Effect of Confinement Pressure on the Nonlinear-Viscoelastic Response of Asphalt Concrete at High Temperatures

Asphalt concrete materials exhibit the nonlinear viscoelastic responses at high stress/strain levels. The traffic loading induces multi-axial stress states within the asphalt concrete pavement structure. Therefore, it is imperative to characterize the nonlinear viscoelastic responses of asphalt concrete under the realistic stress states since these nonlinearities significantly affect the rutting and fatigue damage performance of pavements. Schapery’s (1) nonlinear viscoelastic model has been used extensively by several researchers to characterize the nonlinearity of asphalt concrete materials. However, the available methods for characterizing the viscoelastic nonlinearity are mostly based on the simple uniaxial creep-recovery tests. In this paper, the nonlinear viscoelastic properties of asphalt concrete materials are characterized considering the effects of confinement pressure on the variation of the nonlinear parameters. Dynamic modulus test is used to obtain the linear viscoelastic properties and the time-temperature shift factors. Cyclic creep-recovery tests are performed at high temperature (55°C) and at different confinement levels to characterize the nonlinear viscoelastic responses. The effect of confinement pressure is investigated through usage of triaxiality ratio on the variation of the nonlinear viscoelastic parameters. The analyses showed that the triaxiality ratio has substantial effect on the nonlinear strain response of the asphalt concrete. The significance of these nonlinear parameters on the complex response of asphalt concrete subjected to different loading conditions is also discussed.