Normalization Of Fatigue Characteristics Of Asphalt Mixtures Under Different Stress States

The fatigue performance of asphalt mixture have been studied by a large number of researchers at home and abroad,mainly based on fatigue test of indoor specimens,such as tensile fatigue test,compressive fatigue test,bending fatigue test and indirect tensile fatigue test,because of the various stress pattern,shapes and sizes of these test pieces for the indoor fatigue test,there are relatively big differences,even in magnitudes,which has made it impossible to scientifically assess the fatigue performance of the asphalt mixture using different test methods.Therefore,fatigue tests of asphalt mixtures are carried out under three different stress states including direct tension,uniaxial compression and indirect tension,the testing results under three different stress states were compared and analyzed in the S-N fatigue equation,the study found that traditional S-N fatigue equation could not eliminate the influence of stress states,sample shapes and sizes,then a new method for the analysis of fatigue properties was developed based on the concept of yield criteria,achieving the goal of normalization of the fatigue properties of asphalt mixtures under different stress states,realizing the unification of the results when using different fatigue testing methods,and providing theoretical,methodological and technological bases for the scientific conversion from material fatigue to structure fatigue.Based on the fundamental theory of damage mechanics,the decay of modulus was defined as the variable of fatigue damage,from which the stiffness decay equation was deduced.Fitting the testing results found that all results under different stress states showed very good correlation,based on which the stiffness decay fatigue equations of asphalt mixtures were established and the fatigue modulus decay laws were compared under different stress states.Based on Hooke’s law in two-dimensional stress state,the formula for calculating double modulus of indirect tensile load mode is deduced,and the study found that there was big difference between the tension and the compressive modulus decay laws of indirect tensile fatigue test,and indirect tension-tensile fatigue modulus decay laws was similar to the direct tension and indirect tension,indirect tension-compressive fatigue modulus decay laws was similar to uniaxial compression,indicating that there was big difference between tensile and compressive modulus decay laws of fatigue process of asphalt mixture,but the decay laws of tensile modulus are similar in different stress modes,and the decay laws of compressive modulus are the same.The research results have important theoretical and engineering implications in improving the analysis of load effect and the calculation of the fatigue resistance model of road structure in China’s current asphalt pavement design criterion,playing a fundamental and positive role in advancing the design methods development and improving the precision as well as elongating the service life of asphalt pavement.