Comparison of DSR and BBR tests for determining the Performance Grade (PG) of asphalt binder at low temperature

The current specification requires the use of two different testing devices for determining the Performance Grade (PG) of asphalt binder. The Dynamic Shear Rheometer (DSR) is used for estimating the high PG while the Bending Beam Rheometer (BBR) is the reference method for obtaining the low PG. This is associated to a number of drawbacks both from a practical testing viewpoint (differ-ent specimen preparation) and because of the costs required to purchase two devices. Therefore, if the DSR can be used to characterize asphalt binder at low, intermediate and high temperature, this would be beneficial for practitioners on a testing routine basis. In this paper, the possibility of using the DSR for determining the binder low PG, avoiding BBR testing is experimentally investigated. For this purpose, a plate-plate geometry with a diameter of 4 mm and a gap of 1.75 mm was selected to estimate the material rheological properties and, hence, the low critical temperature. In particular, the slope and the magnitude of the shear stress relaxation modulus master curve, determined with the DSR, are correlated with the corresponding stiffness and m-value from the BBR measurements. The temperature corresponding to the PG grade is determined and compared with the one obtained in the BBR. The experimental results indicate that the low PG obtained from DSR and BBR are equivalent.