Mechanical Properties and Microscopic Mechanism of Cement-Stabilized Calcareous Sand Improved with a Nano-MgO Additive

Abstract

Calcareous sand fractures easily, has poor mechanical properties, and usually needs to be stabilized for engineering applications using additives. In this study, nano-MgO was used to enhance the mechanical properties of cement-stabilized calcareous sand (CCS). Unconfined compressive strength (UCS) and unconsolidated undrained (UU) triaxial shear tests were conducted on nano-MgO-modified CCS (MCCS) specimens, and the microscopic mechanism was investigated using scanning electron microscopy and X-ray diffraction. Finally, models to predict the UCS and shear strength of MCCS were formulated. The results showed that the addition of nano-MgO can enhance the strength and stiffness of CCS, with MCCS reaching its maximum strength of 2.1 MPa at 28 days when the nano-MgO content was 1%. Furthermore, the deviatoric stress first increased and then decreased as the nano-MgO content increased, reaching its maximum value when the nano-MgO content was 1.5%. The optimal nano-MgO content obtained from the UCS tests was different from that obtained from the UU tests. This improvement in CCS strength was due to the nano-MgO filling and cementation of hydrates such as Mg7Si8O22(OH)2, Mg(OH)2, and CaAl2Si3O10(H2O)2. However, too much nano-MgO reduces the strength of CCS because the nano-MgO expands during hydration.