Tough and resilient Stone Matrix Asphalt gets its anti-rutting properties primarily from aggregate, not binder.
The aggregate for SMA is gap-graded, meaning there are fewer middle range particles used in the mix design. The size and shape of the aggregate creates a strong stone-on-stone skeleton for pavement. Since aggregate deforms less than asphalt, SMA holds up under heavy traffic.
SMA uses more oil in the mix along with fibers that reduce the bleeding of the oil. The higher oil content makes SMA more expensive than regular Hot Mix Asphalt pavement.
Since it’s a relatively new product, “it took some time for the issues with the materials to be understood,” explains Lonnie Marchant, UDOT Region Two Materials Manager. Several local contractors have experience with SMA, so more projects will make use of the tough stuff. And UDOT specifications for SMA “are in good shape.”
The first SMA project in UDOT Region Two was recently completed on I-80 between Black Rock and the Salt Lake City Airport. More SMA projects are planned for Region Two during the upcoming construction season.
SMA is not appropriate for every location. Marchant says that SMA “is much more difficult to place,” and so “the material doesn’t lend itself for use on roadways where there are numerous tie-ins, utility adjustments or intersections.”
UDOT’s central materials lab tests SMA for oil content, gradation of the aggregate and compaction of the final product. SMA does not allow use of recycled asphalt pavement.