Study On Fatigue Performance Of Emulsified Asphalt Cold Recycled Mixture Based On Discrete Element Method

Nowadays,the highway in China has entered a period that needs large-scale maintenance and repair.The production of asphalt pavement waste in arterial highway repair works is up to 180 million tons per year.Therefore,it is necessary to accelerate the recycling process of road pavement materials.Cold recycled emulsified asphalt mixture is used more and more frequently in the pavement structure,suitable for cold regeneration layer and lower layer or flexible base,the old material utilization rate can reach 80%～100%years of engineering practice shows that the pavement structure is in good condition,with good engineering and environmental adaptability.Fatigue crack is a common disease form of the Cold Regenerated structure layer of emulsified asphalt.The fatigue property of the mixture greatly affects the fatigue failure performance of the structural layer.The discrete element method has been widely used in the study of the fatigue performance of asphalt mixture.The discrete element method is used to simulate the fatigue test,which can directly analyze the fine asphalt mixture.In the process of mixing ratio design,the determination of water content is an important step,and the size of water content affects the mixing,compaction and the size of the void ratio after the mixture,thus affecting the pavement performance of the mixture,so it is necessary to conduct further study.The determination method of moisture content of cold recycled emulsified asphalt mixture is analyzed,and the fatigue performance of the recycled asphalt mixture is analyzed by discrete element numerical simulation.In this paper,the cold recycled emulsified asphalt mixture is taken as the research object.The design method of cold recycled emulsified asphalt mixture is optimized by improving the optimum moisture content of the mixture.The discrete element simulation method for the fatigue test of the cold recycled mixture of emulsified bitumen is studied,and the indirect tensile fatigue test model is established by using PFC 3D software.The influence of void fraction on the fatigue performance of emulsified asphalt cold recycled mixture was studied.Firstly,based on the energy equivalence principle,the heavy compaction test for determining the optimum moisture content of the Emulsified Asphalt Cold Regenerated mixture is improved.A heavy compaction test method for the cold regeneration of the emulsified asphalt is put forward.Compared with the mixture used in the design method in our country,the road designed by this method is adopted.The fatigue life is increased by 341.1%when the stress level is 250Kpa.Secondly,according to the characteristics of the emulsified asphalt cold recycled mixture and the test equipment conditions,the fatigue test method and the test parameters are determined.The geometric model considering the irregular shape of the coarse aggregate,the gradation characteristics and the void fraction of the mixture is constructed-The viscosity behavior of the emulsified asphalt mortar is described by the Burgers model.The fatigue damage characteristics of the mixture are reflected by the attenuation of the bond radius,and the parameters of the discrete element model are determined and the boundary conditions are set up.The three-dimensional discrete element model of fatigue test is established to simulate the indoor fatigue test.The maximum error of the numerical simulation results and the laboratory test results is 10.11%,and the discrete element model of the fatigue test is stated clearly.It is reasonable and feasible.Finally,based on the indoor fatigue test and the established discrete element fatigue test simulation method,the fatigue cracking behavior of the emulsified asphalt cold recycled mixture is analyzed according to the relationship between the axle load displacement,the tensile strain and the stiffness modulus and the cyclic loading times and the contact conditions in the fatigue test.The fatigue failure process mainly experienced three stages:rapid damage,stable damage and rapid damage.The effect of void ratio on the fatigue performance of cold recycled mixture of emulsified asphalt was analyzed.When the stress level was 300Kpa,the fatigue life of the mixture shortened with the increase of void ratio.The fatigue life of the mixture with the void ratio of 12%is only 6%of the fatigue life of the mixture with the void ratio of 6%,which indicates that the void ratio affects the fatigue performance of the cold recycled mixture of the emulsified asphalt significantly.