Research was commissioned to investigate the long-term acoustic performance of New Zealand standard porous asphalt made to TNZ P/11 Specification for open graded porous asphalt (OGPA). The research findings should be considered applicable only to New Zealand OGPA laid in high-speed environments (speed limits of 80 to 100 km/h).
A method for acoustic measurement was selected, developed and applied using drafts of ISO 11819-2 for guidance. Measurements were made of a set of OGPA sections of different ages from four regions of New Zealand. The oldest OGPA sections were around 8 to 10 years old, which matches current expectations of OGPA ‘life’.
The measurements show OGPA acoustic performance deteriorating at a steady but slow rate over time, yielding about 2 dB(A) deterioration of acoustic performance over 8 to 10 years.
Current asset management of OGPA is largely driven by functional attributes of smoothness and porosity, which also deliver OGPA’s acoustic performance. It appears that current practices of asset management for OGPA functional life are synchronised with what would be prescribed if considering asset management for OGPA acoustic life. Therefore, the research makes no recommendation for changes to asset management of OGPA in high-speed environments, but supports current practices.
Keywords: close-proximity (CPX) method, low-noise road surface, open graded porous asphalt (OGPA), tyre/road noise