Study On Strength Theory Of Asphalt Mixture And It's Application

So far as expressway is concerned, asphalt pavement is one of most typical pavements in China, and highway's transport capacity,safety and stability depend on asphalt pavement's quality, which has relevance with strength of asphalt mixture. Because of it, how to improve strength of asphalt mixture is becoming an important problem. In fact, asphalt mixture in asphalt pavement is said to be in a state of triaxial stress, however, both strength theory of Mohr-Coulomb and axisymmetric triaxial testing method do not include intermediate principal stress, actually, it is not accordance with three-dimensional space in asphalt pavement. Especially, there is no report on both intermediate principal stress and intermediate principal stress's influence on strength in the past research of asphalt mixture. All in all, it is necessary to study intermediate principal stress's influence on strength of asphalt mixture.Based on the world-wide research, influence of intermediate principal stress on strength of asphalt mixture is studied by testing method. Test study shows that strength of asphalt mixture increases with the increase of intermediate principal stress. When both interaction of different factors and temperature difference are considered, orthogonal experimental design significance analysis shows that intermediate principal stress has an obvious influence on strength of asphalt mixture. Therefore, so far as the research of strength of asphalt mixture is concerned, effect of intermediate principal stress should be taken into account. Actually, effect of intermediate principal stress can be considered in twin shear strength theory, hence, twin shear strength theory should be thought of as strength theory of asphalt mixture.Considering the characteristics of testing method for intermediate principal stress's influence on strength of asphalt mixture, testing device for plain strain is designed, meanwhile, the size,shape and making method of specimen of asphalt mixture as well as testing condition are decided. Failure specimens of asphalt mixture from different testing conditions are analyzed. When loading velocity is 2mm/min and intermediate principal stress is taken into account, functional relationship between temperature and strength can be obtained. Functional relationship between loading velocity and strength is established through regression method when intermediate principal stress is considered and temperature difference is from -10℃to 25℃. When both different temperature and different loading velocity are considered, regression relationship of stress-strain is studied. Based on that, considering such condition as mtermediate principal stress,2mm/min of loading velocity and temperature difference, function of curve of stress-strain is obtained. Two typical curves of stress-strain are put forward. Meanwhile, concrete method is proposed to determine elastic limit of asphalt mixture.As a matter of fact, failure criterion of twin shear strength theory can be employed to explain surface's shearing failure of asphalt pavement with rigid base. Consequently, twin shear strength theory should be applied to surface thickness calculation of asphalt pavement with rigid base. Based on numerical calculation, intermediate principal stress,intermediate shear stress and normal stress of asphalt pavement at the location of joint of base are calculated and analyzed by three-dimensional finite element method in this paper. Study of load stress shows that different factor has the same order of shear stress and normal stress; At the same time, study of thermal stress shows that different factor has different order of shear stress and normal stress, meanwhile, order of shear stress and normal stress is changed when the fixed factor has different numerical value. Based on conclusion of both testing study and stress analysis, reviewing the past research results, and combining with twin shear strength theory, method of thickness analysis for asphalt pavement with rigid base is put forward.