Research On Fatigue Damage Characteristics Considering The Difference Of Tensile-Compression Modulus For Asphalt Mixture

In China,a large number of high grade asphalt pavement is conducted by the design method of asphalt pavement,making an important contribution to the development of China's transportation industry.At the same time,it also exposes more and more problems.According to the specifications for design of highway asphalt pavement:in the structural layer design of asphalt pavement,whether it is based on the road surface deflection value or layer bottom tensile stress,the design parameters are the compressive resilient modulus of asphalt pavement.The most basic assumption in its design theory is each layer of asphalt pavement is continuous,uniform,completely elastic and isotropic.In other words,the material exhibits the same mechanical properties in tension and compression.However,the strength and stiffness parameters of each structural layer for asphalt pavement exist the difference of tension and compressive modulus.It is inappropriate to use a single modulus to characterize the mechanical response of the pavement under complex stress conditions.Thus it can be seen the design standard of asphalt pavement is not reasonable to design a road with the compressive resilient modulus as the structural design parameters,which may cause a large deviation between the theoretical calculation results and the actual situation,so is the fact.The tensile,compression and bending modulus are obtained by different test methods according to the existing test procedures for asphalt mixture.The fatigue test method is also diversified which lead to the result that each test is too independent to unite.We can not compare and analyze the test results,which cause unnecessary waste of resources.Based on this,a new test method for the synchronous test of the tension,compression and bending modulus for asphalt mixture is developed to lay a good foundation for the normalization of fatigue test method.Starting from the basic theory of damage mechanics,defined modulus attenuation as damage variable,the stiffness decay equation is also derived.The corresponding model parameters are obtained by fitting the test data,the fitting results show a good correlation,which lead to establish the stiffness decay equation of asphalt mixture.At the same time,the damage evolution law of asphalt mixture in different test methods is compared.In this paper,the causes of the difference of tension and compression modulus of asphalt mixture are explored;the influence factors such as the initial value,the critical value,the breaking point and the slope of the modulus of tension and compression during the fatigue process are compared and analyzed;the decay law of tension,compression and bending modulus in four point bending fatigue test of asphalt mixture is revealed.A new concept of pavement design is selected by the corresponding modulus and its evolution law according to the actual stress state based on the location of each point of asphalt pavement,which makes up for the deficiency of the existing design code of Asphalt Pavement.This study is of great significance to the determination of pavement material parameters,also,it provides theoretical and experimental basis for the design theory and calculation method of asphalt pavement.