Short and Medium Term Durability Evaluation of FRP-Confined Circular Concrete

Evaluation of environmental durability of concrete circular specimens strengthened using externally applied fiber-reinforced-polymer (FRP) composites for confinement reinforcement was studied. FRP-confined concrete cylinder tests were carried out for various environmental exposure conditions including interior, exterior, and freeze–thaw cycling in saltwater. Two types of resin matrix-based FRP composite systems, including epoxy and urethane resin, utilizing either carbon or glass fibers were used. In addition, continuous single and double layer wrapping schemes were applied for confinement for each of the four FRP composite systems. The overall stress–strain behavior of FRP-confined concrete does not change fundamentally but different levels of exposure significantly affect its absolute stress–strain curve. The radial strain and corresponding axial strain at the point of zero volumetric strain is significantly affected by different levels of environmental exposure. It is proposed that the relative FRP composite effectiveness must be used to calculate the ultimate radial strain of FRP-confined concrete. It was found that for the four FRP systems used in this study the ultimate radial strain is not significantly affected by the type of exposure. The writers believe that the results shown in this paper help engineers to understand the short and midterm effects of the environment on FRP confined concrete; long term effects are still under investigation.