In this reported work, thermoplastic polyurethane (TPU) was used as a reactive polymer modifying agent to prepare a modified-asphalt, using a high-speed shearing method. Physical performance tests of the TPU-modified asphalt were conducted before and after short-term aging, and the aging resistance was examined by the change in materials properties. In addition, low-temperature rheological properties, thermal properties, the high-temperature storage stability, and the aging mechanism of TPU-modified asphalt were also investigated. The results showed that the addition of TPU improved the aging resistance of base asphalt, which was evidenced by the increased penetration ratio and decreased softening point of the asphalt, after aging. Similarly, Fourier Transform infrared (FTIR) spectroscopy results verified that TPU improved the asphalt aging resistance. It was found that the TPU functional groups played a role in improving thermal properties, high-temperature storage stability, and in the dispersion of modified asphalt.

Nanoscale polyurethane emulsion which synthesized in previous work was used as polymer modifying agent herein to prepare modified asphalt by gentle agitation method. Rheological properties, storage stability, microstructure and polymer dispersibility of WPU-modified asphalt were investigated using dynamic shear rheological (DSR), segregation test, and fluorescence microscopy. Due to the reaction of active NCO groups in WPU and active hydrogen atoms in asphalt, the modified asphalt system can be stable stored at high temperature. In addition, the nano-particle size of polyurethane emulsion makes polymer uniformly dispersed in modified asphalt and work better.

In this paper, graphene oxide (GO) was synthesized by pressurized oxidation method and GO-modified asphalt was prepared by solution melting method. The structure and morphology of GO was characterized by Raman spectra, Fourier Transform infrared spectroscopy (FTIR) and transmission electron microscope (TEM), and the results showed that single-layer or few-layer large size GO was obtained. The chemical structure of the GO-modified asphalt and the SARA (saturates, aromatics, resins and asphaltenes) components were characterized by FTIR and thin-layer chromatography with flame ionization detector (TLC/FID). In addition, the effect of GO on the physical properties of base asphalt was also studied. The results showed that there was no chemical change in the modification process and that GO was physically dispersed in the asphalt. GO has little influence on the penetration, ductility, softening point and penetration index of asphalt, the adhesion and temperature stability of asphalt are not changed much. The addition of GO differs from the adsorption of light components by polymer-modified asphalt, but fundamentally hinders the thermal oxygen conversion between the components and improved the low-temperature crack resistance of modified asphalt.

To evaluate the effect of polymers and nanomaterials on asphalt after thermo-oxidative aging, the aging resistance of thermoplastic polyurethane modified asphalt (PU-MA), polyurethane/graphene oxide composite modified asphalt (PU/GO-MA) were discussed through experiments and molecular dynamics (MD) simulations. The molecular composition and self-healing ability of aged asphalt were investigated. Base asphalt and virgin asphalt were used as control. The aging experiments of base asphalt, PU-MA and asphalt modified with PU and different content of GO composites were carried out by rolling thin-film oven test. The differential scanning calorimeter, thermal gravimetric analyzer, viscous flow deformation, bending beam rheometer and Fourier transform infrared spectrometer tests were carried out. The molecules and cracks models of asphalt were simulated by MD. The parameters such as mean square displacement, fractional free volume, dipole moment and viscosity were calculated. The results show that PU/GO can affect the transformation among components, increase the melting temperature of asphalt, improve the migration ability of asphalt molecules, enhance the self-healing diffusion movement of asphalt molecules and reduce the energy and viscosity of aged asphalt. In brief, nano and chemical synergistic modification has effects on the properties of asphalt after aging.

In this study, the interface models and nanodroplets wetting models of base asphalt (BA), polyurethane modified asphalt (PU-MA) and polyurethane/graphene oxide composite modified asphalt (PU/GO-MA) with acidic and alkaline aggregates were constructed. The adhesion and debonding effects of modifiers on short-term aged asphalt mixtures were analyzed by molecular dynamics (MD) simulation. The moisture damage resistance of the mixture was evaluated by simulating the wetting characteristics of asphalt and water nanodroplets on the aggregate surface. The contact angle, adhesion work, debonding work and relative concentration distribution can effectively analyse the interface interaction behavior between asphalt and aggregate. The results show that the adsorption effect between aged asphalt and CaCO₃ was stronger, and short-term aging enhanced the interfacial adhesion of asphalt mixtures. Calcite was more hydrophilic, and its resistance to moisture damage was far less than quartz. The difference between the contact angle of water-aggregate and that of asphalt-aggregate can effectively analyze the water sensitivity of asphalt mixture. In addition, different components played different roles in the adsorption of asphalt and different aggregate surfaces. The synergistic analysis of the asphalt-aggregate interface and the asphalt nanodroplet-wetting aggregate surface can more comprehensively reveal the variation principle of asphalt parameters and nanoscale properties of asphalt mixtures.