Effect of Environmental Exposure on the External Strengthening of Concrete with Composites-Short Term Bond Durability

The pressing need for rehabilitation and retrofit strategies that encompasses new and emerging materials and technologies, results from the need to simultaneously repair existing structures while attempting to increase both their performance levels and life spans. A large number of techniques currently exist for strengthening highway bridges ranging from the use of external post-tensioning to the addition of epoxy bonded steel plates to the tension surface. The use of composite plates for the purpose of external reinforcement has considerable potential. However, there is a critical need to investigate the degradation of the composite-concrete interface after exposure to environmental conditions that include moisture, sea water, freezing and freeze-thaw. In this investigation, the effect of five different environmental conditions on the performance of plated beams is considered from aspects related to materials and durability. It is shown that the selection of the appropriate resin system is critical to success, and the dangers of selecting systems with low glass transition temperatures and drastic drops in instantaneous modulus as a function of temperature are discussed. Two different resin systems are compared using the same fibrous reinforcement and an overall view of durability at the concrete-composite interface is elucidated.