The volume of a compacted mix not occupied by aggregate or binder, written as a percentage and calculated from the specimen's bulk gravity and the mix's maximum gravity: Va = 100 x (1 - Gmb/Gmm). Dense-graded mixes are designed at about 4 percent in the lab, and field compaction aims for roughly 6 to 8 percent in place. Too few voids lead to bleeding and rutting; too many let in water and air, so the mat ages, ravels and strips early.
Plant voids are running 2.8, mix is way too rich, back the oil off before it starts flushing in the wheel paths.
Lab voids and field voids are different numbers, about 4 percent in the puck and around 7 percent in the road, and newcomers mix them up when reading test reports.
Also heard as
- voids
- Va
- VTM
Do not mix it up with
- VMA: VMA counts all the space between aggregate particles, binder included; air voids are only the empty part of that space.
Related terms
VMA
Voids in mineral aggregate: the space between aggregate particles available for binder and air.
VFA
Voids filled with asphalt: the share of the aggregate voids occupied by binder rather than air.
Gmm
Maximum specific gravity of the mix: the density it would have if every air void were squeezed out.
Density
How tightly a compacted asphalt layer is packed, reported as a percentage of its maximum theoretical density.
Ndes
N design: the number of gyrations a mix specimen gets in the gyratory compactor, set by expected traffic.