Molecular Dynamics Simulation And Rheological Properties Of Graphene Modified Asphalt Binders

Road infrastructure,especially the intelligent road system,is of great and far-reaching significance for improving the service level of road infrastructure and accelerating the construction and development of transportation power,which is the main direction of transportation development.Pavement is the most basic component of road system,the intelligent pavement material is of great significance.And the idea of self diagnosis,self repair and even electric vehicles charging while walking has been put forward for a long time,but the current research is still few.The key to these intelligentization is to enable existing pavement materials to exhibit electrical or magnetic properties beyond mechanical properties.Recently,low cost,high quality graphene can be prepared using flash Joule heating,thus making it possible to apply graphene modified asphalt（GMAs）on a large scale.According to the percolation theory,when the content of graphene exceeds the percolation threshold,GMAs will have electrical conductivity,which can realize the intelligent asphalt pavement.However,the existing research on GMAs has not involved the percolation threshold and rheological properties after that.Therefore,based on the percolation theory,this paper explores the percolation threshold and rheological properties of GMAs from the perspective of mechanical transformation,and obtains the following results:Molecular dynamics simulation was carried out on all asphalt samples to fit their glass transition temperature.It was found that the glass transition temperature of asphalt increased with the increase of graphene content.According to the simulation results and percolation theory,this paper speculates that when the content of graphene exceeds 6%,the percolation network will be formed in GMAs,and the system will have conductivity.In order to explore the percolation phenomenon,the experiments of rheological properties were designed.According to the simulation results,in this paper,control asphalt and high content GMAs with 2%,4%,6%,8%and 10%graphene were prepared.The strain sweeps and temperature sweeps of all samples were carried out by dynamic shear rheometer（temperature range-30^oC-120^oC）.The results show that with the increase of graphene content,the complex modulus of all samples increases,while the phase angle and damping factor decrease,illustrating that elasticity at above ambient temperatures and rutting resistance at higher temperatures are enhanced after adding graphene.It is worth noting that the complex modulus and storage modulus curve characteristics when the temperature exceeds 100^oC,the corresponding temperature when the phase angle is 90°and the temperature at the storage modulus is equal to the loss modulus(T_G’=G’’)of the change trend with graphene content are simultaneously confirmed,when graphene content exceeds 8%,the percolation of GMAs occurs.Obviously,the modification mechanisms are different before and after percolation threshold.Before the percolation threshold,graphene which has a molecular structure similar to asphaltene enhances asphalt to some extent like increasing asphaltene to the asphalt,and after percolation threshold,graphene improves asphalt because of formed graphene networks.The rotational viscosity test was carried out on all asphalt samples,and the viscosity temperature curves of asphalt were fitted.The mixing temperature and compaction temperature of asphalt were deduced by Arrhenius equation.The results show that the viscosity of GMAs increases with the increase of graphene content.The higher the graphene content is,the higher the working temperature is.When the content of graphene is more than4%,the working temperature is higher than 200^oC,which means that the working performance of GMAs needs to be further improved.