A Computational Approach to Study Reversible Aging in SHRP AAA-1 Asphalt

Abstract

This study is carried out computationally at atomic scale to determine reversible modifications of a specific group of asphalt. The specific asphalt group is defined by Strategic Highway Research Program (SHRP) as AAA-1. The chemical structure of AAA-1 asphalt is modeled using representative molecules drawn by LAMMPS software. LAMMPS molecular dynamics code is employed here to perform atomistic simulations. Simulation outputs give acceptable values of physical, thermodynamic and structural changes of asphalt due to reversible aging. Two factors are considered for reversible aging; they are temperature and physically mixed oxygen molecules to the system. Oxygen molecules varying from 1 to 4% of the molecular weight of model asphalt are mixed to the system. Presence of oxygen reduces heat of vaporization and cohesive energy density of asphalt. It also causes reduction in bond stretching, angle bending, and torsional energy of asphalt molecule. Finally, atomistic simulations prove that the intra-molecular van der Waals energy decreases, whereas; the intermolecular van der Waals energy increases as a result of reversible aging.

Key Words: Asphalt, atomistic simulation, reversible aging, heat of vaporization, cohesive energy density, molecular interaction energy