Prediction Of Permanent Deformation Of Asphalt Mixtures Based On Multi-scale Analysis

Rutting or permanent deformation is the long-term depression accumulated from the wheel path in the asphalt pavement.It has been listed as one of the most common distresses which impacts the driving comfort for drivers and service life of a pavement.A fairly high cost for pavement maintenance is needed if rutting distress occurs in in-service pavements.Hence,rutting prediction and evaluation are of great importance for pavement design,maintenance and rehabilitation.In an attempt to address this issue,extensive researches have been conducted and various models have been proposed to characterize and predict rutting development of asphalt pavement materials.However,Existing two-stage rut prediction models have different forms.These models considering internal material parameters and volume characteristics are complicated,which are difficult to have universal applicability.The effect of material adhesion failure on permanent deformation is not considered,and the development mechanism of rutting in the third stage is not clear.The existing three-stage rut prediction models are purely empirical models with piecewise functions.The relationship between the fitting parameters and the material parameters is difficult to determine.Therefore,it is necessary to propose a mechanicalempirical model with rationalized parameters for rutting prediction.This paper uses a combination of discrete element and finite element numerical simulation to study the permanent deformation performance of asphalt mixtures and asphalt layers in order to break through the inefficiency of discrete element simulation of large-scale tests and the limitations of continuous characteristics of finite element simulation.The dynamic modulus and permanent deformation performance of asphalt mixtures and asphalt layers are predicted based on Multi-scale analysis.Two innovation mechanical-empirical rutting prediction models with wide applicability are proposed,which can reveal the micro-mechanism of permanent deformation of the asphalt mixture,improve the high-temperature stability performance of asphalt mixtures,and reduce the problems such as rutting disease of asphalt pavements.The main steps are as follows:Firstly,an aggregate gradation based mechanistic classification criterion is established as for the multi-scale study of asphalt mixtures.The contribution of aggregates to the bearing capacity and structural stability is demarcated through the meso-contact mechanical response of aggregates in each sieve size.Four internal structures in the mixture are classified and the critical sieve sizes for each gradation are determined.Based on the theory of interlock check between aggregate particles,the internal contact status of the particles is studied,and the internal stress evaluation method was established by comparing the magnitude of the deviator stress in four internal structures.The principle of multi-scale mechanistic classification criterion is verified by the indoor and virtual triaxial compression tests of aggregate mixtures with grading characteristics.Secondly,the theory of aggregate interlock check is extended in the multi-scale mechanistic classification criterion,including the local interlock check theory and the global interlock check theory.A disruption factor is proposed as an index to evaluate the hightemperature performance of the asphalt mixture gradation,and the discrete element model is introduced to establish a virtual uniaxial compression test for auxiliary verification.Thirdly,based on the multi-scale mechanistic classification criterion,the dynamic modulus tests at four scales(asphalt DSR test,asphalt mortar DSR test,asphalt mortar DMA test and asphalt mixture SPT test)are designed to study the dynamic shear rheological properties of multi-scale asphalt mixtures at different temperatures and frequencies.According to the dynamic modulus test results,the master curves of dynamic modulus and phase angle at these scales were constructed.On the basis of the Boltzman superposition principle and Laplace transform under multi-frequency dynamic loads,the master curve of dynamic modulus is correlated with static viscoelastic parameters,then the viscoelastic parameters at different temperatures and different scales can be obtained.After that,the discrete element method is used to simulate the dynamic modulus tests at four scales.Based on the virtual test results,the micromechanical stiffening mechanism of adjacent scales is studied.The micromechanical prediction model of dynamic modulus is modified based on the stiffening mechanism,which can be expanded to do a more accurate prediction of dynamic modulus of multi-scale mixtures with lower frequencies and higher temperatures and higher aggregate(or mineral powder)contents.Finally,in view of the shortcomings of existing rut prediction models,this paper proposes two-stage and three-stage mechanical-empirical rut prediction models based on viscoelastic stress-strain responses,and studies the rut developments by combining the results of the hamburger wheel tracking test of asphalt mixtures with and without water penetration conditions.The proposed rutting prediction models are verified by the finite element numerical simulation results.Then,the two-stage and three-stage rutting models are jointly analyzed to distinguish the rut disease caused by asphalt mixture stripping effect at a high temperature.To further verify the proposed mechanical-empirical ruting prediction model,a double-layer asphalt mixture is designed to test the rutting performance by vertically loaded wheel tester,and the contribution of mixtures in each layer to overall rutting resistance was evaluated.In order to eliminate the viscoelastic energy dissipation effect in the rutting test,an elastoplastic solution was obtained through the elastic-viscoelastic correspondence principle.Eventually,the rutting performance of double-layer structures is evaluated based on the theory of dissipated pseudo-strain energy.