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The Yungang Grottoes, with over 1500 years of history, have been subjected to air pollution since the last century. Field investigations have indicated that acid gases, particularly sulfur dioxide (SO2), have accumulated on the surface of the sculptures and caused various types of decay that reduce their artistic value. To shed new light on the gas–stone interaction process, artificially accelerated weathering was performed on local sandstone in the laboratory. In a specially developed test device, fresh specimens were exposed to gaseous SO2 under different relative humidity and temperature conditions. The physical, mineralogical, and chemical changes of Yungang sandstone were evaluated conjointly using destructive and non-destructive methods. The results show that after weathering, the luminosity of all specimens changed, with a slight alteration in hue toward yellow. The weight increased to various degrees during the aging cycles, which depended on both the accumulation of matter and the detachment of particles. Higher relative humidity and cyclic temperature fluctuations favored the dissolution of carbonates and the hydrolysis of feldspar in sandstone. The concentration of ions, especially dissolved Ca2+ and SO42−, increased considerably over time in the near-surface region of the specimens. A trace of newly formed gypsum was detected in some specimens at the end of the test. Knowing the synergistic impact of different climatic variables will make it possible to identify the mechanisms of the deterioration of sandstone in complex environments. [ABSTRACT FROM AUTHOR]

Water plays a vital role in the weathering process of grottoes. Precipitation is a main water source in the grotto hosting mountain rock. In this study, time-lapse electrical resistivity tomography was adopted to track the movement of infiltrated water in a profile in the Yungang Grottoes. Our one-year monitoring data indicated a good resistivity response to rainfall in the shallow unconsolidated soil layers. There were only resistivity decreases in the near surface 5 m across the whole monitoring profile, and resistivity values quickly returned to a neutral state after the rain stopped. Based on the analysis of a typical rainfall event during the rainy season, we found that the infiltrated water cannot continuously move downwards to recharge local groundwater. It moves horizontally to a nearby gully due to the existence of a hydraulic conductive fine sand layer and low permeable mudstone and sandstone base rocks. An artificial infiltration experiment was carried out to further verify the fate of infiltrated water. Based on mass balance analysis, with 10 m3 of infiltrated water, it only saturated dry soil in the top 1.36 m soil layer on average and this was roughly consistent with our field borehole wetting front verifications at 1.2 and 1.3 m. There were limited horizontal expansions from the infiltrated water. Therefore, based on our monitoring data and analysis, infiltrated water was not the main source of the water involved in the weathering process of the Yungang Grottoes. [ABSTRACT FROM AUTHOR]

The article focuses on the study conducted by the authors on influence of water on the weathering processes of sandstone by using Sandstone from the Yungang Grottoes in China. Topics discussed include deterioration of sandstone which begins from weaker points of the samples, changes in mineral composition of the samples such as quartz grains, feldspar and lithic fragments, and sulfates of calcium and magnesium salt.

Abstract: Yungang Grottoes, in Datong City of Shanxi Province, China, as the state-level key cultural relic preservation organ, have been subjected to severe degradation due to natural and human factors over the years. Since January 2010, site investigation and research on Yungang Grottoes, assisted by the Xi’an Relics Protection Center and Yungang Grottoes Cultural Research Institute, have been carried out in the laboratory of cultural relics conservation materials in Zhejiang University. Our investigation of the deterioration characteristics of these grottoes is presented here. The paper describes about 12 types of diseases in detail represented by dust deposit, salt crystallization and black crust. Relevant samples have been collected and analyzed by means of SEM, FT-IR, XRD and EDAX to study the potential hazard to the sandstones and conservation methods, which could be used to help guide remediation efforts directed at reducing the weathering problem. [Copyright &y& Elsevier]