Application of compressible packing model for optimization of asphalt concrete mix design

Packing of an aggregate blend is a measure reflecting how solid part and air voids would share the volume occupied by the blend. It is usually measured in terms of “packing density”. In this paper, Compressible Packing Model (CPM) is described as a potential technique to optimize aggregate blend by optimizing the packing density in asphalt mixes. Gradation envelops for high-performance asphalt mixes or Enrobé à Module Élevé (EME) were determined for two different mix types (12.5 mm NMAS and 19 mm NMAS) using CPM. Further, asphalt mixes were fabricated using two types of modified asphalt binders. Compactibility and volumetrics of the mixes were assessed. Dynamic modulus test was performed to evaluate the rheological behavior of the mixes at elevated temperatures as well as loading frequencies to develop master curves. Results of this study showed that the gradation limits obtained from CPM were very close to the grading control points of EME mixes and that the asphalt mixes had higher compactibility than the conventional mix. Dynamic modulus test results also depicted the designed mixes could meet stiffness requirement of EME mixes, and the mixes behaved more elastically.