Multi-Scale Performance Assessment of Asphalt Mixtures Modified with Waste PVC Foils of Varying Geometries.

While the utilization of waste polymers in asphalt mixtures is widely studied, the specific influence of additive geometry on performance mechanisms remains underexplored. This study presents a multi-scale performance assessment of asphalt mixtures modified with waste Polyvinyl Chloride (PVC) foils. Waste PVC foils were processed into two distinct geometries, "Wiry" and "Random", and incorporated into mixture at dosages ranging from 5% to 12.5% by weight of bitumen via the dry process. At the macro-scale, Semi-Circular Bending, Hamburg Wheel Tracking, Repeated Creep, and Modified Lottman tests were conducted. At the micro-scale, Scanning Electron Microscopy and EDS analyses were employed to investigate interfacial adhesion. The results demonstrated that the "Wiry" geometry significantly outperformed the "Random" by establishing a three-dimensional reinforcement network. Specifically, the mixture modified with 7.5% "Wiry" PVC yielded the highest Flexibility Index of 24.17, representing a 3.7-fold improvement. Furthermore, this optimum dosage enhanced high-temperature stability and maintained moisture resistance (TSR > 85%), whereas dosages exceeding 10% caused agglomeration and performance loss. Microstructural imaging indicated that the fibrous morphology and calcite-rich surface of the "Wiry" additive facilitate superior mechanical interlocking. Consequently, this study suggests that optimizing waste PVC geometry is as critical as dosage for maximizing the durability and sustainability of flexible pavements.