Normalization Of Fatigue Characteristics Of Cement Stabilized Macadam Under Different Loading Modes

The main base layer stypes of high-grade asphalt pavement in China is cement stabilized macadam semi-rigid base,and the fatigue life of cement stabilized macadam directly affects the quality and life of the whole pavement structure.At present,the fatigue performance of cement stabilized macadam has been studied mainly through laboratory tests,such as tensile fatigue test,compressive fatigue test,bending fatigue test and splitting fatigue test.The test results exhibited large differentce due to the variation of stress mode,forming mode,mixing mode and geometric features of specimens.The influence of mentioned factors above on test results usually cannot be eliminated by S-N fatigue model,which is widely used to analyze fatigue test results of cement-stabilized macadam.Therefore,the obtained fatigue characteristics of cement stabilized macadam under different fatigue test methods has shown quite different.At the same time,the material of semi-rigid base surffer both tension and compression stresses in actual pavement,and the difference of tension and compressive modulus of material was seldom considered in current laboratory tests.Therefore,there is still controversial that which method can reveal the fatigue properties of cement stabilized macadam more accurately and scientifically.To active cope with this problem,the main purpose of this paper is to develop a new fatigue analysis method based on the concept of yield surface,and the uniaxial compression,indirect tension and four-point bending strength and fatigue tests were carried out under different mixing modes in order to verify the feasibility of this method.The results showed that the new method of fatigue characteristic analysis based on yield criterion could reduce or even eliminate the influence of various test types and specimen size on test results,achieving the unified characterization of fatigue characteristics of cement stabilized macadam under different loading modes.Introducing a new parameter ? as an index of "anti-damage safety" under a certain stress state,the unified characterization model of fatigue performance of cement stabilized macadam under different loading modes was also proposed,which provide reference basis for the further development of safety design theory of asphalt pavement.Based on damage mechanics,a method for determining the initial and critical values of modulus attenuation of cement stabilized macadam was defined.According to the fatigue damage equation proposed by Chaboche,the fatigue damage law of cement stabilized macadam under different loading modes was studied with modulus attenuation as the damage variable.The fatigue test results of cement stabilized macadam under different loading modes were fitted and analyzed,and the modulus decay equation of cement stabilized macadam under different loading modes was established.In addition,the modulus decay law of cement stabilized macadam under different mixing modes and different loading modes was compared.The results showed that the modulus decay law of cement stabilized macadam,both vibrant mixing and non-vibrant mixing,could be characterized by the deduced modulus decay equation.There had a similar tendency in the rigidity decay law for cement stabilized macadam with vibration mixing and that with non-vibration under different loading modes,and the fatigue resistance of cement stabilized macadam under vibration condition was better.Based on the difference of modulus of tension and compression,the formulas were obtained for calculating modulus of tension and compression of beams under bending mode.The research found that there was great deference between the bending-tension and bending-compression modulus decay laws of cement stabilized macadam,but the bending-tension modulus and the splitting modulus decay law were analogical,as well as the bending-compression modulus and the compressive resilience modulus decay law.The test results showed that the decay laws of tensile and compressive modulus of cement stabilized macadam under different loading modes were quite different,but the decay laws between tensile and compressive modulus was similar.The new fatigue relationship was obtained by establishing a relationship between the fatigue characteristics of cement stabilized macadam and the strength yield criterion in this paper.Compared with the traditional fatigue curve,the research results could reduce the difference of fatigue test results of cement stabilized macadam under various specimen size and stress modes,and achieve the unified characterization of fatigue life of materials under different stress states.The structural design methods and design accuracy of semi-rigid base asphalt pavement in China could be further improved based on this study,and then prolong the service life of the whole asphalt pavement.