Effects of Aggregate Shape Parameters and Gradation on High-Modulus Asphalt Mix Performance

Studying the performance of an asphalt concrete mix generally focuses on parameters such as the volumetrics of an asphalt mix, asphalt binder type, and content. However, the aggregate source and morphology can also significantly contribute to the performance of asphalt mixes. This paper investigates the influence of aggregate shape parameters (roundness, concavity, shape factor, and elongation) and gradation on the performance of low air-void high-modulus asphalt mix or Enrobe a Module Eleve (EME). Two high modulus mixes based on nominal maximum aggregate sizes of 12.5 and 19 mm were developed using two sources of mineral aggregates. The shape parameters of aggregate fractions were determined using an aggregate image analyzer. Thermo-mechanical tests were performed to evaluate performance of the developed mixes. The compactability of EME mixes was assessed using the Superpave Gyratory Compactor (SGC). The rheological properties of the mixes were evaluated by conducting complex modulus test at a range of temperatures (−10 to 54 °C) and loading frequencies (0.1–25 Hz). Furthermore, Hamburg wheel tracking and four-point bending beam fatigue tests were conducted to assess the rutting and fatigue performance of EME mixes, respectively. The aggregate image results indicated a considerable difference in roundness and concavity parameters of the aggregates. It was also concluded that the difference varies by changing the aggregate source and size. In addition, the performance test results showed that changes in the aggregate shape parameters along with the gradation can affect the performance of the mixes.