Time-temperature superposition and AASHTO MP1a critical temperature for low-temperature cracking

Thermal stress calculations performed as part of the AASHTO MP1a low-temperature criterion are based on stiffness master curves generated from test data obtained at two temperatures. The time-temperature superposition (TTS) principle is considered valid although no verification of the validity has been reported so far. This paper addresses this issue by comparing the master curves obtained from 4-min creep tests performed at two test temperatures with data obtained in a 2.5-h creep test. Due to the presence of physical hardening a limited analysis is conducted to quantify the effects of physical hardening on the calculation of the critical temperature, T_CR. Two methods for calculating T_CR are investigated: the Dual Instrument Method and the Single Asymptote Procedure. The analysis indicates that T_CR is not sensitive to small deviations from TTS validity. However, T_CR as well as the limiting temperatures from Bending beam rheometer stiffness and m-value and Direct tension failure strain are considerably affected by physical hardening.