Fine Aggregate Angularity Research in the Rocky Mountain Region

Most of the states in the Rocky Mountain Asphalt User Producer Group tested five to 24 of their most commonly used aggregate sources. In some instances, the natural fine aggregates and crushed fine aggregates from the same source were tested. In other instances, only crushed or natural fine aggregates were available.

Based on results of this testing, the following conclusions were made:

1. The test seems to accurately differentiate between crushed and natural fine aggregate. There is noticeable difference.
   
2. There is not much difficulty in meeting the minimum uncompacted voids of 45.0% as recommended in Superpave. When 100% crushed material was tested, the crushed fine aggregates met the specification for all but 2 of the 77 different sources.
   
3. There is some concern that more than 20% natural fine aggregate might be allowed in the mixture because of the high angularity of some of the crushed fine aggregates, particularly from quarries.