The Acoustical Durability of Thin Noise Reducing Asphalt Layers

Within the context of the European Noise Directive, traffic noise action plans have been established. One of those actions is to deepen the knowledge about low noise roads, as they are considered the most cost-efficient measure for traffic noise abatement. Therefore, ten test sections were installed in May 2012 in Belgium, with the objective of integrating Thin noise-reducing Asphalt Layers (TAL) in the Flemish road surface policy in a later stage. Eight test sections are paved with TAL with a thickness of a maximum of 30 mm and a maximum content of accessible voids of 18%. The other two sections consist of a Double-layer Porous Asphalt Concrete (DPAC) and a Stone Mastic Asphalt (SMA-10 as a reference section). The acoustical quality of the asphalt surfaces has been monitored in time using Statistical Pass-By (SPB) and Close-ProXimity (CPX) measurements up to 34 months after construction. Texture measurements performed with a laser profilometer are linked to the noise measurement results. Very promising initial noise reductions were found, up to 6 dB(A), but higher than expected acoustic deterioration rates and the presence of raveling led to noise reductions of a max. of 1 dB(A) after almost three years. It is shown that the construction process itself has a large influence on the acoustical quality over time