Study On Numerical Simulation Of Asphalt Mixture Based On CT Technology And Three-dimensional Discrete Element Method

There are many serious problems such as early damage in the road of our country,among which cracking and rutting are the most common.Many road researchers have carried out a lot of research for this purpose,but mainly through indoor macro laboratory experiments.In view of the limitations of indoor macro laboratory experiments,such as large error,poor reproducibility and the inability to study the internal mechanism of the mixture,the discrete element method has gradually been introduced into the research work of road materials.At present,most discrete element method researches are based on the algorithm to generate virtual aggregate,but the virtual aggregate can't completely match the real shape of aggregate particles.Based on this,based on CT tomography technology and digital image processing technology,this paper realizes the three-dimensional reconstruction of aggregate particles in real form,and further builds a three-dimensional discrete element model of asphalt mixture for virtual mechanical tests,in order to deeply analyze the internal mechanism of the mixture and study the influencing factors of the mixture performance which are difficult to control in the indoor macro laboratory experiments.First,based on CT tomography technology,multiple two-dimensional cross-sectional images of the aggregate are acquired.The matlab program is developed to process the image to obtain the coordinate data of the three-dimensional contour points of the aggregate,so as to realize the three-dimensional fine reconstruction of the aggregate particles of the real shape.Based on the coordinate data of the contour points,three indicators are proposed to quantify the shape of the aggregate,a more accurate evaluation method of the aggregate needle flake is established,and the cross section of each fault is analyzed by the convex hull area difference method to comprehensively evaluate the overall angularity of the aggregate.Secondly,multiple aggregate models are generated through the real aggregate reconstruction method to build an aggregate template database.Based on the aggregate template and the Bubble Pack algorithm,the coarse aggregate particle model is generated.At the same time,the influence parameters of model precision are analyzed and the recommended value range is given.According to the volume characteristics of the mixture,a coarse skeleton structure with gradation characteristics is generated.The spheres are arranged regularly in the model test piece,and the spheres are defined according to the principle of overlapping judgment to divide them into aggregate phase and mortar phase.The void phase consistent with the void distribution characteristics of the actual mixture is established,thereby constructing a three-dimensional discrete element of asphalt mixture model.Then,the contact mechanical behavior between the components in the asphalt mixture is analyzed and the suitable contact model is selected.The conversion relationship between macro parameters and micro parameters is established.The meso parameters in the model are calibrated by means such as laboratory tests,and the accuracy of the parameter values is verified based on the laboratory test results.Finally,the split virtual test and the uniaxial penetration virtual test are carried out to analyze the internal mechanism and changes of the stress distribution and transmission,the generation and development of cracks in the mixture during the test.The feasibility of this method is verified through the comparison of laboratory tests.The analysis and research are conducted on the influencing factors of asphalt mixture's low-temperature crack resistance and high-temperature shear resistance.