Multiscale Analysis Of Viscoelastic Damage Behavior Of Asphalt Pavements

The issue of asphalt pavements damage has always been the critical research subject in road area.Due to the heterogenous property of asphalt mixture which contains asphalt bitumen,mineral fillers,aggregates and air voids,and traditional methods of pavement analysis can hardly represent the interaction between the inner components of asphalt mixture and characterize the cracking mechanism and cracking location of asphalt pavements.In order to reveal the mechanism of viscoelastic damage and precisely predict the crack behavior of asphalt pavements,this paper used a two-dimensional multiscale finite element approach to model the mechanical behavior of asphalt pavement at different scales,which takes microstructure and macro mechanical behavior of pavements into consideration.This paper includes the following researches:(1)Digital image processing(DIP)was used to establish the mesoscale finite element model of asphalt mixture.To guarantee the accuracy of the model,DIP was performed on the basis of cross-section image of asphalt mixture specimen.Median filtering,subsection linear intensity transformation,morphological image processing,marker-controlled watershed segmentation and polygon approximation which based on classical Douglas-Peucker algorithm were applied to process the image,and the effectiveness of above techniques were discussed and verified in this paper.(2)The macroscale finite element model and representative volume element(RVE)of asphalt pavements were built at axisymmetric coordinates in ABAQUS.RVE was defined as the smallest element which can characterize the mechanical behavior of asphalt mixture at macroscale.Cohesive elements were defined in asphalt mortar and interfaces between mortar and aggregates,and the constitutive model of cohesive elements follows the bilinear tractionseparation law(TSL).The viscoelastic parameters of asphalt mortar in RVE and asphalt mixture in macroscale model were respectively obtained from laboratory dynamic modulus test and homogenization of RVE.The results of homogenization were validated by dynamic modulus test data of asphalt mixture,showing that the RVE in this paper can reasonably characterize the viscoelastic property of asphalt mixture at macroscale.The semi-circular bending test was conducted to obtain the fracture parameters of cohesive element to ensure the accuracy of damage analysis.(3)The damage behavior of cement-treated based(CTB)asphalt pavement and granular based(GB)asphalt pavement under 5℃ and 35℃ were simulated by the multiscale finite element model,respectively,and the distribution of horizontal stress and damage initiation were analyzed.The results shown that the multiscale analysis can represent the distribution of horizontal stress and damage,and further reveal the damage mechanism of “top-down” crack behavior of CTB pavement and “bottom-up” crack behavior of GB pavement.In addition,this paper investigated the influence of pavement structures,temperatures and shear stress on the damage initiation of pavements.The strength of RVEs after different types of damage were compared,which reflected the damage level of pavements.(4)The temperature filed was introduced into the multiscale analysis in order to characterize the damage behavior of pavements at temperature field.The temperature field of pavement was built by loading real temperature data of a typical city in China.The temperature distributions of pavements were respectively formed in two pavement structures(CTB and GB),two seasons(summer and winter)and two times(midday and midnight)of day,and the distribution of horizontal stress and damage initiation were then simulated and analyzed.The results indicated that the multiscale finite element model can effectively consider the influence of temperature field on the damage initiation.In summer,the existence of temperature field can obviously influence the distribution of transverse stress,and the distribution of damage initiation in RVE showed highly temperature-dependent feature.In winter,due to that the mechanical response of asphalt mixture was approximately elastic,and the influence of temperature field on the horizontal stress in negligible.