Overview
Road network
Approximately 80% of the surfaced road network of 150,000 km in South Africa is surfaced or resealed with surfacing seals, making it the most common type of surfacing used in South Africa.
The popularity of seals stems from them being relatively inexpensive when compared to other surfacing types and have a proven performance history under a wide range of traffic and environmental conditions.
South Africa has a well developed national and provincial road network which traverses a large and some times sparsely populated rural environment.
Due to the relatively low traffic densities on these rural surfaced roads, spray seals are the predominant type of surfacing. This is in contrast to the more built up-urban environments where hot mix asphalt is the preferred surfacing.
The widespread use of seals has been further advanced by developments in modified binder technology, which has extended the range of conditions in which seals are used, largely in situations which would previously have been considered the domain of hot mix asphalt.
Traffic
The traffic patterns, vehicle type and loading vary a great deal in South Africa, with only a small percentage of roads i.e. 2,600 km carrying in excess of 10, 000 AADT in both directions. Heavy vehicles comprise approximately 15% of AADT.
Pavement structures
The pavement structures typically consist of natural gravel bases, while heavier trafficked roads usually have cemented sub bases and crushed stone bases.
Most rural roads at time of construction are surfaced with a double seal or a Cape seal. These are resealed with single seals or slurries. Asphalt surfacings are usually only used on heavily trafficked rural roads, highways, urban streets and intersections.
Climatic conditions
The climatic conditions vary widely, and are defined by three distinct rainfall areas according to their seasonal occurrence, these being summer, winter and all-season. The rainfall increases from less than 125 mm in the west to over 1000mm in the east.
Air and road temperatures are strongly affected by altitude. In all areas of South Africa the maximum air temperature may exceed 35°C while the minimum temperatures in the inland regions might be as low as -8°C. Air temperatures influence the road temperatures which in turn dictate the type of binder to be used.