| The interaction between modifier and asphalt has a great influence on the performance of polymer modified asphalt,and polymer modified asphalt has very obvious thixotropic characteristics related to fatigue failure.Nowadays,there is a lack of quantitative explanation on the microscopic mechanism of thixotropy of asphalt materials.In this study,SBS/rubber composite modified asphalt was taken as the research object,rheological test and molecular dynamics simulation were used to study the microscopic interaction behavior and microscopic mechanism of thixotropy of polymer modifier asphalt.The main research contents and results are as follows.(1)The asphalt molecular model(four-component,twelve molecular),the SBS(styrene butadiene styrene,SBS)molecular model,the SBR(styrene butadiene rubber,SBR)molecular model and the SBS/SBR/asphalt blending system molecular model were constructed by Material Studio.The models were optimized by geometry optimization,annealing treatment and molecular dynamics optimization to provides reliable model for the follow molecular dynamics simulation.(2)The molecular dynamics simulations of the models were carried out at 100 ℃,120℃,140 ℃,160 ℃ and 180 ℃ by LAMMPS(Large-scale Atomic/Molecular Massively Parallel Simulator,LAMMPS).The solubility parameters and intermolecular interactions energy were used as indexes to evaluate the compatibility between modifiers and asphalt.The results show that the compatibility between SBS and asphalt is good at 140 ℃,and the compatibility between SBR and asphalt is good at 160 ℃.When SBS,SBR and asphalt are blended,due to the interference of polymerization modifiers,the interaction energy of SBS-asphalt and SBR-asphalt is higher and the compatibility of the blend system is better at 140 ℃.The above results were verified by segregation test.(3)The radial distribution function and rotation radius of SBS/SBR/asphalt system with different content were calculated,and the agglomeration and adsorption behavior of polymer modifier to asphalt were analyzed.The results show that the addition of polymer modifier aggravates the accumulation of asphaltene and increases the densification degree of the whole molecular system,and the extensibility of the branched chain of each component of asphalt is enhanced,which makes it easier for each component to wrap around the molecule.In addition,SBS/SBR modifier can adsorb the aromatic and saturated components in asphalt,and the agglomeration and adsorption are gradually intensified with the increase of modifier content.The dynamic oscillation test results show that the phase angle decreases and the elasticity increases with the increase of modifier content,which further confirms the aggravation of agglomeration and adsorption behavior.(4)DSR(Dynamic Shear Rheometer,DSR)and LAMMPS were used to carry out variable shear viscosity test and simulation,hysteresis loop test and simulation of composite modified asphalt.And the shear simulation were carried out by NEMD(Non-Equilibrium Molecular Dynamic,NEMD)metthod.Results of experiments and simulations show that: In the stage of low shear rate,the viscosity increases briefly with the increase of shear rate,and when the shear rate further increases,the viscosity shows the characteristic of shear thinning,and when the shear rate is too high,the viscosity tends to be lower.In the increase and decrease cycle of shear rate,the shear stress increases gradually and then decreases gradually to form a hysteresis loop.Due to thixotropy,the internal structure of the material is resistant to shear,which leads to the temporary increase of viscosity and hysteresis loop phenomenon.(5)In order to describe the microscopic state of thixotropy,the intermolecular interaction energy and radial distribution function in the shear process were calculated.The results show that: In the stage of low shear rate,with the increase of shear rate,the damage of shear to intermolecular interaction and intercomponent agglomeration adsorption behavior is lower,and the recovery of internal structure has a certain resistance to shear failure.With the further increase of the shear rate,the shear action causes great damage to the intermolecular interaction behavior and the intercomponent agglomeration adsorption behavior,and the resistance of the internal structure restoration to the shear failure weakens.When the shear rate is too large,the shear almost destroys the intermolecular interaction behavior and the intercomponent agglomeration adsorption behavior,and the restoration of the internal structure can hardly resist the shear failure... |
