Analysis of a Methodology for Torsional Test under Normal Stress and Shear Performance for Asphalt Mixtures

Insufficient shear performance in an asphalt mixture is a primary reason for rutting deformation and pavement surface longitudinal cracking. Thus, it is important to choose a suitable shear test method to evaluate shear performance in an asphalt mixture. Current testing methods mainly evaluate the bonding strength between asphalt layers, and the current shear test method for an asphalt mixture is disadvantaged by high equipment cost and complicated procedures. Our study proposes a torsional test method under normal stress condition, and evaluation was done for four types of asphalt mixture under different temperature conditions. Through the mechanical analysis, the calculation formulas for shear strength and shear parameters (cohesion and internal friction angle) for the torsional test under a normal stress condition were obtained. Testing results were also obtained for shear strength, shear modulus, and cohesion and internal friction angle of the asphalt mixtures. Experimental testing indicated that the method was able to provide repeatable results for the shear resistance of asphalt mixtures at different temperatures and also reflected the difference in shear performance of the various asphalt mixtures and the influence of temperature on shear performance. The failure mode of the specimen was the appearance of an oblique crack of about 45° from the vertical axis after the specimen was destroyed, which accorded with shear failure characteristics. A shear fatigue model was obtained considering different shear stress levels. The torsional test method under normal stress formed a compression-shear action on the specimen by applying torque and normal stress and was used to evaluate the shear performance of the asphalt mixtures.