The effect of dry-wet cycles in sodium sulfate solution on the thermal effusivity of grotto sandstone

In this study, sodium sulfate solution was used to conduct dry-wet cycle tests on grotto sandstone to investigate the evolution and deterioration mechanisms of its thermal effusivity, and a corresponding evolution model was established. The analysis results show that the evolution process of thermal effusivity can be divided into a rapid period and a fluctuation period, with the short-term recovery in thermal effusivity being the main characteristic of the fluctuation stage. The deterioration of thermal effusivity is primarily attributed to the growth of pores and the initiation and expansion of cracks. Accordingly, an evolution model of thermal effusivity accounting for both pores and cracks was established using a negative exponential function. Parameter sensitivity analysis of the model reveals that pores play a dominant role in the evolution of thermal effusivity, but this dominance diminishes rapidly with crack development.