Interfacial adhesion performance between the low-density polyethylene (LDPE) modified bitumen and minerals based on molecular dynamics simulations

Abstract

Since the first plastic scale production, plastic consumption has amplified from 5 million tonnes to 322 million tonnes per year. Correspondingly, plastic waste has increased substantially and is now associated with detrimental effects to humans and wildlife. Therefore, plastic waste is a shared interest of exploration for many researchers as they all hold a common goal to look for safe and sustainable alternative solutions.Many scientists found that the incorporation of waste plastic such as low-density polyethylene(LDPE) can potentially improve the rheological performance and high temperature performance of bitumen. However, the LDPE modified asphalt binder has frequently encountered the adhesive failures resulting from the adhesion loss at the bitumen-aggregate interface, particularly when subjected to the oxidative ageing conditions. Adhesion is defined as the molecular force of attraction in the area of contact between the adhesive materials and substrates. A series studies have been used experiment tests to evaluate adhesion property of the asphalt binder. Although these studies have provided meaningful and progressive insights,it is still necessary for further exploration to better understand the microstructure and physical properties of asphalt binder, particularly when the plastic is incorporated in the binder. However,rat the current stage, the research on adhesion of asphalt binder is limited and there is no established technique which can be used to quantify the adhesive bond strength between the minerals and LDPE modified bitumen at microscale .Only in the past 5 years, some researchers used molecular dynamic (MD) simulations to analyze the effect of oxidative aging on the adhesion performance of asphalt pavement. This is because MD simulation can simulate physical movements of atoms and molecules following Newton’s second law, which is advantageous than traditional experiment and numerical computation in understanding the molecular scale behaviors. Literature search indicates that these studies have no focus on the effect of LDPE on the adhesion between the bitumen and minerals. Hence, this study aims to model and evaluate the interfacial adhesion performance between the LDPE modified bitumen and different. MD simulations are employed to model the interfacial interaction between minerals and bitumen. Additionally, two representative minerals (quartz and calcite) have been selected to build the mineral-bitumen interface models. Results indicate that LDPE can improve the interfacial adhesion between the bitumen and minerals (quartz and calcite). Oxidative aging adversely affects the work of adhesion between the bitumen and quartz while positively affects the adhesive bond energy between bitumen and calcite. On completion of the MD simulations, it was found the different mixing process: dry method and wet method can affect the adhesion performance of asphalt binder. Moving onto the wet method,the work of adhesion between the bitumen and mineral increases once the LDPE directly mixes with bitumen. However, the work of adhesion between the bitumen and mineral decrease once the LDPE is introduced by dry method. This study provides a fundamental understanding to the combined effect of oxidative aging and LDPE on the adhesion between the bitumen and minerals at atomistic scale.