Improvement in Fiber-Reinforced Polymer–Concrete Bond by External Pressure

An experimental study evaluated the improvement in the bond of fiber-reinforced polymer (FRP) and concrete to dry and wet substrates from applied pressure. In the study, 12 full-sized pile specimens, including four controls, were wrapped by using two different glass FRP systems–- a prepreg and a wet layup–-and two different layouts typically used for unidirectional and bidirectional fibers. Wrapping was conducted inside a partially filled tank to ensure that the bonded areas of the dry and wet regions were identical. Sustained pressure was maintained during curing by using pressure or vacuum bagging. Bond improvement was evaluated from more than 400 pull out tests. Results showed that external pressure led to improved bond in both the dry and submerged regions. However, vacuum bagging was better for prepreg systems, whereas pressure bagging was better for wet layups. Transverse fiber layout typically used with bidirectional fibers gave better bond in controls where no external pressure was applied.