Bond stress–slip relationship between basalt fiber-reinforced polymer bars and concrete using a pull-out test

The basalt fiber-reinforced polymer bar is one of the newly evolved materials expected to be used as a structural reinforcement because of its non-corrosive nature and abundant tensile strength properties. The bond stress–slip relationship between fiber-reinforced polymer bars and concrete is necessary to evaluate the load carrying capacity of concrete components or structures reinforced with fiber-reinforced polymer bars. Although the relationship between fiber-reinforced polymer bars and concrete has been studied, the bond stress–slip relationship between concrete and basalt fiber-reinforced polymer bars considering the effect of bar diameter and concrete strength is still lacking. This paper presents an experimental investigation on the bond behavior between basalt fiber-reinforced polymer bars with different diameters (10, 14, and 20 mm) and concrete with two different compressive strengths using a pull-out test. The test results showed that (1) the failure mode between basalt fiber-reinforced polymer bars and concrete was equally contributed from crushing of concrete and failure of basalt fiber-reinforced polymer surface and mainly from delaminated resin-rich surface for the specimens with the concrete compressive strength of 43.6 and 71.8 MPa, respectively; (2) the bond strength between basalt fiber-reinforced polymer bars and concrete decreased with the increase of bar diameter; (3) the slip corresponding to bond strength increased with the increase of diameter of basalt fiber-reinforced polymer bars; (4) the bond strength between the basalt fiber-reinforced polymer bars with diameter of 10 mm and concrete increased by 18.8% when the concrete strength increased by 64.7%; and (5) the formulas for bond stress–slip relationship between basalt fiber-reinforced polymer bars and concrete in consideration of the ratio of concrete cover depth and concrete compressive strength were proposed. The calculation results of the formulas indicated good accuracy with the experimental results.