Evaluating the impact of variability in the source of waste polyethylene on the design of plastic modified asphalt mixtures

Abstract

Use of waste plastics in asphalt mixtures suffers from a serious problem of significant variability with global sources; preventing proper guidelines for field applications. The aim of this study is to address the variability in source of waste plastic and its impact on asphalt mixture design. Polyethylene (PE) obtained from 5 different sources was used as a replacement for asphalt binder through dry mixing at dosage levels of 3 %, 6 %, and 9 % by weight of binder. Two mixing temperatures (151°C, 165°C) with respective compaction temperatures (140°C, 156°C) were utilized during mix production to account for the increase in binder stiffness due to plastic modification. The changes in asphalt mixture volumetrics were correlated to plastic properties such as density(ρ), viscosity (η), melting point (Tm), and Degree of Crystallinity (Xc), apart from plastic source. Construction Densification Index (CDI) and Traffic Densification Index (TDI) values were also calculated for further understanding the workability of PE modified asphalt mixtures. Even though five plastics irrespective of sources could be categorized as PE, the Xc (<65 %) and η (<5594 Pa.sec at 165°C) played a prominent role in ensuring mixtures met volumetric requirements; after increasing the mixing and compaction temperatures. PE with Xc value (> 65 %) and η value (>5594 Pa.sec at 165°C) resulted in reduced workability with increased tendency of PE to behave as a filler. The study further recommends addressing PE in terms of core properties such as Xc and η rather than source or supplier to reduce variability and better understand its suitability in asphalt mixtures.