Near-Field Microwave Detection of Disbond in FRP Composites Used for Strengthening Concrete Structures and Disbond Repair Verification

The use of carbon fiber reinforced polymer (CFRP) composites has been investigated in the past few years as a means to rehabilitate aging concrete structures. The detection of disbonds and delaminations between CFRP laminate and the concrete substrate is a critical issue in this area, as the presence of such defects adversely affects the effectiveness of the reinforcement. Thus, the development of a nondestructive testing (NDT) technique to detect these types of defects is of great interest in this field. Furthermore, any such method should also be capable of verifying the quality of the repair of such defects. Near-field microwave NDT techniques, utilizing open-ended rectangular waveguides, have shown great potential in the past for detecting delaminations and disbonds in complex composite structures. Microwave NDT techniques have the added advantages of providing real-time, noncontact, one-sided, rapid, and robust measurements. This paper presents the experimental results of detecting disbonds in a specially prepared CFRP reinforced mortar sample using near-field microwave NDT techniques, as well as the preliminary results showing the capability of this technique for verifying repair quality.