Shear behavior of normal and high-strength concrete beams reinforced with BFRP bars and basalt macro fibers

Abstract

This research examined the effect of basalt macro fibers (BMF) on the shear resistance and behavior of normal-strength concrete (NSC) and high-strength concrete (HSC) beams longitudinally reinforced with basalt fiber reinforced polymer (BFRP) bars. Twelve BFRP reinforced concrete beams (BFRP-RC) were cast and tested under two-point loads without and with BFRP stirrups. The volume fraction (Vf) of BMF, the concrete compressive strength (fc′), and the existence of stirrups were all evaluated. Three volume fractions of BMF were used (0 %, 0.75 %, 1.5 %) with three classes of concrete compressive strength (30 MPa, 60 MPa, and 90 MPa). The results indicated that adding BMF to BFRP-reinforced-NSC and BFRP-reinforced-HSC beams enhanced the shear resistance. For concrete classes C30 and C90 shear resistance increased by 38 % and 62 %, respectively, when 0.75 % BMF was added, and it increased by 81 % and 115 %, respectively, when 1.5 % BMF was added. The enhancement of shear resistance due to the addition of BMF to BFRP-reinforced-HSC beams was more effective than in BFRP-Reinforced-NSC beams. Moreover, the addition of BMF enhanced the shear resistance of both stirrup-equipped and stirrup-less beams. The experimental results showed that the shear resistance of BFRP-reinforced-HSC beams due to the addition of BMF rather than stirrups is comparable, if not better, with stirrups. For instance, the shear resistance of the beam reinforced with 1.5 % of BMF is more than the beam reinforced with the minimum amount of BFRP stirrups. The post-cracking stiffness of all beams remarkably increased due to BMF addition. Furthermore, the effect of novel BMF on the mechanical properties of concrete was investigated.Additionally, an equation to predict the concrete contribution to the shear strength of FRP-RC beams was developed using the experimental shear strength of the tested beams and the experimental results of 217 FRP-RC beams without stirrups published in the literature. The proposed equation is combined with Said et al. and Narayanan and Darwish expressions to account for FRP stirrups and BMF contributions in the shear strength of the BFRP-RC beams. The mean value and the coefficient of variance (CV) of experimental to predicted ultimate shear strength of the beams (Vu,exp/Vu,pred) were 1.12 and 7.64%, respectively.