Developing quieter pavement surfacings
Recent years have seen the publication in Franc
e, and elsewhere in Europe, of a series of documents that put in place a strategy to reduce the noise from road transport ultimately by at least 30%. In this connection too, several European cities are interested in using quieter pavement surfaces in order to comply with European Directive 2002/49/CE. Reducing noise levels at the source is still the best way of reducing the noise pollution affecting residents. As a high proportion of noise emissions are due to rolling noise (even in urban areas), two solutions spring to mind: reducing the proportion of noise generated by the tyre and reducing that generated by the pavement surfacing. IFSTTAR is focusing its research on the second option.
From “traditional” porous asphalts to asphalt concrete
In the past, porous asphalts (which in France are known as Béton Bitumineux Drainants – BBRd and which have 0/10 and 0/6 grading) were tested in urban areas. Even though they gave substantial acoustic gains immediately after laying, these were considerably reduced by clogging after a few years of service. These difficulties were mainly due to low traffic speeds which prevented self-maintenance of the porous course. It therefore became a matter of some urgency to carry out fresh research into other types of low-noise pavement structure. The outcome was a material with a very small particle size, Very Thin Asphaltic Overlay (Bitumineux à couche Très Mince - BBTM).
France’s major road construction firms have increased their research into these new surfacings, focusing mainly on the grading and the composition of the binder. As a result, Very Thin Asphaltic Overlays with a grading of 0/6 or even 0/4 were trialled on public roads. These surfacings are of interest in terms of the rolling noise generated by vehicle passage (measured as laid down in the ISO 11819-1 standard). For example, a 0/4 Very Thin Asphaltic Overlay emits approximately 9 dB(A)less noise than a 0/10 reference Semi-Coarse Asphaltic Concrete. This improvement should be set against those obtained from 0/10 Porous Asphalt (3 dB(A)) and 0/6 Porous Asphalt (6 dB(A)). The long-term nature of these improvements nevertheless needs to be verified, particularly with regard to binder ageing.
A new generation of noise-optimized surfacings
In parallel with this, research 
has been conducted to design dense (non porous) wearing courses that provide noise reductions that are at least comparable with those obtained with “conventional” porous structures. Much of this research has been performed as part of the ADEME-backed DEUFRAKO Franco-German cooperation programme. The P2RN project (Prediction and Propagation of Rolling Noise) which came to an end in 2009 identified a theoretically optimal texture. The ODSurf project (which deals with the modelling and construction of an optimized dense low-noise wearing course) will be completed at the end of 2015 and is concerned with developing the necessary industrial processes and carrying out the various comparative tests.
