Passive infrared thermography for subsurface delamination detection in concrete infrastructure: Inference on minimum requirements

This paper introduces a computational approach for inferring the minimum requirements for the nondestructive inspection of subsurface delamination in outdoor concrete structures using passive infrared thermography (IRT). The non-linear numerical system was solved using the Finite Element Method (FEM). Complete verification and validation of the numerical model were performed through the analysis of experimental and computational errors, as well as through the comparison of computational outputs of thermal gradients with the contrast values measured in an experiment with solar radiation and passive IRT. The results of accuracy and precision of the computational simulation approach were found to be adequate, from a practical perspective, for the intended use of the model, with the thermal gradient values having an uncertainty of 0.080 ± 0.91 °C and -0.016 ± 0.91 °C for the concrete slab and column sample, respectively. Furthermore, the developed model was used to perform a one-year analysis of the studied case, in order to determine the approximate radiative heat flux required to identify defects with different size-to-depth (S/D) ratios in various concrete components with distinct solar exposures. Finally, the relationship between the calculated radiative heat flux and thermal contrast with the respective environmental variables in place was analyzed graphically.