The effect of using basalt fibers compared to steel fibers on the shear behavior of ultra-high performance concrete T-beam

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The effect of using basalt fibers in the matrix of ultra-high performance concrete (UHPC) T-beam on the diagonal crack-load and ultimate shear capacity was investigated experimentally. The results compared to similar T-beam containing steel fibers in equal percent. The beam was reinforced with longitudinal bars but did not have transverse shear reinforcements. Two parameters were adopted in this study. These were the volume fraction of fibers and the shear span to effective depth ratio. The results showed that using steel fibers in the matrix led to a ductile behavior upon failure more than adding basalt fibers. Adding basalt fibers to UHPC enhances compressive strength more than the addition of steel fibers at equal percent. The enhancement was reflected in the shear capacity of the compression zone of the T-beam. Also, the compression zone in the T-beam was enlarged due to the presence of the flange. Therefore, the flange contributed to raising the compression shear capacity. Incorporating basalt fibers in the matrix of UHPC delayed the initiation of diagonal cracking more than steel fibers did. Adding basalt fibers at 0.5%, 1.0%, and 1.5% raised the cracking shear load by 160% over the non-fibrous one. However, the 0.5% and 1.0% basalt fibers upheaved the ultimate shear capacity more than the 1.5% content. The 1.5% steel fiber content promoted the shear capacity by 133% over the non-fibrous one. Also, the shear span to effective depth (a/d) ratio had a significant effect on the shear capacity of the beam. Increasing the a/d ratio led to decreasing the shear capacity and raising the mid-span deflection of the T-beam. However, the recorded deflection of the UHPC T-beam was low compared to the conventional concrete one.