Study On Fatigue Damage Characteristics Of Aged High Modulus Asphalt Mixture Under Different Test Methods

At present,the domestic and foreign research on the fatigue performance of high modulus asphalt mixture mostly adopts four-point bending,indirect tension and other indoor fatigue tests.However,the stress state of these test methods is quite different from that of the real pavement,and there is a large deviation in the fatigue test results.In addition,when researchers study the fatigue characteristics of high modulus asphalt mixture,they often do not consider the impact of aging on its performance.In fact,the actual pavement has experienced short-term aging and a certain degree of long-term aging when fatigue cracking occurs.The fatigue performance of high modulus asphalt mixture is actually a reflection of its performance under different aging states.The fatigue damage evolution process of high modulus asphalt mixture is also a dynamic change process combined with aging degree.Therefore,it is necessary to carry out experimental research on high modulus asphalt mixture under different aging degrees.Based on this,this paper will study the fatigue characteristics of high modulus asphalt mixture under different maximum nominal particle sizes(AC-13,AC-20)and different aging degrees(long term aging for 1,3,5 and 7 days)based on indoor indirect tensile test and small accelerated loading test respectively.Through the derived stiffness decay model,the modulus decay equations under the two test methods are established.the fatigue modulus decay laws of the two are compared,and the fatigue failure standard based on small-scale accelerated loading test is proposed.The test results showed that the fatigue equation parameters k based on stress ratio and stress level differed greatly by indirect tensile tests,while the parameters n differed very little;the critical modulus and initial modulus values increased gradually with the increase of aging.Through the small-scale accelerated loading test,the increase of cycle times and aging time will have a great impact on the modulus of the mixture.When the number of loadings is small,the deepening of aging has less effect on the high modulus asphalt mixture,but in the late stage of accelerated loading,the difference of residual modulus ratio of each aging degree mixture is larger.The modulus decay rate based on small accelerated loading test is close to the change law of indirect tensile test in the early and middle stage of cyclic loading.In the later stage of loading,the rate change of the former increases first and then decreases,and the latter increases rapidly until the specimen is completely destroyed.The fatigue failure is determined when the modulus decay rate of the small accelerated loading fatigue test reaches the maximum value,and the corresponding number of loadings is the fatigue life,which is about 10%of the average error between the calculated fatigue life.The higher the degree of aging,the smaller the damage at the maximum decay rate,indicating that the higher the degree of aging the higher modulus mixtures are damaged when the damage is small.The research results can provide a theoretical reference for the fatigue life prediction and fatigue damage characteristics study of high modulus asphalt mixtures.