Polypropylene-jute fiber composites from textile waste for external strengthening of reinforced concrete beams

Abstract Polypropylene (PP) composites reinforced with recycled jute fibers (JF) have been investigated as sustainable alternatives for applications in reinforced concrete (RC) structures, contributing to waste reuse and circular economy practices. In this study, polymer matrix composites were produced using polypropylene and shredded jute fibers with contents of 20% and 30% by mass through injection molding. The constituent materials were initially characterized, followed by the mechanical characterization of the composites through tensile strength, flexural strength, elongation, and hardness tests. Concrete mixtures were then produced and evaluated in fresh and hardened states according to standardized procedures. Reinforced concrete beams were manufactured, including reference beams without reinforcement and beams strengthened with externally bonded composite plates, which were subjected to flexural tensile tests. The results indicated that the incorporation of jute fibers reduced the tensile strength of the composites compared with pure polypropylene, with decreases of approximately 18% and 19% for composites containing 20% and 30% fibers, respectively, indicating limitations in fiber-matrix adhesion and stress transfer. However, the presence of fibers slightly improved resistance to plastic deformation, with increases of around 4 and 1% for the respective fiber contents. In the structural tests, the reinforced beams did not show important gains in load-bearing capacity, and failure occurred before the concrete reached its maximum resistant capacity, suggesting limitations related to the bond between the composite reinforcement and the concrete substrate. Despite the limited mechanical gains, the results highlight the potential of natural fiber–reinforced polymer composites as sustainable materials for protective or complementary reinforcement layers in concrete structures.