Performance Evaluation of Recycled and Virgin Fibers in Fiber-Reinforced Concrete for Pavement Applications—Laboratory Test Results

This study evaluates the performance of recycled and virgin fibers in fiber-reinforced concrete (FRC), with a focus on workability, concrete production, and mechanical properties. Fibers were directly sourced from manufacturers and used at dosages recommended by manufacturers and supported by the literature. All fibers improved the modulus of rupture of plain (control) concrete. The fibers investigated included plastic, steel, composite, glass, and basalt fibers. Across most fiber types—regardless of whether they were virgin or recycled—FRC demonstrated improved post-cracking load-carrying capacity, resulting in enhanced residual strength and ductility. Plastic fibers exhibited the best post-cracking performance, with high residual strength, toughness, and effective flexural strength ratios, though they reduced workability. Recycled plastic fibers performed comparably to virgin plastic fibers in terms of post-cracking behavior. Steel fibers had minimal impact on workability and provided good residual strength and toughness; recycled steel fibers performed similarly to the best-performing steel fiber and outperformed other steel fibers. The improved performance of random-shaped and twisted steel fibers was attributed to enhanced fiber–matrix bonding. Recycled glass fiber-reinforced polymer composite fibers from decommissioned wind turbine blades showed some improvement in post-cracking performance, particularly for larger fiber sizes; however, further testing is needed to optimize fiber size and dosage. In contrast, glass and basalt fibers exhibited limited post-cracking performance compared to plastic, steel, and composite fibers. Most fibers increased compressive strength, while improvements in the modulus of elasticity were negligible. Fibers generally reduced drying shrinkage, with a maximum reduction of 21% at 56 days. Overall, FRC performance was strongly influenced by fiber characteristics, including length, surface texture, chemical surface groups, and dosage. Recycled fibers demonstrated comparable performance to virgin fibers and showed potential for reducing greenhouse gas emissions, depending on recycling processes and treatments. These results indicate that recycled fibers are suitable for rigid pavement applications in California. Based on comparative performance, the following fibers are recommended for further evaluation: BarChip R50, BarChip 48, MAC Matrix, Strux 90/40, and Ferro-Green plastic fibers; Flexo and Helix steel fibers; and Recon XL composite fibers.