Strength properties of nano-MgO and cement stabilized coastal silty clay subjected to sulfuric acid attack

The characteristics of nanometer magnesium oxide (nano-MgO) admixed cement in the treatment of clay were studied in direct shear tests. The chemical resistance of the admixed clay cement was investigated by soaking specimens in sulfuric acid solution. Various contents of nano-MgO (from 5 parts per thousand to 20 parts per thousand) were mixed with ordinary Portland cement (OPC) and its effect on the shear strength of cemented silty clay was studied. The test results showed that the optimal nano-MgO content to achieve highest shear strength was 5 parts per thousand. It was observed also that the cohesion was most mobilized at the optimal nano-MgO content. Visual observation of the soak-tested samples revealed that damage to the surface of the specimens became more severe at higher sulfuric acid concentrations. In general, the shear strength of the mixture decreased with an increase in sulfuric acid concentration. Moreover, with an increase in sulfuric acid concentration (0.03 to 0.06 mol/L), both the cohesion and the friction angle decreased. However, the shear strength of the mixture increased with an increase in the soaking period, even in the sulfuric acid environment. Within the first 14 days of the soaking period, the shear strength of the mixture showed a clear change. However, for longer soaking periods (i.e., similar to 21 days), the strength did not change a great deal more.