Evaluation of Cracking Susceptibility of Alaskan Polymer Modified Asphalt Binders using Chemical and Rheological Indices

Asphalt pavement cracking (especially thermal cracking) is one of the most prevalent pavement distresses in Alaska and other northern states in the United States. Rheological indices such as the Glover-Rowe (G-R) parameter and ΔTc have been reported to have potential in evaluating cracking susceptibility (durability) of asphalt binders, though not been applied to Alaskan asphalt binders yet. The objectives of this study are to evaluate the cracking susceptibility of Alaskan asphalt binders by using these indices and other chemical parameters, and to assess the applicability of these indices. A total of 13 plant-produced asphalt binders (neat and polymer-modified) were collected from Alaskan paving projects. Fourier transform infrared spectroscopy tests were conducted to obtain the chemical index (i.e., Carbonyl Index), and dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests were performed to determine rheological indices such as the G-R parameter, the crossover frequency, the rheological index (R-value), and ΔTc. The Carbonyl Index results during asphalt oxidative aging indicated that the modified asphalt binders were less prone to oxidative aging than the neat asphalt binder. However, the ΔTc results reached the opposite conclusion. The modified asphalt binders showed more negative ΔTc values than the neat asphalt binder at long-term aging states (e.g. 40 h pressure aging vessel (PAV)). The G-R parameter results indicated the studied Alaskan asphalt binders were not susceptible to cracking at long-term aging state (e.g. 20 h PAV). In addition, it was found that Asphalt binders from different suppliers could have different cracking susceptibilities (durability) even though they had the same performance grade. The ranking correlation analysis results between Carbonyl Index and G-R parameter (and ΔTc) indicated that both G-R parameter and ΔTc had potential to assess the cracking susceptibility of Alaskan asphalt binders. However, more data is needed to further validate the conclusion. It was not recommended to use crossover frequency and R-value to assess the cracking susceptibility of Alaskan asphalt binders studied since it\u27s the crossover frequency and R-value were difficult to be obtained precisely due to the low phase angle value (sometimes lower than 45° along the whole frequency range). Within the scope of this study, the applicable of the current standard linear amplitude sweep (LAS) testing and analysis protocols to the Alaskan highly modified asphalt binders is questionable