Durability of reinforced concrete structures with externally bonded FRP sheets

Abstract

In the last ten years, upgrading of existing concrete structures by externally bonded fiber reinforced plastic (FRP) sheet has been increasingly adopted in Japan (JCI 1998, JSCE 2001, Ueda et al 2001). Continuous fiber sheets, which are carbon or aramid fiber textiles, are bonded on the surface of existing concrete structures with epoxy resin. The principal purpose of this upgrading technique is to improve mechanical performance of existing concrete structures, namely load-carrying capacity and ductility. Therefore, most of research projects on FRP sheets so far were based on this point of view. However, durability of concrete structures with FRP sheet has not yet been well clarified. Though residual service-life of the upgraded structure is often discussed in practical design, there has been no verification method for its durability. Considering this situation, this study focuses on durability of concrete structures with FRP sheet. Since epoxy resin has originally very low permeability, FRP sheet bonded on concrete surface can protect concrete from ingress of aggressive agents, such as chloride ions, and consequently extend service-life of the structure. Permeability test of reinforced concrete (RC) specimens with FRP sheet was carried out to examine the effectiveness of FRP sheet to reduce chloride ingress into concrete, as well as to increase mechanical performance. Diffusion coefficient of chloride ions within FRP sheet was quantified from the test results and the numerical analysis. On the other hand, FRP sheet is normally applied on existing structures under service. In most studies, sound concrete structures are considered without any fatal material deterioration. However, in actual existing concrete structures, material deteriorations, such as reinforcement corrosion or associated concrete crack, have been sometimes induced before retrofitting FRP sheet. In order to investigate the influence of reinforcement corrosion on strengthening of RC member by FRP sheet, uniaxial tensile tests of RC specimens were carried out in this study. Reinforcement corrosion and corrosion crack were induced in the laboratory. Tensile behavior of RC specimens with FRP sheet was examined. Finally in this study, numerical simulation of performance of concrete structures after retrofitting FRP sheet is demonstrated as a function of time based on the knowledge obtained from the experiments.