Investigation of long-term degradation of the interface in the anchorage zone of GFRP-RC beams

In the long-term service process of Glass Fiber Reinforced Polymer – Reinforced Concrete (GFRP-RC) structures, degradation of GFRP bars and concrete materials can occur, leading to a partial loss of the internal bonding performance of the structure. In this paper, a long-term study on the interface performance of GFRP-RC beams was conducted over an 8-year period to investigate the long-term degradation characteristics of the interface materials and the long-term Effective Anchorage Length (EAL) of GFRP bars. Firstly, a comprehensive analysis from a review perspective was conducted on the long-term degradation mechanisms of concrete and GFRP bars that considers the chemical behavior between microscopic molecules, the two-dimensional (2D) structure observed through micro electron microscopy, and the three-dimensional (3D) structure revealed by micro-X-ray imaging. Secondly, a new EAL calculation model is derived, and the long-term variation parameters of EAL under different conditions are determined. It was observed that the influence of alkaline corrosion and sustained loading is relatively small compared to the influence of initial structural defects on EAL. Finally, a comparison with four international standards revealed that the anchorage length design provided by JSCE-97 and ACI 440–1R-15 is overly conservative for GFRP bars, with values approximately 2–3 times the test results. On the other hand, CSA-S806–12 and CSA S6–19 standards are relatively close to the test values. Considering both design rationality and long-term corrosion resistance, it is concluded that the CSA-S806–12 specification is more reasonable.