Microscopic Analysis Of Asphalt Mixture Uniaxial Penetration Test

The non-uniformly distributed load imposes heavy shear stress on pavementstructure. However, the shear resistance performance has been seldom considered inasphalt pavement design. This may be the major reason which causes large-areadamage of asphalt pavement. Consequently, shear properties of asphalt mixtureshould be emphatically considered. However, the method of evaluating the shearproperties of asphalt mixture, by taking laboratory tests, has not been applied to theactual engineering field on a large scale, due to the complexity of the test methods andthe variability of the test results. The microstructure modeling techniques based onDiscrete Element Method have tremendous potential benefits, because the method ishelpful in decreasing or eliminating costly tests and it is reliable in acquiring thefundamental properties of asphalt mixtures in a micro-scope. Furthermore, the modelscan provide tremendous insight towards understanding the mechanical behavior ofasphalt mixtures, which is a kind of complex and discontinuous media. In order toanalysis the shear property of asphalt mixture from a micro-structural perspective,simulation methods based on the discrete element method, are put forwarded in myresearch, with which shear property characterization as well as micro-structural ofasphalt mixture can be efficiently evaluated. The primary contents of the thesiscontain the following aspects:(1) Establish the numerical model of asphalt mixture uniaxial penetration testbased on the Discrete Element Method, and mechanical response of the model underload were calculated and analyzed, to obtain the variation tendency of the indentercompressive stress and the maximum shear stress of the model as the specimen strainincreasing, as well as acquire the distribution of the displacement vector and thecontact force vector in the model.(2) Analyzed the influence of loading speed on the test results, which drawing aconclusion that the peak strength of the specimen increase with the rising of theloading speed. Tried to establish the relationship between specimen size and indenterdiameter and the diameter of the largest particle, found that the influence of specimensize and indenter diameter on the result of the test is remarkable. As for asphaltmixtures with the grading of AC-25and AC-20, it is recommended to choose thespecimen size with height of100mm and diameter of100mm and to select the indenter with the diameter of28.5mm. However, the standard Marshall Test samplescan be used as standard specimen for AC-13asphalt mixture. The thesis discoveredthe impact of macro factors, which include grading, the diameter of maximum particleand the porosity, and micro factors that involve particle stiffness, parallel bondstrength and parallel bond radius on shear strength of the mixture, end up withsummarizing that the strength of asphalt mixture increase as the porous decrease andthe strength increase as particle stiffness, parallel bond strength and parallel bondradius rising.(3) According to the numerical simulation results, assessing method is proposedto evaluate the shear strength of asphalt mixture based on the discrete element method,By comparing both uniaxial penetration test results and unconfined compressivestrength test results, a formula is proposed to determine the shear parameters ofasphalt mixture C andφ.