Electrochemical behavior of coupled carbon fiber-reinforced polymer (CFRP) rods in concrete

This paper presents results on the electrochemical behavior of carbon fiber-reinforced polymer (CFRP) composite rods in contact with steel or epoxy coated steel bars in chloride-contaminated concrete. Twelve concrete prisms reinforced by CFRP rods electrically connected to plain or epoxy coated rebars were exposed to 80% humidity for 345 days. Four identical specimens that were not electrically connected served as controls. Measured galvanic currents densities were found to be as much as 100 μA cm−2, raising concerns about the degradation of both CFRP and steel. Electrochemical impedance spectroscopy (EIS) tests were performed to detect possible changes in the electrochemical parameters of CFRP due to galvanic interaction with active steel. Equivalent circuit simulations of the pre- and post-galvanic interaction of CFRP rods with active steel were also evaluated. EIS data indicated that the composite surface was altered so as to have porous electrode characteristics. Optical microscopy provided visible evidence of interface changes on the composite surface, supporting EIS data. The preliminary findings suggest that it would be unwise to permit CFRP to be directly in contact with steel in reinforcing or prestressing applications.