Evaluation of Stone Matrix Asphalt (SMA) For Airfield Pavements

Stone Matrix Asphalt (SMA) was developed in Germany over 30 years ago. Its success has led to its usage throughout Europe on both highway and airfield pavements. In 1990, an American Association of State Highway and Transportation Officials (AASHTO) led European Asphalt Study Tour introduced SMA to the United States (U.S.) SMA has demonstrated good performance on highway pavements in the U.S., but has seen little use on airfields. Recently, there has been resurgence in interest in SMA in the U.S. as a more durable paving option than Superpave or other dense-graded mixes. SMA is a gap-graded asphalt mixture with a high percentage (> 70 percent) of coarse aggregate. Gap-graded refers to the fact that SMA mixtures typically have very little material retained on the sand size sieves (e.g. between 2.36 mm and 0.075 mm). SMA is differentiated from dense-graded mixes by its coarse aggregate skeleton, consisting of a limited number of particle sizes, which carries the load. Mastic, consisting of mineral filler, fibers, and asphalt binder, fills the voids between the coarse aggregate skeleton. The percentage by weight passing the 0.075 mm sieve is typically greater than 8 percent. Asphalt contents range from 6 to 7.5 percent by weight of total mix. Fiber, either cellulose or mineral, is generally added to prevent draindown of the binder during construction. SMA has been used extensively on airfields in both China and Norway. Additionally, airfields have been constructed using SMA in Australia, Belgium, Germany, Italy, Mexico, and the United States (U.S.). Additional details on specifications and individual projects are provided in reference. The U.S. Air Force constructed SMA runways in Germany and Italy.