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, 100×150×1000 mm in size, and produced with RWSW additives 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 (2ϕ12, 2ϕ10 and 2ϕ8). 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 hybrid beams with RWSWs vary depending on dosages but are comparable with those of beams-only with the same fibre dosage. A positive effect was obtained for hybrid beams containing 2-3% RWSWs. Besides, RWSWs were found to be highly well mobilized at larger crack widths and the post-cracking strength of recycled-fibre 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 literature and standards. Moreover, an equation was derived to better predict the capacity of the hybrid beams using RWSWs.