Experimental study on mechanical properties and damage degradation mechanism of calcareous sandstone subjected to freeze-thaw cycles

The damage degradation mechanism and physical and mechanical properties of sandstone under the coupling effect of chemical solution and freeze-thaw cycles are studied through laboratory tests. The sandstone specimens soaked in different chemical solutions are studied by freeze-thaw cycle tests. The physical and mechanical properties of sandstone specimens due to different freeze-thaw cycles are measured at the same time. The results show that the damage deterioration mode of sandstone specimens is different under the coupling effect of chemical solution and freeze-thaw cycles. There are two main modes of sandstone deterioration, i.e., the grain spalling and scaling mode, and the fracturing mode. The damage degradation degree of the physical and mechanical characteristics of sandstone due to freeze-thaw cycles is the largest in strong acidic conditions (pH = 3.0), and that in strong alkaline environment（pH=12.0）comes the second, that is, it has a certain degree of mitigation in the neutral to weakly alkaline environment, but the degradation still increases with the increase of cycling times continuously. The greater the concentration of Na₂SO₄ solution, the larger the reduction rate of freeze-thaw coefficient. The damage degradation degree of sandstone subjected to freeze-thaw cycles is the largest in 0.01 mol/L Na₂SO₄ pH=9.0 than that in 0.01 mol/L NaHCO₃ pH=9.0. The freeze-thaw damage of sandstone is closely related to water chemical environment. The chemical solutions have certain chemical etching effect on sandstone, and the coupling effect together with freeze-thaw cycles can give mutual effect on the degradation and damage of sandstone.