Optimum thermal gradient thresholds (OTGT) system for inspecting bridges using Infrared Thermography (IRT)

Researchers have been advancing non-destructive testing (NDT) methodologies for several decades. Infrared thermography (IRT) is particularly noteworthy to researchers within NDT for identifying surface and subsurface defects in bridge decks, owing to its numerous advantages that do not disrupt bridge operations. Conversely, conflicting assertions regarding IRT-based anomaly detection capabilities have been documented. Furthermore, established methodologies, criteria, and scales must be revised since numerous studies have recommended reassessing the thermal contrast value in ASTM D4788-03. This study aims to develop an optimum thermal gradient thresholds (OTGT) system (thermal contrast values) for delamination identification, utilizing existing literature, standards, and field data. Furthermore, a smart model has been developed to deploy the IRT-OTGT system for detecting delaminated spots in the full-scale concrete bridge deck. The IRT-based heatmap generation process utilizes the metadata of the universal coordinate system, enhancing precision. The developed automated model utilizing the IRT-OTGT system was evaluated on four bridges with favorable outcomes. Moreover, the delamination maps generated by the IRT-OTGT were compared with ground-penetrating radar corrosion maps, revealing congruencies in the identified problematic locations. The devised IRT-OTGT system and smart model will enhance the confidence of practitioners in the IRT threshold values for delamination detection and mitigate confusion within the scientific community. Prompt diagnosis and maintenance would prolong the lifespan of bridge structures.