Low-temperature characterization of bitumen and correlation to chemical properties

A comprehensive understanding of the low-temperature performance of bitumen presents a crucial aspect in the durability of asphalt pavements. In order to capture these properties, current low-temperature testing by the bending beam rheometer (BBR) requires a relatively high amount of aged material, which is not always avail-able. In recent studies, the complex shear modulus and phase angle acquired using a 4 mm geometry with the dynamic shear rheometer (DSR) have been used directly as a criterion for the lower performance grade of bitumen. The purpose of the presented study was to assess the application of the previously developed 4 mm DSR test method for material characterization at low temperatures and to develop a correlation between mechanical and chemical properties. BBR and DSR measurements were performed on 8 non-modified and 4 polymer-modified binders. Fourier transform infrared (FTIR) spectroscopy and SARA fractionation were used to gather chemical information about the samples. A strong linear correlation (R2 = 0.93) between the results from BBR and DSR measurements could be observed, allowing an accurate assignment of the low-temperature performance grade for a majority of the investigated samples. Additionally, connections between the FTIR aging index, asphaltene content and the ratio of SARA fractions to the continuous lower performance grade and Delta Tc were observed. This demonstrates the potential of chemical analysis methods to provide information about the low-temperature properties of bitumen.