Determination of the linear viscoelastic limits of asphalt concrete at low and intermediate temperatures

A procedure for determining the linear viscoelastic limits of asphalt concrete at low and intermediate temperatures at stresses and strains typically developed in pavements under traffic loading was illustrated using six mixtures containing different aggregate gradations and nominal maximum aggregate sizes of 12.5-37.5 mm. The mixtures had the same asphalt binder grade. A relaxation test was performed at 150 and 200 microstrains at -20°C, and at 150 and 300 microstrains at -10°C. A novel normalization procedure was developed, which emphasized changes in the mixture response with stress level, significantly improving the power of the statistical analyses. At -20° and -10°C, the proportionality condition was satisfied up to 200 and 300 microstrains. At 4°C, all the mixtures exhibited the same proportionality limit at a given loading time, indicating that the effect of aggregate gradation on linearity limits was not significant. At -20° and -10°C, the mixtures fell within the linear viscoelastic region, considering the typical relaxation modulus values at strain levels experienced in the asphalt concrete layer. Typical in-situ strain values at 20°C fell within the boundary region between linear and nonlinear behavior. At intermediate temperatures, the shear strains should be less than 0.05% to be within the linear viscoelastic region.