Between 2020 and 2022, two graduate students from the Department of Civil Engineering at the University of Cape Town (UCT) completed two studies on the permeability of Terracrete pavers and the factors that influence this. Ryan Moore completed his research in 2020 and Banele Noqayi completed his research in late 2021, both under the tutelage of Prof Neil Armitage from the Department of Civil Engineering at UCT.

Need for permeable paving

Terraforce developed Terracrete eco-pavers in 1998 and launched in 1999 a larger version of Exec with large internal openings, suitable for installing hardwearing, permeable eco-surfaces on roadways, parking areas, or for mixed-use installations such as stormwater detention ponds as well as for general erosion control measures.

Terracrete blocks used adjacent traditional paver to help with drainage of more impermeable surfaces.

Terracrete is now widely accepted as a versatile, cost-effective solution to be used in combination with conventional paving systems or as a standalone solution. 

Good permeability depends on the good design of a subbase and either grassed soil or gravel infill.

Testing the permeability of Terracrete pavers

Moore says: “The long-term infiltration rate tends to the natural soil infiltration rate calculated by the double-ring infiltrometer test shows that Terracrete systems maintain a steady long-term infiltration rate, with minimal maintenance required, and that these pavements can be aesthetically pleasing by increasing the green land on a property.”

The important takeout here is that contractors consider the original soil conditions in their planning – for example, clay soil is likely not to be permeable and needs extra drainage measures.

Noqayi’s conclusions echoed Moore’s findings in that “the infiltration of Terracrete eco-pavers is largely dependent on the underlying soil conditions”, which means the design of the sub-layers is crucial in areas where the soil proves less permeable.

Banele Noqayi doing a drench test at a private residence in Woodstock, Cape Town.

Noqayi also found that vegetation increases the infiltration rate through the root systems of plants, especially when the pavers were not filled entirely to the top to leave space for the growth of grass or other vegetation.

However, Holger Rust, founder and managing director of Terraforce, adds that this strategy may not always be acceptable, in which case loose gravel or stone infill is more appropriate, as stated in Moore’s research results.

Permeable pavers are here to stay

Rust describes a new method of creating permeable and efficient drainage/infiltration in existing paved areas or in new areas that are to be paved with asphalt or interlocking clay/concrete pavers. “The incorporation of drainage lines along edges, around perimeters and at predetermined centres across parking/storage areas or roadways makes it possible to upgrade existing ones or enhances the drainage/infiltration of new installations. This method can also be applied when new service or irrigation lines must cut across existing parking areas, while trees are established at the same time.”

Rust also adds that the Terracrete block is ideally suitable for this purpose, as it is a paving block with openings (40% open) compared to paving blocks with widened joints (approximately 15% open). The bigger openings allow for coarse infill to be used, which means better infiltration and easier maintenance. In addition, something that is often neglected, this allows tree roots to breathe, to absorb water and nutrients that get washed off the paved areas.

For more information, contact Terraforce:
Tel: +27 21 465 1907

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