Strength Investigation of Sand Treated by Enzyme-Induced Carbonate Precipitation Combined with Chitosan

In this study, enzyme-induced carbonate precipitation (EICP) combined with chitosan curing technology was used to improve the mechanical properties of standard sand, and the curing effect of EICP combined with different chitosan contents was studied by macroscopic tests, such as the unconfined compressive strength test, direct shear test, and calcium carbonate content test, and microscopic tests, such as scanning electron microscope (SEM) and nuclear magnetic resonance (NMR). The results show that compared with the pure EICP treatment, the unconfined compressive strength, shear strength, and calcium carbonate content of the sand treated by EICP combined with chitosan were significantly improved, and increased first and then decreased with the increase of chitosan content, reaching the maximum value when the content is 1.5%. The calcium carbonate content is positively correlated with the strength, indicating that calcium carbonate crystals can effectively play a role in filling and cementation. After the incorporation of chitosan, the shape of calcium carbonate crystals is still mainly spherical, but the number and volume become larger. At the same time, the incorporation of chitosan can greatly reduce the proportion of large pores and medium pores, significantly increasing the proportion of small pores, which greatly improves the pore structure.