Bond performance between BFRP bars and fiber reinforced concrete exposed to high temperature

In order to improve the bonding performance of basalt fiber reinforced polymer (BFRP) bars and concrete after high temperature, basalt fibers were added into concrete separately, and basalt fibers and cellulose fibers were mixed into concrete. The bonding performance of BFRP bars and fiber reinforced concrete was systematically studied by the center pull-out test of BFRP bars and concrete. The test parameters included temperature, matrix concrete type, BFRP bar surface form, bonding length, and BFRP bar diameter. The failure modes, bond stress-slip curves, bond strength of BFRP bars and concrete specimens were obtained. The results show that with the increase of temperature, the bond strength between BFRP bars and ordinary concrete, basalt fiber reinforced concrete and hybrid fiber reinforced concrete decreased gradually, between 70 ℃ and 350 ℃, the corresponding reduction rates of bond strength are 17.1%～48.6%, 14.5%～46.8% and 11.4%～48.3%, respectively. Compared with ordinary concrete, the bond strength of BFRP bars with deep ribs, sand coating, and shallow ribs and concrete is increased by 8.4%～18.8%, 56.3%～99.6% and 27.5%～51.8% by adding 0.20% basalt fiber into concrete, respectively. Mixing 0.15% basalt fiber and 0.10% cellulose fiber into concrete results in the increases by 17.6%～35.1% of the bond strength between BFRP bars with deep ribs and concrete. Different surface forms of BFRP bars have a significant effect on the bond strength between BFRP bars and fiber reinforced concrete, and the bond strength between deep rib bars and fiber reinforced concrete is the highest. With the increase of bond length and diameter, the bond strength between BFRP bars with deep ribs and fiber reinforced concrete decrease gradually. Finally, considering the above factors, the calculation formula of bond strength between BFRP bars and fiber reinforced concrete after high temperature was proposed by introducing the shape factor of BFRP bars, fiber reinforcement factor and bond strength reduction factor. The research results can provide data and theoretical support for the fire resistance design of FRP reinforced fiber reinforced concrete structures and the safety assessment of the structures after fire. © 2023, Central South University Press. All rights reserved.