Evolution of microscopic pore structure and deterioration mechanism of sandstone subjected to freeze-thaw cycles

Rock pores crack and expand subjected to freeze-thaw cycles, resulting in the reduction of their physical and mechanical properties, it is necessary to study its evolution and deterioration mechanism. However, the majority of existing studies employ a singular pore testing methodology, and neglecting the impact of the thawing process on frost heave damage in rocks. To address this, this study employs a combination of non-destructive testing techniques, including nuclear magnetic resonance (NMR) and computed tomography (CT) scanning, to comprehensively analyze the evolution of pores during freeze-thaw cycles. Investigating the migration and redistribution of pore water and its effect on frost heave damage in sandstone during the freeze-thaw process. Finally, the study examines the mechanisms of pores frost heave initiation and propagation in sandstone during freeze-thaw cycles. The results demonstrate that freeze-thaw cycles result in an expansion of pore volume at all scales within the samples. However, the degree of expansion varies, with macropores, mesopores, and micropores exhibiting a less pronounced increase in sequence. During the freeze-thaw process, water in sandstone pores redistributes, moving from larger to smaller pores. The saturation of water increases in micropores, but decreases in mesopores and macropores, thereby rendering micropores more susceptible to frost heave initiation in subsequent freeze-thaw cycles. With repeated freeze-thaw, the expansion of rock pores will continue in the direction of the lowest tensile strength, eventually forming macroscopic cracks. This study provides valuable insights into the mechanisms of freeze-thaw disaster genesis in rock masses.