Development of a Novel Theoretical Formulation for Determining the Three-Dimensional Linear Viscoelastic and Permanent Deformation Behavior in Low-Strain Regime of Asphalt Mixtures from Creep-Recovery Test Data

This work presents a novel theoretical formulation for simultaneously determining the axial and transverse creep compliances, Poisson ratio function, and permanent deformation strains of asphaltic materials in low-strain regime based on three-dimensional (3D) creep-recovery test data. First, a back-calculation algorithm was proposed to determine the pure linear viscoelastic (LVE) properties from the data in the recovery phase, based on which the LVE and viscoplastic (VP) strains along axial and transverse directions can be extracted from the total strains. An analytical approximate formula was also proposed to calculate the Poisson ratio functions from the convolutional integral equation that interrelates the axial and transverse creep compliance functions. Then, 3D creep-recovery and complex modulus tests were conducted on one specimen to assess the accuracy of the proposed method. The experimental results showed that the back-calculated creep-recovery functions and the computed Poisson ratio function agreed well with their conjugate quantities determined in frequency domain, despite slight anisotropic responses observed.