Carbon fiber-reinforced polymer (CFRP) laminates have been successfully used as externally bonded reinforcements for retrofitting, strengthening, and confinement of concrete structures. The adequacy of the CFRP-concrete bonding largely depends on the bond quality and integrity. The bond quality may be compromised during the CFRP installation process due to various factors. In this study, the effect of four such construction-related factors was assessed through nondestructive evaluation (NDE) methods, and quantification of the levels of CFRP debonding was achieved. The factors were surface cleanliness, surface wetness, upward vs. downward application, and surface voids. A common unidirectional CFRP was applied to small-scale concrete samples with factorial combinations. Ground-penetrating radar and thermography NDE methods were applied to detect possible disbonds at CFRP-concrete interfaces. Thermography was found to clearly detect all four factors, while the GPR was only effective for detecting the surface voids only. The thermal images overpredicted the amount of debonded CFRP areas by about 25%, possibly due to scaling errors between the thermograph and the sample surface. The maximum debonded CFRP area in any sample was about two percent of the total CFRP area. This is a negligible amount of debonding, showing that the factors considered are unlikely to significantly affect the laminate performance or any CFRP contribution to the concrete member strength or confinement.

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Externally applied carbon-fibre-reinforced polymer (CFRP) laminate is a viable, economic and durable option for strengthening deteriorated, damaged or under-designed concrete structures. Effective stress transfer at the CFRP–concrete interface is an important consideration and quantitative on-site inspection of CFRP application quality is still a challenging issue. In this study, a ground penetrating radar scanning approach was used to examine the bond quality in small-scale concrete beams with flexurally applied CFRP laminates. The parameters considered included the concrete surface roughness, concrete surface voids, epoxy thickness and CFRP type. A three-point bending test and numerical modelling were used to develop simple quantitative relationships between the scanning results and the parametric combinations. Non-destructive evaluation techniques are convenient and provide valuable information for the prediction of the interfacial bond quality and the actual capacity contribution of the CFRP laminate, which will allow a higher confidence level in CFRP application quality and better quality control of concrete structures.

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