Mesotructural Simulation Research On Pavement Performance Of Asphalt Mixture Based On Vecd And Fracture Mechanics

This paper studies the influence of mesoscopic factors on the macroscopic mechanical behaviour of asphalt mixture by combining macroscopic and microscopic methods.Since the mesoscopic factors are difficult to be effectively reflected by the experimental means,and the factors affecting the meso level are numerous,it takes a lot of time and economic cost to carry out comprehensive experimental research.Therefore,the mechanical properties of asphalt mixture were analyzed mainly by virtual random test piece generation and finite element(FE)simulation,supplemented by laboratory tests.The following studies were carried out in this paper:(1)Based on the mesostructure,a three-phase constitutive model system including aggregate,mortar and asphalt-aggregate interface was proposed to characterize the mechanical properties of asphalt mixture.(2)Firstly,the existing fractional viscoelastic constitutive model was systematically analyzed,and the fractional Zener model was selected to characterize the viscoelastic mechanical behaviour of asphalt mortar and interface.Based on the Mittag-Leffler function,the frequency domain-time domain transformation of the fractional Zener model was conducted,and the relaxation modulus in the time domain was obtained.Based on the FE theory and the global Padé approximation,the numerical algorithm of the fractional Zener model was derived.Secondly,according to the viscoelastic continuous damage mechanics theory(VECD)theory,the fractional Zener model was combined with VECD to characterizes the fatigue damage development of asphalt mortar.Finally,based on the CZM framework,the fractional Zener model was used to characterize the traction-displacement response,and the damage evolution equation was established by the energy method.Foucusing on the damage criterion and evolution law under mixed fracture mode,a fracture model for the cracking behavior of the mortar and interface was proposed.(3)A test plans was designed,which were divided into meso-level parameter acquisition tests and macro-level simulation verification tests.The in-situ symmetrical tensile and compressive tester was used to obtain the parameters of the VECD model and the CZM model.The UTM tester was used to obtain the fractional viscoelastic model parameters.The mesoscopic fatigue damage FE model was verified by four-point bending test.The mesoscopic fracture FE model was verified by semi-circular bending test.The self-designed in-situ symmetrical tensile and compressive tester fixture was used to realize the loading of different fracture modes,and the CZM model parameters of the mortar and interface are accurately obtained.(4)Based on the meso-FE model,the dynamic modulus test was simulated,and the dynamic modulus and phase angle master curves were calculated and compared with the indoor dynamic modulus test results.The influence of aggregate modulus on dynamic modulus and phase angle master curves was analyzed,and the modified parameter method was proposed,which greatly improves the prediction accuracy of numerical simulation for phase angle main curve under low frequency range.(5)The mesoscopic finite fatigue damage FE model was established.The fatigue evolution in the mortar was characterized by VECD,and the fatigue evolution at the interface was characterized by CZM.Firstly,the validity of the model was conducted by comparison the simulatin results with the four-point bending test data.Then,using the macroscopic road mechanics response as the input load,the mesoscopic model of the local area at the bottom of the asphalt layer was established as the analysis object.Then,the effects of three mesoscopic factors such as gradation,aggregate direction angle and air void ratio on the macroscopic fatigue damage performance of asphalt mixture were analyzed.Finally,the effects of two macroscopic factors of overload and asphalt layer thickness on the fatigue damage performance of asphalt mixture were analyzed.(6)A mesoscopic fracture FE model based on explicit algorithm was established.The insertion of CZM units was achieved by means of node re-editing.Firstly,the validity of the model was conducted by comparison the simulation results with the semicircular bending test.Next,the effects of the three aggregate geometric characteristics of maximum particle size,aggregate direction angle and aggregate aspect ratio on the crack resistance of asphalt mixture were analyzed.Finally,the effects of void geometry and void size on the crack resistance of asphalt mixture were analyzed.