Road and footpath improvements
Types of treatment
Our road network covers around 2200km in both urban and rural areas, and different types of roads have to cope with different demands.
For example some rural roads can be in exposed areas with harsh weather conditions. Others may be sheltered from the weather but may have to cope with the stress of heavy loads and a lot of heavy lorries.
We have various treatments available for these different conditions.
Whilst we generally try to repair the roads which are in the poorest condition, we also use lower cost preventative treatments which are designed to stop the condition getting any worse and to stop water or oxygen getting through the road surface as both of these can lead to serious damage of road surfaces. This type of treatment is applied before a road reaches an advanced state of deterioration, to prevent the need for a far more costly repair.
There are five distinct types of treatment.
This is the most expensive treatment and is used as a last resort when the road surface and underlying layers have deteriorated to a very advanced stage. Repairs may involve a deep excavation, and replacement of the sub-base stone layer in addition to the upper bituminous layers.
Plane and inlay
This is a common treatment used when only the road surface has deteriorated beyond repair. The surface layer is mechanically removed to a typical depth of 45mm, a tack coat is then applied followed by a new surface.
As long as existing levels are suitable it is sometimes possible to apply a new surface course directly on top of the existing one, with minimal or no patching. This technique provides an improved depth of bound surfacing and can be more cost effective.
This is a hot recycling process where the existing surface course is heated then scored to a depth of approximately 30mm. A thin layer of hot asphalt is then applied over the reheated surface. This achieves a strong bond with the old surface and reduces cost due to reduced material usage. As a recycling process, it also has some environmental benefits.
Retread is used as an alternative to full reconstruction where the cost is high and the road is only used lightly. The process involves breaking up and regrading the existing bound material, adding bitumen where required, followed by dressing the top surface with a layer of bitumen emulsion and small chippings. As an on-site recycling process, there are environmental benefits compared to conventional treatments.
Conventional surfacing materials
Chipped hot rolled asphalt
A traditional surfacing material, this is generally laid at a depth of 45mm and has bitumen coated chips rolled into its surface to provide skid resistance.
Advantages - this is a strong, impervious flexible material with good resistance to cracking
Disadvantages - it is very costly and it can deform under heavy loads. It can be difficult to obtain a good finish during colder weather
Lifespan - 20 to 30 years
High stone content asphalt
This has more stone in the mix than chipped hot rolled asphalt, but more importantly it doesn't need bitumen coated chippings. It provides a stiffer mix than chipped asphalt.
Advantages - provides a very durable surface
Disadvantages - it is costly and it is very difficult to get a good finish if hand laying due to the more stony mix. It isn't suitable on high speed sections of road.
Lifespan - 20 to 30 years
Thin surface courses
These have a smaller stone size than asphalts and are laid thinner, typically 30mm. These materials have a higher stone content than most asphalts and rely on the interlock between the stones to achieve their strength.
Advantages - less expensive than asphalt materials and has very low noise surface. More sites can be overlaid because of the thinner depth. It is very resistant to deformation and rutting and because it is more porous it can help draining problematic, flat areas
Disadvantages - Over time water and oxygen can damage the surface. Slightly reduced durability compared to asphalt. Should not be used on roads subject to high stress
Lifespan - 15 to 20 years
Preventative surfacing treatments
This is a cold laid material containing bitumen emulsion, fine stones and sometimes fibres which is screeded onto the road or footway surface in a thin layer, around 10-15mm thick. This seals the road surface, stops water getting in and stops deterioration. Initially, the material appears dark brown in colour but quickly fades to a dark grey/black colour when it has set.
Advantages - very cost effective, which allows entire estates to be treated at one time. Quick process, and can be used very soon after laying. Stops further deterioration
Disadvantages - can't be used where there are serious underlying defects. Process adds limited strength. The material remains 'live' for a couple of weeks after laying and relies vehicles for compaction. The material may initially look rough until it has been used for a few weeks
Lifespan - 7 to 10 years
This is the application of a bitumen emulsion followed by chipping with a dry, clean stone. Sometimes this is done in two or three layers. Surface dressing is a highly effective technique for sealing the road surface and improving the surface texture and skid resistance of a road.
Advantages - very cost effective and the process is quick so traffic can use it soon after laying. Can be used on many types of roads including high speed and heavily used roads
Disadvantages - there will be loose chippings for several weeks after laying and drivers must keep their speed down. Surface can be noisier than other treatments. Adds no structural strength so road beneath must be structurally sound.
Lifespan - 7 to 10 years