Statistical analysis of favorable conditions for thermographic inspection of concrete slabs

Infrared thermography has been successfully applied as a remote non-destructive testing approach for access to the internal conditions of reinforced concrete bridge slabs. Due to the different thermal properties of concrete and air or water present in the subsurface defects, damaged areas can be detected by the thermal contrast recorded on the inspected concrete surface. Thus, inspections should be conducted at favorable conditions, where the highest thermal gradients facilitate damage detection. In this study, experimental models were created to simulate bridge slabs with different delamination patterns. A multivariate regression analysis was used to explain and predict the thermal behavior of the test samples using data collected at different weather conditions and different periods of the day and the year. Based on experimental and regression analysis, it was observed that environmental conditions have an important influence on the concrete surface temperature variation and, therefore, on thermal contrast. Within the scope of this study, time frames between 12:00 noon and 3:00 pm, with temperatures between 27.5 and 37.9 °C, a high level of direct solar radiation and low atmospheric pressure values set an ideal scenario for thermographic inspections in reinforced concrete bridge slabs under passive heating.