Multiscale Enhancement Mechanism of Carbon Nanotube-Modified Asphalt at High Temperature by Oxidative Aging: A Molecular Dynamics Simulation Investigation

The objective of this study was to investigate the multiscale mechanism of oxidative aging on the high-temperature performance enhancement of carbon nanotube (CNT)-modified asphalt. Molecular dynamics simulations, atomic force microscopy, scanning electron microscopy, and dynamic shear rheometer were used to investigate the phenomena at different scales and ultimately to explain the mechanism of enhanced high-temperature properties. The results show that oxidative aging destroys the colloidal structure of the asphalt and makes the system more compact and active and causes aggregation of asphaltenes, which not only changes the bee-like structure but also enhances the rheological properties of the asphalt. Moreover, CNTs enhance the aging resistance of the asphalt binder due to the pullout properties of CNTs, which strengthens the asphalt interface and impedes the formation of a network structure by the penetration of oxygen atoms. In addition, CNTs and aromatics are most compatible, which makes the CNT-modified asphalt a three-phase composite with the CNT network as the reinforcing phase, the aromatic as the interfacial phase, and the asphalt binder as the matrix phase, which promotes enhanced resistance to deformation. In conclusion, this study provides basic theoretical insights to understand the aging resistance, rheological behavior, and microstructure formation of CNT-modified asphalt.