Mechanical Properties of Fiber-Reinforced Concrete Using Steel Fibers Derived from Discarded Tires

The global accumulation of approximately 1.5 billion discarded tires annually presents a critical environmental challenge, necessitating innovative recycling strategies in the construction sector. This study investigates the valorization of Recycled Steel Fibers (RSF) recovered from waste tires as a sustainable mechanical reinforcement in concrete. While traditional concrete is limited by inherent brittleness and low tensile capacity, the incorporation of RSF aims to mitigate these deficiencies through a multi-scale crack-bridging mechanism. Concrete mixtures were prepared with RSF dosages of 0%, 1%, 2%, 4%, and 6% by weight of cement. The experimental results demonstrate that while workability decreases with higher fiber content, stabilizing at a slump threshold of 20 mm for dosages of 4% and 6% due to fiber interlocking, the mechanical enhancements are substantial. Compressive strength improved by up to 22.2%, while tension-dominated properties saw the most significant gains, with split tensile and flexural strengths increasing by 44.7% and 47%, respectively. Highly robust regression models (R2 > 0.97) and error analyses (RMSE < 0.09 MPa) validate the predictive accuracy of the strength gains. Furthermore, a sustainability analysis reveals that substituting industrial fibers with RSF reduces the carbon footprint by 11.2% and enhances the Eco-Efficiency Index by 43.9%. These findings confirm that high-dosage RSF-reinforced concrete is a technically viable and environmentally responsible solution for resilient infrastructure, offering a net economic benefit of approximately USD 26,500 per 1000 m3.