Decay of sandstone subjected to a combined action of repeated freezing–thawing and salt crystallization

The weathering of rocks controls the shape of the Earth’s surface and affects their suitability as building stones. Frost weathering and crystallization of soluble salts are considered to be important factors in rock weathering. Although the crystallization of salts and ice presents obvious chemical differences, both of them produce crystallization pressure. Few studies seem to have been done on the effects of the combined action of repeated freezing–thawing and salt crystallization on the rocks. This paper studies the weathering of rocks under the combined effect of freezing–thawing cycle and salt crystallization cycle. The results show that, with the increase of freeze–thaw cycles, the samples soaked with MgSO₄ solution tend to turn red and the surface particles fall off more seriously. The mass of the sandstone is increased at the beginning of the freeze–thaw cycle and then decreases. Roughness, residual moisture, and MgSO₄ crystal affect the thermal conductivity. Samples soaked with 40% MgSO₄ solution lost the most mass and have the lowest thermal conductivity. There are two main factors that cause damage to sandstone: (1) crystallization pressure of salt and (2) frost heave action of ice. Crystallization pressure of salt and frost heave action of ice can reduce the cohesive force between particles, making the particles fall off, which is the most important factor of sandstone damage.