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Salt crystallization and phase change in porous media cause significant deterioration of cultural heritage made of stones and bricks. In this study, laboratory experiments on salt weathering of sandstone from the Dazu rock carvings (DRC) in Chongqing, southwest China, were carried out by exposing them to cycles of temperature and humidity change. Mirabilite, the main component of the salts in DRC that readily undergoes phase change, was utilized for the study. Three groups of Dazu sandstone (DS) samples with high (2.4 mol/L), moderate (1.5 mol/L) and low concentrations (1.0 mol/L) of sodium sulphate were prepared; and two conditions, high‐temperature with low‐humidity and low‐temperature with high‐humidity, were designed to simulate the fluctuations of temperature and humidity in the Dazu area. After several cycles, the dehydration and moisture absorption of DS under these two conditions forces the phase change of sodium sulphate between thenardite (Na2SO4) and mirabilite (Na2SO4·10H2O), causing different levels of damage. A combination results of sample length, weight, microstructure, and mechanical property variations show that the damage effect of the thenardite formed during dehydration is more significant than that of mirabilite in moisture absorption. During these cycles, there is noticeable salt migration and the local concentration of salts is influenced by the microstructure of the stone and the distribution of clay minerals. Samples with high salt content show disintegration of the stone into powder, while those with moderate salt concentration show flaking and salt accumulation on the surface. These types of damage correspond with observations of natural weathering in the field. The experiment shows that no obvious damage takes place when the salt content is lower than 0.67%. These results contribute to a better understanding of the effects of salt weathering on sandstone and provide references for choosing correct prevention and protection measures for the world heritage site DRC. [ABSTRACT FROM AUTHOR]

An experimental work is presented that aims to improve our understanding of water–rock reaction, under both neutral and acidic conditions, and its effects on the mechanical deterioration of sandstone in Chongqing, southwest China, where a lot of heritage rock statues are carved in the same strata. SCB tests were conducted to evaluate the weakening of fracture toughness of Chongqing sandstone after water and acid erosions, and a high-speed camera was employed to capture its cracking behaviors under different hydrochemical conditions. Microstructural observation was also carried out to investigate the cracking path at a micro-scale, and the chemical analyses of sandstone soaking water in a duration of up to 120 days allows to reveal the evolving process of water–rock reaction. The results show that compared to acid solutions of pH = 3 and 5, the strength weakening effect of distilled water on Chongqing sandstone is more severe. Crack propagation rates captured by the high-speed camera vary between 20 and 60 mm/s in the SCB tests. There is no significant difference in the data for dry and water-saturated samples, and the same for the samples in the two acid fluids. Yet the crack growth rates of the latter two groups are apparently greater than those of the former two. The chemical reaction between water / acid solutions and Chongqing sandstone is mainly pertinent to the cementation and grain boundaries, which weakens grain contacts and promote crack propagation. This mechanism results in a low KIC, long crack length, i.e., more tortuosity along grain boundaries, and high crack propagation rate. [ABSTRACT FROM AUTHOR]