Mechanical Properties and Microscopic Mechanism of Cement-Stabilized Calcareous Sand Improved with a Nano-MgO Additive
Wei Wang, Jiale Luo, Na Li, Ben Li, Jian Li, Shaoyun Pu
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.