Noise abatement of asphalt concrete pavements: Part 2. Estimation of acoustic properties

Based upon the non-destructively estimated viscous and thermal characterist ic lengths using an impulse-echo-approach, the acoustic properties of pavem ent surface-layers made of various asphalt concrete mixtures are evaluated. these properties include the characteristic impedance, the surface acousti c impedance, as well as the absorption and spherical reflection coefficient s at th pavement surface. Experimental results explain field observations t hat consistently indicate the superior noise-abating properties of open-gra ded, ie, porous, asphalt-concrete pavements. Results demonstrate that porou s pavements significantly reduce noise-source strength due to tyre/pavement interaction, and expediently dissipate the generated sound fields. to desc ribe both effects, two non-destructive noise-rating parameters are also pre sented and discussed.