Research On Rutting Flow Deformation Of Asphalt Mixture Microstructures Based On Discrete Element Method

Rutting is the main damage form of pavement composed of asphalt mixture.It will not only affect driving safety,but also shorten the service life of pavement.The filling property of fine aggregate and the skeleton performance of coarse aggregate in the mixture directly affect the formation of its strength.The traditional rutting research is limited to the analysis of various mechanical properties in the mixture from a macro perspective.This method not only has the problems of time-consuming,labor-intensive,high input cost and poor repeatability,but also the variability of the results is large.Therefore,based on the discrete element method and digital image processing technology,this paper realizes the simulation of the microstructure composition of asphalt mixture with spherical particles and irregular polygons,and discusses the influence of structural factors on its macroscopic performance from the mesoscopic level,in order to provide theoretical support for the design of long-life asphalt pavement.The main steps are as follows :Firstly,based on the indoor test,combined with FISH language,this paper realizes the visual design of three classical gradations,and generates an ideal spherical discrete element model with different fine aggregate contents.Then,through the uniaxial compression simulation experiment,the constitutive relationship which is very consistent with the indoor test results is obtained.After ensuring the feasibility and rationality of the model,the state of compaction deformation and flow deformation of asphalt pavement rut under cyclic load is simulated comprehensively.The stress field,displacement field and deformation of asphalt mixture with different fine aggregate content are compared and analyzed,and the mechanism of rut formation and the relationship between fine aggregate content and optimal skeleton structure are revealed.Subsequently,in order to quantify the influence of the coarse fraction and subdivision ratio of the coarse aggregate in the skeleton on the mechanical properties of the asphalt mixture,based on the ideal disc discrete element model,a two-dimensional reconstruction of the asphalt mixture section is proposed by using MATLAB image processing technology and discrete element method,and a discrete element model that is very close to the statistical distribution of the real asphalt mixture structure is obtained.Finally,9 groups of asphalt mixture models with different skeleton ratios are designed and generated by the above digital method.The meso-mechanical indexes such as contact characteristics,contact force distribution,coordination number and angle distribution of force chain are statistically analyzed.To explore the influence of coarse fraction and subdivision ratio in coarse aggregate on skeleton performance.The research shows that:(1)The overall deformation of asphalt pavement rutting is significantly affected by the upper and middle layers,and the deformation of the middle and upper layers in each type of specimen accounts for up to 70 %.Among them,the skeleton dense asphalt mixture SMA with fine aggregate content of 22 % can improve the internal stress of the mixture,reduce the pavement deformation,increase the vertical transmission efficiency of stress,and make it have better rutting resistance.(2)In the skeleton dense mixture,the standard dense gradation(M type)asphalt mixture has the highest content of particle coordination number,the most balanced distribution of contact force range,and the minimum change of force chain strength with time and coarse material ratio at each angle,which makes the mixture of this gradation type have good internal contact,small anisotropy,uniform transmission path,and can form a more stable skeleton structure.In this paper,a geometric modeling method of asphalt mixture combined with digital image is innovatively proposed,and the microscopic mechanism of rutting simulation specimen with real morphological characteristics is discussed.It provides a reference for deeper microscopic research and reduces the economic losses caused by repeated indoor tests.