Chipseal is the most common type of road surface in New Zealand. Economical, flexible and hardwearing, it provides an adaptable, cost-effective and safe surface for road users. We regularly monitor all chipseal surfaces to make sure they continue to perform at their best.
State highways may need resurfacing when:
they lose skid resistance
they lose their waterproof qualities, which results in potholes.
High-traffic roads generally need resealing about every seven years, while roads carrying less traffic can last 15 to 20 years before they require resurfacing.
Chipseal is made of sprayed hot bitumen, or cold bitumen emulsion (bitumen that's sprayed on cold), with crushed stone, known as 'chips', rolled into the surface. It's usually applied to state highways that carry lower traffic volumes (those outside the main urban areas), with the more expensive 'asphaltic concrete' typically reserved for high-traffic state highways. Asphaltic concrete (hot mix) is a mixture of bitumen and stones, and is less noisy and harder wearing than chipseal.
The 'chips' in chipseal are small, sharp-edged rocks. In the South Island they come from rivers, while in the North Island they're sourced mostly from quarries. In both cases the rock must be dense, strong and not slippery when it gets wet.
Chipseal has different colours in the North and South Islands. In the South Island it's more grey than black because the greywacke that washes off the surfaces of the Southern Alps into the rivers contains quartz, which makes the rock grey. North Island chipseal used more pure volcanic materials, such as andesite and basalt, which means North Island roads are darker.
Chipseal is used to:
improve road safety by improving surface grip, and therefore reducing the length it takes to stop when braking in an emergency and providing greater texture, which prevents vehicles aqua-planing
extend the life of the road
improve the waterproofing abilities of the road surface – this preserves the road foundation and prevents ruts forming
provide value for your maintenance dollar – a dollar spent on chipsealing to prevent structural failures will save $8 in structural rehabilitation costs later.
Firstly a thin layer of bitumen is spread onto the existing road. Then a layer of sealing chip is applied onto the bitumen. The sealing chips are rolled into the bitumen to provide initial bond. The road is then re-opened to traffic. Loose chips are swept up. Further sealing chip compaction occurs with managing the traffic over the site.
Bitumen is a liquid when it is hot and hard when cold. So it is important that we apply chip seals at the hottest time of the year, as this ensures that the new seal will become strong and long lasting. It can crack in cold weather. Also, wet road conditions will affect the bond between the bitumen and the road. This could lead to chipseal failures.
Sealing chip can be flicked up from the road surface and hurt people passing by or damage vehicles – especially windscreens. Hot bitumen can also splash up and stick to your paintwork.
If you get into difficulty at a chipseal site, please park up in a safe location and inform the site supervisor of your concern. The site supervisor will be able to assist you and log your report.
Summer is the best time to reseal roads, as the warm temperatures and dry air helps the new seal to stick to the existing road surface. If we did the work in winter, the cold ground would mean the new surface would harden and crack, plus the stones in the chip seal could pop out if exposed to cold weather within four weeks of application. Then we'd just have to do the work all over again next year – causing you more inconvenience.
Also, most New Zealanders take time off work in January and sometimes February, which means we can avoid delaying thousands of commuters and causing peak time traffic jams.
If the road looks brown or dusty or muddy then it's likely that we are waiting for the new seal to set before we let cars, trucks and bikes drive over it and churn up the newly laid road surface.
We still need warm ground temperatures to help the asphalt or chip seal to set and stick to the road surface. It's extremely dangerous for road workers to be spraying hot, black-coloured bitumen at night. Sometimes we do work at night to minimise disruption to drivers on key routes.
A smooth, skid-resistant surface free of pot holes and slippery sections helps reduce the risk of crashes and keeps you and your loved ones safer as you travel on state highways. If we are reconstructing the road, which involves taking the top layer off strengthening it and relaying it, then it will give the road a longer life.