An active infrared system for identifying the flaking disease in Qingyang North Grotto Temple

Abstract

The grotto temples, which are a type of stone cultural heritage, have immense historical, cultural, and scientific value. Owing to long-term natural weathering and human activities, grotto temples are highly susceptible to the flaking damage. This damage pattern arises owing to the varying cohesion between the inner and outer layers of sandstone. However, due to the intrinsic constraints imposed by the internal environment of grotto temples, current methods still fail to produce accurate evaluation results in a nondestructive manner. In this study, an active thermal stimulation device was specially designed to identify flaking damages in grotto temples. Using this device, field tests were performed in Cave 32 of the Northern Grotto Temple in Qingyang. Infrared detection data obtained from field tests revealed that the different air layer thicknesses significantly affect the corresponding thermal behavior. A cooling index (CI) is proposed as an indicator to express the air layer thickness. To avoid damaging the structures and to further reveal the functional relationship, a finite element model (FEM) of a flake was built according to the actual size and measured parameters of the surrounding rock mass. By combining the above methods, the relationship between the CI and air layer thickness was established, where a linear tendency was obtained. Finally, the effectiveness of the developed device in reliably quantifying the air layer thickness associated with the configuration of flaking was determined, revealing the broad application prospects of the device in heritage conservation.