Ageing of low noise road surfaces

Low noise road surfaces are a well known and effective measure to reduce tire-road-noise and thus overall traffic noise. However, it is observed that all kinds of low noise road surfaces lose their noise reducing properties to some extent over time - which could be described as an "acoustic ageing".For porous road surfaces, the acoustic ageing is mainly caused by clogging of the open pores which reduces the sound absorption and thus the noise reduction capacity of the road surface. The main parameters relevant for the acoustic ageing of porous surfaces are lifetime and traffic volume.For dense low noise road surfaces, the acoustic ageing is caused by an acoustically unfavorable change of the surface texture, which depends on the traffic volume.Recent results for the acoustic ageing of porous and dense low noise road surfaces will be shown. The results allow for estimating the acoustic lifetime of different types of road surfaces. Different approaches to extend the acoustic lifetime will be discussed.