Flexural rigidity and ductility of RC beams reinforced with steel and recycled plastic fibers

This study compares between the mechanical properties of concrete either reinforced with recycled plastic (RP) or end-hooked steel (EHS) fibers with volume fractions of 1, 2 and 3%. Also, the effects of the fiber type and volume fraction on flexural responses were investigated using experimental program composed of seven reinforced concrete (RC) beams. Generally, results showed that the RP and EHS fibers remarkably enhanced both the mechanical characteristics of concrete and the flexural capacity of RC beams. Specifically, concrete matrix that reinforced with 2% volume fraction of RP or EHS fibers exhibited the highest capacities among all tested specimens. On the other hand, the compressive and the tensile strengths of the fibrous concrete which strengthened with 3% volume fraction (either RP or EHS fibers) were lower than their counterparts that reinforced with lower volume fraction (2%). As the fiber volume fraction increased up to 2%, the peak load of the RC beams increased followed by a reduction for higher fiber volumes. The peak load of the RC beam specimens reinforced with 2% of RP and EHS fibers were 57.1 kN and 60.7 kN, respectively compared to 39.6 kN for the control RC beam. Both RP and EHS fibers had a positive effect on the (effective/gross) flexural rigidity ratio, especially when used with volume fraction lower than 3%. RC beams reinforced with 1% of RP and EHS fibers yielded higher ductility in comparison with 2 and 3%. An analytical model constructed based on the distribution of stress-strains along the height of the RC beam was used to estimate the bending moments at different stages. Results well agreed with the experimental records.

Automated summary

The study compared the mechanical properties of concrete reinforced with recycled plastic and end-hooked steel fibers, finding that 2% volume fraction of fibers exhibited the highest strength. As fiber volume fraction increased, the peak load of RC beams increased but decreased after exceeding 2%.