Mechanical properties and microscopic mechanisms of enzyme-induced calcium carbonate precipitation (EICP)-reinforced clay mixtures with rubber particles

The utilization of enzyme-induced carbonate precipitation (EICP) to enhance the strength of rubber particles mixed with clay as lightweight backfill materials can effectively absorb waste tires and promote the sustainable utilization of rubber particles in geotechnical engineering. In this study, the strength characteristics and mechanism of the composite-modified clay are systematically investigated using the EICP technique combined with rubber particles. The results show that the EICP treatment can improve the unconfined compressive strength of the mixed clay with tire particles, and the best treatment effect was achieved when the concentration of the cementation solution is 0.5 mol/L. As the concentration of cementation solution increases, the CaCO₃ content also increases, but the conversion rate decreases. The strength and modulus of elasticity of the EICP-treated clay mixed with rubber particles first increase and then decrease with the content of rubber particles, and the optimal content of rubber particles is 5%. The optimal amount of rubber particles to incorporate is 5%. The microstructural analysis reveals that the CaCO₃ produced by the EICP significantly improves the bonding between rubber particles and soil particles, while also filling the pores. The results of the study can provide a theoretical basis for the utilization of the EICP-treated rubber particles mixed with clay as filling materials.