Mixture Design and Compaction

The majority of current bituminous mix design procedures depend heavily on volumetric analysis, and on measuring density after a given compaction effort. There have been many questions about the influence of the compaction method on performance, and the lack of suitable simulation of field compaction in the lab. There are also concerns about the interactive effects of the laboratory mixing and compaction temperatures on the laboratory compaction methods. While there are no agreements on which method is the best in terms of simulating field conditions, there is agreement that density alone does not correctly reflect the potential of mixture to resist the damages caused by traffic loading. One of the evolving concepts to complement density and more accurately estimate this potential is characterization of aggregate skeleton and particle to particle interaction using imaging technology. However, methods of reducing images to engineering characteristics that can complement mix design procedures, and perhaps allow better simulation of field compaction, are still not in reach. This section is focused on giving background about various widely-used compaction methods, and about imaging techniques used for characterizing bituminous mixtures. It also covers a project carried out by the RILEM group on introducing the newly developed iPas software for image processing and analysis of 2D images of asphalt mixtures. As a part of this work, the software was used and verified in a large experiment that included many leading bituminous testing laboratories, from various countries.