National Asphalt’s key role in bringing one of many breakthrough technologies to the South African roadbuilding industry has taken the country’s asphalt pavements to the next level.
Sub-Saharan Africa’s harsh climatic conditions and the fact that the region’s roads are still very much the main arteries on which both people and goods are transported necessitate the construction or resurfacing of roads that are highly resilient and resistant to traffic-induced wear.
Such heavily trafficked road surfaces are prone to deformation through rutting and cracking, and end up so warped or damaged that they become dangerous for road users. To achieve a high-performance surface, the right approach and product are required. Ever the leader in asphalt supply in South Africa, National Asphalt was part of the first official in-country trials using highmodulus asphalt (EME).
First introduced in France in the 1980s as Enrobés á Module Elevé, EME binder is a bitumen of exceptional hardness that makes for asphalt pavement that is highly resistant to flexing. As a result of its strength, a thinner pavement layer can be laid, which means fewer materials and machine hours are required. The lifespan of standard-thickness roads using EME is significantly longer than regular asphalt pavement and these layers also require less maintenance.
In reducing the amount of virgin asphalt (by combining EME with reclaimed asphalt) required in roadbuilding and resurfacing, National Asphalt is setting a precedent in responsible and sustasustainable materials supply. The lower maintenance requirements of EME pavements also present road owners with significant savings in the longer term.
While EME produces an undeniably stronger pavement than a standard bitumen treated base, observing the correct construction practices is vital in ensuring that the pavement performs to the desired level.
The grading, binder type and content need to meet the exact specifications required. Mixing and compaction temperatures are very specific – the
former being between 160°C and 180°C and the latter needing to remain above 140°C at all times during the process.
Furthermore, a firm substrate is required for compaction to be effective and ensuring that the specified thickness is achieved is of utmost importance. Thorough, uniform compaction then ensures that in situ voids are between 4% and %. Voids on either extreme may compromise pavement durability.
The appropriate surfacing then needs to be applied to negate thermal cracking brought on by temperature fluctuations and construction joints need to be sited very specifically. Longitudinal joints for the various layers should never coincide with vehicles’ wheel paths and the joints across the different layers must be staggered and stepped.
National Asphalt has been involved in numerous applications of EME mixes across the country and the company’s EME mixes are proving to be particularly appropriate for major metros’ bus rapid transit network routes. In establishing an extensive footprint of static plants across the country, which it has supplemented with a fleet of mobile asphalt plants, the company has placed itself in a position where it is able to supply EME and reclaimed asphalt mixes efficiently and cost-effectively, wherever they may be required.
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