Electrochemical impedance based interfacial monitoring for concrete beams strengthened with CFRP subjected to wetting–drying cycling and sustained loading

Environmental exposure and mechanical loads would cause interfacial degradation between the concrete and carbon fiber reinforced polymers (CFRP) and thus premature failure for concrete structures strengthened with externally bonded CFRP, while reliable monitoring techniques are still in demand. This paper presents an investigation into electromechanical impedance (EMI) based monitoring for concrete beams strengthened with CFRP subjected to wetting–drying (WD) cycling and sustained loading. Concrete beams were fabricated and strengthened in flexure with externally bonded CFRP plates. Strengthened beams were subjected to aging tests (WD cycling and sustained loading) and four-point bending tests, whilst the EMI method was applied to monitor the interfacial performance between CFRP and concrete. WD cycling and sustained loading degrade the interfacial performance and reduce the transferrable force via the CFRP-concrete interface. The EMI signals can reflect the changes in the interfacial performance and show good sensitivity to debonding of CFRP plates under sustained loading and monotonic bending. The main characteristics for estimating whether interfacial damage occurs are proposed based on the EMI response. More importantly, the EMI technique is practical and promising for monitoring the existing strengthened structures even when no EMI history data are available.