Reinforcing Winton's Asphalt: A Journey to Better Roads

19/04/2023

Our South Island team has been working on a unique infrastructure project on SH6 in Winton, a small town between Queenstown and Invercargill.

The project involved rehabilitating the main street of Winton, which is 1.5km in length. Reasonable pavement was identified over a very soft subgrade with a CBR of 1-2% using test pits. The thickness of the Asphalt Concrete layer was sufficient for most of the site, but there was a 300m section in the middle of the site that had less existing pavement than the rest of the road. 

While the original proposal of Structural Asphalt Concrete may have been a viable option, it would have required extensive excavation and rebuilding of the 300m section towards the north end, adding cost and significant time to the project. While this approach would have been feasible, our team of experts recognised that there was a more economical and sustainable solution we could offer.

To tackle this, our team proposed reinforced asphalt treatment which has the potential to last for 10 years or more. This solution was unique, given that there is little New Zealand experience with this treatment and no design tools available to support it. Despite this, we presented the solution to our client as a trial, and they recognised the value in our proposal.

To make this happen, we turned to Cirtex for support and technical expertise. Their Hatelit reinforced grid, made by Huesker in Germany, became our hero on this journey. This high-modulus polyester material is typically laid over old cracked Asphalt or Concrete to control the migration of cracking. However, we saw an opportunity to try something new and decided to incorporate the Hatelit reinforced grid into our reinforced asphalt treatment.

Our aim was to reduce the degree of bending that the asphalt has to do under a tyre, ultimately making the road last longer. The second function was to control the behaviour of the crack. Without the reinforcing, the crack would just keep going up to the surface. However, with the grid, the crack hits the grid and disperses it throughout the pavement, greatly reducing the time taken for the crack to reach the asphalt surface.

International research showed that, depending on the amplitude (applied load), the reinforced asphalt block could last 4-6 times longer than un-reinforced asphalt. We used this data, along with the technical expertise of Robert Patience, Downer’s Senior Principal Pavements Engineer, to predict that a reinforced asphalt option would last in the order of 9-12 years, while new un-reinforced asphalt would only last 3-4 years.

"In urban environments where it is critical that we are in and out quickly and cause as little disruption as possible this type of product really does give us another fantastic tool to help our clients get that little bit more life from their road assets" Says Shaun Magee, Downer Regional Engineering Manager. 

Construction on the Hatelit section started last week, and we were thrilled to see the first 180m of the Hatelit go down. With Cirtex reps on site, we are excited to see how far this journey takes us. Throughout the construction process, the team has been taking note of any lessons learned, with a view to improving our knowledge and capability to apply this treatment elsewhere in the future.

We also want to acknowledge the local Waka Kotahi team in Southland who, without their willingness to let us give this treatment a go, this exercise would not have been possible.

This trial project in Winton showcases our commitment to innovating to improve our communities infrastructure. With a collaborative approach and a willingness to try new solutions, the team has been able to potentially set a new standard for reinforced asphalt in New Zealand. By implementing innovative solutions to today's roading problems, we are paving the way for safer, more durable roads that benefit communities and the environment. Stay tuned for more updates on this exciting project!