Study on the degradation mechanism of petroglyph carrier surfaces in Baiyin: Under water-temperature-salt coupling effects

The Baiyin petroglyph cluster in Gansu, China, stands as a significant piece of evidence for early human cultural exchange, showcasing distinct regional cultural traits and anthropological art value. However, the sandstone carrier of the petroglyphs has formed a composite degradation pattern characterized by crack development, void formation, and flaking peeling due to the freeze-thaw and chemical coupling weathering, driven by thermodynamic cycles and aqueous chemical processes, leading to the preservation crisis of some petroglyphs. Based on selected environmental characteristics relevant to the Baiyin petroglyph sites, laboratory freeze–thaw tests were conducted with controlled top-down infiltration of water or salt solutions to represent episodic precipitation/snowmelt infiltration and subsequent lateral moisture migration along exposed sandstone surfaces. Mass, hardness, and P-wave velocity were measured at 5-cycle intervals, while surface morphology, pore characteristics, microstructure, mineralogy, and chemical composition were characterized at 10-cycle intervals. The results show that freeze–thaw cycling progressively deteriorated the physical properties and pore structure of the sandstone, while the degradation response varied markedly with solution chemistry. Na 2 SO 4 produced the strongest macroscopic and pore-structural deterioration, whereas (NH 4 ) 2 SO 4 caused faster mineralogical changes, indicating that salt type controls not only the magnitude of deterioration but also the dominant surface-degradation pathway. A surface-porosity-based damage model was further used to quantify the damage evolution under the tested conditions.