U. S. requirements for aggregates constitute a compromise between high quality conditions and the necessity of taking into account the economics of manufacturing asphalt mixtures. The number of properties specified are limited, while the requirements themselves are somewhat broad (see Table 5.5), compared with the European standards. The requirements also vary from state to state. Similar requirements are used in the United States for SMA airfield surfacing (ETL 04-8).
Additionally, the possibility of using reclaimed dusts (baghouse fines) from an asphalt mixing plant is a fine example of the pragmatic approach to the selection of aggregates for asphalt mixtures.
Dusts, mineral powders, hydrated lime, and pulverized fly ashes are allowed, while lumps and organic impurities are excluded as fillers in the United States.
