Cape Seal Roadway Surfacing Treatments

The Cape seal process was developed in South Africa by the Cape Province, centered around Cape Town in South Africa. It grew out of a process of applying a hot premix of crusher dust and asphalt over a 19-mm seal. This procedure, first specified in 1950, was largely an effort to improve the durability of the existing single- and multicoat chip seal methods; initially, it was used only on new roads whose traffic did not exceed 300 heavy vehicles per day. Hot mix was used as a wearing course on the more heavily trafficked roads. With time, improvements made to this practice led — around 1957 — to the modern Cape seal process: a 19-mm chip seal coated with two layers of slurry seal and a 13-mm chip seal coated with a single layer of slurry.

In Australia, the use of Cape seals dates back to early sixties and, as in South Africa, was used primarily for new construction. In Australia’s practice, anionic slurry was applied over large stone chip seals to improve ride and to increase durability.  The first projects using Cape seal in the U.S. represent technology transferred from South Africa, much like the transfer that has occurred in recent years regarding stone mastic asphalt (SMA). The Cape seal process appears to have been introduced by Robin Campbell in a paper submitted to the 1977 International Slurry Surfacing Association (ISSA).

Reference:  Evaluation of the Cape Seal Process as a Pavement Rehabilitation Alternative