Study On Rubber Asphalt Compatibility Based On Molecular Dynamics

The reaction between rubber and asphalt is mainly characterized by similar compatibility,and the advantages and disadvantages of compatibility have a significant effect on asphalt modification.Tests on macroscopic scales are unable to interpret the compatibility mechanism between rubber and asphalt and analyze the factors affecting compatibility accurately.Therefore,molecular dynamic is introduced to study the compatibility between rubber and asphalt by using Material Studio 2019.The influence of Rubber type,rubber dosage and compatibility reaction temperature on compatibility of rubber and asphalt is analyzed,and combined with macroscopic tests,the compatibility mechanism is interpreted on molecular level.The research content is as follows:First,combined with rubber asphalt needle penetration,ductility,softening point,180℃rotary viscosity and softening point difference,the basic performance of two different types of rubber asphalt was analyzed.The optimal rubber dosage was determined at about 20%.The optimum compatible reaction temperature was around 180℃.And through the test results,it was found that the compatibility of desulfurized rubber and asphalt was significantly enhanced.The desulfurized rubber asphalt was better in performance index,and the viscosity was significantly reduced.Secondly,the compatible molecular models were established by Material Studio 2019 to carry out the molecular dynamic simulation of ordinary rubber and matrix asphalt and desulfurized rubber and matrix asphalt.By calculating the difference between the solubility parameters and interaction energy,the compatibility indexes of two types of rubber and matrix asphalt were discovered performing better at 20%dosage and 453K(180℃).Under this condition,the difference between the solubility parameter was the smallest,and the compatible effect was the best.At the same time,the values of difference of solubility parameters between the desulfurized rubber and the asphalt were reduced by 60%to 78%,which showed that the compatibility of desulfurized asphalt was better than that of ordinary rubber asphalt.At the same time,the interaction energy between ordinary rubber asphalt and desulfurized rubber asphalt molecules can be elevated at the crest value at 453K(180℃),and there was a optimum dosage of 20%.Under this condition,the molecular movement was severe.And the two molecules were sufficiently compatible with the strong inter-molecular interaction.The interaction energy between the desulfurized rubber asphalt can be increased by about 50%to 75%,indicating that compared to that of ordinary rubber asphalt,the structure of the desulfurized rubber asphalt molecule was more stable.By comparing the two rubber asphalt simulation results,the desulfurized rubber bitumen produced a different amount of small molecules during compatible process.Nevertheless,in the compatible process of desulfurized rubber with the asphalt,there was no large number of small molecules,which indicates that the desulfurized rubber was more compatible with the asphalt,and conducted to the better molecular integrity.Thus,the performance of desulfurized rubber asphalt was better and more stable.Finally,through the calculation of specific surface area,it was found that the specific surface area of desulfurized rubber was larger,so the porosity was higher,which is more conducive to the compatibility of rubber and asphalt.The results of scanning electron microscopy and infrared spectroscopy showed that the desulfurized rubber was more soluble in asphalt,which was consistent with the results of molecular dynamics simulation.At the same time,it was found that the crosslinking bonds of the grid structure of the desulfurized rubber were destroyed during the desulfurizing process,which resulted in the formation of some oxygen-containing functional groups and polar groups on the surface of the rubber powder.These functional groups can react with alkanes,olefin and aromatic hydrocarbons in asphalt to enhance the compatibility of desulfurized rubber and asphalt.What’s more,in the process of preparing modified asphalt,high temperature and high speed shear environment resulted in the part of the active functional group in the desulphurizing powder material exchange with matrix asphalt matrix in full,with a large number of chemical reaction.The crosslinking structure formed by the system was more stable,making the compatible stability of desulfurizing rubber modified asphalt improved.