New Approach to Determining the Stiffness Moduli of Asphalt Mixtures from IDT Testing

An indirect tensile test (IDT) is used to obtain material parameters of wearing surfaces such as used pavements of ordinary roads or bridges. In the general (classical) approach, tensile and compressive displacements in orthogonal directions of any test specimen are assumed to have similar creep compliances to simplify the calculations. Consequently, the Poisson’s ratio is obtained from the equation as a function of time. On the other hand, Poisson’s ratio estimated via the IDT test using this assumption is actually found not to be varying with time. In other words, it is independent of time. Thus, the classical approach assuming equal creep compliances under tensile and compressive stresses results in inaccurate Poisson’s ratio estimation, which obliges change in the calculation method. This study proposes a new method that assumes two different creep compliances under tensile and compressive stresses. It also presents the variation of stiffness moduli depending on time and the ratio between tensile and compressive creep compliances.