Viscoelastic poisson's ratio of asphalt mixtures

The Poisson's ratio (PR) of asphalt mixtures is a fundamental material property that is an important input parameter to viscoelastic pavement models. It is typically assumed that PR of asphalt is time independent or, in cases where the time dependency of viscoelastic PR is considered, calculated as the negative ratio of the time-dependent transverse and axial strains measured in a uniaxial creep test. This paper presents analytical and experimental results demonstrating the errors involved in these assumptions. The first part of this study derives an expression for viscoelastic PR. The second part of this study reports the results of various experimental tests to measure axial and transverse strains of asphalt concrete specimens under different loading conditions. The viscoelastic PRincreased with time in the tensile relaxation test and ramped tensile test, whereas it slightly increased at the beginning of the compressive relaxation test and was subsequently virtually constant. The error introduced by incorrectly determining the PR as the negative ratio of transverse to axial strains in the time domain was found to be significant.