The Permanent Deformation Of Asphalt Pavement Under Complex Conditions Based On Dynamic Modulus

Permanent deformation is one of the main damage types of asphalt pavement,which has a serious adverse effect on driving comfort.Many countries,including China,regard permanent deformation as an important technical index of asphalt pavement design and recommend corresponding test methods.Asphalt layer and permanent deformation as a pavement structure check target calculation model has appeared in our current specifications for design of highway asphalt pavement(JTG D50-2017),but the model for stress analysis is based on the elastic layered system and the circular uniformly distributed load,and asphalt mixture are made under the condition of 20 ℃,10 hz dynamic modulus,apparently with the actual stress state of pavement structure is very different,so it is necessary to permanent deformation of asphalt mixture forecast model to do further research.Based on the existing research results,this paper analysis the variety of asphalt mixture permanent deformation test and the advantages,disadvantages and applicability of permanent deformation forecast model,finally using dynamic uniaxial creep test to obtain the permanent modified asphalt mixture parameter,choose VESYS permanent deformation forecast model research environment temperature,thickness of asphalt layer,loading frequency,loading waveform,driving speed on the influence of permanent deformation of asphalt layer.In this paper,the dynamic modulus parameters of asphalt mixture are transformed into viscoelastic parameters.The finite element constitutive model of viscoelastic parameters of asphalt pavement is established on the basis of measured wheel load,interlayer contact and pavement temperature field.The basic conclusions of this study are as follows:1)The permanent deformation of asphalt pavement is greater than that of elastic layered system considering the viscoelastic parameters of asphalt mixture,the measured tire ground pressure,the contact between layers and the pavement temperature field.Therefore,the formula for calculating the permanent deformation recommended by the specification may be less than the estimated permanent deformation of the road surface.2)The waveform and frequency of load action in pavement structure are not a certain value,but vary with the different conditions of vehicle speed,pavement thickness and calculation point depth.The change of load action waveform and frequency will change the permanent deformation of pavement by changing the modulus of asphalt mixture.3)While meeting the technical requirements of the specification for asphalt mixture,the proportion of asphalt mixture in the middle surface layer is reduced,the contribution rate of permanent deformation of the middle surface layer will be reduced,and the total amount of permanent deformation of the road surface is also reduced.Therefore,the permanent deformation of asphalt pavement can be reduced by appropriately reducing the oil content of middle pavement on the basis of meeting the checking calculation indexes of other pavement structures.4)For the pavement structure of two-layer asphalt surface,the permanent deformation of asphalt surface mainly occurs in the lower layer.For the pavement structure of the three-layer asphalt surface,the permanent deformation of the asphalt surface mainly occurs in the middle upper surface layer(accounting for more than 70%of the total permanent deformation of the asphalt surface layer),and the contribution rate of the permanent deformation of the middle surface layer is the largest,.Within a certain range,the permanent deformation of the asphalt layer decreases as the thickness of the asphalt layer increases,while the contribution rate of permanent deformation of the upper layer increases gradually while the middle and lower surface layer decreases gradually,that is,the permanent deformation mainly develops to the road surface.