Colorado Public Works Journal, Fall/Winter 2022

4 /The Road Ahead WWW.CO-ASPHALT.COM LOCAL AGENCY NEWS The Value of Using Stone Matrix Asphalt (SMA) on High Traffic Streets and Roads Over 5 million tons of stone matrix asphalt (SMA) have been placed on Colorado roads and highways since 1994. SMA is often the surface material of choice where a highly durable, long lasting and skid resistant surface is required, including Interstate highways, urban arterial roadways, high volume intersections and bridge decks. Stone Matrix Asphalt (SMA) is a tough, stable, rut-resistant mixture. The SMA design concept relies on stone-on-stone gap-graded aggregate to provide strength with a PG 76-28 polymer modified binder to provide durability. Rut resistance relies on aggregate properties rather than asphalt binder properties. Therefore, SMA is almost exclusively used for surface courses on high volume interstates and U.S. roads. Because SMA mixes have a high asphalt binder content, as the mix sits in the HMA storage silos, transport trucks, and after it is placed, the asphalt binder has a tendency to drain off the aggregate – a phenomenon known as “mix draindown.” Mix draindown is typically combated by adding cellulose or mineral fibers to keep the asphalt binder in place. SMA in Colorado is produced and generally available from May 1st thru Oct 31st. The availability of SMA is highly dependent on the production of PG 76-28 polymer modified binder, which is usually only produced in Colorado from May thru October. SMA Construction Season