Colas ensures noise doesn’t break the sound barrier

Colas, the leading road construction and maintenance group, and its subsidiary, Somaro, a specialist in safety equipment and road signs and signals, in partnership with the Ecole Polytechnique, have developed a new type of noise barrier for roads with an unequalled level of sound absorption. Depending on the configuration, the barrier’s performance is 30% to 50% greater than that of the most effective sound panels currently available on the market.

This innovative product, for which a patent application has been filed and which has earned the Siemens Prize for Applied Research 2003 for the Ecole Polytechnique (the reputed French school of engineering), is based on a number of theoretical and experimental studies on the properties of irregularly shaped objects. It has been proved that the geometry of objects is of great importance in the deadening of noise. Resonators with a jagged or ragged geometrical shape can therefore deliver better sound deadening than ordinary geometrically smooth systems.

Considering these properties, and bearing in mind, moreover, that it is very difficult to manufacture irregularly shaped objects using inexpensive industrial processes (such as moulding, for instance), the challenge for the team consisted in developing the morphology of an acoustically absorbent material that would be appropriate for moulding.

A prototype was built in the form of a panel measuring 4m by 4m, associating a very sophisticated surface morphology, composed of cone and pyramid frustums arranged in repetitive fashion, with the use of wood-cement concrete. (A frustum is the remainder of a pyramid or cone whose upper section has been cut off by a plane parallel to its base.) Measurements performed in a reverberation chamber — as stipulated by the standards in force — have resulted in the classification of the new noise barriers in the ‘very high absorption’ category, with unrivalled performance.

This new high-performance soundproofing wall is perfectly adapted to a motorway environment and is ideal for entrances to tunnels with heavy traffic. However, the technology is also suitable for high-speed railway lines and busy airport zones. With a cost that will remain competitive and a design enabling it to blend easily into landscapes, Colas’ noise barrier should soon undergo significant industrial and commercial development, for the greater benefit of local neighbourhoods currently affected by noise pollution.