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.

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).

MoDOT has for the second time in about 10 years, performed the local calibration of the mechanistic-empirical pavement design guide software, now designated as AASHTOWare Pavement ME Design. Cold-temperature creep compliance and tensile strength of hot mix asphalt (HMA) are the two inputs to the thermal cracking module within the software and are required for local calibration.The test protocol used for this work is American Association of State Highway and Transportation Officials (AASHTO) test method T 322, "Standard Method of Test for Determining the Creep Compliance and Strength of Hot Mix Asphalt (HMA) Using the Indirect Tensile Test Device." MoDOT-supplied materials were a) 18 different sets of the top lifts (layers) separated from six inch diameter pavement cores, and b) 54 boxes of 150 mm diameter gyratory-compacted specimens (GCSs). The 54 boxes of GCSs were produced from 27 different plant-produced mixes compacted to two levels of air voids per mix. Creep testing was performed at 0, -10, and -20°C (32, 14, and -4°F, respectively) and tensile strength testing was performed at -10°C. Poisson's ratio was estimated from the creep testing results. With a few exceptions, expected trends of increasing creep compliance with increasing temperature, and decreasing tensile strength with increasing air voids were confirmed during top-lift core and GCS-derived specimen testing. With a couple of exceptions, GCS-derived specimen testing resulted in the expected trend of increasing creep compliance with increasing air voids, at all temperatures. Although they are not required for local calibration of the thermal cracking module, estimated Poisson's ratio values were reported but did not always follow expected trends (e.g. maximum value of 0.5), especially during the top-lift core testing.