Molecular-based asphalt oxidation reaction mechanism and aging resistance optimization strategies based on quantum chemistry

Understanding the oxidation reaction mechanism of asphalt is critical to improving its aging resistance. Here, quantum chemistry (QC) was used to study the oxidation reaction mechanism of 12 typical asphalt molecules. On this basis, the molecular models of aged asphalt were established, and the aging resistance optimization strategies of asphalt were proposed. The results show that the oxidation sites for oxygen-containing or heteroatoms-free molecules are on aromatic carbons (I molecules). Reducing hydrogen and hydroxyl radicals can improve its aging resistance. The oxidation sites for sulfur- or nitrogen-containing molecules are on heteroatoms (II molecules). Reducing oxygen free radicals content can improve its aging resistance. The molecules containing sulfur and cata-condensed polycyclic aromatic hydrocarbons (PAHs) (such as R5) have the strongest oxidation reactivity. Reducing its content can improve asphalt aging resistance. Combining the QC and experiment results, LH90 contains more I molecules, while UP70 and MM70 contain more II molecules (especially As3 and R5). The aging resistance of UP70 and MM70 is poor than LH90. Reducing the content of As3 or R5 molecules or the content of oxygen radicals can improve the aging resistance of UP70 and MM70. These findings lay a foundation for designing and preparing asphalt with excellent aging resistance. (c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

Understanding the oxidation reaction mechanism of asphalt is crucial for improving its aging resistance. In this study, quantum chemistry was used to investigate the oxidation reaction mechanism of 12 typical asphalt molecules and establish molecular models of aged asphalt. Based on these findings, optimization strategies for improving the aging resistance of asphalt were proposed. The results showed that the oxidation sites for oxygen-containing or heteroatoms-free molecules were on aromatic carbons, while for sulfur- or nitrogen-containing molecules, the oxidation sites were located on the heteroatoms. Reducing the content of hydrogen, hydroxyl radicals, or oxygen free radicals can effectively enhance the aging resistance of asphalt. Additionally, it was found that molecules containing sulfur and cata-condensed polycyclic aromatic hydrocarbons exhibited the highest oxidation reactivity. By combining the quantum chemistry analysis with experimental results, it was observed that the content of I molecules was higher in LH90, while UP70 and MM70 contained more II molecules (particularly As3 and R5). As a result, UP70 and MM70 showed poorer aging resistance compared to LH90. The aging resistance of UP70 and MM70 can be improved by reducing the content of As3 or R5 molecules or the content of oxygen radicals. These findings are significant for the design and preparation of asphalt with excellent aging resistance.