Objective characterisation of reinforced concrete with progressive corrosion defects through clustering and thresholding of infrared images

The research in this paper focuses on detection and quantification of subsurface damage in reinforced concrete (RC) structures by the analysis of infrared images. Experimental investigations were performed on RC slabs with embedded reinforcing bars (rebars). The corrosion mechanism in rebars was accelerated using an electrical circuit setup. The initial temperature of the slabs was adjusted in the environmental chamber and IR images were taken at regular intervals while they were exchanging heat to laboratory air through convection. Records of IR images were post-processed using an objective thresholding method proposed based on unsupervised k-means clustering. The results were discussed in context and with respect to the ASTM D 4788–03 recommendation for minimum detectable thermal contrast (0.5 °C) from delamination in bridge concrete by infrared thermography (IRT). The conclusions lead to recommendations for improved practical implementation of IRT that contribute to the broader prospects of structural health monitoring (SHM).