Damage to asphalt roads is frequently caused by waterlogging and overloading. While asphalt pavement remains an economical choice, Indonesia imports 75% of its supply, coinciding with a growing crisis of low-value plastic waste e.g., Low-Density Polyethylene (LDPE), Polystyrene (PS), and Polypropylene (PP) that is economically challenging to sort and recycle. This study proposes a novel solution by utilizing a blended mixture of these plastics (40% LDPE, 30% PP, 30% PS) to simulate unsorted waste streams for modifying Asphalt Concrete-Wearing Course (AC-WC) pavement. The dry mixing process was employed to substitute asphalt at dosages of 0%, 8%, 10%, 12%, and 14% by weight. The research methodology encompassed material characterization, aggregate gradation design, and Marshall testing to determine the Optimum Asphalt Content (OAC) and Optimum Plastic Content (OPC). The durability of the optimal mix was subsequently rigorously assessed through prolonged water immersion at 60 $^{\circ}\mathrm{C}$ for durations of 30 minutes, 24, 48, 72, and 96 hours. Results indicated that a 10% plastic substitution at an OAC of 6.3% yielded the highest Marshall stability, with all volumetric parameters within specified tolerance limits. The mixture exhibited exceptional resistance to moisture damage, evidenced by an Index of Retained Stability (IRS) of 94.64% after 24 hours, surpassing the 90% requirement. Furthermore, the Retained Marshall Stability was 87.40% after 96 hours. Additional durability metrics, including the First Durability Index (FDI) and Second Durability Index (SDI), were analyzed to comprehensively evaluate the performance degradation over time. The findings conclusively demonstrate that modifying asphalt with this blended, unsorted plastic composition is not only feasible but also enhances mechanical properties and durability, offering a viable and sustainable strategy for large-scale plastic waste management in infrastructure development.