Micromechanical Study On The Migration And Creep Characteristics Of Asphalt Mixture In Hot And Humid Environment

Shear failure is a common form of damage of asphalt pavement,especially in the hot and humid environment.It is difficult to precisely analyze its failure mechanism from traditional laboratory tests at the microscopic level.While the numerical simulation method can be used to study its failure development mechanism at the microscopic level.In this paper,the migration characteristics of asphalt mixture and the mechanical response of creep deformation are analyzed at the microscopic level by means of discrete element particle flow.Firstly,AC-13 asphalt mixture's laboratory test such as,Hamburg rutting test at different temperatures,humidity and loads,as well as the dynamic creep test at different temperatures and loads were conducted to obtain macroscopic test data such as the permanent deformation of asphalt mixture and provide a support for the discrete element modeling.Then,a two-dimensional discrete element virtual specimenwas constructed according to the digital image processing method and the virtual Hamburg rutting test was conducted.Test results showed that the rutting depth of the specimen increased with the increase of testing temperature,load and the humidity,and the deformation of specimen was the worst under the coupled action of humidity,high temperature and heavy load.The rutting depth of the specimen reached about 14 mm at the temperature of 60?,the load of 0.9MPa,and the loading times of 8000 under the immersed condition.The internal contact force of the specimen was mainly distributed uniformly below the loading wheel area and presented a"fan" shaped,while distributed non-uniformly in both sides area of the loading wheel.The displacement of both asphalt mortar and coarse aggregate presented a "V" shaped distribution,and the asphalt mortar particles migrated downward in the early stage of loading while migrated upward in the middle and late stage of loading.The porosity of specimen below the loading wheel area decreased under the action of load and gradually tended to be stable,while the porosity of specimens in both sides area of the loading wheel decreased previously and then increased under the action of load.Finally,the discrete element model was constructed by random particle generation of irregular aggregates,and the virtual dynamic creep test was carried out on it.Results showed that the axial strain of asphalt mixture increased continuously in the loading stage,while the deformation recovered in the unloading stage but not completely;the higher the temperature and load,the greater the axial strain.When the specimen was damaged,the phenomenon of internal stress concentration became obvious and the distribution of contact force chain was non-uniform,while the distribution of internal force chain was relatively uniform at the early stage of loading.In addition,the factors influencing the virtual test were explored and analyzed.It was indicated that,the larger the modulus of Burgers model,the smaller deformation of the specimen;the porosityand the shape of coarse aggregate had great influence on the deformation of asphalt mixture.