Stone Mastic Asphalt Pavement Technology for the New Millennium

Since the 1960s, Stone Mastic Asphalt (SMA) pavement surfaces have been used successfully in Germany on heavily trafficked roads. Because of its excellent performance characteristics, road authorities in Germany as well as major European Countries quickly adopted SMA as a standard wearing course. As a consequence of an asphalt study tour in Europe of an American delegation in 1990, SMA test sections were constructed in several states in the United States. During the last few years, SMA has become one of the most popular asphalt pavements. This paper gives an overview of the history of SMA, its performance characteristics, its composition as well as its applications. This paper will also discuss the advantages of bitumen-compounded fibre pellets and the causes of fat spots which are one of the most objectionable occurrences in SMA mixtures. 1. History of Stone Mastic Asphalt Stone Mastic Asphalt (SMA), an asphalt paving mixture, was originated in Germany in the 1970s to provide maximum resistance to rutting caused by the studded tyres on European roads. Strabag, a large German construction company, led to the development of SMA. After the use of studded tyres was no longer allowed, it was found that SMA provided durable pavements which exhibited such high resistance to rutting by heavy truck traffic and proved to be extremely effective in combating wear. In recognition of its excellent performance a national standard was set in Germany in 1984. Since then SMA has spread throughout Europe, North America and Asia Pacific. Several individual Countries in Europe now have a national standard for Stone Mastic Asphalt, and CEN, the European standards body, is in the process of developing a European product standard. In the United States, Australia, New Zealand and in Asia, the use of SMA is increasing in popularity amongst road authorities and the asphalt industry.