Morphological damage and strength deterioration of red sandstone under freeze–thaw cycles

Insight into the growth of internal microstructure and surface morphology is critical for understanding the robustness of red sandstone artifacts in frigid environments. Since freeze–thaw (F-T) cycles can exacerbate the surface deterioration of water-bearing sandstone, a series of investigation on fresh and weathered water-bearing sandstone samples with different F-T cycle numbers (i.e. 0–100) is performed in this study, including three-dimensional (3D) laser scanning, scanning electron microscope (SEM) and computed tomography (CT) scanning tests, thermal property tests, Brazilian tests, and multi-field numerical simulations. Our results demonstrate that with increasing F-T cycles, the surface fractal dimension and specific surface area of red sandstone samples increase, and the pore size distribution inside rocks shifts from ultrananopores (10–100 nm) to micro-pores (0.1–100 μm) and ultramicropores (100 μm+). Spatially, the pores generated by the F-T cycles are more prominent near the surfaces of rock samples. Numerical simulation indicates that the uneven pore distribution leads to surface degradation. After 100 F-T cycles, the intergranular (IG) cement of the samples cracks, and the IG fractures are widened; eventually, due to the structural integrity weakening, the tensile strength is drastically reduced by over half. The thermal properties of the water-saturated sandstone can be improved during the F-T cycles, and a strong coefficient of determination of 0.98 exists between the fractal dimensions of sandstone surface and the tensile strength. When assessing the mechanical properties of stone artifacts under F-T cycles, the morphological damage of red sandstone should first be investigated when in situ sampling is inappropriate.