Paving the way for rural roads
The need for permeable surfaces that allows for more natural absorption of water and pollutants, permeable interlocking concrete pavers (PICP)
PICPs have interlocking shapes; notched corners; or enlarged joints between them. The PICPs reduce stormwater runoff from roads, parking lots and walkways. This is provided that the openings are filled with aggregate mixes permeable to water.
Terracrete, a PICP developed by Terraforce in 1999, is ideally suitable for this purpose, as it is a paving block with larger openings (40% open), compared to paving blocks with widened joints (15% open).
“The bigger openings allow for coarse infill to be used which means better infiltration and easier maintenance. This allows tree roots to breathe and absorb water or nutrients that get washed off the paved areas.”
Designed with strength, Terracrete pavers are capable of accommodating vehicular traffic, making them suitable for the paving of grassed roads and parking areas.
Rust says, “from an aesthetic point of view, they are very versatile. A grass driveway, a rustic gravel driveway, or an attractive pattern of Terracrete pavers can add the finishing touch. With a grass finish, they can add a park-like or pastoral feel to areas normally needing hard paving.”
On African soil
In some African countries, there is an increased need to prevent the loss of topsoil and improve water absorption in urban or rural settings.
In Eswatini, Michael Toepfer from EFS Construction (Terraforce Licensed Manufacturer), tested the effectiveness of Terracrete permeable hard lawn pavers. Installing a test strip on a rural road on his and a neighbour’s property.
Says Toepfer, “The blocks (25 Mpa concrete mix, machine-made) installed June 2019 – in situ – as strips the width of car tyres. A little river sand is put down first to level out the surface before the blocks are laid.
The blocks are filled with loose stones to maintain permeability.
Where a driveway joins the road, the strip was extended to 7m long and 4.2m wide. Additional widening on the far side, to add extra stability and access and also to provide space for cars needing to pass each other.”
Toepfer completed and progressed the strips in stages over a few months. Testing each stage on how it would cope with regular traffic of approximately 50 vehicles per day.
In August 2019 he added some shaping and planting to the wider section of the road. “The goal is to mimic how nature would deal with stormwater runoff.
The purpose to guide the water into the grassed areas and provide erosion control.
On the outer side of the fully paved section, a simple runoff channel is created with the Terracrete blocks. One section is composted, then grassed and the blocks filled with in situ stones. In March 2020, wider sections added for extra stability surrounded by Kikuyu grass.”
Toepfer is happy to report that over 10 months the test strip has performed extremely well.
“After heavy rainfall (15 mm per hour) the rest of the road is heavily eroded and washed out. The test section is still in perfect nick. The section with the grass verges performs the best, in my opinion, it really absorbs any excess water.
Not a single block cracked, and even if it did, it is easy to replace blocks as they break.
Used by Municipalities
South African municipalities have started employing more ‘green’ methods to address erosion and stormwater management.
In 2015 the Roads and Stormwater Department of the Mossel Bay Municipality set out to correct a challenging section of gravel road.
The section of road with an incline of 17% was difficult to negotiate. After reviewing several products on the market, Altus Eitner, from Streets & Stormwater / Project Planning & Management, Mossel Bay Municipality. Chose the 350 x 350 x 90mm permeable paver Terracrete, manufactured to a 30MPa crushing strength by Mobicast Concrete Products, licensed Terraforce manufacturer, Southern Cape.
Don’t forget the roots
Large holes and a unique interlock the blocks are fully permeable and plantable. The roots of the plants anchor the blocks and anchor against floods. The holes allow worms and bugs to pass through the block without sterilizing (smothering) the area.
“Another beneficial aspect of the units is the size. The blocks are larger than other paving. The blocks provide a stable platform for the mowing of the grass. Block strength increased to 30 Mpa works for low volume roads eg. implemented at Stasiekop Weg Road with approx. 17% gradient.”
The damaged section of road is graded to a uniform profile. A cross fall is included in the side drainage channels. Next a 2.8m wide by 100mm deep strip is cut into the length of the road. The in situ bed is compacted with a 10-ton vibrating roller – using added water where necessary. To create a uniform, smooth working surface, it should be compacted to 92% MOD AASHTO. Terracrete units are laid on a prepared surface bed. The pavers are wired together with 3.1mm galvanised fencing wire.
At specified intervals, 900 mm long galvanised Y-standards are driven into the ground and connected to the wiring of the blocks. The block voids are filled with 2% cement stabilised soil. The voids with the 900mm anchors are filled with concrete.
The yellow brick road
The road has been in extensive use for the past 5 years to the entire satisfaction of the Municipality and the local Ratepayers Association. Says Val Marsh, Chairperson, Great Brak Heights: “The residents using this road are as upbeat as Dorothy in the Wizard of Oz, as she skipped along the yellow brick road! Continuing with the movie theme and addressing the municipal officials and employees – May the Force be with you.”