Bond behaviour of NSM FRP strips in service

Most fibre-reinforced polymer (FRP) systems for strengthening of existing structures use an epoxy resin-based adhesive. Chemically, epoxy resins are defined as plastics. Compared with concrete, epoxy resins show material properties more sensitive to service conditions, for example creep during sustained loading and increased temperature, respectively. These effects can become critical for the durability and the load-carrying capacity of the strengthening. In consideration of applications under elevated temperatures or strengthening systems based on permanent bond stresses the benefit may be limited by the material properties of the epoxy resin. In order to predict reliably the long-term performance of adhesively bonded FRP reinforcement it is important to develop experimentally validated design models. This paper reports experimental long-term tests investigating the properties of epoxy resins and their impact on the bond behaviour of near-surface-mounted (NSM) FRP strips. Based on these experimental results material models, bond models and a simplified calculation method are developed and presented in this paper.