Mechanical properties and microstructural mechanism of MICP-cemented coral sand modified with xanthan gum

Coral sand foundations in island and reef environments typically exhibit low strength and high porosity. This study investigates the synergistic effect of xanthan gum (XG) and microbial-induced carbonate precipitation (MICP) on the mechanical properties and microstructure of coral sand. Coral sand specimens incorporating 0.5%–2.5% XG were treated via MICP and evaluated through unconfined compressive strength (UCS) tests, computed tomography (CT), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Compared with MICP treatment alone, the addition of XG increased the binder content by 53.57%–88.43%. At an XG content of 1.0%, the UCS reached a maximum of 6.23 MPa, which is 2.56 times that of the MICP-only group. Micro-CT analysis revealed a denser structure with reduced porosity and pore size, while SEM and XRD indicated that XG provided additional nucleation sites for calcite crystals, thereby enhancing interparticle bonding. These findings provide a biochemical strategy for reinforcing coral sand foundations in island and reef environments.