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Services | Stone Matrix Asphalt
Stone Matrix Asphalt (SMA) was originally developed in Europe as an impervious/highly durable wearing surface for bridge decks. It was introduced to the United States in 1990 and has been growing in popularity ever since, especially for heavy load/traffic routes. Georgia and Maryland have done extensive studies on SMA and are now expanding their use of the pavement as well as spreading the word to other states. Kentucky has placed several SMA projects to date and based on the results, the state plans to do more in the future.
SMA is a hot mix asphalt consisting of two parts – a coarse aggregate skeleton and a binder rich mortar. It is made up of a mixture of crushed coarse and fine aggregates, mineral filler, asphalt cement and a stabilizer for the binder, such as polymers and fibers.
The philosophy of SMA is that the coarse aggregate skeleton stone portion provides a stone on stone contact to prevent rutting and provide skid resistance. The mix is held together with sufficient specialized mortar to prevent draindown of the binder and to provide the mix with durability.
Benefits of Stone Matrix Asphalt:
- Rut resistant
- Durable
- Skid resistant
- Reduced spray
- Reduced hydroplaning
- Reduced noise
Fly ash can be used as a high quality, cost-effective mineral filler in SMA mixes. Mineral fillers increase the stiffness of the asphalt mortar matrix, improving the rutting resistance of pavements. Mineral fillers also help reduce the amount of asphalt draindown in the mix during construction, which improves durability of the mix by maintaining the amount of asphalt initially used in the mix. Fly ash will normally meet mineral filler specification requirements for gradation, organic impurities and plasticity. Carbon content, or LOI, is generally not a concern for SMA, as ashes with up to 10% LOI have performed well in laboratory tests. Also, fly ash is hydrophobic, reducing the potential for asphalt stripping.
When used as a mineral filler in SMA, fly ash must be in a dry form and is typically transported to the plant in pneumatic tankers and stored in silos. The fly ash is metered into the SMA mix using an auger.
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