Porous road pavements: Acoustical characterization and propagation effects

Measurements of the acoustical properties of some porous road pavements are presented here and an acoustical method for monitoring the performance of these surfaces is presented. Porous road pavements have been used previously because of their driving qualities and drainage capacities during rainy days (i.e., the elimination of water splash and spray) but they have also been found to reduce traffic noise substantially. Reductions in A-weighted sound levels of 3-5 dB, compared to a dense pavement structure, have been measured. To study further their acoustical performance, measurements over real road surfaces have been carried out and the results compared to theoretical predictions based upon models describing the surface impedance and sound propagation. For the impedance characterization, both a phenomenological and a microstructural model were used. Both approaches introduce a viscous and a thermal dependence to account for the different phenomena inside the porous structure. By incorporating these models into the theoretical propagation predictions, it is possible to evaluate the impact of porous asphalt on highway noise levels. A nondestructive testing technique has been designed for determining in situ the noise reduction performance of porous road pavements. (C) 1997 Acoustical Society of America.