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Stone mastic asphalt is more commonly referred to as SMA
Stone mastic asphalt, or SMA, was developed in Germany in the 1960’s to provide a more hard wearing surface layer for roads, highways, highly trafficked car parks and other commercial areas.
Stone mastic asphalt consists of a high content of coarse aggregate (70% – 80%) which interlocks, and is filled with a mastic mixture containing bitumen (6% – 7%), filler (10%) and fibres (less than 1%). The high content of aggregate creates a greater stone on stone contact than bitmac to provide a more stable and durable finished surface than tarmacadam, which resists deformation.
Advantages of Stone Mastic Asphalt
- SMA provides a more textured and durable wearing course than bitmac making it more resistant to ruts.
- The surface texture characteristics of SMA means that the noise generated by traffic is lower.
- SMA can be manufactured and installed with the same plant and equipment required for normal bitmac.
- The mastic mixture in SMA surfacing makes it more flexible and hence less likely to crack when compacted on unreliable sub-bases.
Disadvantages of Stone Mastic Asphalt
- The higher binder and filler contents, together with the fibre additive results in higher material costs.
- The mixing time for SMA is greater than that for bitmac which, together with the time taken to add extra filler, will result in reduced productivity and increased cost.
- Lower friction levels result in initial skid resistance being low until the top binder film is worn off by traffic.