Permanent Deformation Characterisation of Gap-Graded and Continuous Graded Aggregate Blends for Bituminous Mixtures

One of the major parameters which influence the performance of bituminous mixtures is a packed aggregate skeleton with minimum particle rearrangement during traffic loading. The current practice of aggregate design for bituminous mixtures is mostly based on the Fuller-Thomson model to achieve maximum density. However, this approach does not explicitly take into account the volumetric requirements of the bituminous mixture in terms of rutting and fatigue. This study investigates the mechanical behavior of bituminous mixtures prepared using aggregate gradations, designed based on binary particle packing model of Powers (1964) extended to multicomponent packing by Lees (1970). One control sample and two designed gradations are analysed, in which the first one is a continuous gradation, whereas the second one is a gap gradation. A binder content of 5% is used for the three bituminous mixtures. Samples are subjected to dry rut wheel testing and repeated creep and recovery test with a modified test protocol to quantify their rutting performance. Test results indicate superior rut resistance of the gap-graded aggregate mix. Also, the link between aggregate gradation, compactability, and rut resistance of bituminous mixtures is established for a given binder content.