Utilizing infrared thermography for the condition assessment of tunnel Lining with tiled surface in various temperature conditions

Based on the Tunnel Operations Maintenance Inspection and Evaluation (TOMIE) Manual, the ceramic tiles are widely favored by tunnel owners due to their convenient installation and cost-effectiveness. They possess remarkable fire resistance, are easy to clean, and boast a sleek glazed surface that reflects light effectively. Often, concrete tunnel walls remain concealed as they are adorned with architectural coverings such as ceramic tiles. It is vital to inspect tile-clad walls for any signs of cracks, delamination, or missing tiles, as these issues could signify defects in the underlying concrete substrate. Numerous studies have been conducted on the time and temperature parameters for utilizing passive thermography to evaluate the condition of pavements and roads. However, there is a lack of research on optimizing data collection timing based on indoor temperature conditions to improve thermography's effectiveness in identifying unbonded tiles. In this paper, multiple experiments were conducted to investigate the thermal behavior of tiled structures subjected to repetitive and continuous temperature fluctuations. These fluctuations were induced both on the surface and beneath the tiles to analyze the temperature range within which thermography can effectively assess tiled structures. Two distinct thermal induction methods were applied to bonded and unbonded tiles, each in separate indoor test configurations. In the initial setup, vertical tiles experienced internal temperature variations, while in the second setup, horizontal tiles were subjected to varying ambient temperatures. The test outcomes demonstrated that the thermal approach maintained consistent accuracy during both heating and cooling phases. Additionally, it was observed that between these two transitions, there existed a dormant period during which thermography was unable to discern surface temperature disparities between bonded and unbonded regions. In the lab, the duration of each transition and the accuracy of thermal tile inspection during each transition were quantified. Subsequently, a field experiment was conducted to apply a thermal assessment to the wall of a tiled tunnel.