Determination of Viscoelastic Poisson’s Ratio and Creep Compliance from the Indirect Tension Test

The indirect tension test has received extensive attention due to its capability to test field cores from thin asphalt layers. For that reason, the fundamental viscoelastic material property, creep compliance, or complex modulus has been determined by employing the indirect tension testing system. However, if the creep compliance or complex modulus is to be determined from such a multiaxial testing mode, another crucial material property must be introduced, that is, Poisson’s ratio. It is well known that the Poisson’s ratio of a viscoelastic material is a function of time or frequency; nevertheless, it has been commonly assumed to be a constant and a time- or frequency-independent property. In this study, computation algorithms for determining the time- and frequency-dependent Poisson’s ratio of asphalt mixtures were developed based on the theory of viscoelasticity. From the comparative study, it was found that the Poisson’s ratio determined from the frequency domain corresponded well to that determined from the time domain. Further study performed on the sensitivity of Poisson’s ratio clearly showed that the time-dependent Poisson’s ratio was an important property in determining accurate creep compliance, and an inappropriate assumption for Poisson’s ratio overestimated or underestimated the measured creep compliance.