Influence of incorporating annealed fiber scraps on the physico-mechanical properties of ordinary concrete

Abstract

Concrete is generally reinforced with steel bars tied together with annealed fibers, a process that generates metal fiber scraps, a form of construction waste. The presence of these residues around the construction site is a subject of debate among professionals; some see them as potential reinforcement of concrete, whereas others consider them as waste. This study aimed to evaluate the influence of adding annealed fiber scraps on the physical and mechanical properties of ordinary concrete. Composites were designed with fiber contents ranging from 0 to 0.75% of the concrete volume. Tests were carried out on cylindrical specimens (Ø16 cm, H32 cm) for most characterizations: compression and splitting tests, and on prismatic specimens (7×7×28 cm³) for flexural strength. After wet curing at room temperature of the laboratory (22±2°C) for 7, 14, and 28 days, the samples underwent a series of physical and mechanical tests. The results showed that workability decreased gradually as fiber content increased. Apparent density, water-accessible porosity, and capillary water absorption slightly increased with fiber content, reaching a maximum at 0.75%. On the other hand, the mechanical properties are improved: the compressive strength, splitting tensile strength, and dynamic modulus of elasticity increase significantly, with optimal gains of 15%, 18%, and 12%, respectively, compared to the control concrete. The addition of fibers also reinforced the concrete, as shown by the stress-strain curves. Those for fiber-reinforced concrete showed a slight improvement in the flexural tensile strength and displacement to failure, and a post-peak stabilization phase highlighted by the higher residual strength with fibers, unlike the control concrete, which showed brittle failure without a stabilization phase. Considering these results, annealed fiber scraps can be used as reinforcements in ordinary concrete, particularly for structural elements subject to bending, such as floors, beams, and slabs.