Factors affecting debonding of FRP (fiber-reinforced polymer) rehabilitated concrete beams

Abstract

Many existing concrete structures are in need of replacement or rehabilitation due to functionally obsolete or structurally deficient members caused by deterioration and overloading. The current trend is leading towards rehabilitation using epoxy bonded fibre reinforced polymer (FRP) strips. This paper presents an experimental study that focussed on the factors affecting debonding of FRP rehabilitated concrete beams. Fifteen steel reinforced concrete beams were constructed and tested under four point bending. Thirteen of these beams were pre-loaded before being externally retrofitted (rehabilitated) with a carbon fibre-reinforced polymer strip. Different methods of surface preparation along with two methods of end anchorage were investigated. The effects of water and moisture on bond strength were also considered. Two levels of pre-loading were trialled prior to rehabilitation in order to determine the extent at which rehabilitation becomes ineffective. Beams with T-end FRP strips showed the most consistent improvement due to rehabilitation, with one beam resisting the highest load of all beams tested. The T-end FRP strips reduces the shear stress between concrete-FRP interface, thus effectively delaying the strip end debonding failure. It was also found that the bond produced by sand-blasting is superior to that produced by wire brushing. The beams preloaded to 70% capacity before rehabilitation responded with increased stiffness and moment capacity than those preloaded to 100% capacity.