Low temperature cracking is considered one of the primary distress modes of asphalt pavements built in northern climates. The detrimental effects of low-temperature cracking of asphalt pavements have motivated new work in fracture testing of hot-mix asphalt (HMA). A comprehensive study was conducted to investigate the effect of various factors on the fracture resistance of asphalt mixtures at low temperatures. The Semi-Circular Bending (SCB) and Disc-Shaped Compact Tension Test (DCT) fracture tests were performed at three low temperatures to measure the fracture energy for 28 asphalt mixtures, which represent a combination of factors including binder type, binder modifier, aggregate type, asphalt content and air voids. In this study, the analysis from the experimental data indicates that fracture energy is strongly dependent upon temperature and significantly affected by type of aggregate and binder modifier. The results of the analysis show the significance of air voids in the SCB test, but no statistical difference was found for the DCT test data. The analysis also illustrates that richer mixtures, ones with more asphalt than the design optimum, are not necessarily more crack resistant.

Low-temperature cracking is a significant distress in asphalt pavements built in the northern United States and Canada. As temperature decreases, thermal stresses develop in the restrained asphalt surface layer; and when the temperature reaches a critical temperature, cracking occurs. The current guides use thermal stress as a critical input parameter in the low-temperature performance model. In this paper, statistical and graphical analyses are performed to compare thermal stresses that develop in an idealized asphalt pavement calculated from mixture creep data obtained using indirect tensile test (IDT) and bending beam rheometer (BBR) test. In addition, the idea of obtaining thermal stresses from binder BBR creep data is further investigated. Thermal stresses calculated using IDT and BBR mixture creep data, respectively, are similar. Thermal stresses calculated from binder creep data are significantly different than thermal stresses calculated from mixture creep data. The effect of physical hard...

The oxidative aging that takes place in the asphalt binders used in the construction of asphalt pavements significantly affects the performance of the pavements during their service life. In this paper two issues that still generate a lot of debate in the research community are investigated: how far aging penetrates inside the asphalt layer and how reasonable laboratory aging tests simulate the aging occurring in the field. Cores were obtained from three cells at MnROAD facility and the binders were extracted and recovered from 25 mm slices cut along the depth of the cores. The properties of the recovered binders as well as the properties of the original binders aged in laboratory conditions were investigated, using standard testing procedures part of the current specifications as well as additional test methods. The results indicated differences in aging effects with location inside the asphalt layer and significant differences between the recovered and the laboratory aged binders.

The creep compliance is one of the main material characteristics used to describe low temperature behavior of the asphalt mixtures. It also serves as a primary input to the current thermal cracking model in the US that is used to predict thermally induced cracking in asphalt pavements over their service life. The current standard method in the US to determine creep compliance of asphalt mixtures is the Indirect Tensile (IDT) test. This paper investigates the feasibility of using the Bending Beam Rheometer (BBR) device to determine the low-temperature creep compliance of thin asphalt mixture beams (127x12.7x6.35mm). The BBR was used to evaluate 20 different asphalt mixtures and the results were compared with the standard IDT results. Direct comparison of the BBR and the IDT results indicate that both methods produce slightly different creep compliance curves and the relative ratio between the BBR and the IDT results varies with time and temperature. A simple phenomenological relation was proposed that gives good predictions of the IDT results based on the BBR creep compliance. Furthermore, short-term aged asphalt binders used in the mixtures were also tested in the BBR. Modified Hirsch model was applied to the BBR results on both mixtures and binders and it was shown that this model is capable of producing quite accurate results in forward and inverse predictions using considered dataset. It was concluded that the BBR can be used in practical and surrogate estimation of the mixture creep compliance but proposed scheme requires validation on other mixture types.