Effect Of Fibers On Bond Behavior Between GFRP Rebars And Matrix Of Self-Compacting Concrete

One of the effective ways to avoid the problem of corrosion of steel reinforcement in concrete is to use fiber reinforced polymer (FRP) reinforcing bars as alternative. Because of the differences between FRP bar and steel bar in the production technique and mechanical properties, the bond stress of FRP bar embedded in concrete is not as good as steel bar embedded. Good bond behavior between FRP bars and concrete is a fundamental issue for reinforced concrete, and it is meaningful for the application of FRP bar in the civil engineering to improve the bond performance of FRP bar and concrete.Self-compacting concrete (SCC) have good workability such as fluidity, ability of filling and ability of resistance to segregation, which can enhance the bond strength of FRP bar embedded in concrete and strengthen the grasp force between FRP bar and concrete. Adding fibers to concrete can improve the performance of concrete: unorderly distribution of structural steel fibers can retard the extension of interior microcracks, and limit the development of macroscopical cracks, and enhance the toughness after concrete members cracking; traditional micro PP-fiber can prevent the early plastic cracking of concrete; macro PP-fiber can not only enhance the early cracking resistance behavior, but also improve significantly the toughness and the cracking resistance after concrete indurate. But it is still uncertain whether the adding fibers to concrete can enhance the bond strength of FRP bar embedded in concrete.On the premise of ensuring the good workability and mechanical properties of self-compacting concrete, the influence of different type of fiber (steel fiber, macro PP-fiber and micro PP-fiber) and addition magnitude of fiber on the bond behavior between FRP bars and concrete are studied by pull-out test and beam test aiming at finding out an effective way of improving the bond behavior of FRP bar embedded in concrete. A new way of evaluating bond ductility is proposed according to the bend toughness evaluation measure of DBV and RILEM. The results show that adding micro PP-fibers to concrete will decrease the bond strength of FRP bar embedded in concrete to some extent; adding suitable hybrid of steel fiber and PP-fiber or macro fiber to concrete can both enhance the bond strength and improve the bond ductility; the bond strength between FRP bars and concrete will be enhanced with increasing of steel fiber content. Finally based on the test results and former works, the ascending branch of the bond-slip curve is modeled, and the modeled curve corresponds with the test curve greatly; In addition, a new equation for bond strength and embedment length of GFRP rebar is proposed and provide principles for design code, which takes types of GFRP bars, position in the cast into consideration.