Flexural behavior of BFRP bar–hybrid steel fiber reinforced UHPC beams

Abstract

Ultra-high-performance concrete (UHPC) has the potential to overcome the durability limitations of conventional concrete. Basalt Fiber Reinforced Polymer (BFRP) bars can mitigate the corrosion effects of steel bars and fully exploit the properties of UHPC. Industrial Steel Fibers (ISF) are a widely used component in the preparation of UHPC. To reduce environmental pollution and costs, this study proposes using recycled tire steel fibers (RTSF) instead of ISF in the production of UHPC. RTSF will be combined with BFRP bars to prepare hybrid steel fiber UHPC beams. The study investigates the effects of RTSF substitution for ISF and BFRP reinforcement ratio on the flexural performance of UHPC beams. The study indicates that the beam's bending failure modes include concrete crushing, equilibrium, and BFRP bar tensile failure. The replacement rate of RTSF has a dual effect on the flexural performance. As the RTSF replacement rate increases from 0 % to 100 %, the cracking load and ultimate capacity of the beams decrease by 2.86 % and 10.38 %, respectively, while the mid-span deflection of the beam increases by 7.94 mm when it reaches failure. When the replacement rate of RTSF is 60 %, the beams exhibit optimal bending performance, and their ultimate capacity can be increased by 2.95 % compared to the capacity when the replacement rate is 0 %. The failure mode of the beams is significantly influenced by the reinforcement ratio of the BFRP bars. Increasing the BFRP reinforcement ratio from 1.12 % to 7.12 % resulted in a 65.8 % decrease in maximum crack width and a 57.6 % decrease in mid-span deflection, while the ultimate load is increased by 78.6 %. The proposed theoretical calculation formula can effectively predict the flexural capacity of BFRP bar hybrid steel fiber UHPC beams, providing a theoretical basis for the application of FRP reinforced hybrid steel fiber UHPC beams.