Federal Highway Research Institute

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New developments in asphalt road construction

New developments in asphalt road construction are required. Traffic safety and driving comfort are at the forefront of all these considerations. The road surfaces should be created in such a way that they are light in colour, grip well and do not reflect in wet weather. The overall construction must be resistant to deformation. Before a new development can become a standard construction method, it must prove itself. Until then, it remains regarded as a special method of construction.

The new and further development asphalt of construction methods increasingly focuses on the aspect of noise reduction, because some 60 per cent of the population in Germany feel disturbed by the noise caused by road traffic. Sound reduction at the point of origin – in this case the place of contact between the tyre and the road surface – represents an extremely effective method of reducing noise. The use of optimised top asphalt layers enables a significant reduction in tyre/road surface noise to be achieved.

Open-pore asphalt

The high requirements of noise protection often make the use of open-pore asphalt necessary. Approx. a quarter of the top layers in this construction method consist of hollow cavities, which enables sound to be absorbed. This excellent sound-absorbing effect, however, is offset by high construction and maintenance costs as well as a limited useful life.

New developments in asphalt road construction use limited expenditure in attempting to approach the sound-reducing effect of open-pore asphalt while improving the useful life. Two construction methods worth mentioning are “low noise stone mastic asphalt” (LN SMA) and “noise optimised top asphalt layer” (NOA), which make use of an optimised surface structure (texture) in attempting to reduce the amount of noise created.

Yet another new method is the "porous mastic asphalt” (PMA), also known as "mastic asphalt with open-pore surface”. Here the basic idea is to make the lower zone of the lop layer as dense as possible – id est similar to mastic asphalt, while having an open surface texture. In conjunction with a small maximum grain size, this creates excellent acoustic properties. This is achieved by means of a special asphalt mix composition.

Trial stage

Although all these three methods are in the trial stage and have not yet been adopted into the technical standards, they demonstrate a promising acoustic effect. The long-term experience for the LN SMA method dates back to 2005, for NOA to 2007 and for PMA to 2009. In view of the long useful life required of top asphalt layers of up to 20 years, it will take a few years yet to be able to decide on their long-term reliability.