Degradation of carbon fiber reinforced polymer from cathodic protection process on exposure to NaOH and simulated pore water solutions

Abstract

In this research, the degradation behavior of laminated carbon fiber reinforced polymer (CFRP) strip anode in an electrochemical process was evaluated in an alkali electrolyte (NaOH solution) and simulated pore water solution (containing both alkalis and chloride components) so as to simulate CFRP performance in cathodic protection of atmospherically exposed steel-reinforced concrete. Experiments were conducted with three levels of applied current (0, 0.5, and 4 mA) corresponding to current density of 0, 0.77, and 6.15 A/m2 of anode surface, respectively. The degradation behavior and mechanism was investigated by degradation rate measurement, scanning electron microscopy (SEM), X-ray diffraction, and Fourier transform infrared spectroscopy (FTIR). The result showed that in both solutions, an accelerated degradation rate was observed with the increase in the level of applied current. For an applied current of 4 mA, the degradation rate was approximately 12.4 and 13.6 µm/day for NaOH and pore water solutions respectively. SEM micrographs showed that in both the solutions, the degradation to CFRP occurred at the surface and diffused into the polymer through holes. FTIR results showed that for NaOH solution more oxygen-related bonds were observed after ICCP process. This indicates that oxygen produced at the anode caused the oxidization of epoxy polymer in CFRP and resulted in the softening of polymer. In the pore water solution, the decrease in the intensity of C–N bond and the increase in intensity of C–Cl bond showed that chlorine was preferentially produced at the anode instead of oxygen and acted as the main source for CFRP degradation. The breakage of C–N bond caused the epoxy in CFRP to transform into fine powder and subsequent loose the carbon fibers.