Experimental analysis of torsional behavior of hybrid fiber reinforced concrete beams

Abstract

This experimental study intended to compare the effect of hybrid fiber between carbon fiber (CF), basalt fiber (BF), and steel fiber (SF) on the torsional behavior of reinforced concrete (RC) beams. Thirteen RC beams were tested under pure torsion and loaded until failure. Beams were divided into four series: A, B, C, and D. Series A consisted of four beams: one without fibers, and others with one type of fiber (CF, BF, and SF). Each one of series B, C, and D contain two types of fibers: (CF and BF), (BF and SF), and (CF and SF) with a varying fiber content of 0.25%, 0.50%, and 0.75% in term of volume. This paper represented the results of the torsional moment, twisting angle, crack pattern, fracture modes, ductility, and energy absorption of specimens. Experiments showed that the use of a hybrid of SF and CF enhanced torsional moment, angle of twist, and energy absorption more than the hybrid of BF and CF or BF and SF. Conversely, the positive effect of the hybrid of BF and SF on ductility was greater than other hybrids. Therefore, the maximum torsional strength increased by 22.3%, 28.6%, and 65.2% when a hybrid fiber of (0.75% BF and 0.75% CF), (0.75% BF and 0.75% SF), and (0.75% CF and 0.75% SF) added, respectively. Moreover, the ultimate torsion was predicted by different theories and code provisions and a formula was developed to take the effect of hybrid fiber on the ultimate torsion of hybrid fiber reinforced concrete (HFRC) beams.