Shear Properties of Asphalt Mixtures under Triaxial Compression

In order to study the influences of confining pressure and temperature on the shear properties of asphalt mixtures, triaxial tests were conducted at 40 °C, 50 °C, and 60 °C, with the confining pressure ranges from 0 to 1 MPa for the widely used continuous-graded AC (Asphalt Concrete)-13, open-graded OGFC (Open-Graded Friction Course)-13, and gap-graded SMA (Stone Mastic Asphalt)-13 asphalt mixtures in China. A nonlinear regression/prediction model of triaxial strength for asphalt mixtures was proposed. The results show that confining pressure and temperature had a significant effect on the shear resistance of asphalt mixtures. With increasing temperature, the shear strength of the asphalt mixture gradually decreased due to the decreasing of cohesion strength; the shear strength of the asphalt mixture increased with the increase of confining pressure. Meanwhile, the cohesion strength increased and the friction angle decreased gradually with the increase of confining pressure. When the confining pressure was close to 0.6 MPa, the Mohr–Coulomb failure envelope bended down, so the linear Mohr–Coulomb criterion is not suitable to describe the failure behavior of asphalt mixtures. Therefore, a power function failure envelope was put forward to characterize the nonlinear shear properties of asphalt mixtures. The nonlinear evolutional laws of shear parameters, which includes cohesion strength and friction angle, were also proposed for asphalt pavement material and structure design. Among these asphalt mixtures, the gap-graded SMA-13 asphalt mixture exhibited better performance on the resistance to shear failure, and it was recommended as the upper layer material to improve the shear performance of asphalt pavement