Investigation on the cooling medium effect in the characterization of asphalt binder with the bending beam rheometer (BBR)

In this paper, the possibility of using air as an alternative cooling medium for testing asphalt binder in the bending beam rheometer (BBR) is considered and evaluated. For this purpose, five asphalt binders were characterized with the BBR; creep stiffness, m-value, performance grade (PG), thermal stress, and critical cracking temperature were computed both for ethanol and air. In addition, the rheological Huet model was fitted to the experimental measurements to further investigate the effect of the cooling medium. It was found that air measurements result in stiffer materials, with higher low PG, higher thermal stress, and critical cracking temperature. The parameters of the Huet model confirm such a stiffening effect when air is used. Based on the material response observed in this study, further research is recommended before potentially replacing ethanol with air in the BBR, as the latter appears to provide a substantially different material grading.