Combined effects of salt, cyclic wetting and drying cycles on the physical and mechanical properties of sandstone

Salt weathering has considerable effects, and it has recently become the subject of interest among researchers and engineers, especially in terms of sandstone heritage buildings and sandstone monuments. However, the impacts of salt weathering on sandstone after wetting-drying cycles have been neglected in the literature. Under the conditions of the long-term or gradual underground seepage of water into sandstone heritage buildings and monuments, salt accumulation and recrystallization occur in sandstone when the rate of evaporation is sufficiently high, and they reduce rock stability. In view of this problem, experiments subjecting sandstone to up to 50 wetting-drying cycles were conducted using water and solutions containing concentrations of 4%, 6% or 8% magnesium sulfate (MgSO4). The physical and mechanical properties were tested after different wetting-drying cycles. The results show that the wetting-drying cycles impacted the sandstone samples soaked in a salt solution more than the samples that were soaked in only water. Thirty cycles is the threshold number in terms of changes in P-wave velocity, thermal conductivity and tensile strength. A correlation analysis was conducted, and it showed that both color lightness and thermal conductivity are good parameters for evaluating tensile strength. The results contribute to the evaluation process and protection of sandstone heritage buildings and monuments against salt weathering.