Development of an atomistic-based chemophysical environment for modelling asphalt oxidation

Asphalt is the primary binding and waterproofing component in road pavements and roof shingles, and is expected to meet certain minimum performance requirements based on its rheological properties. With an optimum mixture design, desirable performance of asphalt can be ensured in its early service stage. However, being an organic end product of petroleum serving under the general open-to-air conditions, asphalt can lose the desired rheological properties with time due to oxidative hardening or aging that frequently leads to increase in viscosity, separation of components, and loss of cohesion and adhesion, and thereby becomes hardened. Oxidative hardening of asphalt can cause reduce mixture performance and eventually lead to failure of pavements and roof tiles. The study of asphalt oxidative hardening has thus far focused on the changes in the physical properties, mainly the viscosity and ductility of bulk asphalt. Such phenomenological approaches meet the direct engineering needs; however they do not contribute to understanding the fundamental physicochemical mechanisms of asphalt hardening. From this standpoint, this research study aims at exploring the chemical basis of asphalt oxidative hardening by establishing an ab initio quantum chemistry (QC)-based chemophysical environment in which the possible chemical reactions between asphalt ingredients and oxygen, as well as the changes in their physical behaviour can be readily studied. X-ray photoelectron spectroscopy (XPS) was used to validate the bulk asphalt model, of which the results showed high agreement to the model predictions.