Study On The Influence Of Moisture Factors On The Mechanical Response Of Asphalt Pavement In South China

A series of water damage phenomena in the service process of asphalt pavement show that water is very important.At present,most of the research considering the water factor focuses on the material level.In the research of structural response calculation,only the influence of liquid water is considered.Therefore,in order to comprehensively analyze the influence of moisture factors on the response of pavement structure,starting from the establishment of moisture concentration field model,based on the actual moisture distribution of pavement structure,this paper further establishes the relationship between moisture and mixture viscoelastic parameters,and realizes the process by using finite element language,so as to establish the finite element model of pavement structure under the influence of actual non-uniform moisture concentration field;On this basis,considering the liquid water saturated pavement caused by rainfall conditions,a finite element model of asphalt pavement structure considering the influence of liquid water and water vapor is established to quantify the influence of liquid water and water vapor.In order to clarify the water vapor distribution of pavement structure,it is necessary to establish the finite element model of non-uniform water vapor concentration field of pavement structure.Combined with the research purpose of balanced water vapor field,this paper selects penetrating water and gas diffusion as the water and gas movement type,designs penetrating water and gas diffusion test,and measures and fits the water and gas diffusion coefficient of each layer of mixture at different temperatures.The moisture field of pavement structure is established by cyclic loading the temperature and humidity on the hottest day in Yichun,where the research project is located.It is found that except the upper layer,other positions are basically in a relatively constant moisture concentration.The above temperature,water and gas fields are exported for subsequent modeling.Based on the establishment of water and gas field,in order to connect the water and gas field with the response calculation of pavement structure,it is necessary to obtain the viscoelastic parameters of mixture under different water and gas concentration,then establish the viscoelastic parameter conversion method considering water and gas,and realize the process in the simulation by using finite element language.In this study,the moisture concentration curing test is designed to measure the dynamic modulus of the mixture after curing for 6 months with different moisture concentration.It is found that the moisture concentration of the mixture has a great influence on the dynamic modulus of the mixture at low frequency and high temperature.The degree of this influence is AC-13C>AC-20C>AC-25C mixture.On this basis,the generalized Sigmund model and combined shift factor are used to unify the under different water and gas concentrations to the main curve under the conditions of 20℃and 0.35 g/m~3.The goodness of fit of the three gradations is more than 0.95,which shows that the theory is accurate and effective.In order to convert the parameters required by the finite element method,this paper uses the viscoelastic parameter conversion method to convert the dynamic modulus parameters in the main curve of three graded asphalt mixtures at 20℃and0.35 g/m~3 into Prony series of relaxation modulus.At the same time,for the joint shift factor,this paper uses the UTRs subroutine in ABAQUS to write the statement and user-defined statement to realize the finite shift factor considering the concentration of water vapor,and finally realize the finite viscoelastic parameter considering water vapor.In order to verify this method,the virtual dynamic modulus test is designed,and the calculation are compared.The goodness of fit is 0.9997,which shows that the theory is accurate and effective.Based on the above research results,the finite element model of pavement structure is further established.In this paper,the long-term influence of water and gas on pavement structure is regarded as the main influence of water and gas on pavement structure;liquid water is regarded as a short-term action,which changes the stress state mainly through the effective stress principle.Then,a pavement structure model considering moisture is established to analyze the influence of moisture.It is found that the modulus attenuation effect caused by water vapor is obvious in the hottest day of summer.The attenuation of surface modulus caused by moisture has the greatest impact on the upper layer of pavement structure.The horizontal tensile strain under the wheel increases by 110.68%,which increases the risk of upper layer cracking;At the same time,moisture reduces the stress of the surface layer and turns to the base layer.Further,the fatigue life of the surface layer is quantified with the help of the fatigue life calculation formula in the specification.Considering the actual non-uniform water and gas field,the fatigue life is reduced by 12.246%.It shows that the conventional method represented by code overestimates the fatigue resistance of pavement structure in calculating fatigue life,resulting in the dangerous design of pavement structure.On this basis,with the help of seepage theory,the influence of liquid water is added to the above model to characterize the mechanical response of pavement structure under saturated seepage caused by rainfall.It is found that liquid water mainly affects the vertical stress of the base and increases the load borne by the base.But what is more serious is that the effect of liquid water will produce pore water pressure,mainly effects on the surface,and the pore water pressure changes alternately between pressure and suction;The maximum value appears at the upper layer below the wheel and decreases successively along the direction of pavement depth.This shows that the pore water pressure generated by liquid water will peel off the surface asphalt and aggregate,resulting in water damage.In conclusion,the analysis and calculation of this study can infer the causes of water damage from the perspective of structural response.That is,the attenuation of mixture modulus caused by moisture will increase the horizontal strain of the surface layer.The upper layer is most seriously affected in the hot environment in summer,which increases the probability of fatigue cracking.With the participation of liquid water caused by rainfall,the alternating pore water pressure of the surface layer will lead to the spalling of asphalt aggregate,and finally show a series of water damage phenomena.Therefore,for the rainy areas in the south,the influence of water factors must be fully considered in the pavement structure design,so as to improve the ability of material modulus to resist moisture attenuation and reduce the influence of moisture,so as to improve the water damage resistance and fatigue life of pavement.