Epoxy and its role in the long-term performance of bonded FRP material systems

Since 1997, the authors have been investigating the performance of fiber-reinforced polymer (FRP) material systems that are bonded to concrete structures for strengthening purposes. The research includes experimental and modeling efforts with laboratory-scale specimens, although this paper focuses on the experimental results. The first part of this paper reviews some general background on epoxy chemistry and how it relates to the handling and thermomechanical characteristics of bonded FRP materials in civil infrastructure applications. The second part reviews specific experimental results on the effects of sustained load and elevated temperature on FRP/concrete bond, and the third part presents the most recent experimental results of ongoing long-term study of FRP/concrete bond in indoor and outdoor environments. It is shown that bond strength can increase slightly under short term sustained loading in association with a small amount of creep of the partially cured epoxy. Over a loading period of 6 years in indoor and outdoor environments, only slight reductions in bond strength, relative to predictions based on the concrete strength at the time of measurement, have been observed.