Research On Nonlinear Fatigue Damage Properties Of Asphalt Mixture Based On The Decay Of Strength And Stiffness

The asphalt pavement is the main type of pavement structure. Asphalt mixture ofasphalt pavement construction materials, the fatigue performance directly affects theperformance and service life of the pavement. Meanwhile, the asphalt mixture as aviscoelastic material, the mechanical properties of the asphalt mixture related withloading and test temperature. This paper relies on the National Natural ScienceFoundation Key Project of"Investigation into Fundamental Issues in AsphaltPavement Structural Design". For the material characteristics of the asphalt mixture,direct tensile fatigue and the different remaining number of fatigue strength test arecarried out. The aim of this study is to understand the process of asphalt mixture infatigue damage of production, evolution and accumulation under repeated loading,and reveal the decay law of stiffness and strength of asphalt mixture in fatiguedamage. Nonlinearity fatigue damage properties of asphalt mixture based on the decayof the dynamic modulus and residual strength are investigated. Results to improve andrefine the existing asphalt pavement structural design has important theoreticalsignificance and practical value.Firstly, direct tensile strength test is carried out at different loading speed. Thetest results show that the effect of loading speed on strength of asphalt mixture issignificant, and their relationship curve can be fitted by power function. Direct tensilefatigue tests are carried out at five kinds of stress level. The fatigue equation based onreal stress ratio is established by the concept of dynamic load strength and real stressratio. This fatigue equation can not only reflect the fatigue damage under repeatedloading, but also cover the strength failure under one loading. A new calculationmethod of tensile strength structure coefficient is put forward by fatigue equationbased on real stress ratio.Secondly, the deformation and the decay law of modulus of the direct tensilefatigue are analyzed in different stress levels. A power-law decay of dynamic modulusmodel is built. The dynamic modulus decay law with nonlinear characteristics isdetermined. The dynamic modulus with the life of the faster decay, and the decayparameter m with the stress level increase by the greater the stress level. Correctionmodel to consider the critical value of fatigue damage is put porward. The nonlinearfatigue damage evolution equation based on the decay law of stiffness is established. The fatigue test is carried out under two-stage stress levels. The law of nonlinearfatigue damage cumulative of asphalt mixture is verified. And the test results areexplained intuitively and reasonably using two-stage loading route figure.Thirdly, the residual strength test of asphalt mixture is carried out in differentstress levels. Degradation of residual strength of the power function model isestablished. The decay law of the residual strength under different stress levels isrevealed. The nonlinear fatigue damage evolution equation based on the residualstrength degradation is established. Under the conditions of same material and liferatio, the damage based on residual strength is greater than the damage based onstiffness. Strength is better than stiffness as fatigue damage variable. Combined withthe advantages of the residual strength and stiffness of damage variable, a definitionof damage variable based on residual strength and stiffness is unified. A powerfunction by the damage variable Dsand Dfbased on the residual strength and stiffnessis built.Finally, based on the nonlinear fatigue damage properties of asphalt mixtures, anew asphalt pavement axle load conversion method is established with consideringthe degree of damage or loading history impact. The nomogram of axle loadcorrection factor B changes with the years is given. Through examples the impact ofthe traffic on the road is underestimated by the current axle load conversion method.Research results have important meaning for promoting the development of axleload conversion method, further perfecting the asphalt pavement design methods andimproving the durability and service level of asphalt pavement.