Characterization of the deterioration of externally bonded CFRP-concrete composites using quantitative infrared thermography

Defects embedded in externally-bonded CFRP-concrete composite structures reduce the interfacial bond strength and durability. This paper classifies these defects into two types: flaws and delaminations. Flaws are formed during the first application of the CFRP strips onto the concrete surface due to poor workmanship. Delaminations are formed due to stress concentrations related to chemical/physical degradation of the binding layer. In this study, an aggressive environment was simulated by placing the specimens in water baths with elevated temperatures (40 °C and 60 °C). The sizes of the CFRP-flaws and delaminations were determined by (i) quantitative infrared thermography (QIRT) and (ii) processing of visual images after opening-up the CFRP by direct shear. Experimental results show that apparent flaw sizes determined by QIRT were in good agreement (88% accuracy) with actual flaw sizes determined by the image processing method. The results also show that flaws exhibited little change but the bonding layer showed significant deterioration after exposure to high water temperatures.