Research On Fracture Of Asphalt Mixture In Mesoscale

Asphalt pavement as a kind of flexible pavement has been widely used throughout the world.However,new forms of destruction have emerged at the same time.In the recent year,it has been found that many asphalt roads which are open for 2-3 years will appear many small cracks one the vehicles' wheels tracks.As time goes,fatigue crack growth behaviors,which not only affect driving comforts but also get the rain seeped through,accelerate the destruction of the pavement structure.However,the existing design specifications of various countries in the world are often based on macro-mechanical research.It is believed that fatigue failure starts at the lower part of the asphalt surface and gradually expands upwards which cannot explain this type of cracks.Thus,crack phenomena pose a severe challenge to application and design of asphalt pavement structures.this paper studies asphalt mixtures' crack initiation and expansion law of surfaces and internals.Firstly,a random generation algorithm for two-dimensional polygon aggregates and three-dimensional polyhedral aggregates was developed.The aggregate particles that are generated by the algorithm cover factors like aggregate size,aggregate form,and aggregate gradation.This lays the foundation for establishing a microscope scale of an asphalt mixtures mechanical model.Furthermore,considering the cohesive model is an important method of crack initiation and expansion behavior of composite-material simulation,this paper developed an efficient and accurate method of which the cohesive unit is fitted into the finite-element model of asphalt mixtures.A two-dimensional(2D)and three-dimensional(3D)finite element model of asphalt mixture was generated by using the random aggregate model and then,the proposed cohesive element embedding method can achieve adding more aggregate-slurry interfaces and the mortar cohesion unit of the slurry.At the meantime,using the Python for the secondary development of the finite-element Abaqus,this model can automatically update the original input file,generate microscopic heterogeneity fracture model,and provide a physical model for subsequent research.Finally,the use of two and three-dimensional asphalt mixtures created to carry out uniaxial stretching and direct numerical simulation of shear fracture model,the asphalt was observed micro cracks evolution and macro cracks in the levels of aggregation during the whole process.This research also obtains micro-cracks evolution and the macroscopic cracks law and analysis the influence of aggregate content,aggregate distribution,and cohesive parameters on the cracking behavior.The model was expanded from 2D to 3D and the numerical simulation results show that the crack characteristics of the 3D model are more realistic than the 2D model's.