Time–Temperature Superposition and AASHTO MP1a Critical Temperature for Low-temperature Cracking

Abstract

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.

Keywords:

• Asphalt binder
• Time–temperature superposition
• Master curves
• Thermal stress
• Physical hardening

Acknowledgements

Support provided by the National Cooperative Highway Research Program (NCHRP-IDEA Grant 84) and the Ontario Ministry of Transportation (MTO Contract 9015-A-000190) is gratefully acknowledged. The binders from test sections on Highways 118 and 17 were kindly made available through the Ontario Ministry of Transportation.