Multiscale Insights into the Electrochemical and Mechanical Performance of CFRP Bars in a Real Concrete Environment under Anodic Polarization

Impressed current cathodic protection (ICCP) is an effective method for mitigating steel corrosion. Carbon fiber–reinforced polymer (CFRP) bars offer dual functionality in ICCP-integrated concrete structures, serving as both anodes and concrete reinforcement. This study investigates the behavior of CFRP bars subjected to anodic polarization in real concrete environments, rather than simplified solution-based conditions. Experimental evaluations were performed, including electrochemical monitoring to verify anodic performance, uniaxial tensile tests to assess residual mechanical properties, and microscopic characterizations to identify degradation mechanisms. Electrochemical measurements, including variations in feeding voltage and instant-off potential, confirmed the stability and reliability of CFRP bars as ICCP anodes. Tensile tests revealed a progressive reduction in residual strength with increasing current density and polarization duration, with negligible influence of concrete strength (30 and 60 MPa). Empirical models were developed to predict residual tensile strength, secant modulus, and ultimate strain based on electrochemical exposure parameters. As the current density or polarization time increased, the CFRP failure mode transitioned from longitudinal splitting fracture to lateral fracture, accompanied by a significant reduction in the fracture zone length. Acidification of the concrete adjacent to the CFRP–concrete interface was observed, with the concrete being powdery and porous. X-ray diffraction analyses revealed the depletion of alkaline hydration products and the formation of Friedel’s salt near the anode. Scanning electron microscopy showed resin dissolution, fiber–resin interface delamination, and cracking formation within the resin matrix. Fourier transform infrared spectroscopy confirmed hydrolysis and oxidative degradation of the resin, accelerated by exposure to OH− and Cl− and by moisture ingress, leading to progressive internal damage of the CFRP bar from the exterior inward.