Not all roads are the same. Although the driver rarely gets to set foot on the road surface as they move by in their vehicle there is actually a huge variety of surfaces that their tyres make contact with.
Underneath the vehicle, there are many different types of road surfacing material, each chosen for a particular site depending on countless variables. The components of the road surface can be influenced by:
• the type of road
• the volume and speed of traffic
• the location amongst others.
Getting these variables right and applying the correct surface option can literally be a matter of life and death.
Reactive versus Planned
There are two types of road maintenance practice: reactive and planned.
Planned maintenance is something the local authorities set in place at the start of the year for implementation during the upcoming year. Planned projects are generally larger and more complex, often resulting in a greater impact on the public. The projects tend to be less urgent than reactive work, ensuring the public benefit as much as possible from the work with minimum disruption.
Reactive maintenance is the day-to-day work that cannot be predicted. Emergency repairs are usually carried out where defects in the road or pavement have become an issue or danger to the road user or the pedestrian. The public may request urgent problems to be fixed that that could potentially be safety hazards, or report faults that have caused accidents.
The quickest and most cost effective way to remedy the problem is to isolate and treat only the defected area leaving the surrounding road in its present condition. Common emergency repairs cover the treatment of potholes and cracks, for instance, and the methods used to effectively treat these defects vary.
Current issues surrounding the increased numbers of potholes have resulted in more reactive maintenance, as councils struggle to keep up with public demand. But there are concerns that the more reactive maintenance is carried out, the more problems will occur, and you end up fire-fighting problems instead of planning long-term solutions. Although reduced budgets are already stretched to their limit, there could be a long-term benefit in the complete resurfacing of certain stretches of roads using planned maintenance arrangements to lower the amount of reactive work needed.
Anti-Skidding Technology
Skidding is the loss of friction between the tyres and the road surface, causing the vehicle to move uncontrollably. An important factor in road design is how to reduce the possibility of skidding. It is important for a road surface to create enough friction between itself and passing tyres to reduce the possibility of skidding. This however must be achieved without causing too much damage to the tyre, erosion to the surface and whilst maintaining a suitable ride quality for the road user in variable weather conditions.
Over time, passing traffic causes the surface to become polished, thereby reducing its micro-texture and consequently reducing its friction/skid resistance ability. Special anti-skid, hardwearing surfaces are used in hazardous areas such as traffic lights and junctions.
There are numerous methods used to test the skid resistance of a road surface including the portable pendulum tester, the grip-tester, the pavement friction tester and the Sideways Force Coefficient Routine Investigation Machine (SCRIM).
Prolonging Road Life
Surface dressing is a low cost method of increasing the life of a road and costs less than re-surfacing. It is used to create a fresh hardwearing surface with increased texture and therefore skid resistance. It also seals the surface of the road preventing the penetration of water, whilst arresting the disintegration of the existing surface.
An added advantage of surface dressing is that it can be repeated cost-effectively, for example every five years, thereby extending the life of the pavement even further. However, care must be taken as repeated layering can increase the risk of areas ‘fatting up’ and may cause bleeding of excess binder in hot conditions.
By The Side of the Road: Footways
There are many types of footway across the country, all planned and designed for specific purposes. During the design stage, consideration goes not only into visual appearance but also into cost-effectiveness, suitability, availability of material, ease of maintenance and environmental protection. The approach to footway design and construction is greatly dependent upon the type of user the pavement is likely to entice. Footways are categorised into one of three types:
- pedestrian only
- light traffic (bicycles) and
- heavy traffic (motor vehicles).
Clearly heavy traffic footways must be designed to withstand greater loading than the other categories. The ability of a footway to withstand greater loading is achieved by increasing the depth or density of the underlying base course and sub-base of the pavement or in some cases by use of alternate thick rigid surfacing, such as concrete, often seen in cycle paths.
Another important aspect of footway design and construction is the use of edge restraints e.g. kerbs. In addition to their use as footway edge constraints, kerbs aid the prevention of water penetration into the footway by forming a channel to aid drainage of surface water, and provide a raised anti-vehicle barrier to create a boundary between vehicles and pedestrians.
Going Green: Recycling Our Roads
In every industry recycling targets and initiatives to reduce carbon footprints are becoming more and more important. This is good news for the environment and can end up saving companies a great deal of money. Roads surfaces are recyclable due to the plastic properties (fluid when hot and solid when cold) of the bituminous materials used, and due to the fact that most of the aggregate contained within its matrix will be of the same quality as it was when it was originally laid.
The recycling process is extremely valuable when working with scarce aggregate of high quality. Although there are variations of the recycling process, dependent on the intended use of the finished product, most follow the same initial procedures.
When recycling a road surface the existing solid surface must first be broken up or planed before being crushed into smaller more manageable pieces. These small pieces are then graded by type and heated to a temperature-dependent of the material being recycled in order to reduce the bituminous binder to its fluid state. At this stage a small amount of extra bituminous binder, cut-back oil or flux oil may be added to the mixture to achieve the desired ‘workable’ consistency.