Mechanical properties and microscopic characterization of cement stabilized calcareous sand modified by nano SiO2

The accessible crushing property of calcareous sand leads to poor mechanical properties. Cement is usually used for solidification treatment in engineering. Nano-SiO2 (NS) can further improve the strength of cement-stabilized calcareous sand (CCS). In this study, the mechanical research of NS modified CCS is carried out through unconfined compression strength (UCS) test, split tensile strength (STS) test, and one-dimensional consolidation (ODC) test. The results show that when the CCS was solidified with 4.5‰ NS, the unconfined compressive strength reaches the maximum after 7–14 days of solidification, and the strengthening effect of NS is reflected in the early hydration stage. The addition of NS increased the splitting tensile strength at 7 days and 14 days by 100% and 48%,respectively. The ratio of splitting tensile strength to unconfined compressive strength was about 0.11, which was consistent with the curing law of solidified soil. Moreover, the addition of NS can reduce the compression coefficient of the sample, improve the compression modulus, and improve the compressive deformation resistance of CCS. The scanning electron microscopy (SEM) was used to study the microscopic mechanism. SEM test showed that the addition of NS produced more needle-like hydrates, and the nucleation effect of NS made the hydrates more tightly cemented. The porosity was obtained after the binary processing of SEM images, and the relationship model between the microstructure parameter porosity and UCS was established.