Advanced Materials Research Vol. 1185

Abstract: Ultra-high-performance fiber-reinforced concrete (UHPFRC) exhibits outstanding compressive strength but tends to fail in a brittle manner under flexural loading when fibers are absent. This study evaluates the effectiveness of recycled tire steel fibers (RTSF) in improving the flexural strength, ductility, and toughness of UHPFRC beams. Thirty six doubly reinforced beams were cast and tested under three-point bending with reinforcement ratios of 0.009, 0.019, 0.028, and 0.043. The specimens were grouped as non-fiber control, mono RTSF (13 mm, 1.5% by volume), and hybrid RTSF (13 mm at 1.5% + 16 mm at 1.5%). Load deflection and stress strain responses were analyzed to assess structural performance. Beams without fibers failed abruptly, whereas those reinforced with RTSF demonstrated significantly greater ductility and energy absorption. The mono-fiber beams achieved a peak load of 264.46 kN, while the hybrid fiber beams attained a peak stress of 128.66 N/mm², 29% and 23% higher than those of the mono and non-fiber beams, respectively. These results confirm that incorporating RTSF, particularly in hybrid form, effectively mitigates brittle failure in UHPFRC and provides a sustainable, locally sourced solution for achieving superior strength, ductility, and toughness.