## 5 Conclusions  
This study investigates the effects of sulfate weathering on sandstone and limestone under specific climatic conditions. Simulated experiments were conducted to observe the apparent morphological characteristics of the rock samples and analyze the changes in macroscopic and microscopic indicators, including wave velocity, uniaxial compressive strength, mineral content, and pore size distribution. The relationship between pore characteristics and macroscopic indicators was analyzed, and the entropy weight-TOPSIS method was employed to assess the differential sensitivity of various weathering indicators in the two rock samples under sulfate erosion. The study aimed to comprehensively explore the weathering conditions of the rock samples based on multiple macroscopic indicators. The main findings are as follows. 1. Under sulfate erosion, the sandstone samples exhibited notable surface damage, including particle detachment, edge dulling, and increased crack and fissure width. The deterioration process occurred from top to bottom and from outer to inner layers. In contrast, the limestone sample showed only salt efflorescence on the surface, with minor damage to the edges and less noticeable changes in other areas. Some common characteristics of damage to rock cultural heritage sites under the influence of sulfate surface weathering include salt efflorescence, powder-like and flocculent detachment, and cracking. 2. The macroscopic indicators of both rock types, such as mass, wave velocity, and compressive strength, decreased to varying degrees, with sandstone deteriorating at a much faster rate than limestone. The number of cycles affecting both rock samples  
Figure 15: Comparison of the differential sensitivity of weathering indicators in sandstone and limestone based on the entropy weight–TOPSIS method. (**a**) Comparison of weight factors for different weathering indicators in two types of rocks; (**b**) curve showing the variation in damage level of rock samples after different numbers of cycles. could be fitted with linear or exponential functions for wave velocity and compressive strength, but notable differences existed in their trends of change. The combined effects of the rock lithology and sulfate damage mechanism led to a gradual decrease in the calcite content and an increase in the dolomite content in the limestone sample. Additionally, the number of pores larger than 100 \(\upmu\)m distinctly increased. In the sandstone sample, there was an obvious decrease in the content of calcite and feldspar minerals, a decrease in the number of pores smaller than 10 \(\upmu\)m, and a significant increase in the number of pores larger than 14 \(\upmu\)m.
3. Sulfate weathering induced physical and chemical reactions that accumulated microstructural damage in the surface layer of the rock samples, resulting in visible instantaneous macroscopic damage and a series of changes in macroscopic indicators, such as reduced mass, decreased wave velocity, and weakened strength. The pore damage factor of sandstone was approximately 2-4 times higher than that of limestone. The pore damage factors of both rock types could be fitted with exponential (\(y=ae^{(x/y)}+c\)), exponential (\(y=a+b/(1+e^{(x-c)/d})\), and linear (\(y=ax+b\)) functions for wave velocity, surface hardness, and compressive strength, respectively (where \(a\), \(b\), \(c\) and \(d\) are constants). However, there were notable differences in the magnitude and rate of change. 4. The entropy weight-TOPSIS method was used to comprehensively evaluate the rock damage state by normalizing multiple indicators, assigning weights to different weathering indicators, and calculating the relative proximity to the distance between the best and worst solutions for each indicator. The weight factor for mass loss was the highest in the sandstone sample, while the porosity of the limestone sample reflected a sensitivity to sulfate erosion.