Influence of nylon fibers recycled from the scrap brushes on the properties of concrete: Valorization of plastic waste in concrete

A vast amount of nylon waste is being generated as paintbrushes, and how to reuse post-consumer nylon waste is a new crisis. The eco-friendly development of fiber reinforced concrete (FRC) is a major challenge in the construction industry considering the high cost of engineered fibers. Thus, owing to high tensile strength, recycled nylon fiber (RNF) derived from nylon waste can be used in FRC as an eco-friendly and cheaper alternative to engineered fibers. This study assessed the influence of RNF on the properties of medium-strength concrete. Therefore, concrete mixes were prepared and studied with various volume fractions of RNF i.e., 0.05%, 0.1%, 0.15%, 0.25%, 0.5%, 0.75%, 0.85% and 1%. Physical (density, and ultrasonic pulse velocity-UPV), mechanical (compressive strength-CS, splitting-tensile strength-SPS, and flexural-tensile strength-FS), and permeability (water absorption-WA and chloride penetration depth-CPD) properties of all mixes were examined and compared. The experimental findings proved that higher volume fractions of RNF showed a ‘reducing effect’ on CS. For best SPS and FS, results recommended doses of RNF are 0.25%, and 0.75%, respectively. At optimum RNF doses, net improvements of 24.2% and 14.1% were noticed in FS and SPS, correspondingly w.r.t control mixture. RNF enhanced the crack-resistance of plain concrete by delaying the failure under tensile and flexural load. The incorporation of a 0.05–0.5% volume fraction of RNF was beneficial to minimize the WA and CPD. Minimum permeability is achieved at the incorporation of 0.1–0.15% of RNF, for instance, at 0.15% RNF, WA and CPD of concrete were reduced by 11.5% and 29.2%, respectively w.r.t control mix.