Development of workability and compactability indicators for hot mix asphalt

With the recent changes to higher PG binders and to the coarser superpave type mixes, workability and compactability has become a more important topic. Concerns have been raised about mixes that are drier and more difficult to compact. It is particularly problem with the dense graded, widely used type C and type D mixes in Texas. Several new ideas are under consideration either to modify the existing mix-design criteria or include new and simple cracking test procedures.

This report provides the overview of the mix-designs and the laboratory evaluations of the three commonly used Texas mixes which are type B; Type C and Type D based on the Texas gyratory, and balanced mix-design procedures. Parameters were developed from the compaction curve to predict the performance of the mixes. The developed parameters could be as part of design procedure and eliminate the mixes which are too difficult to compact in the field and mixes that reach early compaction on traffic loading. To measure the stability of mixes two indices called WEI and CEI were developed. These indices used to analyze mixes with different constituents such as binder grade, percent of binder, gradation. Construction details of the three field sites are also discussed in this report. The energy indices developed from lab molded mixes were than compared to the field data and came up with a recommended threshold values for workability and compactability for HMA.