Stone Mastic asphalt (SMA), otherwise known as Stone Matrix Asphalt / Split Mastic Asphalt, was developed in Germany in the mid of 1960's and it has spread throughout Europe and across the world in 1980's and 1990's respectively. The excellent performances include resistant to mechanical and temperature deformation, cracking, and particularly rutting, resistant to weathering actions such as aging and low temperature cracking. Durability is excellent even under slow moving heavy traffic. The textured surface increases skid resistance and provides environmental and driving comfort by reduced noise level, and improved visibility in rainy days.
SMA provides a deformation resistant, durable, surfacing material, suitable for heavily trafficked roads. SMA has found use in Europe, Australia and the United States 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 resist permanent deformation. The stone skeleton is filled with 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. The deformation resistant capacity of SMA stems from a coarse stone skeleton providing more stone-on-stone contact than with conventional dense graded asphalt (DGA) mixes. Improved binder durability is a result of higher bitumen content, a thicker bitumen film and, lower air voids content.
This high bitumen content also improves of flexibility. Addition of a small quantity of cellulose or mineral fibre prevents drainage of bitumen during transport and placement. The essential features, which are the coarse aggregate skeleton and mastic composition, and the consequent surface texture and mixture stability, are largely determined by the selection of aggregate grading and the type and proportion of filler and binder.