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.

Introduction and Research Approach -- Findings -- Interpretation, Appraisal, and Applications -- Conclusions and Recommendations -- References -- Appendixes.

Low temperature cracking is a major distress for flexible pavements in cold regions. Most tests that are used currently to predict asphalt mixture performance at low temperatures require long time and effort to perform the test and analyze the data. A new laboratory test called the Ohio CTE device (OCD) has been developed as a more practical alternative to predict the asphalt mixture performance at low temperatures. This study presents an evaluation of the Ohio CTE device (OCD) in terms of effort for sample preparation, testing time, repeatability of test results, and complexity of the analysis of test data. To assess the ability of the Ohio CTE device (OCD) to predict the low temperature performance of asphalt mixtures, results obtained from this test were correlated to three other common low temperature tests, including the creep compliance and indirect tension test (IDT), the thermal stress restrained specimen test (TSRST), the asphalt concrete cracking device test (ACCD). Nine asphalt mixtures prepared using the same aggregate blend and different asphalt binders were included in this study. High correlation was observed between the Ohio CTE device (OCD) test results and results obtained from the other laboratory tests. In addition, the Ohio CTE device (OCD) was found to be advantageous over the other low temperature tests in that it requires significantly less time to prepare the test samples, which suggests that the Ohio CTE device (OCD) can be used as a routine test for low temperature characterization of asphalt mixtures.

This work presents the results of RILEM TC 237-SIB (Testing and characterization of sustainable innovative bituminous materials and systems). The papers have been selected for publication after a rigorous peer review process and will be an invaluable source to outline and clarify the main directions of present and future research and standardization for bituminous materials and pavements. The following topics are covered: - Characterization of binder-aggregate interaction - Innovative testing of bituminous binders, additives and modifiers - Durability and aging of asphalt pavements - Mixture design and compaction analysis - Environmentally sustainable materials and technologies - Advances in laboratory characterization of bituminous materials - Modeling of road materials and pavement performance prediction - Field measurement and in-situ characterization - Innovative materials for reinforcement and interlayer systems - Cracking and damage characterization of asphalt pavements - Recycling and re-use in road pavements This is the proceedings of the RILEM SIB2015 Symposium (Ancona, Italy, October 7-9, 2015).