Paving the way for rural roads

Permeable interlocking concrete pavers (PICP) are becoming increasingly popular as sustainable paving solutions that combine functionality with environmental benefits.

Terracrete: An Innovative PICP Solution

Terracrete, a PICP developed by Terraforce in 1999, is ideally suited for this purpose. Unlike paving blocks with widened joints (typically 15% open), Terracrete features larger openings (40% open), offering significant advantages:

• Allows for coarser infill material, resulting in better water infiltration
• Provides easier maintenance over time
• Enables tree roots to breathe and absorb water or nutrients from runoff
• Designed with sufficient strength to accommodate vehicular traffic
• Suitable for paving grassed roads and parking areas

According to Terraforce, “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.”

Case Study: Eswatini Rural Road Project

In Eswatini (formerly Swaziland), there’s an increased need to prevent topsoil loss and improve water absorption in both urban and rural settings. Michael Toepfer from EFS Construction, a Terraforce Licensed Manufacturer, tested the effectiveness of Terracrete permeable hard lawn pavers by installing a test strip on a rural road.

Toepfer’s approach included:

• Installing 25 MPa concrete mix, machine-made blocks in June 2019
• Laying the blocks in strips the width of car tires
• Using river sand underneath to create a level surface
• Filling the blocks with loose stones to maintain permeability
• Creating wider sections (7m long by 4.2m wide) where driveways joined the road
• Adding extra width in passing areas for vehicles to safely overtake each other

The project progressed in stages over several months, allowing testing with regular traffic of approximately 50 vehicles per day. By August 2019, Toepfer added landscaping elements to the wider road sections.

“The goal is to mimic how nature would deal with stormwater runoff,” explains Toepfer. “The purpose is to guide the water into 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 composted and grassed, the other filled with in-situ stones for comparison.”

Impressive Performance Results

After ten months of testing, Toepfer reported excellent performance:

“After heavy rainfall (15 mm per hour), the rest of the road was heavily eroded and washed out, while the test section remained in perfect condition. The section with grass verges performed best, in my opinion, as it really absorbed any excess water.”

The durability was impressive as well—not a single block cracked. And even if damage had occurred, the modular design allows for easy block replacement.

Municipal Implementation in South Africa

South African municipalities have begun employing more environmentally friendly methods to address erosion and stormwater management. In 2015, the Roads and Stormwater Department of the Mossel Bay Municipality used Terracrete to solve issues with a challenging section of gravel road.

The road section, with a steep 17% incline, was difficult to navigate. After reviewing several products, Altus Eitner from Streets & Stormwater/Project Planning & Management selected the 350 x 350 x 90mm Terracrete permeable pavers, manufactured to a 30MPa crushing strength by Mobicast Concrete Products, a licensed Terraforce manufacturer in the Southern Cape.

Ecological Benefits of Terracrete

A key advantage of Terracrete blocks is their environmental compatibility:

• Large holes and a unique interlock design make them fully permeable and plantable
• Plant roots anchor the blocks against floods
• The openings allow worms and insects to pass through
• Prevents “sterilizing” (smothering) the soil beneath

“Another beneficial aspect of the units is their size,” notes a municipal representative. “The blocks are larger than other paving, providing a stable platform for grass mowing. The increased block strength of 30 MPa works well for low-volume roads, as demonstrated on Stasiekop Weg Road with its approximately 17% gradient.”

Installation Process

For the Mossel Bay project, the installation process included:

1. Grading the damaged road section to a uniform profile with cross-fall in side drainage channels
2. Cutting a 2.8m wide by 100mm deep strip into the length of the road
3. Compacting the in-situ bed with a 10-ton vibrating roller (adding water where necessary)
4. Compacting to 92% MOD AASHTO to create a uniform, smooth working surface
5. Laying Terracrete units on the prepared surface bed
6. Wiring the pavers together with 3.1mm galvanized fencing wire
7. Driving 900mm long galvanized Y-standards into the ground at specified intervals
8. Connecting the standards to the block wiring
9. Filling block voids with 2% cement-stabilized soil
10. Filling voids with the 900mm anchors with concrete

Long-Term Success

The road has been in extensive use for five years, meeting the full satisfaction of both the Municipality and the local Ratepayers Association.

Val Marsh, Chairperson of Great Brak Heights, enthusiastically reported: “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.”