Active sensing for disbond detection in CFRP strengthened RC beam

Carbon fiber-reinforced polymer (CFRP) laminates are widely used for retrofitting and strengthening reinforced concrete (RC) beams and slabs. In order to guarantee proper coupling of a CFRP layer with a host structure, the bonding condition between them has to be monitored. In this study, preliminary results for developing a CFRP debond monitoring system has been presented. The goal of this study is to develop a new concept and theoretical framework of nondestructive testing (NDT), in which debonding can be detected "without using past baseline data." First, the concept of time reversal acoustics, which have been previously applied to body wave propagations, is extended to complex guided wave propagations that appear in a FRP strengthened RC beam because of its complicated geometry and boundary conditions. Also, features that are sensitive to damage of the structure are extracted by comparing the "known" input with the "time-reversed" response signal without referencing to past baseline data. Active sensing devices such as lead zirconate titanate are used to create "known" input waveforms as well as to measure the "time-reversed" responses. Once damage-sensitive features are identified, statistical classifiers are also being developed to establish decision boundaries without using prior reference data and to minimize false indications of damage. Finally, monotonic and fatigue load tests of large-scale CFRP strengthened RC beams are conducted to demonstrate the potential of the proposed debonding monitoring system.