CAPE TOWN’S FIRST MAJOR PERMEABLE PAVING PROJECT COMPLETED :

The project entailed removing an asphalt surface and re-laying the entire square with concrete block paving (CBP).  Most of the ±20 000m² project involved the use of conventional concrete block pavers (CBPs) apart from a ±5 000m² strip at the bottom end of the square which has been surfaced with a PCBP system. The PCBP strip has more than sufficient infiltration capacity to handle the storm water run-off of the entire square.

Permeable paving was chosen as the most suitable means of storm water rain attenuation as other systems such as catch pits or ponds were deemed unsuitable for controlled water dispersal by the Cape Town City Council’s Spatial Planning and Urban Design Department.

The project entailed laying conventional pavers and Aquaflow permeable paving blocks in colour demarcated squares, 25 000 pavers in each square. The pavers, which measured 220mm x 210mm x 80mm, were supplied in three colours, sandstone, burgundy and dark charcoal by Concrete Manufacturers Association (CMA) member, Inca Concrete Products (Western Cape).

Inca manufactures Aquaflow permeable paving and sustainable urban drainage system (SUDS) blocks under license to the British CBP manufacturer and SUDS design company, Formpave. Fellow CMA member, Concor Technicrete, jointly holds the Aquaflow rights to the rest of South Africa with Inca.

The permeable paving strip comprises a sub-base layer of: compacted insitu base; a geofabric cloth laid on it; a layer 250mm 63/10 aggregate; a layer of 100mm clean 20mm aggregate and a top layer of 50mm 5mm aggregate on which the permeable pavers were laid.

The water percolates through this base and is removed via perforated pipes wrapped in geofabric to the existing flood drains. A high water table and a layer of clay in the insitu base inhibits the infiltration of moisture into the ground.

CMA director, John Cairns, says PCBP has already been embraced by engineers and architects in Gauteng and KwaZulu-Natal. For example, the Aquaflow system has been used on the 13 000m² parking lot on the West Campus of the University of the Witwatersrand and on the driveway and yard areas of the affordable housing development, The Reeds, in Fairland, Johannesburg,” he said.

Bob Low, technical consultant to Inca Concrete Products – one of the largest black economic empowered concrete suppliers in South Africa –  highlights the many advantages and benefits to the developer of this green paving option.  It:

• Minimises storm water management issues which simplifies planning;
• Puts money in the developer's pocket because there's no need to install costly,   
  storm water, water collection and detention systems;
• Eliminates collection and detention areas, increasing the effective developable area, which also 
  saves the developer money;
• Lessens the chance of erosion and water seeping into basements;
• Makes for a better appearance because permeable paving eliminates the need for ugly surface
   run-off measures;
• Lowers maintenance costs because permeable surfaces require fewer repairs and need to be
  resurfaced less often;
• Channels water to the root systems of plants and trees in the vicinity, resulting in healthier
  vegetation;
• Removes pollutants at point;
• Re-harvests water through retention tanking systems – hence water conservation, and
• Gives credits on green certification programmes.

The main contractor on the Grand Parade project was Kaulani Civils South and Engineers, and the lead consultant was Iliso Consulting Engineers. The paving was laid by Highland Paving.

Preparation of the sub-grade layer prior to the laying of the sub-base material.

A bird's eye view of the half completed PCBP system project at Grand Parade Square.

A perforated drainage pipe rests on the first layer of geofabric.  The pipe is wrapped with a protective material to prevent the entry of fines.

Freshly graded aggregate prior to the laying of the second geofabric layer, the bedding material and the Aquaflow pavers.

Aggregate 200mm deep is spread out on the first layer of geofabric.

The completed permeable paving surface (foreground) on a particularly wet day. The effectiveness of the system can be clearly seen in the contrast between the PCBP surface and the conventionally paved surface in the background.

A close up of the two types of paved surface. The PCBP surface is covered the sandstone block on the right, whereas the conventional paving system is covered with the charcoal and burgundy pavers on the left.

DATE:  June, 2009
ISSUED BY: David Beer Communication Consultants
FOR:  Concrete Manufacturers Association 
ENQUIRIES:  John Cairns (011) 805 6742;   Bob Low (021) 904 1620
David Beer (011) 478 0239 or 082 880 6726.  Email: bigsky@ibi.co.za