Microscopic Analysis Of Asphalt Mixture Uniaxial Penetration Test Based On Discrete Element Method

Rutting has been an important factor affecting the service level of asphalt pavement,and it is also one of the main diseases that restrict the service life of asphalt pavement,which is closely related to the shear performance of asphalt mixture.There are a lot of research on the shear performance of asphalt mixture,and the aggregate characteristic of mesoscopic research,but there is no comprehensive macro morphology and microstructure characteristics and shear performance of comprehensive research.Therefore,this study combined with the indoor rutting test,test shear strength of the specimens in different depth,then combined with digital image processing technology and the discrete element methods to refactoring two-dimensional model and simulate uniaxial penetration test.Mesoscopic mechanics characteristics and coarse aggregate space movement characteristics would be analyzed in order to reveal the rut formation mechanism of asphalt mixture develop new ideas,which have certain theory value and application prospect.Based on the comprehensive analysis of domestic composite structure of semi-rigid base surface,the SMA-13 and AC-20 combination was determined.Shear strength of different rut depth under different working conditions were tested through the uniaxial penetration test.Results showed that the shear strength of the rut rised with the depth of rutting under three working conditions,while the bump contact gradually decreases.Under the same rut depth,the shear strength of pavement under standard condition was higher than that of high temperature and overloading condition,which indicated that high temperature and overloading have weakened the shear strength.Besides,the percentage change under high temperature condition was the greatest,which showed that high temperature was the main reason for the shear strength weakening.The ratio of shear strength in bump contact and shear strength in rut was used to characterize actual capacity of the road.The ratio decreases with the rutting depth.The function fitting between the ratio and rutting depth was approximately linear.This declared shear strength of rutting area was nonuniform.The more unstable the pavement structure,the lower actual bearing capacity.Based on discrete element method,using the image of asphalt mixture specimen to reconstruct two-dimensional uniaxial penetration test pieces,then simulate uniaxial penetration experiment.Results showed that virtual experiment curves between deformation and shear stress was along with the laboratory test results,which verified the validity of the simulation.Internal state of mesoscopic mechanics of asphalt mixture were analyzed,and found that the tension and compression stress distribution,coarse aggregate and its morphological characteristics,performance of asphalt and aggregate adhesion performance are the influence factors of shear performance of asphalt mixture.Research on asphalt mixture inside the coarse aggregate morphology and trajectory showed that as the rut deformation degree deepening,coarse particle axis direction intended to 90°,and the main shaft direction Angle standard deviation decreases,coarse particle direction Angle difference is becoming more and more small,coarse particle state steady,the rut area was compacted.The comparison before and after the uniaxial penetration test proved that displacement of top layer and following layer in the X and Y direction presented different change.The top layer particles produce vertical displacement,and the following layer particles mainly produced transverse displacement.The coarse particle displacement angle before and after virtual experiment were compared.Compact degree of rut area improved with the increase of rut deformation degree,As a result,the displacement angle of coarse particles under load gradually decreases,and the internal structure tends to stabilize,resulting in an increase of shear strength at the groove area.Spindle direction angle standard deviation of top layer was selected to characterize mesoscopic parameters.Function fitting showed that the mesoscopic characteristic parameters,the rutting depth and deviation ratio set up specific function relationship between each other.