Study On The Mechanism Of The Segregation Of Asphlat Mixtures

This paper aimed at the inhomogeneous distribution of asphalt mixture in asphalt pavement construction,and attempted to establish a simulation model of asphalt mixture construction segregation by means of discrete element method.Based on this model,the influence of gradation design factors such as coarse aggregate gradation and asphalt mortar properties on asphalt mixture construction segregation was analyzed,and the construction segregation of asphalt mixture based on gradation design was established.The evaluation index was analyzed,and the segregation mechanism of asphalt mixture construction was summarized.Specifically:Firstly,a micro-mechanical model suitable for analyzing segregation of asphalt mixtures during construction was established in the discrete element software.Firstly,the appropriate discrete element software was selected.By comparing the capability of discrete element software PFC and EDEM in particle segregation analysis,the new discrete element tool EDEM was selected as the applicable software to continue this study from the aspects of modeling and mechanical function realization,calculation efficiency and parameter meaning clarity.Secondly,the simplified assumption of particle contact model for segregation analysis of asphalt mixture construction was put forward.Thirdly,based on the Hertz-Mindlin particle contact model considering JKR adhesion,the simplified assumptions were realized,and the key parameters were selected,analyzed and calibrated: the key parameters include the elastic modulus of asphalt mixture particles,the surface energy density between particles,the coefficient of collision recovery between particles and the coefficient of friction between particles.Then,through the established micro-mechanical model and selected parameters,the simulation stacking experiment was designed to explore the uneven distribution of particles in the movement of unloading and horizontal throwing.The fine aggregate concentrated on the upper part of the stack while the coarse aggregate concentrates on the edge of the stack.After dumping,the coarse aggregate concentrates on the far part of the horizontal initial velocity direction and the edge part of both sides of the stack,while the fine aggregate concentrates on the near end of the horizontal initial velocity direction and the middle part of the stack.The above phenomenon is the same as the distribution of coarse and fine particles obtained from the construction site investigation.All above phenomenon can be explained as a segregation mechanism: After the fixed stack,the falling particles first contacted with the middle part of the higher stack,and the smaller particles had a weaker ability to overturn the surface texture of the formed stack,which was easy to accumulate or adhere to the coarse particles in the middle of the stack along the gap of the stack.The larger particles had a better ability to overturn the surface texture of the formed stack,so the larger particles located at the edge of the stack are larger.Finally,a suitable index for evaluating the non-uniformity of particle distribution in discrete element software was selected.Based on this index and design-Expert software,31 groups of mixtures test schemes were designed to analyze the influence of the ratio of aggregates with different particle sizes to the total mass of coarse aggregates and the surface energy density of asphalt mortar on the segregation degree of asphalt mixtures.The influencing factors of the segregation degree and the proportion of coarse aggregates were analyzed.And the regression equation and segregation evaluation index of asphalt mixture construction based on gradation design were obtained.In the end,the segregation mechanism and the methods of reducing segregation in asphalt mixture construction were summarized and concluded.