DESIGN AND CHARACTERIZATION OF ASPHALT MIXTURES BASED ON PARTICLE PACKING AND MECHANICAL MODELING
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Existing asphalt mixture design approaches are mainly empirical based "trial-and-error" methods. Based purely on volumetrics, such design methods have little consideration of the mechanical performance of the mixtures. With the trend of moving the pavement research into more mechanistic based methods and targeting the ultimate goal to good field performance, it is necessary to develop a sophisticated mix design and characterization methodology which can help the designer understand the expected engineering performance of the mix at the early stages, at the same time, to have a more efficient tool to evaluate the quality of the mixtures. This research develops a comprehensive aggregate gradation and asphalt mixture design method that estimates the mechanical properties of the mix at early stage. In this method, strong correlations between aggregate properties, volumetrics, and mechanical properties are identified, making the VMA (Voids in Mineral Aggregate) an excellent media to link the properties of aggregates and asphalt binder to their engineering performance. The concept of the design procedure, especially the aggregate gradation design procedure, is largely based on an analysis of aggregate packing and interlocking. As a fast and convenient design method that emphasizes more on the mechanical performance of the mix, the new design method can be used to evaluate the quality of an existing gradation and mix design, and adjust the gradation of a new mix to satisfy both volumetrics and mechanical properties. In addition, the characteristics of asphalt mixture are studied using micromechanical based discrete element method (DEM) and macromechanical modeling. In DEM simulation, an image based ball clumping technique is used for simulating the angularity properties of aggregate particles. The DEM model is established and calibrated to describe the viscoelastic (dynamic modulus and phase angle) and viscoelastic plastic (strength) properties of asphalt mixtures with or without damage involved. As for macromechanical modeling, a constitutive model for characterizing the permanent deformation of asphalt mixture is explored by taking consideration of the directional distribution of aggregates (anisotropy), and the damage induced by plasticity.