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

Based upon the non-destructively estimated viscous and thermal characteristic lengths using an impulse-echo approach, the acoustic properties of pavement surface-layers made of various asphalt concrete mixtures are evaluated. These properties include the characteristic impedance, the surface acoustic impedance, as well as the absorption and spherical reflection coefficients at the pavement surface. Experimental results explain field observations that consistently indicate the superior noise-abating properties of open-graded, ie, porous, asphalt-concrete pavements. Results demonstrate that porous pavements significantly reduce noise-source strength due to tyre/pavement interaction, and expediently dissipate the generated sound fields. To describe both effects, two non-destructive noise-rating parameters are also presented and discussed.