Salt Accumulation in Heritage Sandstones Under Continuous Wick Effect Conditions

During the weathering of stone monuments, salt accumulation and crystallization lead to salt damage. In this study, we investigated the evolution of heritage sandstone salt accumulation, considering the porous system of the stone and humidity conditions. Two types of heritage sandstone were collected from the North Grotto Temple (NGT sandstone, coarse sandstone) and the Leshan Giant Buddha (LGB sandstone, fine sandstone) to conduct a salt weathering test simulating the continuous wick effect under different relative humidity conditions. We monitored the sandstone evaporation rate and macroscopic surface phenomena during the simulation test. We analyzed the sandstone after 10, 20, 40, 80, and 160 days of salt solution rise (capillary action) to investigate the salt accumulation within different stone sections and on the stone surface. Additionally, ultrasonic wave velocity tests were conducted to determine salt damage within the sandstones. Results showed that salt accumulation increased over time in both sandstone types and increased along the direction of capillary rising height, but showing different increasing gradients (i.e. with increasing height, salt accumulation increased only slightly in the NGT sandstone but rapidly in the LGB sandstone). Notably, different salt distributions in sandstones further affected the development of salt damage and variations in the evaporation rate. This study aims to comprehensively understand weathering and salt accumulation in monumental rocks, providing valuable suggestions to effectively preserve these monuments.