Effect of FRP bar degradation on interface bond with high strength concrete

An experimental investigation is described on the durability performance of FRP bar-concrete interface bond, purposely focused on the surface material degradation of FRP bar by using a concrete mix with high compressive strength. A total of 48 pullout specimens with four different types of FRP bars were cast for bond strength tests. Additional specimens were also cast for concrete compressive strength test, visual inspection of FRP-concrete interface, and scanning electron microscopy analysis to evaluate the environmental effects. Specimens were exposed to the following conditions: tap water maintained either at ambient temperature or 60 °C, and air of thermal cycling from −20 to 60 °C. The environmental conditioning resulted in bond strength reductions of 4–10% for CFRP bars and 0–20% for GFRP bars. The conditioning also increased the free-end slip before the peak bond strength was reached. The degradation of bond was related mainly to the deterioration of FRP bar and less to concrete. The interface bond failure mode and degradation mechanism due to FRP bar damage are characterized.