Optimizing pavements' acoustic properties by using superfine twinlay porous asphalt wearing courses

Abstract

Paper presented at the 21st Annual South African Transport Conference 15 - 18 July 2002 "Towards building capacity and accelerating delivery", CSIR International Convention Centre, Pretoria, South Africa.The acoustic properties of a conventional thin single layer porous asphalt surface can be further optimized by introducing a thick double layer system (know as Twinlay) with a superfine top structure consisting of single-grain aggregate mixture. The superfine top structure assists in minimising tyre vibration (which will result in subsequent reduction in noise production) and also increases flow resistance which then gives us the desired short-wavelength texture. The Standing-Wave Apparatus or Impedance Tube can be used to assess the mixture’s ability to absorb sound before construction of a pavement in the field. Compared to conventional porous asphalt surfaces Twinlay offers a number of advantages as mentioned in this paper. The purpose of the investigation was to minimise noise production by minimising tyre vibration, to optimise sound absorption and to compare locally designed Superfine Twinlay mix with the acoustically optimized European mixes which were manufactured using local aggregates. This paper gives results of an investigation into the acoustic properties of porous asphalt mixtures in the laboratory only, no field investigations were conducted.