Study On Rubber Modified Asphalt Based On Molecular Simulation Technology

The waste tire rubber asphalt is highly concerned by the road construction industry because of its good temperature resistance,fatigue resistance and skid resistance,road noise reduction,low construction cost and environmental advantages of waste recycling.In recent years,with the development of solid state physics,quantum chemistry,statistical mechanics,computational methods and other related disciplines,as well as the unprecedented improvement of computer data processing ability,computer material design has become possible.This provides a more powerful means for us to understand and study the internal structure and nature of matter.A scientific,reasonable and reliable numerical simulation model can not only analyze the micro behavior of crumb rubber modified asphalt,but also reduce the research burden.Therefore,the research on rubber modified asphalt based on molecular simulation technology is of great significance for exploring the mechanism of rubber powder modification and evaluating the performance of rubber powder modification.Based on the four components of asphalt,according to the relevant test data,this paper uses materials studio 2017 software to build the molecular model of rubber modified asphalt,and verifies the accuracy of the model and boundary conditions,and studies the physical properties of the model through the method of molecular dynamics:(1)First of all,after geometric optimization and energy minimization of the Tahe AH-90# asphalt molecular model,the molecular dynamics simulation is carried out under different force field summation methods,and the change curve of model density with temperature is obtained.Compared with the actual asphalt test data,the Compass II force field can obtain more accurate results,and the results obtained by Atom based summation method are less discrete.The accuracy of the model and the selected simulation conditions are verified from the aspects of system energy,density,cohesive energy density and solubility parameters.The results show that the model can represent the real asphalt material and the selected simulation conditions are also reliable.Comparing the density,bulk modulus and Young’s modulus of three kinds of asphalt molecular models,we can get that Xi’an 90# asphalt > Tahe AH-90# asphalt > Karamay90# asphalt,with the increase of temperature,the three physical indexes of the model show the law of decreasing,the glass transition temperature of the three kinds of asphalt molecular models belongs to the temperature range of 0℃ ~ 20℃.(2)In this paper,NBR1,NBR2,NBR3,NBR4,NBR5,NBR6 were constructed by using SBR as the representative molecule of synthetic rubber.The density of the rubber was between 0.91g/cm3 and 0.93g/cm3.The molecular potential energy of NBR6 is higher than that of other rubbers,and the non bond energy and density change with time shows that the intermolecular force in NBR6 is also strong,which makes the NBR6 system more stable and difficult to degrade.(3)A molecular model of rubber modified asphalt was constructed by NBR1 ~ NBR6 with Tahe AH-90 asphalt,Xi’an 90 asphalt and Karamay 90 asphalt respectively.According to solubility analysis,NBR1 was the best rubber compatible with Tahe AH-90 asphalt;NBR3 was the best rubber compatible with Xi’an 90 asphalt;NBR6 was the best rubber compatible with Karamay 90 asphalt.At 160℃,NBR1 and Tahe AH-90 asphalt have the best compatibility.At 180℃,NBR3 and Xi’an 90 asphalt and NBR6 and Karamay 90 asphalt have the best compatibility.From the perspective of molecular potential energy,the same conclusion is still obtained.(4)Three kinds of rubber modified asphalt with the best compatibility were selected to control the content of rubber powder(5%,10%,15%,20%,25%,30%,35%).From the perspective of mechanical properties,the dynamic analysis of modified asphalt models with different rubber content was carried out.It was found that the mechanical properties of matrix asphalt were improved by adding rubber.When the rubber content was 20%,the mechanical properties of modified asphalt were the best.(5)By fitting the MSD data of Tahe AH-90 asphalt and six kinds of rubber modified asphalt,the diffusion coefficient of asphalt at different temperatures was calculated.In the range of 60 ~ 100 ℃,the kinetic energy of heat energy conversion overcomes the intermolecular force,thus the increase of diffusion coefficient is intensified.NBR1 is more active in the modified asphalt,and its absorption of light components is more intense,which indicates that NBR1 can react with asphalt more quickly.(6)The diffusion coefficient of oxygen in asphalt system with 1% oxygen content was analyzed.It was found that with the increase of temperature,the diffusion coefficient of oxygen in asphalt system increased gradually.The addition of rubber powder can significantly reduce the diffusion of oxygen,thus improving the thermal oxygen aging resistance of asphalt,and the modification effect of NBR1 is better.With the increase of water content,the diffusion coefficient and the interaction energy between water and asphalt increase.When the water content reaches 2.5%,the diffusion coefficient tends to balance.The addition of rubber can significantly reduce the diffusion of water molecules in asphalt and the interaction between water molecules and asphalt molecules,so as to improve the water resistance of asphalt and reduce the damage of water to asphalt.