The acoustical aspects of porous road surfaces as studied in france are described in this paper. The first part discusses the advantages of porous asphalt and shows how and why, in france, two experimental approaches are carried out: thin porous layers (about 4 cm) for the interurban and urban network, and thick porous layers (40 to 50 cm) for the urban network. The second part presents a theoretical model: the absorption coefficient as a function of frequency is obtained from the layer thickness and three physical parameters representative of the porous medium. The influence of these parameters on the absorption is described. It is clearly shown that above a certain value, thickness has no influence on the absorption properties (i.E., Increasing the thickness becomes acoustically useless). This is called the "superthickness" condition. In the third part, experimentalresults obtained in the laboratory and in situ are compared with the theoretical calculations. The influences of humidity, gaps in the grading, binder content, and number of layers are also presented. The last part deals with noise reduction as measured with rolling vehicles (pass by, coast by). Experimental programs in progress are described and some results are given. Evolution of noise level versus road aging is also discussed. This paper appears in transportation research record no. 1265, Porous asphalt pavements: an international perspective 1990.
Abstract