| Asphalt concrete is a heterogeneous material that consists of multiple components. Characterization of the internal structure of this complex material by means of digital image processing (DIP) has been a topic of interest for many researchers. Previous research has shown that applications of DIP and analysis methods for Hot Mix Asphalt (HMA) mixtures are not fully developed and implemented. Finding the most appropriate and efficient methods for obtaining, processing, and analyzing images of asphalt concrete is a current challenge.;Density of HMA is currently the most accepted quality control parameter for asphalt pavements. However, mixtures of similar density can show very different response to loading, in particular for accumulation of permanent deformation under traffic loading. This observation indicates that density of asphalt mixtures is not a sufficient performance criterion, and could be misleading in some cases. For this reason, it is necessary to find alternative means to quantitatively determine sufficient level of compaction and resistance to loading to minimize permanent deformation (rutting) of asphalt concrete. Identification of aggregate-to-aggregate contact points (i.e., aggregate proximity) by means of DIP techniques provides a fresh look at evaluating performance of asphalt concrete.;The main objective of this study is to advance the available knowledge and techniques of applying digital imaging for identification of internal structure of HMA, and determine the relationship between the internal aggregate structure and mechanical performance of the mix. Based on the results of this study, when accounting for >80% of the total aggregate in a mixture, mixtures of the same aggregate gradation compacted to the same density (i.e., percent air voids) can have a distinctly different internal aggregate structure. Such results suggest that a more complex parameter, or perhaps an interactive effect of multiple parameters, of the binder and aggregates are influencing the resultant aggregate skeleton and aggregate proximity. The aggregate skeleton and proximity can be used to define internal structure parameters which have been shown to correlate to resistance to permanent deformation, when the same aggregate gradation is studied. Challenges remain to define parameters derived from DIP that correlate with mixture response irrespective of gradation of aggregates. |
