CoMParative Study On Torsional Shear And Triaxial Test Of Asphalt Mixture

Asphalt mixture is the main pavement material used in China's highways,and the ruts and cracks caused by insufficient shear strength of asphalt mixture are the main failure modes of asphalt pavement.However,research scholars have great differences on the shear performance of asphalt mixtures.The triaxial test method is used to calculate the shear strength in the asphalt mixture test procedure,while the new asphalt pavement design specification is indirect by the uniaxial penetration test method.Convert the shear strength.Many scholars still have controversy about these two test methods.After exploring the variation of shear performance under different conditions,this paper gradually perfects the torsional shear test method under normal stress conditions.The test method enables the cylindrical asphalt mixture test piece to be under compression and shear state,and then obtains the cohesion force C value and the internal friction angle ? value of the asphalt mixture according to the Mohr-Coulomb theory and geometric derivation.In coMParison with the principle of determining the shear strength of asphalt mixture by triaxial method,it was found that the test piece was tested in the full-limit state during the triaxial test,which could not obtain the strength of the test piece itself in the natural state.In the torsional shear test,the asphalt mixture is in a natural state without a limit,which is more in line with the actual engineering conditions,and can more effectively deterline the shear strength of the asphalt mixture.In this paper,the mixture ratio of AC-13 and AC-20 asphalt mixture is designed according to the test conditions and test steps required by the torsion test for different particle size grades,different asphalt types,different temperatures and different loading rates.The asphalt mixture was subjected to a torsional shear test under different normal stress conditions.Finally,the reliability of the shear test of the asphalt mixture in different particle size grades,different asphalt types and different temperatures was tested by triaxial test.The test results show that:(1)the shear resistance of AC-13 is better than that of AC-20;(2)CoMPared with the matrix asphalt,the viscosity of SBS modified asphalt is higher,Which can effectively improve the cohesion of asphalt mixture and improve the shear resistance.(3)The shear resistance of asphalt mixture is greatly affected by the ambient temperature.When the temperature exceeds 40?,the shear performance decline trend is particularly obvious;(4)within a certain loading rate range,the asphalt mixture is affected.The viscous drag effect,the torsional shear strength of the asphalt mixture will increase,but the too fast loading rate will lead to a large test error;(5)the triaxial test and the torsional shear test can better reflect the asphalt mixture resistance The change rule of the shear index,but the triaxial test makes the asphalt mixture test piece in the full-limit state,and the strength of the test piece in the natural state cannot be obtained.However,the whole process of the torsional shear test is in the unconfined state.In the test,the test piece is in the state of compression and shearing in the form of simulated road surface,and it is not bound by other external forces,and the strength of the test piece in the natural state can be obtained.(6)According to the correlation analysis results of the two C and cp values of the asphalt mixture,it can be seen tihat the variation of the confining pressure in the triaxial test has little effect on the internal friction angle,but has a great influence on the cohesion.