Study On Experimental Method And Rotational Shear Testing Apparatus Of Asphalt And Asphalt Mixtures

Distresses on asphalt pavements such as swells and ruts are essentially caused by the insufficiency of high temperature stability and shear resistance of asphalt mixtures. Extensive studies on test apparatus and test methods of shear resistance of asphalt and asphalt mixtures have been carried out over the years. Currently, the dynamic shear rheometer (DSR) test and the Superpave shear test (SST) are the traditional methods of testing dynamic properties and evaluating high temperature stability for asphalt and asphalt mixtures. However, due to the single function of DSR and the high price of SST, these methods are not widely used.Utilizing a micro motor, an inverter, a torque sensor, a displacement sensor, a temperature sensor and a computer automatic controlled system software self-developed, a series of practical and economical test devices with functions of static and dynamic shear performance testing under rotational loading are designed and assembled for the experimental study of static shear performance and dynamic properties of asphalt and asphalt mixtures. These devices are applied to the failing strength test, the dynamic viscoelastic performance test, the oscillation (fatigue) failure performance test, the creep and repeated creep recovery performance test and the stress relaxation test and cyclic loading test. The computer automatic controlled system software can automatically complete the test process, process the test data and draw the graphs. The strain-controlled dynamic load modes such as sine, cosine, triangle is also developed for the loading function.To validate the operation stability of the test apparatus and the feasibility of the test method, a failure performance test using more than470asphalt specimens (divided into25groups) and a oscillation failure performance test using more than150asphalt specimens (divided into17groups) are conducted. The effects of factors such as the shear loading rate (0.1～2.0rad/s), test temperature (6～40℃), asphalt type (AH90asphalt, rubberized asphalt and SBS modified asphalt), asphalt thickness (0.5～3.5mm), and specimen diameter (30mm and21mm) are taken into account in these tests. In addition, a rotational shear failure performance test for AC-13using93specimens with square section is also conducted at the room-temperature of20℃to investigate the effect of rotational shear rate. To investigate viscoelastoplastic deformation and deformation recovery performance of the asphalt specimens, an asphalt rotational shear creep performance test and a stress relaxation performance test under various stress levels are implement, and a cyclic loading test including3asphalt types and4stress levels is also carried out at the room temperature of20℃.The test results show that the devices for the rotational shear failure performance test, the oscillation failure performance test, the creep and repeated creep recovery performance test run stably and the test methods are feasible. The devices and the methods have better economical efficiency and broader scope of application than DSR. The device of stress relaxation test can’t completely constrict the synclastic rotation displacement of the rotation axis in the "continuous loading" stage, which will affect the accuracy of test results. But for the cyclic loading stress relaxation test, the effect mentioned above can be ignored when the "continuous loading" stage is very short.Based on the test apparatus and test results described in this paper, following conclusions can be drawn:(1) Several rotational shear failure modes for the asphalt specimens such as yielding, brittleness fracture, pure bonding interface failure and mixed mode failure of bonding interface and asphalt fracture are observed; the failure modes, failure shear stress, shear deformation modulus and failure loading time of asphalt specimens are affected significantly by the loading rate, test temperature and types of asphalt.(2) In the process of the oscillation failure, complex shear modulus curve shows a significant downward trend, while the change of the phase angle is not obvious; the period of loading function has a certain influence on complex shear modulus and phase angle; complex shear modulus and phase angle are also significantly affected by the test temperature; thickness of asphalt and diameter of the specimen have little effect on complex shear modulus and phase angle.(3) Asphalt type and stress level have great effect on deformation recovery performance.(4) Loading rate has strong effect on shear failure loading time, failure stress, failure strain and deformation modulus of asphalt mixtures.