Molecular Dynamics Simulation Of Fusion Behavior Of Virgin And Aged Asphalt And Its Adhesion To Aggregate

With the development of asphalt recycling technology,the research of using all kinds of recycled light waste oil to produce regenerant is emerging one after another.In the actual geothermal regeneration project,on the one hand,promoting the integration of virgin and aged asphalt is the key strategy to improve the performance of recycled asphalt mixture.On the other hand,the interface between recycled asphalt and aggregate is prone to defects and affect the overall service life.As a common disease type of Asphalt Pavement,water damage is due to the peeling of asphalt at the interface,and the interface phase is often difficult to capture and observe.Therefore,through molecular dynamics simulation,this paper explores the diffusion and fusion behavior of old and new asphalt,the adhesion behavior with aggregate after fusion,and the damage behavior of hydrodynamic pressure on interface adhesion under geothermal regeneration.Firstly,the chemical composition of raw materials was analyzed by infrared spectrum,thin layer chromatography and X-ray diffraction test.According to the deterioration process of light oil,the molecular models of virgin and aged asphalt,traditional regenerant,three waste oil regenerants and basalt aggregate were established and assembled by Monte Carlo method.The density,molecular order,glass transition temperature and compression ratio of the assembled raw material model were calculated to verify the rationality of the model,which could be effectively used in subsequent research.Secondly,in order to explore the diffusion and fusion behavior of virgin and aged asphalt,a double-layer diffusion model of virgin asphalt-aged asphalt（including regenerant）with vacuum layer on the top was established,molecular dynamics simulation was carried out,the influence of different regenerant molecules on the stacking morphology of oxidized asphaltene molecules was quantitatively evaluated,and the diffusion speed and fusion degree of virgin and aged asphalt were evaluated by mean square displacement and relative concentration,The solubility parameters and free volume fraction of aged asphalt were calculated to explore the driving mechanism of waste oil promoting asphalt diffusion and fusion.The results show that waste oil can improve the diffusion rate of asphalt molecules by increasing the free volume fraction of aged asphalt,reduce the difference of solubility parameters of virgin and aged asphalt and promote the integration of them;Waste cooking oil can greatly improve the diffusion rate of vigin and aged asphalt molecules,but the compatibility between fat molecules and asphalt was poor.After the addition of waste engine oil,the number of virgin and aged asphalt molecules involved in the fusion was the most;Compared with the CIS molecular chain in waste cooking oil and the single benzene ring molecule in traditional regenerant,the trans molecular chain in waste dry vegetable oil and the conjugated aromatic ring molecule in waste engine oil can more effectively eliminate the asphaltene aggregation in old asphalt.Then,in order to systematically describe the molecular behavior of the interface formed by the bonding between recycled asphalt and basalt,the interface contact model between different recycled asphalt and the main oxides in basalt was established.According to the proportion of each oxide in basalt,the parameters characterizing the interface between recycled asphalt and basalt aggregate were weighted,including asphalt cohesion energy,asphalt basalt interface adhesion energy and four component distribution of asphalt on the surface of basalt.The results show that the distribution of light components on the surface of basalt was greater at low temperature,and the distribution of asphaltene and colloid was greater at high temperature;The adhesion between Si O₂ and asphalt in basalt was less affected by temperature,which was the main source of adhesion energy of asphalt aggregate interface at low temperature;Long term aging will make the cohesion of asphalt become stronger,which is not conducive to the adhesion between asphalt and aggregate.The addition of waste oil can improve the deterioration of adhesion energy caused by aging;Among the four kinds of recycled asphalt,the adhesion energy between waste cooking oil recycled asphalt and basalt was the largest at room temperature and high temperature,and the adhesion energy between waste oil recycled asphalt and basalt was the largest at low temperature.Finally,in order to analyze the change law of dynamic water on the molecular behavior of the interface system,the interface contact model between recycled asphalt and the main oxides in basalt under different dynamic water pressure was established to study the thermodynamic process of water intrusion into asphalt mixture.The adhesion behavior of the interface was studied by analyzing the cohesion energy of asphalt,the adhesion energy of asphalt aggregate interface and the distribution of asphalt and water concentration on the aggregate surface.The results show that the dynamic water pressure can promote the water to enter the asphalt,and the hydrophobic aromatic ring structure in the waste oil will promote the water in the recycled asphalt to enter the asphalt aggregate interface;After the water film is formed at the interface,the whole recycled asphalt was pushed away from the basalt surface,and the four components of asphalt leave the interface at different rates.Under the same hydrodynamic pressure,more light components were lost at low temperature.With the increase of temperature,asphaltene and colloid on the aggregate surface are lost rapidly,resulting in the overall stripping of the aggregate surface;Compared with the other two kinds of waste oil recycled asphalt and traditional recycled asphalt,the water damage resistance of waste engine oil recycled asphalt aggregate interface was better.Under the coupling action of high temperature and 0.5MPa hydrodynamic pressure,the decrease of interface adhesion energy is only-55.7%.