Investigating The Combination Homogeneity Of Aggregate Blends Using Discrete Element Method

In the composition of asphalt mixture,aggregate blend accounts for more than 90%of the total mass,which has an important impact on the performance of asphalt mixture.Homogeneity is an important performance of asphalt mixture,which directly affects the mechanical properties and service life of asphalt pavement.The combination of aggregate blend essentially consists of a large number of aggregates with different sizes in a certain proportion.The combination homogeneity of aggregate blend mainly depends on the composition proportion of aggregates with different size.The combination of aggregate blend is homogeneous when the composition proportion of aggregate is reasonable.The combination of aggregate blend is inhomogeneous when the composition proportion of aggregate is unreasonable.The homogeneity of asphalt mixture is closely related to the proportion of aggregates with different sizes.Therefore,the research on the combination homogeneity of aggregate blend is helpful to obtain homogeneous asphalt mixture and asphalt pavement and reduce the occurrence of asphalt pavement diseases.Firstly,the combination homogeneity and mixing homogeneity of aggregate blend were described.The difference between combination uniformity and mixing uniformity was analyzed.Two homogeneity evaluation indexes were constructed respectively according to the coefficient of variation(CV)of particle number and the distance between the particle center of mass and the geometric center of the mold(d).Secondly,the discrete element software EDEM was introduced.The simulation test scheme of the combination of aggregate blend was elaborated.The application methods of two homogeneity indexes in simulation test were illustrated.The results showed that Grid Bins can be established and the aggregate number of each Bins can be exported in Analyst of EDEM,and then CV value of aggregates with different sizes can be calculated in aggregate blends.In Analyst of EDEM,the mass center of aggregates and the geometric center of the mold can also be outputted,and then d value of aggregates with different sizes can be calculated in aggregate blends.The laboratory tests of aggregate blend combinations were conducted in order to verify the feasibility of the simulation test.One-way ANOVA was used to analyze and evaluate homogeneity results between laboratory tests and simulation tests.The results showed that it is feasible to study the combination homogeneity of aggregate blend using simulation test.In addition,the efficiency of simulation test is higher than laboratory test,which can reduce the influence of human factors on the test results.Thirdly,the simulation tests of the combination of aggregates with two sizes,the combination of aggregates with three sizes and the combination of aggregates with four sizes were conducted using EDEM.Each aggregate combination included a variety of aggregate blends with different particle composition proportion.The homogeneity of aggregates with different sizes was quantitatively described using CV value.A method for analyzing the combination homogeneity of aggregate blends was proposed.The combination proportions of aggregate particles which can make the aggregate blends homogeneous were explored.The results indicated that the combination homogeneity of aggregate blends can be analyzed according to the homogeneity of the homogeneity of aggregates with different sizes.The particle size difference between aggregates has little influence on the composition proportion.The combination of aggregate blend is homogeneous when the mass fraction of large-size aggregate particles is 50% ～ 67%,and that of small-size aggregate particles is 33% ～ 50%,the combination of aggregate is homogeneous.Finally,the method for evaluating the homogeneity of aggregate gradation was put forward,which is based on the study of the combination homogeneity of aggregate blends.The homogeneity of upper limit,middle limit and lower limit of AC-13,AC-16,SMA-13 and SMA-16 are analyzed respectively.The results showed that the upper limit of AC-13,SMA-13,AC-16,SMA-16 and the lower limit of SMA-16 have poor homogeneity.The middle value of AC-13,the lower limit of AC-13,the middle value of SMA-13,the lower limit of SMA-13,the middle value of AC-16,the lower limit of AC-16 and the middle value of SMA-16 have good homogeneity.