South Africa’s roads could be lasting much longer if the country made more use of EME (“Enrobés á Module Elevé”).

Developed in France in the 1990s by road construction specialists Colas, EME has been applied locally by asphalt experts National Asphalt, with great success. According to Dave Bennett, general manager at National Asphalt, the first official paving trial was done on South Coast Road the high-wear road into the Port of Durban.

“The heavy traffic load of large trucks carrying containers and goods in and out of the port meant that the road was lasting only about three months between repairs,” says Bennett. “We replaced the road with an EME asphalt about six years ago, and it is still holding up well to this day.”

Since then, National Asphalt has laid down about a million tonnes of EME on the country’s roads, mainly in Durban to serve the high-wearing bus lanes in the city’s rapid transit network and N3. In a more recent project and a first for the City of Cape Town, EME is being used in on a new circle intersection on Jan Smuts Street. It was also installed in the Western Cape’s famous Huguenot Tunnel.

Using a hard grade of bitumen, EME imparts a high stiffness and structural strength to the pavement. The added strength even allows for the road’s layer thickness to be reduced by about 30% on average, with the associated cost benefits. Alternatively, EME asphalts of the same thickness have a life span of 5 to 10 times that of regular asphalt.

In spite of its inherent stiffness, EME binder has very good workability and compactability. This means that no specialised production method is required, however attention to detail during the paving operation is extremely important and only experienced contractors should install EME as there is no room for error.

“Experienced contractors will find that there is no difference in the road-building process when using EME, as it lays like conventional asphalt,” Bennett explains.

He highlights that the roll-out of rapid transit bus routes in a number of South Africa’s cities presents an ideal opportunity for the authorities to benefit from this cost effective asphalt technology.

“With its capacity to resist the impact of heavy buses, EME asphalt can add years of extra life to these roads,” says Bennett. “The savings of maintenance costs by metropolitan councils would be significant, not to mention avoiding the transport disruption that roadwork invariably causes.”

National Asphalt’s extensive footprint of asphalt plants around the country enables it to supply EME asphalts efficiently and economically. It is also able to ensure best practice in terms of responsible and sustainable materials supply, by reducing the amount of virgin aggregates in mixes. It does this by combining virgin aggregate with reclaimed asphalt for roadbuilding and resurfacing, thereby promoting reuse and recycling of existing material.

The in-house design of National Asphalt’s new asphalt plant at its Laezonia site north of Johannesburg will give customers the comfort of lower environmental impact while still enjoying competitive pricing of asphalt supply.

The 120 tonne capacity plant, which has boosted the company’s capability in the region, incorporates several tried-and-tested improvements based on the company’s extensive industry experience. According to Dave Bennett, general manager at National Asphalt, among these is better burner fuel efficiency and reduced hydrocarbon emissions.

“The plant design reduces emissions from the combined aggregates, efficiently burning this up before it goes to the bag house,” Bennett says. “This gives our new installation a far cleaner and environmentally friendly stack than a conventional plant.”

Dust is removed using both a pre-cleaner and a bag house. In the pre-cleaner, material sized between 0,6 mm and up to 2 mm is dropped into a rotary valve, from where carefully controlled volumes are fed back into the plant. Material smaller than 0,3 mm, and right down to 0,075 mm, is caught in bags, removed using pulsing and similarly fed back into production.

Recognising the growing importance of using recycled asphalt (RA), the innovative design of the new National Asphalt plant employs efficient heating methods to reduce environmental impact as well as fuel costs.

While many plants in the market use super-heated virgin aggregate to heat the RA, the super-heating process consumes considerable fuel resources. Significantly, the design installed at the National Asphalt Laezonia plant does away with the requirement to super-heat. This has been done by ‘scavenging’ heat through both conductive and radiant heat transfer to the RA and the combined mix.

“The plant is built according to specifications developed by National Asphalt over time, and which represent the best value to our customers,” Bennett says. “Asphalt users in and around Gauteng can now benefit from the increased efficiency, economy and environmental benefits of our new facility,” he concludes.

With the aim of assisting the Gauteng Department of Roads and Transport’s (GDR&T) Tswelopele Contractor Development Programme in the Tshwane region, leading local asphalt expert National Asphalt has developed a comprehensive solution that optimises labour in construction without compromising cost, quality and productivity.

The company is collaborating with Siyeza Consulting, one of GDR&T’s newly appointed consulting engineering firms working on the Tswelopele programme, exploring ways to boost service delivery on road repairs by maintenance contractors. This intervention will help ensure key GDR&T contractor/service delivery objectives and targets are met. These include optimum budget expenditure, local labour enhancement, accredited contractor training, skills transfer and mentorship to underpin quality delivery of all road maintenance services to the department.

According to Gerald Gundu of Siyeza Consulting Engineers, many of these contractors are focused on pothole repair work, edge breaks and minor patchwork, and there was a need to find a viable asphalt solution.

“The objectives of Tswelopele include increasing the capacity, equity ownership, sustainability and quality of the technical and business practices of targeted learner contractors,” says Gundu. “As part of contractor development, Siyeza Consulting Engineers asked National Asphalt to demonstrate its products and technologies which these contractors could use.”

An aspect of the Tswelopele initiative is to create labour-intensive techniques for road repair and maintenance. This is aimed at employment creation and upskilling small contractors who would start at a Construction Industry Development Board (CIDB) level 1 and complete the Incubator Programme with a CIDB level 4 status after three years.

The asphalt solution proposed by National Asphalt is LT40 – or ‘Hot-Mix-in-a-Bag’ – which offers contractors ease of use of a quality continuously graded low temperature asphalt but with results that compare with traditional Hot Mix Asphalt (HMA).

“National Asphalt LT40 has zero waste materials, cuts down on time spent in queues at HMA plants, or product loss arising from bad weather,” says Pascal Garrioch of National Asphalt. “It also improves contractors’ productivity, allowing them to proceed directly to site with all the tools necessary to begin work without delay.”

“Heating of material on site using the mobile oven trailer means quality asphalt material is readily available and on hand 24/7,” he says.

Conventional HMA needs to be applied at around 150°C and must be laid within a few hours of manufacture. National Asphalt’s LT40 can be applied at between 80°C and 100°C and can be reheated for ongoing use without compromising any physical or technical properties or benefits of the asphalt mix.

Garrioch emphasises that the product is perfect for edge-breaks, minor patching, pothole repairs and the reinstatement of trenches with the application process carried out in the same way as traditional HMA repair.

“LT40 is supplied in 25 kg bags, and is heated to between 100 to 110⁰ C in a specialised oven which is supplied on a custom-built trailer,” he says. “Once at the right temperature, the product is shovelled onto a wheelbarrow and taken to the repair site where it is placed in the prepared area, spread, levelled and compacted accordingly.”

Contained in sealed plastic bags, LT40 has a shelf life of up to 12 months, allowing contractors to purchase and store the product for use at their convenience.

“The mobile hot-mix-in-a-bag oven trailer is the latest innovative alternative technology for maximising labour-intensive construction methods with improved quality in the maintenance and repair of paved roads,” says Gundu. He notes that the construction method and benefits of the technology explored are being assessed for suitability to labour-intensive projects, along with suitable funding models that could facilitate its uptake by learner contractors and small to medium enterprises.