Comparison And Analysis Of Shear Test Method For Asphalt Mixture

With the increase of traffic volume and axle load in China,the asphalt pavement produces rutting,cutting-slippage problems.More and more road practitioners are aware of the seriousness of the shear failure of asphalt mixture,and study in-depth the asphalt mixture shear performance.However,China's current highway design specifications didn't clearly put forward test methods and evaluation indicators of asphalt mixture shear performance.Therefore,a test method for effectively evaluating the shear performance of asphalt mixture is of practical significance to enhance the road performance and service life of asphalt mixture.It is of great significance for the construction and design of asphalt mixture.Based on the analysis of the test method for evaluating the shear performance of asphalt mixture at home and abroad,a new torsional shear test method under normal stress condition is proposed,and corresponding test device is developed.The test principle is,to apply evenly normal stress on the asphalt mixture test piece through the jack,and then to turn vertical force into torque through the rack and gear,which makes the cylindrical specimen in the shear state and conforms more to the status of the actual asphalt pavement force.On the basis of summarizing the strength theory is used to analyze the stress deformation characteristics of the specimen in the torsional shear test under the normal stress condition.Finally,the shear strength calculation formula of the asphalt mixture,which is suitable for the test method,is deduced.It shows that the failure state of the specimen is shear failure,and the maximum shear stress is at the four equinox points on the top cross section.Using four kinds of gradation AC-13,AC-20,AC-25 and SMA-13 to have mix proportion design,and through high temperature stability and water stability to verify the optimum asphalt aggregate ratio.The specific test conditions and torsion test steps are described,through geometry and mechanics analysis,calculation method of shear strength and parameters is derived,and then through the unconfined compressive strength test under the same conditions,four kinds of asphalt mixture's shear strength cohesion C and internal friction angle ? can be calculated.Through the torsion test of AC-13 under the condition of normal stress at different temperatures and different loading rate,conclusion can be got that,with the increase of temperature,the shear strength of asphalt mixture material reduce drastically;in addition to it,there has certain correlation between the shear strength and the loading rate,with linear growth relationship.Through the uniaxial penetration test of AC-13,AC-20,AC-25 and SMA-13 under the same conditions,and comparing the results with the torsion test,it can be found that the test method was feasible.The shear strength of different gradation,different temperature and different loading rate is compared with that of torsion test by uniaxial penetration test,and the correlation between shear performance and shear performance is analyzed.