Bond performance of fiber reinforced polymer bars in normal- and high-strength concrete

The structural performance of reinforced concrete (RC) members depends on the bond between the reinforcing bars and surrounding concrete. Unlike steel bars, fiber-reinforced polymer (FRP) bars are manufactured with different fiber types (glass, basalt, carbon, and aramid) and have different mechanical properties and surface configurations (sand-coated, deformed, grooved, sand-coated over helical wrapping). These differences impact the bond performance between the FRP bars and concrete. This paper investigates the bond performance of new generation and different FRP bars embedded in concrete. A total of 87 pullout specimens were constructed and tested until failure. The test results are presented and discussed. The test parameters include (i) fiber type (glass or carbon), (ii) surface configuration (sand-coated, deformed, or grooved), (iii) No. 4 to No. 8 (13 to 25.4 mm diameter) bar diameters), and (iv) concrete strength (normal- or high-strength concrete: NSC or HSC). Specimens with deformed 10 M or 15 M steel bars were also fabricated as controls and tested for comparison. The embedment length and block dimensions were also considered to ensure pullout-failure mode. The test results reveal that increasing the bar diameter generally reduced the bond strength of the FRP bars, while the bar diameter had insignificant impact on the steel bars. There was a positive relationship between the concrete compressive strength and the bond strength gained. The anticipated failure modes with the high concrete strength were at the fiber resin interface due to the high confinement generated by high-strength concrete. With the lower strength, failure usually occurred at the resin-concrete interface. In addition, the test results were used to assess different analytical models for bond stress-slip relationships.