Evaluation of bending beam rheometer for characterization of asphalt mixtures

The feasibility of characterizing asphalt mixtures at low temperatures by means of the Bending Beam Rheometer (BBR) is investigated in this paper. The main difficulty in implementing this test method into current practice is the use of thin beams that may not capture the overall behavior of the actual asphalt pavement. The volume of material tested may not be representative, especially when the asphalt mixtures contained aggregate sizes that are larger than the smallest dimension of the beam. Three-point bending creep tests were performed on beams of different sizes: 6.25 x 12.5 x 100 mm (1x), 12.5 x 25 x 200 mm (2x), 18.75 x 37.5 x 300 mm (3x). The experimental results showed that a representative creep stiffness of asphalt mixtures can be obtained from testing at least three replicates of the thin (1x) mixture beams. Specimens of different sizes were analyzed based on digital image analysis and finite element modeling. The volumetric fraction and the average size distribution of aggregates obtained from image analysis of the 3x, 2x, and 1x specimens were found to be very similar. Detailed information on the internal structure of the specimens was investigated by estimating their spatial correlation functions. No large differences were observed between the correlation functions of the specimens of different sizes. Finally, the results from two-dimensional finite element simulations were used to determine the differences between the Young's modulus of two-dimensional projections of the 3x and 1x specimens.