Analysis Of The Diffusion Of Rejuvenator Into Asphalt Based On The Molecular Dynamice Simulation

With the improvement of Chinese highway network, a considerable number of asphalt pavements are about to reach its service life, and need to be repaired or even rebuilt. In order to follow the concept of sustainable development, the regeneration technology of asphalt pavement is booming. To some extent, the practical effect of the rejuvenator is mainly determined by the influence depth. So it is necessary and great significative to study the diffusion of the rejuvenator. Considering the limitations of the traditional test method, we use the molecular dynamics simulation method to study the diffusion process under normal temperature according to the service conditions of regeneration fog seal,First, the molecular dynamics model is constructed. Refer to the latest research results, 12 kinds of molecular are selected to represent the asphalt materials. And then calculate the number of molecules of different materials according to the four component test result of new asphalt, short-time aged asphalt, long-time aged asphalt and rejuvenator to construct the molecular model. On this basis, the force field parameters, potential energy function, boundary condition, temperature and pressure control condition, time step, and so on are determined. At last, the model is verified according to the calculated thermodynamic parameters and the image information. The results show that the stability of the system can be well explained by the existing asphalt colloid theory, asphalt material can be well characterized by this model.Secondly, the diffusion mechanism is analyzed. The diffusion between the long-term aged asphalt and the rejuvenator is simulated at the temperature of 25℃ after the system relaxation of both. On the one hand, from the aspect of energy exchange, the driving force and the resistance force of the diffusion process are analyzed. The results show that the Van der Waals force and electrostatic force is the promotion effect of the diffusion. The diffusion is spontaneous, and there is no obvious inhibitory. The diffusion process will end with the stability of the system. On the other hand, the molecular migration law is analyzed based on the diffusion coefficient which is calculated by the mean square displacement and the displacement probability distribution of the atom in diffusion direction. The results show that the diffusion process is mutually, while the rejuvenator molecules migrate into the asphalt, the asphalt molecules are also moving into the rejuvenator. The microstructure voids can be filled by each other’s molecules soon, and these molecules continue to move along the voids.Then the effect of temperature on diffusion is analyzed according to the simulation result. The results show that the rise of the temperature can reduce the dependence of the diffusion process on the molecular force. The reduction rate of the system Van der Waals potential and Coulomb potential decreased. But the diffusion coefficient calculation result and displacement distribution shows that with the rise of temperature, the molecular movement is more active. The diffusion coefficient of the rejuvenator and asphalt is increased in general. This also proves that the molecular heat movement is also a very important factor.The effect of aging degree on diffusion is analyzed according to the simulation result. The results show that the structure of asphalt has greater impact on energy exchanges within the system. For the Van der Waals potential, the short-time aged asphalt group drop fastest, and then the long-time aged asphalt group. And the reduction of the coulomb potential of the new asphalt group is most obvious. The other two groups are almost the same. The diffusion coefficient calculation result and displacement distribution shows that the rejuvenator moves fastest in long-time aged asphalt because of the porous structure. The diffusion of asphalt is influenced by its structure, the short-term aging asphalt moleculars move the fastest, followed by the long-term aging asphalt.At last the diffusion law of different compositions is analyzed. The results show that the molecular saturate A is most conducive to the diffusion, followed by saturate B and naphthene aromatics B, and the naphthene aromatics A is most unfavorable. It can be found that small molecule chain is easier to diffusion; in contrast, polycyclic body molecular is harder. Through analysis of diffusion coefficient of the asphalt components, summed up that the small molecular or chain with low aromatic content is favorable for diffusion.