Detection of CFRP-concrete interfacial debonding using active microwave thermography

Abstract

Active microwave thermography (AMT), a thermographic technique that utilizes a microwave-based thermal excitation, is proposed as an efficient technique for non-contact, real-time inspection of embedded flaws. This study examines the use of AMT to detect interfacial debonding of the carbon fiber reinforced polymer (CFRP)-concrete interface. CFRP-concrete interfacial damage is caused by external mechanical loading and monitored under AMT. CFRP strips bonded to concrete prisms are tested in direct shear to initiate debonding. AMT is used to monitor the CFRP surface thermal profile in an attempt to detect and monitor interfacial damage. Correlations between the mechanical response (namely, applied load vs. composite displacement relative to the substrate, i.e., slip) and AMT results (namely, temporal CFRP thermal response) are found. High thermal contrast, TC, defined as the CFRP surface thermal response caused by loading, is observed where interfacial debonding initiates and propagates along the bonded length. An increase in the TC slope occurs when a load drop occurs, which indicates local debonding occurrence or mobilization. At different load levels, the interfacial slip and surface temperature distributions along the bonded length show similar trends. These correlations indicate that initiation and propagation of CFRP-concrete interfacial damage can be monitored by the AMT technique.