Study On Mechanical Properties Of Road Aggregate Based On Discrete Element Method

Aggregate is an important part of pavement materials such as asphalt mixture.The fine gradation of aggregate and the action of impaction and friction between particles have significant influence on the bearing capacity and stability of the flexible pavement structure.However,because the aggregate is a discrete structure and has nonlinear mechanical characteristics,the traditional mechanical test and calculation methods based on the continuum mechanics theory are difficult to describe the influence of gradation change and morphology change on the mechanical properties of the aggregate.Numerical model based on discrete element method to establish the aggregate,virtual uniaxial penetration test,triaxial compression test and triaxial shear test,the test is not different gradation composition and different morphological characteristics of aggregate on the bearing capacity and deformation characteristics of loads,based on the analysis of aggregate material in mesoscopic mechanics response of the loads and the structure characteristics of change,from the mesoscopic level research on the aggregate gradation composition,morphology of macro mechanical properties of the influence of the relationship,and explores the aggregate level matching relationship between the road performance of asphalt pavement,provide a reference for asphalt mixture design.It mainly includes the following aspects:(1)Linear contact model was used to establish a numerical model of aggregate and conduct a virtual triaxial compression test.By analyzing the macroscopic mechanical response of samples under different microscopic parameters,the relationship between microscopic parameters and macroscopic parameters was established.(2)Seven groups of different gradation composition design,generate reflect the characteristics of virtual real graded aggregate sample,virtual uniaxial penetration test and the triaxial compression test bearing capacity and deformation characteristics of aggregate,and through the extraction in the process of penetration test specimen of the distribution and change of contact force and displacement distribution and change,the ball field coordination number and other information to establish a mesoscopic structure and macroscopic mechanical properties of aggregate,gradation composition on the mechanical properties of aggregate is studied the influence of the relationship.The results show that the median gradation of AC-20 has a higher bearing capacity and resistance to deformation than that of SAC-25 with a pass rate of 4.75 mm of 35%.The bearing capacity of SAC-25 with a pass rate of 4.75 mm of 40% is poor,and that of SAC-25 with a pass rate of 4.75 mm of 30% is poor.(3)The indoor Marshall test,rut test and split test of asphalt mixture were carried out for different gradation aggregates to study the influence of gradation composition on road performance of asphalt mixture.The results show that the CBR value of AC series graded aggregate is the same as the Marshall stability and rutting stability of asphalt mixture,and the bearing capacity of aggregate has a certain influence on the bearing capacity of asphalt mixture.The average penetration displacement of SAC series gradation aggregate is the same as the rut deformation of asphalt mixture.The bearing capacity of aggregate has no significant influence on the tensile strength of asphalt mixture.(4)Based on the three dimensional geometry,the aggregate particles reflecting the three dimensional shape characteristics were constructed,and with ellipsoid,hexahedron,acicular,flaky particles to describe 3 d shape characteristics of coarse aggregate,with tetrahedral,pentahedron,hexahedron describe the edges and corners of aggregate particles,cluster particles surface friction coefficient which is used to describe texture characteristics of aggregate,the virtual triaxial shear test,uniaxial penetration test and triaxial compression test,analysis of particle morphology on the mechanical behavior of aggregate impact.The results show that the cubic aggregate has the best shear resistance and bearing capacity,while the spherical particles have poor shear resistance and bearing capacity.The shear resistance and bearing capacity of rough and broken gravel aggregate are better than that of smooth and nearly spherical gravel aggregate.The discrete element simulation test accurately reproduces the whole process of the laboratory test,realizes the observation of the internal micromechanical response and structural characteristic change of the aggregate,and to some extent explains the micromechanical mechanism of the aggregate under the action of load and the internal mechanism of permanent deformation.