Analysis Of Dilative Mechanical Behavior Of Asphalt Mi×tures And Its Numerical Simulation

Shear dilation can be defined as the process of volume expansion of asphalt mixtures under shear deformation. Shear dilative behavior may play a key role in the formation of rutting. To understand and solve the shear dilation of asphalt mixtures play a vital role against rutting, which are the objective and important scientific issue of this dissertation. Triaxial contraction test and partial triaxial contraction test were used to systematically study the shear strength and volumetric deformation characteristic of asphalt mixtures, which were also employed to analyze the shear dilation mechanism and shear dilation deformation. The microstructure of asphalt mixtures was analyzed using X-ray CT technique and image processing technology during the process of shear deformation failure. The dilation mechanism of asphalt mixtures was studied based on the microstructure. The deformation of asphalt mixtures is transformed from the continuous medium to discontinuous medium due to the occurrence of shear dilation behavior of asphalt mixtures. Based on the discontinuous medium mechanism theory and discrete element method, the viscoelastic plastic constitutive model was built to simulate the microstructure of asphalt mixtures under triaxial contraction test. According to the simulation result, the shear dilation deformation of asphalt mixtures was evaluated and estimated. Combining the microstructure and macro performance of asphalt mixtures to study the dilation deformation, which can be used to effectively analyze and forecast the rutting. The contents are carried out in this dissertation as following:(1) The interlock of particles and the bonding between particle and fine aggregate matrix (FAM) were analyzed by the microstructure of asphalt mixture to explain the mechanism of shear dilation.(2) The Reynolds dilatancy theory, Drucker-Prager failure criterion and microstructure fabric theory were used to analyze the loading balance condition of asphalt mixtures. Based on these theories, the shear dilation model was proposed.(3) The triaxial contraction test was conducted using Universal Test Machine 25 multifunctional material system and the radial displacement transducers to characterize the stress-strain relationship of axial, radial and volumetric deformation under different testing temperatures and testing time. Also, the dilation behavior characterization and its influence factors of asphalt mixtures were analyzed.(4) The partial triaxial contraction test was designed using finite element method and was verified through the laboratory test. The feasibility of partial triaxial contraction test was elaborated to study the shear dilation deformation of asphalt mixtures. At the same time, the testing method and processing of partial triaxial contraction test were present for the asphalt mixtures.(5) The shear dilation behavior, stress-train relationship, passion ratio and dilatancy gradient of asphalt mixtures were analyzed using Reynolds and stress-dilatancy theories under partial triaxial contraction test. And the comparative analysis between partial triaxial contraction test and triaxial contraction test was carried out to summarize the shear dilation deformation of asphalt mixtures.(6) The asphalt mixtures specimen was scanned using the X-ray computed tomography (CT) technology. The microstructure of CT pictures were processed using the ring blocking segmentation Otsu's method, MATLAB software, and Image-Pro Plus image processing method. And the processed pictures were reconstructed to obtain the air void of asphalt mixtures which was considered for the discrete element simulation.(7) The air void and circumference of asphalt mixtures specimens were captured using X-ray CT scanning technique and image processing technology under triaxial contraction test and no test to analyze the shear dilation deformation characterization of asphalt mixtures. And the micro cracks during the process from existence to evolution were analyzed to evaluated dilation mechanism of asphalt mixtures.(8) According to the result of mixture sieving and asphalt mixtures pictures obtained by X-ray CT technique, the polyhedron algorithm was proposed to build the virtual aggregate. The air void phase, fine aggregate matrix phase and coarse aggregate phase were constructed through discrete element method and PFC3D software. Burgers model was employed to simulate the viscoelastic property of asphalt mixtures. And the parameters of Burgers model were captured using creep test and diametral contraction test, which were calculated in microscopic parameters that were put in discrete element simulation.(9) The laboratory test and discrete element modeling of triaxial contraction test were contrasted and analyzed. The results show that the numerical simulation results are in good agreement with the experiment results. Also, the dilation deformation mechanism of asphalt mixtures was described through cracks and shear band in microscopic and macroscopic scales.