Voids in the mineral aggregate, the space between aggregate particles in a compacted mix that is filled by effective binder plus air voids, expressed as a percent of total volume. A minimum VMA guarantees room for a binder film thick enough for durability, and the minimum rises as the aggregate gets finer: 14 percent for a 12.5 mm mix and 13 percent for a 19 mm mix. Low VMA is a classic production problem when baghouse fines or crushed sand fill up the aggregate skeleton.
VMA dropped to 13.2 on the 12.5 mix, there's no room left for oil, check what the baghouse is sending back.
When VMA collapses during production, the usual suspects are baghouse fines coming back heavier than designed or a crushed-sand pile running finer than the design sample.
Also heard as
- voids in mineral aggregate
Related terms
Air voids
The small pockets of air between binder-coated aggregate in compacted mix, given as a percent of total volume.
VFA
Voids filled with asphalt: the share of the aggregate voids occupied by binder rather than air.
Fines
The dust-sized part of the aggregate passing the No. 200 sieve, which stiffens the binder into a mastic.
NMAS
Nominal maximum aggregate size: the sieve size used to name a mix, such as a 9.5 mm or 19 mm mix.