Experimental investigation and analytical prediction of flexural behaviour of reinforced concrete beams with steel fibres extracted from waste tyres

In recent years, studies on the use of car tyre wastes in concrete have gained momentum. Especially, the effect of recycled waste steel wires (RWSWs) from tyres to be mixed into concrete for using in newly designed reinforced concrete buildings on the performance of construction elements is a fairly new research area. In this study, the bending behaviour of 12 reinforced concrete beams was investigated having 1/3 geometric scale, 100 x 150 x 1000 mm in size, and produced with RWSWs additive in different volumetric ratios (1%, 2%, and 3%) under vertical loads. Another main parameter selected in the study was the amount of varying tension reinforcements (24)12, 24)10, and 24)8). The load-carrying, stiffness, ductility, and energy dissipation capacities of the RWSW reinforced bending beams were compared with the primary aim of this study which was to examine and present the contribution of RWSWs on the improvement of the bending performance of the reinforced concrete beams. The results revealed that the mechanical properties of the hybrid beams with RWSWs vary depending on dosages but are comparable with those of the beams-only with the same fibre dosage. A positive effect was obtained for the hybrid beams containing 2-3% RWSWs. Besides, RWSWs were found to be highly well mobilised at larger crack widths, and the post-cracking strength of RWSW mixes was significantly higher. Considering both mechanical properties of the beams and fresh properties such as the workability, 2% of RWSWs is recommended to be utilised in the reinforced concrete beams. On the other hand, the results were compared with the predictions of the methods given in the literature and standards. Moreover, an equation was derived to better predict the capacity of the hybrid beams using RWSWs.