Stone matrix asphalt, also called stone mastic asphalt, a gap-graded mix in which coarse crushed stones bear directly on each other while a rich mastic of binder, fines and fiber fills the gaps. Binder contents run 6 percent or more, usually polymer-modified, and cellulose or mineral fibers keep the binder from draining down in the trucks. SMA resists rutting under heavy traffic and lasts a long time, but it costs more and must be rolled hot with steel-drum rollers, never rubber tires.
No rubber-tire roller on the SMA, the mastic will pick up and you'll have bare stone in every tire track.
Drain-down shows up as binder puddled in the truck bed and fat spots on the mat; missing or clumped fiber is the first thing to check.
Also heard as
- stone matrix asphalt
- stone mastic asphalt
Related terms
Polymer-modified asphalt
Binder blended with an elastic polymer, usually SBS, to resist rutting in heat and cracking in cold.
Gradation
The distribution of particle sizes in an aggregate blend, reported as percent passing each sieve.
Pneumatic roller
A rubber-tired roller whose offset tires knead the mat, closing surface voids during intermediate rolling.
Pickup
Mix sticking to roller tires or drums and tearing out of the mat, leaving pockmarks behind.