Old Concrete Makes Way for New Asphalt

Abstract

Back in the middle seventies, the latest civil pavement engineering techniques and technology transformed the old single carriageway trunk road which linked the Western Cape towns of Cape Town and Somerset West together as well as connecting them to the eastern part of the country. This transformation changed this road into a modern dual carriageway facility. This new facility was constructed with the then latest technology involving slip form paved concrete. All went well until a new phenomenon involving the interaction of sodium monoxide in cement and the alkali minerals in the local crushed rock caused the concrete to expand and evidenced severe failure. Although this early failure was kept in check for over 40 years, the section of this road which forms part of the transport hub at Cape Town International Airport, has finally been reconstructed giving way to a highly modified bituminous binder based pavement. The new pavement consists of an asphalt base, surfacing and friction course all produced with modified bituminous binders. The supporting layers have been constructed by recovering and crushing the old concrete and combining with further cement to form the stabilised supporting layers. This is regarded as a fully green approach to salvaging old problematic pavement materials. With minimal effort and modification sound subbase layers have been created to provide the necessary support to the construction of modern asphalt layers to produce a more flexible pavement alternative for safe travelling on this busy route.