Study On Characteraistics Of Microscopic Structure And Void Decay For Porous Asphalt Pavement

Asphalt pavement paved with porous asphalt mixture has advantages such as drainage in rainy days,anti-skid,noise reduction and other traditional dense pavement do not have.However,the air gap decay in porous asphalt pavement is easy to occur due to its large gap,which makes it lose basic structural performance during the use of porous asphalt pavement.And porous asphalt mixture is a composite material containing aggregate,asphalt mortar and large gap.Its structural void decay must be related to the internal void structure,spatial distribution and volume content.At present,the study of voids in porous asphalt mixture is mainly based on indoor test,which is characterized by high cost and poor repeatability.Therefore,the discrete element simulation method is used to study the void structure and decay of the porous asphalt mixture from the mesoscopic structure level,which can provide the theory and basis for improving the pavement service life and the pavement maintenance technology.The research mainly includes:Firstly,in order to obtain the void information of 6 specimens with different gradations,the best digital image processing technology was used.Then the void characteristic parameters,pore size distribution and void fractal dimension of porous asphalt mixture were calculated.The meso void characteristics of the mixture were studied from 3 aspects: air void,gradation and nominal maximum aggregate size.It is found that the gap characteristic parameters,pore size distribution and fractal dimension are closely related to the air void,nominal maximum aggregate size and gradation of asphalt mixture.Secondly,the program simplified the irregular aggregate into a polyhedral structure and generated coarse aggregate that actual gradation was satisisfied according to the irregularity of the aggregate.On this basis,the three-dimensional model of porous asphalt mixture was generated,and a model foundation for subsequent virtual rut test was established.The contact types of the materials in the mixture are determined,and the macroscopic parameters determined by the creep test are transformed into microscopic parameters to be applied to the numerical simulation.The research shows that the discrete element method can establish a threedimensional rutting plate model as the actual one well.Thirdly,the virtual test was simulated by PFC3 D,and the accuracy of the simulation was verified through laboratory tests.The gap of the cutting model was obtained based on digital image processing,the two-dimensional void characteristic parameters were calculated and the void distribution rules in each aperture range were analyzed.Then on the basis of the virtual rutting test,the horizontal displacement and vertical displacement distribution of the mixture were obtained simultaneously.It shows that the number and the area ratio of gap between 2 and 4mm increase after loading.The distribution of vertical displacement is likely "U",and the maximum horizontal displacement occurs at a certain depth on both sides of the loading region.Finally,The void decay law of porous asphalt mixtures under various factors such as ambient temperature,load and load time was found.The results show that temperature,load and time have good correlation with the deformation and void decay of asphalt mixture.And the void decay model of porous asphalt mixtures based on important factors is also established.