Salt Solution Attack–Induced Freeze–Thaw Mechanical Degradation and Its Correlation with Strength Characteristic of Mode-I Fracture Sandstone

The safety and durability of rock mass engineering face rigorous testing in cold regions, prompting experimental study of the effect of chemical corrosion and freeze–thaw (F–T) cycles. By taking the actual environment of the joint rock in the hydro-fluctuation belt of a typical bank slope in the Three Gorges Reservoir region of China as an example, the interactive relationship between chemical corrosion and F–T cycles is studied. An F–T cycle test scheme is adopted to explore the F–T degradation of mechanical properties and the damage degradation mechanism of mode-I fracture sandstone immersed in different chemical solutions. Experimental results show that there is significant F–T damage that deteriorates mechanical properties under different chemical corrosion attacks but that peak strain and yield properties of the specimen increase. In the first 0–20 F–T cycles, the deterioration of the mechanical properties of sandstone immersed in the alkaline Na₂SO₄ (pH = 12.0) solutions is the smallest; that in the acid Na₂SO₄ (pH = 3.0) solutions is the greatest. With the increasing number of F–T cycles, the F–T degradation degree of the mechanical properties in Na₂SO₄ (pH = 12.0) solutions gradually increase, but that is still smaller than that in the acid Na₂SO₄ (pH = 3.0) solutions, and is relatively great compared with that in neutral solutions. The damage to the microstructure inside sandstone gradually increases with repeated F–T cycles; the edges and corners of the mineral grains gradually disappear or become smoother. In addition, the roughness of the mineral grains gradually decreases, eliciting a looser structure. Statistical analysis reveals an obvious relationship between the damage degree of mechanical parameters and ion concentration in chemical solutions, with higher ion concentrations leading to greater deterioration degrees of physical and mechanical parameters. Correlations among physical and mechanical properties of specimens, F–T damage variable degree, and ion concentration are obtained.