Characteristics of Typical Minnesota Aggregates

Abstract

The consensus aggregate properties recommended in SUPERPAVE and selected mixture properties were evaluated for a wide range of Minnesota aggregate sources obtained from 16 construction projects completed in 1993. Measured aggregate properties included the sand equivalent (SE) and fine aggregate angularity for the fine aggregate fractions, and percentage of fractured faces and flat and elongated particles in the coarse aggregate fractions. Laboratory-compacted samples were prepared and tested to determine air voids, voids in mineral aggregate (VMA), tensile strengths, and an assessment of the moisture sensitivity of the mixtures. Only 3 of 29 SE values for individual stockpiles were less than 40 percent. These values were not significantly affected by changes in either the general mineralogy (i.e., igneous, limestone, mixed) or the percentage passing the 0.075-mm (No. 200) sieve. Single regression analyses indicated no significant relationship between SE and either mixture moisture sensitivity or VMA. While all 25 stockpiles tested had fine aggregate angularity values greater than 40, 9 stockpiles had values below 45. It was suggested that since Minnesota aggregate gradations commonly pass through the SUPERPAVE re-stricted zone (one purpose of which is to limit the use of rounded natural sands), the minimum fine aggregate angularity value be set at 45 for all mixtures to preclude the use of 100 percent natural sands. A significant number of Minnesota coarse aggregate stockpiles have a moderate to high content of flat particles (20 to 50 percent).