Study on the performance of low water-binder ratio cement mortar with excavated soil exposed to NaCl freeze-thaw environment

In this paper the mechanical strengths (compressive and flexural strengths) of cement mortar with subway excavated soil and low water-binder are studied. Moreover, the following NaCl freeze-thaw resistance is investigated. The water-binder ratio of cement mortar is 0.3 and the corresponding soil-cement ratios are 0%, 5%, 10%, 15% and 20%. The mass and mechanical strengths losses, the loss of the relative dynamic elastic modulus and permeability coefficient of chloride ions are determined during freeze-thaw cycles. Besides, the scanning electron microscope (SEM) photos of cement mortar are observed to study soil’s influence on the microstructures of cement mortar and x-ray diffraction is determined to study the crystal composition. Results show that the mass and mechanical strengths losses and the permeability coefficient of chloride ions increase in the form of quadratic function with that of the number of freeze-thaw cycles. However, the relationship between the relative dynamic elastic modulus and freeze-thaw cycles is quadratic function. Additionally, the relationship between the permeability coefficient of chloride ions and freeze-thaw cycles fits positive linear function. Moreover, the mechanical strengths and freeze-thaw resistance of cement mortar are deteriorated with soil introduction. The cement mortar with a soil content of 5% exhibits the lowest strength and the worst freeze-thaw resistance, but a high soil content of 15% displays that the mortar with low water-binder ratio and soil content shows the best freeze-thaw resistance.