Thin asphalt layers (of less than 40 mm thickness) are oftenused for surfacings in South Africa. As these layers are placedon either stiff (cemented) or flexible structures it is importantthat they be rut resistant, durable and have good fatigue properties.Stone Mastic Asphalt (SMA) has been gaining worldwide acceptanceas a stable, durable and fatigue-resistant surfacing mix. Theobjective of this project was to develop a SMA design method suitedfor southern African conditions. This paper discusses:
- the recipe mix design methods prescribed by the various roadauthorities;
- basic principles of volumetric design;
- a theoretical model to determine the volumetric properties ofSMA mixes, and
- various compaction methods, including the gyratory compactorand the Marshall impact hammers.

In the design of SMAs the applicability of grading envelopesis compared with volumetric properties. The laboratory resultsare compared with those obtained from the model. The K-mould apparatus,a dynamic triaxial loading and data acquisition system, was usedto determine the rut resistance ie. dynamic creep and effectivestiffness (Esec) of the material.