The mechanical performance and microstructural evolution of cement-reinforced coral sand

The coral sand has been widely used in island reef engineering. This study investigates the effects of cement content and curing age on the mechanical properties of cement-reinforced coral sand (CRCS) through uniaxial compression tests, and low-field nuclear magnetic resonance is used to characterise the hydration process and interparticle pore structure. Benefiting from irregular shape, high internal porosity and rough particle surface, coral sand forms better interlocking and provides an internal curing effect during hydration, thereby yielding higher uniaxial compressive strength than conventional sands at identical cement content and curing age. The early hydration process is characterised by the gradual consumption of capillary water and gel water, which can be divided into primary attenuation, secondary attenuation and stable stages, with the transverse relaxation time T2 relaxation curve tending to be stable after 96 h of hydration. Meanwhile, with increasing curing age from 14 to 90 days, the pore-size distribution evolves from unimodal to bimodal and then back to unimodal, accompanied by an obvious shift of the dominant pore region toward finer pores. The overall results demonstrate that hydration products strengthen interparticle bonding, facilitate continuous pore filling and refinement and gradually densify the load-bearing skeleton of CRCS.