Mechanical characterization of cold recycled asphalt mixtures reinforced with waste polyester and nylon fibers

Cold recycling offers substantial environmental and economic benefits, but concerns regarding performance, particularly strength, moisture susceptibility, and reduced flexibility when active fillers are used, limit its widespread use. This study evaluated virgin and pre-consumer waste polyester and nylon fibers in Cold Recycled Asphalt Mixtures (CRM) stabilized with emulsified asphalt, with and without cement. Performance was assessed using dry and wet Indirect Tensile Strength (ITS), Indirect Tensile Strength Ratio (ITSR), the indirect tensile asphalt cracking test (IDEAL-CT), and the Semi-Circular Bending (SCB) Illinois Flexibility Index Test (I-FIT). Waste and virgin fibers generally enhanced dry ITS and fracture resistance but reduced wet ITS and ITSR. Combining cement and fibers mitigated moisture-related drawbacks while partially restoring flexibility. Waste nylon fibers generally matched or outperformed virgin polyester, while waste polyester performed mostly comparably to virgin polyester. These findings demonstrate the potential of waste fibers as sustainable and effective reinforcement for CRM.