By Kristin Dispenza
The Pacific Highway upgrade is the largest road infrastructure project in Australia. As part of the upgrade, the Nambucca Heads to Urunga (NH2U) section of highway opened to traffic in 2016. Located north of Nambucca, the project included the use of two concrete pavement types: plain concrete pavement (PCP) with transverse tining and continually reinforced concrete pavement (CRCP) with a 10 mm stone mastic (SMA10) surface used in areas where low noise pavement was required.
When this section of road opened to traffic in 2016, nearby residents requested additional noise mitigation treatments. While no further treatment was required under the project conditions of approval, Roads and Maritime Services agreed to conduct a trial of pavement treatment options for the PCP to reduce tire/pavement interface noise.
Grinding and subsequent grooving of the concrete pavement was identified as a viable trial treatment and Seovic Civil Engineering Pty Ltd, a member of the International Grooving & Grinding Association (IGGA), was selected as the preferred contractor. Seovic proposed a specific grinding technique known as the Next Generation Concrete Surface (NGCS), which was developed in the United States by IGGA and the American Concrete Pavement Association at Purdue University in Indiana. Roads and Maritime elected to perform the trial under full-scale operational road conditions and worked with IGGA to determine the best test scope and procedures.
Trial project scope
Three types of grinding were performed on three different test sections, with a fourth section of stone mastic asphalt used as a control:
- Section 1: A three-pass operation consisted of conventional diamond grinding (CDG) followed by a flush grind with 3.2-mm-wide blades spaced at 0.9 mm. Grooves were then installed at 16.0 mm (5/8 inch) spacing using 3.2 mm wide blades to a depth of 3 to 5 mm.
- Section 2: CDG was performed followed by grooving using 3 mm (0.100 inch) spacers.
- Section 3: A two-pass operation was performed with the first pass being a flush grind and the second pass installing grooves at 14 mm (9/16 inch) spacing using 3.2 mm wide blades to a depth of 3 to 5 mm
- Section 4: An existing low noise pavement of SMA10 (stone mastic asphalt) as a control.
The overall area of the trial was 88,000 square meters, with CDG on 30,000 square meters and NGCS on 58,000 square meters.
Noise data from Section 1 (NGCS) was compared with Section 2 (CDG) and SMA10 surfaces. SLR Consulting Australia Pty Ltd, a third-party specialist, took pre-grind measurements in June 2018 and post-grind measurements in November 2018.
Two types of noise measurements were performed: Statistical Pass-by (SPB) and the internationally recognized On-Board Sound Intensity (OBSI). Noise levels of individual vehicles were processed to give the Statistical Pass-by Index (SPBI). SPB measurements gauge noise from vehicle tires as well as aerodynamic noise, body noise, engine, and exhaust noise. To account for variations in noise associated with different vehicle types, SPB measurements are categorized into three classifications based on vehicle size: short vehicles with two axles, two-axle trucks and buses, trucks and buses with three or more axles.
In a comprehensive report by SLR, “Nambucca Heads to Urunga: Low Noise Diamond Grinding Pavement Noise Monitoring,” SPB test results showed that both NGCS and CGD achieved a noise reduction over pre-trial conditions while the SMA10 saw a slight increase. SPB measurements on Sections 1 and 3 showed that NGCS reduced noise by approximately 4 dB for the first classification of vehicle. In Section 2, CDG reduced vehicle sound levels of both the first and third classification by around 2dB. The report notes that several factors introduced uncertainty into some of the SPB measurements, e.g. nearby construction, inherent variability in noise levels emitted by trucks within the same class, and small speed and sample sizes.
OBSI uses microphones and sound intensity probes mounted on a moving test vehicle to capture tire/pavement interaction noise at its source, better excluding vehicle engine, vehicle body, and aerodynamic noise. OSBI test results give a more targeted assessment of the type of noise pavement grinding and subsequent grooving are designed to reduce.
The SLR report shows that NGCS on both Sections 1 and 3 achieved noise reductions exceeding 6 dB. In Section 2 (with CDG) there was a reduction of approximately 2 dB. Changes on the SMA10 section were marginal. The report concluded that, “the diamond ground concrete pavements produced comparable noise levels to the traditionally ‘low noise’ 10 mm stone mastic asphalt pavement.”
Jason Seovic, Director of Seovic Civil Engineering, reports, “the riding quality on this work after NGCS also has an outstanding IRI of 0.614 m/km or 39 in/mile–it rides like velvet. This ground-breaking work opens up a whole new application for low noise concrete surfaces and is a boost for concrete highways in urban areas or near rural towns. The provision of a small additional thickness now included at construction for future surface texture rehab grinding also provides sustainability, in that contemporary and future concrete pavements will probably require no new resurfacing material for a half century or more.”
“As a result of undertaking this trial, Roads and Maritime Services has a strengthened knowledge of the grinding treatments available and are pleased with the results demonstrating the low-noise diamond grinding of the PCP produced comparable noise levels to traditional low noise SMA10 pavement,” said Yvonne Bowles, Senior Project Manager, Roads and Maritime Services. “This now provides opportunities to integrate the surfacing treatment into future infrastructure where it meets the project requirements and we will continue to work with the industry to ensure learnings are captured and ongoing development of the treatments is undertaken.”
“The results of the low-noise diamond grinding trial on the Nambucca Heads to Urunga project are consistent with the former trial on the Hunter Expressway undertaken in 2014. Not only is the noise result equivalent to the asphalt surface, it is likely to have better acoustic durability. NSW road noise policy has been updated to include NGCS, called LNDG in Australia, and our policy documents are evolving to recognize improved surfacing techniques with more emphasis on the whole of life performance,” said Peter Carson, Senior Project Manager, Roads and Maritime Services.
“The IGGA and its members have been working with Australian transportation authorities to incorporate CDG and other diamond saw cut textures into the RMS tool box since the year 2000, with great success,” said John Roberts, executive director of the IGGA. “The successful roll out of the NGCS further exemplifies the versatility and cost effectiveness of diamond saw cut textures when transportation specifiers are faced with the unique challenges of this modern era.”
The International Grooving & Grinding Association (IGGA) is a non-profit trade association founded in 1972 by a group of dedicated industry professionals committed to the development of the diamond grinding and grooving process for surfaces constructed with Portland cement concrete and asphalt. In 1995, the IGGA joined in affiliation with the American Concrete Pavement Association (ACPA) to form today what is known as the IGGA/ACPA Concrete Pavement Preservation Partnership (IGGA/ACPA CP3). Today this partnership serves as the technical resource and industry leader in the marketing of optimized pavement surfaces, concrete pavement restoration and pavement preservation around the world. The mission of the IGGA is to serve as the leading technical and promotional resource for the acceptance and proper use of diamond grinding and grooving as well as PCC preservation and restoration. For more information, visit http://www.igga.net/.
Kristin Dispenza is the AOE of the International Grooving & Grinding Association. She can be reached at Kristin.firstname.lastname@example.org.