Blogs Highways Highlight

Surface dressing is a cost-effective road maintenance technique used to seal and protect existing road surfaces, typically those that are just starting to fail (but may still appear to be in reasonable condition). It involves spraying a coating of bitumen onto the road surface, followed by spreading one or more layers of stone chippings over the bitumen. As the bitumen sets, the chippings stick to the road surface and are further pressed into the road surface by a roller.

Surface dressing is like giving a road a protective coat to keep it in good condition. This process helps to waterproof the road, improve skid resistance, and prevent water damage, extending the life of the road by up to 10 years.

In Buckinghamshire, approximately 250,000 square metres (equivalent to 35 football pitches) of road are surface-dressed each year. This year our teams will be focusing on completing all the county’s surface dressing in July - when hopefully, weather conditions are best. We generally only surface dress rural roads in the county. It takes two or three weeks for the dressing to completely settle down and vehicles running carefully on the surface help it to embed.

Surface dressing is weather dependent because it relies on the right conditions for the materials to stick properly and set safely. Bitumen needs a dry surface to bond well with the road. If the road is wet, the bitumen can’t stick properly and the stone chipping won’t stay in place. Likewise, if it rains during or shortly after application the bitumen can wash away, loosening chippings meaning they may not embed properly and the surface can become slippery and unsafe.

The ideal weather and conditions for surface dressing are: dry, warm (typically above 15°C) low wind and no rain forecast for at least 24 hours.

The road is re-opened immediately after the dressing has been laid. Temporary advisory speed signs are installed on site to keep traffic speeds to approx. 20mph to avoid damage to vehicles from flying stones/chippings until our teams are confident the dressing has settled down. The surface settles and becomes smoother over time with steady traffic helping to press the road surface. Our teams return to the site a couple of times over the first 2-3 weeks post surface dressing to sweep away any excess loose chippings, with a final sweep after 3-4 weeks.

Surface dressing has many benefits including:

• Helping to seal the road to stop water seeping into the road foundation, weakening it and causing damage (e.g. preventing potholes). Take a look at how potholes are formed here!
• Improving grip for vehicles and providing a good resistance to skidding on smooth or slippery roads, making the road safer.
• Extending the life of the road without needing full resurfacing - A high-quality surface dressing can last around 10 years, and roads can be re-dressed using this treatment up to three times before resurfacing is required.
• Minimising disruption - Road traffic can be allowed to run on the new surface almost immediately, avoiding lengthy closures and ten times less disruption.
• Up to ten times cheaper than other methods of restoring road surfaces (and about 25% of the cost of complete conventional resurfacing!)

Our teams give advance notice of surface dressing works to residents and drivers wherever possible and provide advisory warning signs from the time we start work to the time when the road is ready for normal use. Information is also captured in our weekly roadworks communications and shared on our Buckinghamshire Highways Facebook page (@BucksHighways).

To help us complete surface dressing near you, please ensure your vehicle is not left on the road which is to be treated, try to avoid inviting visitors or arranging deliveries when work is to take place, keep to the recommended speed limit on recently treated roads and never overtake on a newly treated surface. Inconsiderate drivers travelling above the recommended speed cause chippings to be thrown up which can damage other vehicles and property.

Microsurfacing is a road maintenance technique that gives a new top layer to the road making it smoother, safer, and longer-lasting—without needing a full resurfacing. It can be likened to giving the road “a fresh coat of paint” but with special materials that help to seal cracks, improve grip and protect the surface of the road.

A thin layer (approx. 10-15mm) of a special mixture – made of bitumen, water, fine stones and additives is spread over the road. The mixture is cold, which saves energy, and is applied directly onto the existing road surface. Usually, two layers are applied (up to 25mm thickness); an initial layer to smooth out defects, bumps and dips, and then a top final layer to help seal the road and restore grip.  It sets quickly, often within an hour or two and the road is ready to drive on the same day.

Microsurfacing is often regarded as a messy process as the mixture is laid in a semi-liquid form to ensure that all cracks are treated. The laying of the mixture also often means inspection chamber covers and road gully gratings need to be adjusted after the surfacing has been completed. Once the mixture is completely dry, our teams will return to sweep up any loose stones from the mixture, adjust or raise any ironwork to the new road level and repaint road markings where applicable.

We generally use microsurfacing on urban estate roads in Buckinghamshire like cul-de-sacs, but the technique can be used anywhere.

Microsurfacing has many benefits including:

• Quick to apply meaning its ideal for helping to fix minor cracks and wear
• Improving skid resistance making the road safer
• Extending the life of the road without needing full resurfacing - A high-quality microsurfacing can last between 5 - 10 years
• Minimal disruption - Road traffic can be allowed to run on the new surface after a few hours once the mixture has cured and hardened, avoiding lengthy closures and disruption.
• Cost effective (about a third of the cost of resurfacing!)

Microsurfacing is weather dependent because it involves a water-based mixture that needs the right conditions to set and cure properly. If it rains during or immediately after the mixture has been laid the water can’t evaporate and the surface might wash away or stay soft. Similarly, if the temperature is too cold the mix can take much longer to dry and therefore harden.

The summer months (with hopefully warmer and dry weather) enable the microsurfacing mix to set quickly and evenly and ensure the surface is strong and long-lasting. The ideal conditions for microsurfacing are dry, warm (above 10°C) and with no rain for a few hours after the work is complete.

And the sooner the mixture dries, the sooner the road can reopen!

Grouted Macadam is a specialised road surfacing material. It combines open-graded asphalt (a type of porous, thick, sticky, black material designed to allow water to drain through the pavement, reducing runoff and improving safety) with a grout infusion (a sort of paste for filling gaps and crevices) to create a durable, often jointless surface. It is used as an alternative to traditional asphalt and concrete, offering high strength, impermeability, and resistance to wear.

Grouted Macadams can be laid thinner than normal surface courses at about 25mm so is perfect when replacing a failing surface over the top of a concrete constructed road.

There are 2 types of grouts commonly used in Buckinghamshire

• Bituminous Grouted Macadam – This is used where urban covered concrete roads are failing (delaminating). The grout seals the surface, preventing water from getting in and improving flexibility.
  
  Approx. 40% of the roads in Buckinghamshire have been constructed using underlying concrete blocks or bays for rigidity, and covered using a surface material for safety. Reflective cracking – which can lead to potholes! - occurs when the concrete bays expand and shrink due to changes in temperature. When using the Grouted Macadam technique for road resurfacing, we often proactively cut into the newly laid material where the concrete joints are below. We fill these joints with a flexible sealing material which means the concrete can expand and shrink without damaging the surface layer above. This reduces the risk of future potholes forming.
  
• Cementitious Grouted Macadam – This uses a cement-based grout, creating a hybrid between asphalt and concrete with high resistance to heat and heavy loads. This process is often used in Buckinghamshire on roundabouts where the stresses, of turning movements of vehicles, is highest.

Grouted Macadam is weather-dependent because its installation process requires specific conditions to ensure proper bonding and durability. Here’s why:

• Temperature Sensitivity: The grout used in Grouted Macadam needs to cure properly, and extreme temperatures (too hot or too cold) can affect its setting time and strength.
• Moisture Levels: Excessive rain or humidity can interfere with the grout’s ability to penetrate the macadam structure (compacted layers of crushed stone), leading to weaker adhesion.
• Drying Time: The material needs sufficient drying time before it can handle traffic. Wet or damp conditions can delay this process.
• Freeze-Thaw Resistance: If applied in freezing conditions, the grout may not bond correctly, leading to premature cracking or failure.

The use of grouted macadams ranges in price based on the grout type. A bituminous grout is approx. double the cost of microsurfacing, but the process is still cheaper than a normal surface course material so another great tool to have in Buckinghamshire Highways road resurfacing toolbox!