## 7 Discussion and Conclusions  
The MD model of multi-layer graphite xGNP nanoplatelets was created and used for the investigation of the effect of modification on the control asphalt binder model. The control asphalt binder model was composed of three components: asphaltenes, aromatics, and saturates at a certain ratio. The xGNP modified asphalt binder model was generated from the addition of the xGNP model in the control asphalt binder model. The conjugate gradient method and PPPM were used for energy optimization, and the Savitzky-Golay filter was used to smooth data. The Amber Cornell Extension Force Field and ESP charge were used in these asphalt models, and the physical properties of the MD binder models were calculated including density, the glass transition temperature, viscosity, and thermal conductivity. The following conclusions may be made. (1) The densities of these asphalt binder models were computed, and the addition of the multi-layer xGNP model increased the density of the xGNP modified binder model compared to that of the control binder model. The molecular number in MD systems significantly affects the data variation for density calculation. The density of MD asphalt binder systems decreases with the increase in temperatures. (2) The glass transition temperature of the xGNP modified asphalt binder model is around 250 K, and it is better than the results of the reference, 298 K-358 K [18]. This glass transition temperature is better than previous results (around 300 K [24]) for the control asphalt binder model, because it is the same as the glass transition temperature of SHRP asphalt binders, around 250 K, from laboratory results [42]. (3) The Muller-Plathe method was used to calculate the viscosity of the control and xGNP modified asphalt binder models. The 20 layers in the MD asphalt models were separated for this calculation. The addition of xGNP particles in the control asphalt binder matrix improves viscosities of the modified asphalt at different temperatures, and the same effect of multi-layer xGNP models in the control asphalt binder model was observed. Compared to the experimental viscosities of the xGNP modified asphalt binder, the viscosities of the MD simulation is close to the experimental results at the temperatures of 403 K, 423 K, and 443 K. The relationship between viscosities and temperatures in the data of the MD simulations is also the same as that of the laboratory results. (4) The experimental data shows that the xGNP particles in the control asphalt binder increase the thermal conductivity of the modified binder at room temperature. During the calculation of thermal conductivity, the Muller-Plathe method was used in these MD simulations, and the multi-layer xGNP  
Figure 11: Thermal conductivity results of MD simulations. model in the control binder model also improves the thermal conductivity of the control binder model at room temperature. The thermal conductivities of the control and xGNP modified asphalt binders increase with increasing temperatures, and the same trend is observed in the data of MD simulations. Therefore, the multi-layer xGNP graphite particles in the asphalt binder can improve viscosity and thermal conductivity of the asphalt binder, and the xGNP model in the control asphalt binder model can also enhance the density, glass transition temperature, viscosity and thermal conductivity of the control binder model. It is obvious that the same trend of experimental data and MD results is observed during the testing and MD calculations of different properties of asphalt. It is likely that the xGNP particles can be utilized and generalized for pavement construction and heat sinks.