Static and fatigue bond assessment of CFRP–concrete joints extracted from 60-year-old bridge girders after 7 years of service

The bond durability between carbon fiber-reinforced polymer (CFRP) and the concrete surface under real-life conditions is a crucial factor in the application of external strengthening of reinforced concrete structures with CFRP. This paper investigates the bond behavior under static and fatigue loading of a CFRP external strengthening system applied to 60-year-old bridge girders after 7 years of exposure to real service conditions. The single lap shear test was used in this research to investigate the shear bond performance of CFRP–concrete joints under static and fatigue loading. The experimental results of the shear tests on CFRP–concrete joints were compared with the results of control tests carried out on new samples prepared in the laboratory. The results indicate that the bond strength of the CFRP–concrete joints extracted from the bridge decreased by 30% in comparison with the reference samples. In addition, it was revealed that the failure mode changed from cohesive failure in the concrete to failure of the adhesive/concrete interface and cohesive failure of the adhesive layer after exposure to service conditions. Moreover, fatigue test results showed that the CFRP–concrete joints extracted from the bridge showed a significant degradation in fatigue life and interfacial bond stiffness compared to the control samples.