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New surface offers smoother ride on unsealed roads

 

 

thumbnail 9 MF-Unsealedroads-235JULIA WADE

Unsealed roads around Kaipara have been the site of an innovative experimental roading application, aimed at easing the potholes and pitfalls of travelling around the district’s vast metal roading system.

With the cost of sealing roads set to be over $600,000 per km compared to $55-85,000per km for unsealed, as well as the maintenance costs being over three times that of a metal road, sealing Kaipara’s roading network would prove to be a heavy burden for rate payers.

However, due to a ‘high level of customer dissatisfaction’ and call for more attention to be given to the district’s roads, Kaipara District Council (KDC) have developed a more durable and lower maintenance ‘winning formula’ surface.

Northland Transport Alliance (NTA), a collaboration between Northland local government and NZ Transport Agency, teamed up with roading contractors Ventia to introduce the new mix of gravels, clay and fines which sets solid as it compacts.

NTA project sponsor Aram Goes says the trial sites have been in operation for over two years and are showing little sign of wear.

“The harder, compacted surface is less likely to pothole or corrugate which means the road surface stays strong, giving a smoother, more comfortable ride with reduced dust and costs less to maintain,” he says. “Now we’re ready to begin the network reconstruction in earnest.”

Large sections of unsealed roads are common in many districts Goes says and all roads ‘behave quite differently’ due to different factors like weathering and use. Managing customer expectations regarding roads is also ‘hugely challenging and time consuming’.

“What we’re hoping is that this experiment will demonstrate the science applied to roading. We will look at the unsealed roads like we would on a sealed network, which has pieces of tarseal laid with a date of birth and a design life so we can plan a renewal date. Unsealed roads haven’t been looked at like this, so this project will be piloting how we can take an unsealed road and create treatment lengths.”

Funding for the improvement of unsealed roads derives from a Government Provincial Development Unit, with KDC receiving $3.1m in February 2018 with a further $4.9m dollars granted in November 2020 from the Infrastructure Reference Group. Goes says reconstruction is the full package.

“It involves pavement rehabilitation, water drainage, applying bound wearing course, replacing culverts if necessary, cutting vegetation and shoulder benching. It is more effective than the reactive model of simply grading and regravelling existing roads and fixing potholes.”

Research for the new roading application was based on the ‘Paige Green formula’, developed by a South African doctor who studied how aggregates performed over time, NTA senior asset manager Andy Brown says.

“The biggest benefits are its resistance to rutting and corrugation and it helps to shed water into the drains. It’s recognised through international research that it is the right approach to unsealed roads.”

Kaipara is also the first district in the country to trial the new application and has received a lot of interest from collegues, NTA project leader Bernard Petersen says.

“It’s quite unique, we are leading the way… at a Low Volumes Road conference a few years ago we got a lot of positive feedback from the engineers… and I’ve been contacted by others wanting copies of our research papers,” he says. “We’re aiming to get back to the conference this year to represent the research, and to let others know it does work.”

Developing a framework to prioritise roads has also been an essential part of the work, and will allow council to focus on roads which will benefit the most.

The new approach to unsealed roads will also support Kaipara’s economy with local contractors being prioritised for works associated with the programme, creating opportunities to expand service offerings and build their capability.

Over the next year, NTA plans to reconstruct priority roads in addition to those that are due for routine maintenance and through NTA, Kaipara will also be sharing the new network management approach with other councils to help improve the quality of all unsealed roads throughout Northland.

Kaipara mayor Dr Jason Smith says the new roading mix and approach will be a game changer for Kaipara.

“As it’s rolled out across the district’s 1200 kilometres of dusty gravel roads, this innovation will improve lives for people here, and save lives too. Every sector in the growing Kaipara economy will benefit from having a smoother journey.”
 

Dust factor

The new application is also potentially less harmful due to producing less airborne dust. NTA senior asset manager Andy Brown says one of the first noticeable factors about the new application is that the dust blowing off the back of cars settles on the ground a lot quicker,

‘not like the white clouds that travelled for miles and could be seen from quite a distance away’.

Last year the Focus published a story regarding the health hazards of roadside dust particles, based on the Northland Regional Council’s (NRC) report, ‘Ambient PM10 2019/2020’ which monitored airborne dust along selected Northland country roads, and showed that at certain times last summer, Hakaru’s Settlement Road recorded over three times the limit of safe levels of PM10 – tiny liquid or solid specks such as fumes, smoke, mist, fog, sea salt and dust [see Nov 9 issue].

NTA currently do not have any technical content about dust ‘other than what we see’ but are providing samples of the new wearing course from the roadside, to Waka Kotahi research projects. NTA senior asset manager Andy Brown says a big piece of research needs to be done down the track’.

“NTA are questioning whether PM10 are the harmful particles, there is a perception that dust is bad, but we need to understand what the particles hanging in the air actually are,” he says. “There is no silver bullet for an unsealed road, this new application is touching on the best that we can do, the only way to stop dust is to seal the road, but that comes at a cost.”

Materials for the new roading application have been sourced from licensed quarries. In order to gain a license, quarries must have a resource consent which stipulates they have to demonstrate their product does not hold any harmful materials, NTA project leader Bernard Petersen says.

“Unless the Northland Regional Council – who are responsible for air and water control – come to us with other technical facts, our position is we do what we do for the road and to save the ratepayer money. Putting loose gravel on and grading it off is not particularly smart… now we’ve got treatment length mentality and lifecycle replacement with less visible dust.”

 

Less dust, more stability, the new aggregate trials have been years in the making, with a large amount of research and the applied expertise from a highly qualified team, from left, NTA project leader Bernard Petersen, KDC externally funded programme manager Joanne Reid, the Ventia team project manager Ryan Leach, contract manager Tim Ward and project engineer AJ Rudsdale, with NTA senior asset manager Andy Brown. PHOTO/JULIA WADE

 

“The biggest benefits are its resistance to rutting and corrugation, and it helps to shed water into the drains. It’s recognised through international research that it is the right approach to unsealed roads.”


 
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