Volume 39, Issue 1 (January 2011)
Alternative Procedure for Determination of Hot Mix Asphalt Creep Compliance
Creep compliance function is one of the fundamental properties of viscoelastic materials. In asphalt research, creep compliance is used in the prediction of low-temperature cracking, which is a prevalent distress in asphalt pavements in northern parts of the United States and Canada. The thermal cracking prediction model included in the current version of the Mechanistic-Empirical Pavement Design Guide requires the creep compliance of hot mix asphalt (HMA) materials as a primary input. The current AASHTO procedure for determining creep compliance of HMA is based on the indirect tension (IDT) test. The IDT test is performed on relatively thick cylindrical specimens, which makes this test unsuitable for field cores from thin layers and construction lifts. In addition, thick specimens do not allow for investigation of the gradual aging that occurs in asphalt layers due to oxidation and volatilization. This paper outlines the procedure that uses the bending beam rheometer (BBR) as an alternative to the IDT test to determine the low-temperature creep compliance of HMA using thin beam specimens. Twenty different HMA mixtures are tested at three temperature levels using both the IDT and the BBR instruments. The analysis of test results is presented in two parts. First, the variability in creep compliance values obtained from the IDT and the BBR tests is discussed. Next, the artificial neural networks (ANNs) are trained to (1) predict IDT results from BBR measurements using design parameters of HMA mixture and testing temperature as the model inputs and (2) backcalculate HMA creep compliance from the binder creep compliance and vice versa. It is concluded that testing HMA beams can be used instead of IDT specimens for the low-temperature characterization of HMA mixtures, and the ANN can be successfully used for the backcalculation of the creep compliance measured by both IDT and BBR devices.