Microstructure deterioration of sandstone under freeze-thaw cycles using CT technology: The effects of different water immersion conditions

In cold regions, rock structures will be weakened by freeze-thaw cycles under various water immersion conditions. Determining how water immersion conditions impact rock deterioration under freeze-thaw cycles is critical to assess accurately the frost resistance of engineered rock. In this paper, freeze-thaw cycles (temperature range of - 20 °C–20 °C) were performed on the sandstones in different water immersion conditions (fully, partially and non-immersed in water). Then, computed tomography (CT) tests were conducted on the sandstones when the freeze-thaw number reached 0, 5, 10, 15, 20 and 30. Next, the effects of water immersion conditions on the microstructure deterioration of sandstone under freeze-thaw cycles were evaluated using CT spatial imaging, porosity and damage factor. Finally, focusing on the partially immersed condition, the immersion volume rate was defined to understand the effects of immersion degree on the freeze-thaw damage of sandstone and to propose a damage model considering the freeze-thaw number and immersion degree. The results show that with increasing freeze-thaw number, the porosities and damage factors under fully and partially immersed conditions increase continuously, while those under non-immersed condition first increase and then remain approximately constant. The most severe freeze-thaw damage occurs in fully immersed condition, followed by partially immersed condition and finally non-immersed condition. Interestingly, the freeze-thaw number and the immersion volume rate both impact the microstructure deterioration of the partially immersed sandstone. For the same freeze-thaw number, the damage factor increases approximately linearly with increasing immersion volume rate, and the increasing immersion degree exacerbates the microstructure deterioration of sandstone. Moreover, the proposed model can effectively estimate the freeze-thaw damage of partially immersed sandstone with different immersion volume rates.