Verification of time-temperature superposition principle for viscoplastic strains of asphalt mixtures obtained from creep-recovery tests in the low-strain regime

The creep compliances, total, and viscoplastic (VP) strains of various asphalt mixtures were determined from creep-recovery tests at different temperatures to construct their master curves. In order to ensure the reliability of the obtained results, the agreement between quantities in the time and frequency domain as well as sources of bias in testing were investigated. A viscoelastic and a VP model were used to respectively characterise the reversible and irreversible deformation of the materials. The behaviour of the specimens exerted by a constant stress at various temperatures were then predicted using independent values of the viscoelastic and VP reduced times. Owing to the good agreement between prediction and measurement, the time-temperature superposition principle in the VP domain was verified. In general, the shift factors were uncorrelated with each other. However, at elevated temperatures, the gaps between them became unimportant, enabling the extension of viscoelastic shift factors into the VP domain.