Hard-to-recycle plastic as asphalt modifier: Mechanical performance and potential environmental impacts

This paper discusses the incorporation of hard-to-recycle plastic waste into asphalt via a wet process, focusing on the mechanical performance and potential environmental benefits of using EVA and PU from the local footwear industry, given the high availability of waste and the low recycling rate. Polymer-modified binders were produced via a wet process in a pilot mixer mill with 1 % or 2 % plastic waste discarded by a local footwear industry (EVA and PU - typically excluded from the conventional recycling stream) and HDPE and LDPE. Incorporation of EVA, HDPE, and LDPE increased failure energy by 15–37 % without compromising the modified-binder´s cracking performance, contributing to increase the mixtures' tensile strength (up to 69 %) and resilient modulus (up to 200 %), which resulted in acceptable cracking tolerance (CT Index > 70), moisture susceptibility (TSR > 70 %), and rutting resistance (FN > 100). PU-modified binders are within acceptable limits, but underperformed relative to the EVA, HDPE, and LDPE. From a cradle-to-gate perspective, the additional transport and energy required for waste incorporation offset the carbon dioxide emission savings from reduced virgin binder consumption. The plastic waste-modified mixtures increased human health and environmental impacts by 15 %, with no relevant changes in resource scarcity. The results confirm the potential of using hard-to-recycle plastics to produce asphalt mixtures, syncing pavement engineering performance with suitable environmental impacts.