The First Concrete Freeway in South Africa

The first concrete freeway in South Africa was constructed between 1970 and 1971. It consisted of a dual carriageway, two-lane freeway with plain/jointed concrete pavement (PCP) for the traffic lanes and asphalt for the two shoulders. Three years after opening wider than normal hairline cracking was observed close to the transverse joints. Five years later surveys revealed failure occurring at about 1% of all the joints. Upon investigation it was found that failure was due to a chemical reaction between the high alkali cement and the local aggregate (Hornfels/shale of the Malmesbury Group) – known as alkali-aggregate reactivity (ASR). The expansive reaction initially caused a mosaic of fine cracks on the surface. Water entered the cracks and joints, eventually leading to pumping and a loss of fine material from the affected concrete, which resulted in structural failure at the joints and eventually pieces of concrete coming loose. By 1983 the concrete pavement reached the stage where rehabilitation was required. A computer model of the existing pavement was developed, and several rehabilitation options were investigated. The more feasible options were constructed as trial sections at the east end of the freeway during a contract in 1983. The test sections were subjected to heavy vehicle simulator (HVS) testing to calibrate the computer models and establish the most cost-effective rehabilitation option. The most viable rehabilitation measure was the construction of a bitumen rubber stress-absorbing membrane interlayer (SAMI), followed by a 40 mm bitumen rubber asphalt overlay. This paper will touch on the effects of alkali-aggregate reactivity on this pavement, summarise the findings of the trail sections and provide details of the rehabilitation measures implemented during 1985 and 1986. Most notable is the fact that while it was estimated at the time of design that the rehabilitation measures should provide a relatively maintenance-free pavement for at least seven years, it actually lasted more than 30 years.