Study On Numerical Simulation Of Asphalt Mixture Based On X-ray CT And Discrete Element Method

During the operation of asphalt pavements in China,early damage is very common,and diseases such as cracking and rutting are particularly serious.To this end,the researchers have carried out a lot of research,but most of them focus on macroscopic experiments,which is not only time-consuming and laborious,but also unable to deeply explore the mechanical mechanism inside the mixture.At the same time,the asphalt mixture is a multi-phase composite system,and its mechanical properties are complex.The macroscopic experiments assume that it is a homogeneous material and thus has limitations.In recent years,the discrete element method has gradually been introduced into the field of road research.In order to make up for the shortcomings of macroscopic experiments and deepen the understanding of the mixture from a mesoscopic perspective,this paper uses the discrete element method combined with X-ray CT tomography and digital image processing technology to conduct preliminary exploration from 3D aggregate model to mixture virtual experiment,and it is expected to provide some reference for future research.Firstly,the cross-sectional image is obtained by X-ray CT scanning aggregate,and the image is processed to obtain the coordinate data of the contour surface of the aggregate.Based on the coordinate data,the basic parameters characterizing the morphological characteristics of the aggregate are calculated,and a more effective evaluation method of the aggregate needle shape is established.The angular texture features of the aggregate are described by the angular-texture feature values.Finally,the aggregate is subjected to three-dimensional virtual screening by coordinate transformation and minimum circumscribed rectangle method.Secondly,based on the coordinate data,the three-dimensional discrete element models of aggregate and aggregate skeleton are generated in PFC^3D,and the influence of each relevant parameter on the generation result and operation efficiency is studied.The evaluation index of the force characteristics of the skeleton structure is established,and the virtual loading test is used to study the internal force characteristics of the aggregate skeleton structure and the mechanical properties such as resistance load,stress transmission and stress diffusion et al.Then,based on the relevant parameters,calculating the volume of each file of coarse aggregate.By generating the various aggregates one by one and the regularly arranged balls in the model space,and judging the relative position of the aggregates and the small balls,the coarse aggregate phase and the asphalt mortar phase composed of small balls is generated,and its density is adjusted.Then,the void distribution of the actual test piece is combined to generate a void phase,thereby constructing a three-dimensional discrete element virtual test piece of the asphalt mixture;the appropriate contact model is selected,and the mesoscopic contact parameters are obtained through the indoor uniaxial static load creep test and the split test,combined with the conversion relationship between the macroscopic parameters and the mesoscopic parameters.Finally,the virtual bending test of the mixture is carried out to observe the stress change and crack generation and expansion process inside the test piece,analyze the intrinsic mechanical mechanism of the fracture of the test piece and the influencing factors of the crack resistance of the mixture;the virtual triaxial shearing test of the mixture is carried out,and the test results ware analyzed and compared with the actual test to verify the feasibility of the virtual test,and the influence of various factors on the shear performance of the mixture is studied.