Abstract
Sandstone grottoes, with their elaborate carvings and decorations, hold high historic, artistic and scientific values and therefore constitute an important part of China’s stone cultural heritage. Although capillary water accounts for severe pathologies at the grottoes, so far there have been limited comprehensive investigations concerned with the capillary water absorption behavior of sandstones. Aiming at three significant and famous sites in China, i.e., Yungang Grottoes (YG), Dazu Rock Carvings (DZ) and Leshan Grand Buddha (LS), capillary water absorption tests were performed on samples from local sandstones. During the test, evolution of cumulative inflow was measured and variation in the height of capillary rise over time was also monitored by combining visual observation and infrared thermography. Scanning electron microscope and mercury intrusion porosimetry were adopted to characterize the pore structure. The results indicate that all the tested sandstones had a medium capacity of water uptake. Kinetics for capillary water absorption was the highest for LS sandstone and the lowest for DZ sandstone. Differences in macroscopic properties were contributed to microstructural features such as average pore diameter and pore size distribution. An irregular shaped water front was only observed in LS sandstone due to its heterogeneity. Infrared thermography provides an efficient and nondestructive way to detect the transition zone between wet and dry portions of the sample, which was not visible to the naked eyes. A proper understanding of the interaction of the sandstones with capillary water is essential for revealing the deterioration of grottoes and the underlying mechanisms.
Highlights
China’s grotto sites, distributed all over the country, are masterpieces of abundant stone carvings, stone tablets, murals and clay sculptures, reflecting the evolution history of Chinese Buddhist art
This study focuses on three representative sites, i.e., Yungang Grottoes, Dazu Rock Carvings and Leshan Grand Buddha, which are listed as the National Key Cultural Relics Protection Units and World Heritage Sites for their outstanding universal values (Fig. 1)
In Yungang Grottoes (YG) sandstone, albite was absent whereas its clay content was almost two times that of the other sandstones
Summary
China’s grotto sites, distributed all over the country, are masterpieces of abundant stone carvings, stone tablets, murals and clay sculptures, reflecting the evolution history of Chinese Buddhist art. Capillary water can negatively impact the physical and mechanical properties of stone and eventually cause material losses. Such phenomena undoubtedly emphasize the necessity to identify the interaction between stones and capillary water. The Yungang Grottoes are located at the southern foot of Wuzhou Mountain, 16 km west of Datong City in Shanxi Province. They were first carved under the charge of royalty in 453 AD during the Northern Wei Dynasty, extending for 1 km from east to west. The groundwater level is about 10 m below its bottom so that the whole body of grottoes is completely in the aeration zone
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