Research For Torsional Shear Test Method Under Normal Stress Conditions For Asphalt Mixture

With the changes in China’s transportation structure and traffic volume and axle load,traffic channelization increase the highway asphalt pavement of rutting,load type cracking,pushing and shoving package,such as new diseases,These diseases are mainly the lack of shear performance of asphalt pavement surface.Currently road workers generally recognized the seriousness of the shear failure,and further study of asphalt mixture shearing performance.However,the existing test methods by technology and equipment constraints cannot be studied in depth,it is difficult to get a unified evaluation index.Therefore,a test method that can effectively evaluate the shear resistance of asphalt mixture is of great significance to prevent and reduce the disease of pavement and improve the service life of asphalt pavement.Based on the analysis of the test methods of evaluating the shear resistance of asphalt mixture at home and abroad,this paper puts forward a new method of torsion shear test under the condition of normal stress,and develops the corresponding test equipment.The test principle is through the jack on the asphalt mixture material specimen evenly applied normal stress,with the gear rack and the vertical force into torque,so that the cylinder specimen in compression shear state,more in line with the actual asphalt pavement stress state.In summary based on the strength theory of,use the knowledge of geometry,physics and mechanics of materials,the stress and deformation characteristics of the specimens under normal stress condition are analyzed,finally,the formula for calculating the shear strength of the asphalt mixture which is suitable for the test method is deduced.Through ANSYS finite element analysis,the shear stress distribution and displacement deformation of asphalt mixture were analyzed,which showed that the failure state of asphalt mixture was shear failure,and the maximum shear stress was located at the top of the cross section at the top four points.Selection of AC-13、AC-20 two kinds of common asphalt mixture under different temperature and different stress conditions to do torsional shear test under normal stress conditions,it is concluded that with the increase of temperature,asphalt mixture shear strength decreases sharply;in addition,shear strength and normal stress increases linearly.Finally the liner regression showed the cohesion c and internal friction angle φ of mixture according to the Mohr-Coulomb theory,compared them with the results of three main test methods,the test method is feasible through analysis.Use AC-13 asphalt mixture under different stress levels,different normal stress conditions and other influencing factors to do torsion shear fatigue test under normal stress conditions,the shear fatigue life of asphalt mixture is concluded,and stress level and shear fatigue life on a single log curve is linear relationship,and use the relationship regression the shear fatigue equation.