DEFINING EFFECTIVE AGGREGATE SKELETON IN ASPHALT MIXTURE USING DIGITAL IMAGING
Roohi Sefidmazgi, Nima
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Characterization of the asphalt mixture microstructure using two dimensional (i.e., 2-D) imaging techniques is an economically efficient approach. However, the features that have been captured and quantified using 2-D imaging techniques in most published research have been limited to simplistic analyses of aggregate structure. This dissertation focuses on introducing a more elaborate method for characterization of the internal structure of aggregates. New microstructural indices are introduced and related to the performance of asphalt mixtures. The aggregate internal structure provides the skeleton of the asphalt mixture, which plays an important role in rutting resistance. In this research, it is shown that this structure can be characterized using a combination of newly developed image analysis indices namely: number of aggregate-to-aggregate contact zones, ratio of contact length to area, and contact plane orientation. These parameters are defined for both the total aggregates and for the effective load bearing aggregate structure, referred to as the ?skeleton? in this study. A software developed in a previous study and significantly modified for this dissertation, is used to process digital images of a set of asphalt mixtures with different gradations, binder contents, types of modification, compaction efforts, compaction temperatures, and methods. The results demonstrate a correlation between the internal structure indices and the mixture rutting performance. Additionally, the indices were successfully used to show the effects of compaction effort, compaction method and temperature, gradation of aggregates, and binder modification on the mixture internal structure. The results indicate potential for using this method for quality control of mixtures during production.