The aging mechanism of asphalt aromatics based on density functional theory, Frontier Orbitals, IR, SARA, and GPC

Abstract

To investigate the effect of ·OH radicals on asphalt Aromatics aging, density functional theory was utilized to calculate the Gibbs free energy, reaction energy barrier, and temperature associated with asphalt aromatic decomposition, thermal oxygen aging, and UV aging. To study chemical structural activity, Frontier Orbitals theory and Fukui Functions were employed to determine Frontier Molecular Orbitals and Fukui Index. The findings reveal that the activity of aromatic compounds is primarily concentrated near the naphthalene ring, which is prone to etherification reactions. The alkyl activity of aromatic compounds is quite low, rendering them less susceptible to nucleophilic, electrophilic, and radicals' reactions. One reason for thermal oxygen aging of asphalt is the direct interaction between asphalt molecules and O2. On the other hand, UV aging occurs due to the splitting of O2 into ·O radicals, which in turn generate ·OH radicals which can oxidize asphalt. The results of quantum chemical calculations were cross-validated by infrared spectroscopy IR, SARA, and GPC methods. IR spectroscopy analysis showed that thermal and ultraviolet aging would increase carbonyl and benzene derivatives in aromatic compounds, while thermal aging would not increase hydroxyl groups. SARA further confirmed that asphalt aging would enhance molecular polarity. GPC confirmed that The molecular weight of asphalt aromatic components increases after aging. This article provides useful experience for using quantum chemistry to study the mechanism of asphalt aging.