Meso-model And Pure Torsion Simulation Of Asphalt Mixture Based On Random Coarse Aggregate

The increasingly complex traffic situation makes the asphalt pavement under the wheel load produce nonnegligible shear stress,and the shear resistance of the material is not considered in the design process of asphalt mixture,which may be the root cause of the initial damage of pavement.Because of the complex mechanical properties of asphalt mixture,it is difficult to explore the internal mechanism of asphalt concrete pavement’s initial damage under the condition of meeting the macro design index by traditional macro test research and numerical simulation.The meso pure torsional shear mechanical analysis of asphalt mixture is of great significance to make a new exploration to solve this problem.Firstly,based on Delaunay algorithm,the random coarse aggregate’s geometric model of asphalt mixture is established.And the gradation curve and VCA_mix（voids in coarse aggregate of asphalt mixtures）of random coarse aggregate geometric model are evaluated.The grading curves of two-dimensional and three-dimensional random coarse aggregate geometric models obtained by virtual screening method are distributed between the upper and lower limits of the gradation.The VCAmix of two-dimensional and three-dimensional random coarse aggregate geometric models are calculated which are respectively 38.08%and40.01%and both close to the measured value that is 37.17%.Secondly,considering the random distribution of voids in the gap of coarse aggregate,the meso-scale finite element model of asphalt mixture is established based on the unstructured finite element mesh and the geometric model of random coarse aggregate.According to the information of unstructured mesh and the geometric model of random coarse aggregate,the element set of coarse aggregate are selected under the judgment rule of position relationship,besides,the element set of pore elements that meet the requirements of porosity and asphalt mortar elements are selected considering the pore distribution in the gap of coarse aggregate.According to the node information,element information and the element sets of coarse aggregate and asphalt mortar,a finite element model is established by input file of ABAQUS software.Finally,according to the established meso-finite-element model of asphalt mixture,the torsional shear simulation of asphalt mixture under the condition of low temperature and linear elasticity is studied.In order to study the influence of meso-structure on the pure torsional shear mechanical properties of asphalt mixture,the shear stress distribution of coarse aggregate and asphalt mortar in the meso-model and the shear stress distribution of the edge of coarse aggregate in the bottom end face are analyzed;in order to study the influence of the elastic modulus of coarse aggregate and mortar on the torsional shear stress,by controlling the single variable,different elastic modulus of aggregate and asphalt mortar are adopted to carry on the simulations.According to the above research,the following conclusions are obtained:（1）The meso-structure of asphalt mixture has an important influence on the torsional shear stress distribution,which can not be ignored;（2）with the increase of elastic modulus of coarse aggregate,the maximum shear stress of test specimen and the shear stress of coarse aggregate show a general uptrend,and the shear stress of asphalt mortar shows a downtrend;（3）with the increase of elastic modulus of asphalt mortar the maximum shear stress of the test specimen and the shear stress of the coarse aggregate decrease,and the shear stress of asphalt mortar shows a trend of increase.