Structural performance of reinforced concrete beams incorporating recycled hybrid fibers under varying transverse reinforcement configurations

This exploratory study examines the material- and member-level response of a waste-derived hybrid concrete containing processed face-mask fibers, waste binding-wire fibers, and scrap-tire rubber. Conducted in Nepal, the work was motivated by waste valorization and the need to assess locally sourced materials for resource-conscious construction. Four recycled-material combinations—BW + M + R, BW + M, BW + R, and rubber only—were screened through compressive, splitting tensile, and flexural strength tests. The BW + M + R mixture, containing nominal batching dosages of 1.5% binding wire, 0.25% mask fiber, and 0.5% rubber, produced the most balanced mechanical response and was selected for beam testing. Four reinforced concrete beams were tested under four-point loading: a conventional reference beam without recycled inclusions and with full stirrups, and three hybrid-concrete beams with full stirrups, localized stirrups in selected shear-span regions, or end stirrups only. The layouts were idealized detailing scenarios used to examine the response of the combined material–reinforcement systems as stirrup continuity decreased; they were not intended to establish an equivalent fiber-for-stirrup replacement. The reference and full-stirrup hybrid beams provide the closest direct comparison of material influence. Relative to the reference beam, the measured ultimate shear force, apparent displacement ductility, and recorded load–deflection energy of the full-stirrup hybrid beam were 13.6%, 24.7%, and 98.3% higher, respectively. The localized-stirrup hybrid beam developed 3.4% greater ultimate shear force, but its strength-normalized shear parameter and energy absorption were only 0.4% and 1.6% higher, respectively. The end-stirrup beam showed 9.5% lower ultimate shear force and 12.1% lower energy absorption, although its apparent ductility increased. The results suggest that the recycled hybrid system can provide supplementary crack-control and post-cracking benefits when used with adequate transverse reinforcement, but the tested system did not compensate for the absence of stirrups in the main shear spans. Because one beam was tested per configuration and matched non-fiber reduced-stirrup controls were not included, the findings are exploratory. The system should therefore be regarded as a waste-derived supplementary crack-control system rather than a validated substitute for conventional transverse reinforcement.