Innovative use of builders’ rubble

Builders’ rubble is a valuable construction material and the Solid Waste Management Department at the City of Cape Town (CoCT) has recognised that it has no place occupying valuable landfill airspace. The city is now maintaining separate stockpiles of clean builders’ rubble (less than 10% contamination with other material), which attracts a significantly lower landfill gate fee.

However, due to a struggling construction industry and a perception in the public sector that builders’ rubble is a liability in construction, the large stockpiles of builders’ rubble at the Coastal Park Landfill had grown to approximately 450 000 m3 , restricting operations and planning at the landfill. In response, the CoCT prioritised the use of builders’ rubble in the earthworks contract for the construction of its new materials recovery facility (MRF) at Coastal Park.

The process

Site surveys and geotechnical studies revealed that the builders’ rubble stockpiled at the landfill was suitable for the production of 19 mm aggregate, G7 and G9 materials (as per COLTO specifications) for the bulk earthworks and construction of detention ponds and a section of bioswale. Furthermore, material suitable for the production of both sub-base and base material for the layer works of access roads was identified for the above earthworks contract. In response, the tender document was tailored to require the inclusion of builders’ rubble, with pricing requested for both builders’ rubble, which on average was offered at a cheaper rate, as well as commercially available virgin material, thus driving green procurement.

Approximately 60 000 m3 of rubble sourced from the Coastal Park stockpile was subsequently used in the earthworks and bulk services contract. Certain portions only required screening to produce suitable aggregate to meet the technical specifications, while other material was screened, crushed and, in some cases, blended to achieve the required grading. The CoCT found that builders’ rubble is a useful construction material when the quality and performance of the material is well matched to the application and recommends that municipal construction tenders make provision to favourably consider appropriate builders’ rubble sources.

The CoCT’s Green Procurement Action Plan is designed to facilitate the use of recycled or recovered materials in its operations and projects. Further projects at the Coastal Park Landfill, including the construction of a new landfill cell, are also designed to include locally available builders’ rubble.

As the CoCT continues to provide waste diversion projects, it hopes to increase the number of citizens participating in this sustainable behaviour.