Quantum-Chemistry Study of Asphalt Oxidative Aging: An XPS-Aided Analysis

Asphalt derived from crude oil (or petroleum) is an important base organic material for many industrial purposes. Oxidative hardening occurs throughout the service life of asphalt materials, which could significantly change the desired physicochemical properties. The study of asphalt oxidative hardening has thus far been 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 do not help understand the fundamental physicochemical mechanisms of asphalt hardening. From this standpoint, this paper aims at exploring the chemical basis of asphalt oxidative hardening by establishing an ab initio quantum chemistry (QC) based physicochemical environment, in which the possible chemical reactions between asphalt ingredients and oxygen, as well as the incurred changes in their physical behavior, 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, and thereby prove the validity of the QC-based models developed for studying the oxidative behavior of general asphalt materials.