Nondestructive detection of delamination in painted concrete structures through square pulse thermography

Active infrared thermography (IRT) is effective for detecting and characterizing subsurface defects in concrete structures. Even though painted concrete (PCo) structures have been applied worldwide (especially for buildings) and subsurface defects, such as delaminations, can develop in their core, active IRT-based defect detection in previous studies focused on normal concrete (NCo) structures rather than PCo structures. Hence, the detectability of delaminations in NCo and PCo structures is investigated in the present study by applying square pulse thermography (SPT), a common approach for active IRT. The results demonstrated that delaminations in PCo, under the same parameters, are more detectable in IR images than in NCo structures. In addition, the effect of the width-to-depth ratio of a defect in PCo structures on the detectability during SPT inspections is presented. Interestingly, overheating is evaluated to determine an effective heating regime for SPT surveys on PCo structures. Finally, the empirical thermal diffusivity coefficient of PCo structures is estimated, which has not been previously determined.