Effect of basalt minibars on the shear strength of BFRP-reinforced high-strength concrete beams

This research examined the effect of a novel type of stiff nonmetallic macro fibers, basalt macro fibers (BMF), on the shear strength and behavior of high-strength concrete (HSC) beams longitudinally reinforced with basalt fiber-reinforced polymer (BFRP) bars. Nine BFRP reinforced concrete beams (BFRP-RC) were cast and tested under two-point loads without BFRP stirrups. The volume fraction of BMF (Vf) and the BFRP longitudinal reinforcement ratio (ρf) were all evaluated; three volume fractions of BMF were used (0%; 0.75%; 1.5%), with three longitudinal reinforcement ratios (0.71%, 1.71%, and 2.54%). The results indicated that adding BMF to HSC-BFRP-RC beams enhanced the shear resistance. For concrete compressive strength of 90 MPa, the results show that adding BMF enhanced the shear resistance for all flexural reinforcement ratios; however, it is more effective in beams reinforced with a higher flexural reinforcement ratio. For beams reinforced with flexural reinforcement ratios of 0.71% and 2.54%, the shear resistance increased by 95% and 98%, respectively, due to adding 0.75% BMF, compared to 136% and 210% when 1.5% of BMF were added. And the post-cracking stiffness of all beams remarkably increased due to BMF addition. Furthermore, the effect of BMF on the mechanical properties of HSC was investigated. Finally, ACI 318–19, ACI 440.1R-15, and ACI 544.4R-18 were evaluated to predict the ultimate shear strength of HSC-BFRP-RC beams reinforced with BMF. The experimental results correspond well with ACI 544.4R-18 predictions of the shear strength of fiber-reinforced concrete (FRC) beams without shear reinforcement.