Stone mastic asphalt

Stone mastic asphalt (SMA), also called stone-matrix asphalt, was developed in Germany in the 1960s. It provides a deformation resistant, durable surfacing material, suitable for heavily trafficked roads. SMA has found use in Europe, Australia, the United States, and Canada as a durable asphalt surfacing option for residential streets and highways. SMA has a high coarse aggregate content that interlocks to form a stone skeleton that resists permanent deformation. The stone skeleton is filled with a mastic of bitumen and filler to which fibres are added to provide adequate stability of bitumen and to prevent drainage of binder during transport and placement. Typical SMA composition consists of 70−80% coarse aggregate, 8−12% filler, 6.0−7.0% binder, and 0.3 per cent fibre.

SMA has many advantages ;

• SMA provides a textured, durable, and rut resistant wearing course.
• The surface texture characteristics of SMA are similar to Open graded asphalt (OGA) so that the noise generated by traffic is lower than that on DGA but equal to or slightly higher than OGA.
• SMA can be produced and compacted with the same plant and equipment available for normal hot mix, using the above procedure modifications.
• SMA may be used at intersections and other high traffic stress situations where OGA is unsuitable.
• SMA surfacings may provide reduced reflection cracking from underlying cracked pavements due to the flexible mastic.
• The durability of SMA should be equal, or greater than, DGA and significantly greater than OGA