SMA is a hard-to-compact mixture, and as a gap-graded mixture, it is characterized by a higher compaction resistance than materials with continuous gradation. The conclusions of tests carried out in Germany (Renken, 2004) on an SMA mixture revealed the following:
• An increase of the filler content brings about a drop in compaction resistance.
• An increase of the coarse aggregate content (particles larger than 2 mm) causes a sharp rise in compaction resistance.
• An increase of the binder content slightly reduces the compaction resistance.
Additionally, practice has proved that an increase in the manufactured sand content results in an increase in compaction resistance and that the opposite is true for the quantity of binder (those are commonly known relations). SMA mixtures with a low content of voids (1.5-2.5% v/v) are compacted more easily than those with a content greater than 4% v/v (Schroeder and Kluge, 1992).
When producing an SMA mixture, substantial deviations in batching the filler, binder, and coarse aggregate fraction also promote changes in compaction resistance, in addition to alterations in other properties.
