Time-Temperature Superposition for Asphalt Concrete at Large Compressive Strains

A study was performed to evaluate whether time-temperature superposition principles would continue to apply to the behavior of asphalt concrete beyond the commonly assumed small strain (<100 με) limits. A series of unconfined uniaxial compression constant crosshead displacement rate tests were performed to large-strain values. The measured axial stress versus axial strain data were cross-plotted to produce stress versus reduced time master curves and corresponding temperature shift functions at various strain levels to determine the maximum strain level at which time-temperature superposition remains valid. The results suggest that asphalt concrete remains a thermorheologically simple material well into the postpeak region (i.e., that time-temperature superposition is valid throughout the useful stress-strain response). The results further suggest that the temperature shift function a_T may be only a weak function of strain level. For many practical engineering purposes, however, the differences between the small-strain and large-strain temperature shift relations may be of negligible importance.