Developing Mixed-Mode (I/II) Fracture Resistance Curves for Asphalt Concrete Mixtures at Low Temperatures

Abstract

Mixed mode (I/II) loading conditions occur frequently in the asphalt layers of pavements. Therefore, a low-temperature fracture analysis based on mixed mode loading turns out to be of utmost importance. In this research, asphalt concrete (AC) mixtures were prepared using two aggregate gradations and PG58-22 bitumen. AC beams were produced by the mixtures and notch offset values of 48 mm, 75.2 mm, and 107.2 mm were fabricated in the beams in order to be tested in a modified single-edge notched beam (SE(B)) setup. The tests were carried out at two temperature levels of-5 °C and-15 °C. Using the modified SE(B) setup and capturing and processing digital imaged from the growing crack during the tests, fracture resistance curves (R-curves) in mixed mode (I/II) conditions could be constructed for each mixture. The results revealed that increasing the mode mixity and impairing the tensile mechanism in the fracture of asphalt beams could significantly contribute to higher fracture resistance of the mixtures. Mixtures with the highest mode mixity exhibited greater crack tip blunting energy by up to 25%. Similarly, energy dissipation in the unstable crack propagation zone is also increased being a desirable characteristic in post-peak performance of the mixtures.