A Critical State Soil Mechanics approach has been taken to understand the interactions between the different aggregates and bitumen present in an asphalt mix. A series of conventional drained triaxial tests have been performed on samples of the aggregate used in Dense Asphaltic Concrete (DAC). These aggregate samples contained no bitumen and were prepared at two densities. The dense aggregate samples had a void ratio equivalent to the asphalt (DAC) samples where the bitumen was assumed to be part of the void space. The loose aggregate samples were prepared at a void ratio that was as loose as physically possible. The behaviour of the aggregate samples was compared to the asphalt samples when loaded continuously at a rate of 0.3% strain/hour. It has been found that at these slow rates of loading, the aggregates control the behaviour of the asphalt and the 5% bitumen content had little effect. Transitional soil behaviour of the aggregates was also observed as the dense and loose aggregate samples did not approach a unique critical state line when sheared to failure. The microstructure of the particle arrangements in the dense and loose aggregate samples was also observed under optical microscopes. Different particle arrangements were characteristic of the dense and loose samples. More bulky grain-to grain contacts were evident in the dense aggregate samples as the fines in the loose aggregate samples tended to flock together and form bridges between the bulky grains. As a result of this transitional soil behaviour, it was difficult to define Critical State Soil Mechanics parameters for DAC as required for advanced numerical modeling. This difficulty was also a consequence of the challenges in performing triaxial tests on the dense aggregate material.