Investigation of microstructure characteristics of porous asphalt with relevance to acoustic pavement performance

Both spatial characteristics and the structure of air voids have certain impacts on the acoustic properties of porous asphalt, with regard to sound absorption behavior. Aside from global parameters of the microstructure, like porosity, certain geometrical characteristics of air voids also have an effect on sound absorption and acoustic parameters. Spatial parameters of the microstructure like 3D fractal dimension or pore diameter distributions are determined from X-ray CT scans, using methods of digital image processing. Geometrical parameters of different porous asphalt samples are compared, and the relationship between the geometry and the acoustic behavior is studied in great detail. In particular, an evolution of the microstructure caused by long-term soiling processes - changes which usually materialize during porous asphalt's service life - and their effects on spatial and acoustic parameters are analyzed. A defined laboratory procedure for artificial soiling has been used to study soiling mechanisms, enabling the correlation to certain soiling states to be drawn. The design of the study shows how more basic analyses of the acoustic deterioration of porous asphalt due to soiling effects during its service life are possible, with the consideration of changes in the air void microstructure.