Molecular dynamics study of rejuvenator effect on RAP binder: Diffusion behavior and molecular structure

This study developed molecular dynamics (MD) models to study the rejuvenator diffusion behavior and its impact on molecular structures and thermodynamic properties of asphalt binder in Reclaimed Asphalt Pavement (RAP). A two layered model was developed to study the inter-diffusion process between rejuvenator and RAP binder. Results show that the inter-diffusion process can be described by Fickian equation. Molecular Dynamics (MD) simulations yield reasonable diffusion coefficient which is comparable to experimental result. A mixture model was prepared to investigate the effect of rejuvenator on molecular interactions of saturate, aromatic, resin, and asphaltene (SARA) fractions in RAP binder. Thermodynamic properties including density, surface energy, and cohesive energy density of RAP binder were studied. It was found that oxidative aging changed both thermodynamic properties of RAP binder, and adding rejuvenator could restore thermodynamic properties to those of virgin binder to a certain extent. The visualization of molecule-molecule radial distribution functions (RDFs) suggests that rejuvenator increases the self-association of asphaltene in RAP binder. The study findings directly contribute to better understand the rejuvenator diffusion behavior which is difficult to observe from laboratory experiments. The developed MD models serve as benchmark for further study of rejuvenation using computational experiments. (C) 2017 Elsevier Ltd. All rights reserved.