rigid soaking mold is invented to prepare high-strength MTM samples. The effects of the cementation solution concentration (CSC), the concentration ratio of urea to calcium chloride (CRUC), aggregate particle size, and soaking time on the mechanical properties of MTM are researched. The results show that the strength of the MTM sample increases first and then decreases with the increase of CSC. The mean UCS of MTM samples reaches the peak of 8.19 MPa when the CSC is 1.5 M. The strength performance of MTM samples is relatively better when the CRUC is 1. For MTM samples with graded particle size, the sample with the particle size of 0.4-0.8 mm has the highest strength of 5.03 MPa. For MTM samples with full particle size, the mean UCS increases from 1.18 to 12.88 MPa with the increase of the maximum particle size from 0.2 to 2 mm. The MTM sample with full particle size has a higher strength when the maximum particle size is larger than 0.8 mm. The strength of MTM samples increases within 9 days over the soaking time and then tends to be stable at the later stage. The calcium carbonate mineral in the MTM sample is mainly calcite and a small amount of vaterite, and the strength of MTM is positively correlated with its CaCO3 content. The CaCO3 content of the sample shows a high surrounding and low middle distribution.