Study on the interfacial contact behavior of carbon nanotubes and asphalt binders and adhesion energy of modified asphalt on aggregate surface by using molecular dynamics simulation

In this work, a comprehensive study has been conducted on the interfacial contact behavior of carbon nanotubes (CNTs) and asphalt binders as well as the influence of multi-walled carbon nanotubes (MWCNTs) embedded into asphalt on the adhesion ability of asphalt on aggregate surface at atomic scale. CNT/asphalt composite and asphalt-aggregate interface models were investigated by molecular dynamics (MD) simulations to evaluate the molecular interactions of materials. The interfacial adhesion characteristics of functionalized single-walled carbon nanotubes (SWCNTs) and MWCNTs with asphalt binders were investigated by performing pull-out simulations and the interactions of SWCNTs and asphalt components were analyzed. The obtained results showed that asphalt components with low molecular weight were more easily adsorbed by SWCNTs than higher weight components. For CNTs/asphalt composite model, Van der Waals (VdW) energy is much higher than electrostatic energy accounting for a great portion of interaction energy. Although functional groups on the surface of CNTs can increase interfacial interaction, this increase is far less than the enhancement of interaction energy and interfacial shear stress between MWCNTs and asphalt binders. Therefore, MWCNTs are regarded as a better additive to be inserted into asphalt binders to enhance the interfacial adhesion of CNTs/asphalt composites. In addition, the results of adhesion energy change of asphalt-aggregate interface models indicated that MWCNT addition into asphalt significantly increased the adhesion ability of asphalt on aggregate surface (especially for alkaline aggregates).