1373033 - Low temperature performance characterization of asphalt bitumen: a Finnish case study

Asphalt bitumen is one of the main constituents of asphalt mixture used for pavement applications. This material exhibits significant time-temperature-dependent behavior. Hence, low temperature properties of asphalt bitumen play an essential role in designing asphalt mixtures in cold regions, such as Finland. Therefore, characterizing the low temperature properties of bitumen in a fast and accurate way is a critical task in Finland. Currently, the two parameters in the European asphalt bitumen characterization system were not designed for low temperatures: penetration value for intermediate temperatures while softening point temperature for high-temperatures. Hence, an alternative bitumen characterization system, Performance Grade (PG), originally developed in the U.S. was introduced to better understand the low temperature response of asphalt bitumen. In the PG system, parameters measured by Dynamic Shear Rheometer (DSR) were developed for high and intermediate temperature properties, while Bending Beam Rheometer (BBR) results were proposed for low temperature properties. However, due to the characteristic of the BBR test, such as the large volume of materials required, different cooling media compared with the field, and physical hardening phenomenon, limit its use. Several research groups attempted to use low temperature 4mm DSR as an alternative to BBR, and then different correlations were established between DSR and BBR results.

In this study, local Finnish asphalt bitumen were used to validate the current correlations between low temperature DSR and BBR. Ten different types of asphalt bitumen provided by Finnish suppliers, including unmodified, modified, and recycled, were measured by low-temperature DSR and BBR. Next, three parameters: critical temperatures of creep stiffness and relaxation modulus, and the difference between them were calculated based on the BBR results. Then, five different methods proposed by previous researchers were selected. The frequency domain DSR data was first converted into time domain BBR results to calculate creep stiffness and relaxation modulus. Then, the related three critical temperature parameters were calculated based on these methods. Finally, visual and numerical evaluation was conducted with statistical analysis of these five models. Results indicate that no single model can be used as a universal model to characterize the low temperature properties of Finnish source bitumen. A comprehensive Finnish bitumen database should be developed to better understand the low temperature behavior of bitumen used in cold regions.