SOUTH AFRICA’S FIRST PERMEABLE PAVING CONTRACT COMPLETED:

Permeable paving functions in one of two ways, either soaking surface storm water back into the ground-water table, or storing and then channeling it into storage sumps or tanks as “grey” water to be used for cleaning purposes, flushing toilets and the hydration of gardens. In this instance the former option was selected.

Permeable rather than conventional run-off paving was specified for The Reeds because the storm-water drainage system in this part of Fairland was built some 35 years ago and lacks the capacity to handle any additional run-off.

The permeable paving blocks were custom made for the project by Concrete Manufacturers Association (CMA) member, Concor Technicrete. Some 89 000 square units and 94 000 rectangular units were supplied to cover an area of 4 320m².

John Cairns, CMA director, says he believes that permeable paving is set to take off in a big way in South Africa.

“Until now local engineers have resisted the system mainly because they mistakenly believed that water and sub-base material don’t mix. However, the system has been used successfully for the past 20 years in Europe and for the past 10 in Australia, and there are engineers who are prepared to use the system. In addition, local councils are likely to begin approving new building projects with the proviso that some or all the paving is permeable,” observes Cairns.

The Reeds system was laid in the following manner: 500mm of top soil was removed and the exposed surface was then covered with an SABS approved BIDIM A5 geotextile membrane manufactured by Kaytech Engineered Fabrics.

Rockfill comprising 160mm stone 500mm deep formed the next layer followed by a second layer of geotextile membrane. The stone was non-friable so as to avoid breaking up too much when being graded by a 10 ton roller. Once compacted, the rockfill was covered with 80mm of coarse washed river sand and this in turn was compacted. To this was added another 20mm of washed river sand for bedding. The same sand was also used for jointing.

Rated at a compressive strength of 30MPa, the paving blocks were laid in a pattern specified by Concor Technicrete. Based on an overseas design, the pavers included vertical slots (three millimetres deep) at either end through which the water will flow into the sub-base. When newly laid, the absorption rate will be approximately 9 000lt per square metre per hour. Over the long-term this rate will reduce to roughly 1 000lt per square metre per hour which means a cubic metre of water will still be absorbed in an hour.

Cairns says that besides water conservation permeable paving has other benefits.

“Developers will see the economic benefits when they realise they no longer have to build storm water drainage and can add extra accommodation units to their developments. Roads can also be built with permeable paving which once again saves on storm-water drainage. Roads will remain dry even if they are completely level,” concludes Cairns.

The main contractor on The Reeds project was ASH Plant-Hire & Civils. Other members of the project team included Lidwala Consulting Engineers and paving contractors, Special Perfect Paving.

Rockfill is carefully graded during the construction of South Africa’s first permeable paving surface using solid paving blocks.

A 10 ton roller compacts rockfill comprising 160mm stone some 500mm deep during construction of the permeable paving surface at The Reeds, an affordable housing development in Fairland, Johannesburg.

South Africa’s first permeable paving project using solid paving blocks nears completion at The Reeds in Johannesburg.

A section of the completed permeable paved surface at The Reeds, an affordable housing development in Johannesburg.