Emerging Downstream Plastic Waste Disposal Solutions in the United States: A Review of Plastic-Modified Pavement

Plastic pollution has been a persistent and urgent global crisis that has surpassed the capacities of current waste management systems. With only about 5-6% of global plastics currently being recycled and microplastic identification in human and environmental samples, there is an urgent need for alternative sustainable waste management systems. A recent downstream recycling technology that has gained recognition is waste plastic-modified roads. This review aims to provide a comprehensive evaluation of plastic roads as a transitioning alternative from downstream waste mismanagement to a circular plastic economy. Factors, including mechanical performance, various modifier contents, potential environmental impacts, economic feasibility, and sustainable ethics, are examined and contextualized within U.S. environmental regulations. Main findings revealed that certain material compositions exerted beneficial effects on the pavement’s durability and rheology; however, severe variability arose in storage stability resulting from poor adhesion between polymer and asphalt components. Longitudinal environmental impacts were uncertain, primarily due to unclear long-term circularity of plastic roads, inconsistent findings across toxicity studies, and the absence of environmental benchmarks. Future areas of research should focus on the mitigation of storage stability issues, chemical toxicity content, reclaimed asphalt pavement (RAP), and the establishment of MP release thresholds and relevant environmental standards.