Asphalt mixture is the most widely used pavement material all over the world.In China,more than 90%of service expressways are asphalt pavement.However,current asphalt pavement design method still has irrationality.Even though maximum tensile stress theory is used as failure criterion,pavement structure under the effects of wheel load is in three-dimensional complex stress state.Obviously,one-dimensional strength theory cannot reflect the failure characteristics and the resistance of pavement structure.So it is necessary to study the failure criterion of asphalt mixture under three-dimensional complex stress state.Due to limitations of test equipment,there are almost no studies in related area.Under this background,this paper develops a new triaxial test method,according to the investigation of strength characteristics of asphalt mixture under complex stress state through plane isobaric/axial tensile test,plane isobaric/axial compression test,plane tensile and compression/axial tensile test,to reveal the general rules of asphalt mixture's strength failure.The failure mode is divided into three types:tensile failure,shear failure and rheological failure.The tensile meridian and compression meridian in the stress space and strength envelope in the p plane where hydrostatic pressure is greater than zero are obtained,and the failure criterion of asphalt mixture under complex stress state is established,providing theoretical method and scientific basis for structure design as well as strength check of asphalt pavement under three-dimensional stress state.
In order to analyze the effect of different loading frequencies on the fatigue performance for asphalt mixture,the changing law of asphalt mixture strengths with loading speed was revealed by strength tests under different loading speeds.Fatigue equations of asphalt mixtures based on the nominal stress ratio and real stress ratio were established using fatigue tests under different loading frequencies.It was revealed that the strength of the asphalt mixture is affected by the loading speed greatly.It was also discovered that the fatigue equation based on the nominal stress ratio will change with the change of the fatigue loading speed.There is no uniqueness.But the fatigue equation based on the real stress ratio doesn't change with the loading frequency.It has the uniqueness.The results indicate the fatigue equation based on the real stress ratio can realize the normalization of the asphalt mixture fatigue equation under different loading frequencies.It can greatly benefit the analysis of the fatigue characteristics under different vehicle speeds for asphalt pavement.
