Acoustic optimization of asphalts using Acoustic Void Content Analysis AVCA on drill cores

Porous (PA) and semi dense asphalts (SDA) are popular measures to reduce roadside noise levels. A key feature in these pavements is the noise reduction in the mid- and high-frequency range, thanks to acoustically active (from the surface accessible) pores. To achieve long-term noise reductions, the void content should be kept to a minimum while still ensuring accessible pores. This delicate optimization process requires a detailed understanding of the void structure. With older pavements, one would like to know the exact location of dirt (originating from tire abrasion, agriculture and construction sites etc.) limiting the number of active pores. This paper presents a methodology to determine the acoustically active pore structure of PA and SDA pavements, using CT-scans of drill cores. We use image classification algorithms to separate stones, mastics, dirt and pore-volume. A subsequent path analysis calculates the amount of active and clogged pores. The resulting 3D-model of the active pore structure is used to estimate its impact on the acoustics. This methodology provides detailed insights into the acoustically effective design of asphalt mixtures, serves as an ideal basis for their optimization, and allows for the quantification and localization of dirt so that it can be adequately removed.