If a pothole repair is classed as permanent, it should last for as long as the road surface it’s in, right? Well, not necessarily. The definition of a permanent repair seems to depend on the way that the reinstatement is carried out.
Pothole repairs fall into three categories: temporary, semi-permanent and permanent. In simple terms, a temporary repair is simply fill and go, whereas a permanent one will involve a way of bonding new and old material and compaction. And semi-permanent is somewhere in between.
A temporary repair is required when a road authority, or its contractor, considers the pothole to be a significant hazard and has to take swift action. This could be due to its size or location, including the type of road and how heavily trafficked it is. In such cases, road crews will be targeted to execute a temporary repair within 48 hours or even less, with a more permanent repair then planned as part of an ongoing maintenance and repair regime.
Temporary repair methods, as you might suspect, can be quite quick and dirty. The ‘throw and go’ approach sees patching material thrown into the hole without cleaning out water or debris first, with compaction left down to the traffic that will pass over it. Cold-mix materials are often used for temporary repairs because they are convenient and fast.
Spray injection patching is also classed as temporary. This involves spraying hot bitumen emulsion with surface dressing-type aggregate into the pothole, covering it in chippings and allowing the traffic to compact it. A 2019 guide to pothole repair by ADEPT, the Association of Directors of Environment, Economy, Planning and Transport, reported that this method had been found to be effective for country roads. There are injection patching systems that aim to be more thorough, with ways to remove water and blow out debris.
A semi-permanent repair could involve hot or cold asphalt and would include the removal of water and debris. Having cut vertical edges outside the failed material for the pothole, the new asphalt would be added and compacted. For smaller potholes, the edges may be left as they are but this will hinder compaction and possibly reduce durability.
Permanent repairs go a step further. After the pothole area has been prepared by cutting vertical edges and cleaning it out, a bond coat is applied to the base and sides of the opening and then hot asphalt – or sometimes cold asphalt – is added and compacted.
There are several factors that affect the durability of a pothole repair. Among the most important are the way that the pothole is prepared, the bond between existing and new material and the make-up of the repair material itself. National Highways’ surface repair standard states that repair material should be compatible and consistent with surrounding materials; cold mix material can only be used in a hot mix road surface on a temporary basis.
Most repair methods have a weakness: the joint between old and new (the seam). If there’s no bond coat, or if the coat hasn’t been diligently installed and isn’t performing perfectly all the way around the patch, water will get in and widen the crack leading to ravelling and eventually another pothole. How long that will take depends on factors such as the volume and weight of traffic and weather conditions.
The Thermal Road Repairs system was created to completely remove any joints and hence any weak points. Because it involves heating up the existing road material in and around the area of the pothole in a controlled way until its workable, adding a small amount of new hot material, mixing the two and finally compacting, it creates a seamless repair with new and old material becoming one due to the heating and compaction processes. That means that you really do have a permanent repair.
Some of our customers are even finding they can cut out the temporary repair step and go straight to a permanent – and seamless – solution. Obviously, the practicalities of this approach will depend on the road and the traffic management required, but a Thermal Road Repairs fix is faster than a traditional ‘permanent’ one because it doesn’t require time to cut away around the edges of the pothole to create vertical edges, the removal of waste material and for new material to be brought to site in a separate vehicle. All the required hot material for the Thermal Road Repair process is on hand as needed, stored in a small hot box in the repair unit.
There can’t be a one-size-fits-all pothole repair system: different methods suit different situations. For any road authority which is trying to work out what the best combination of solutions for them might be, our advice is to talk to others in a similar situation about technologies that have – and haven’t – worked for them.
One question you might want to ask yourself: if the seam is the potential cause for pothole failure, wouldn’t you want to adopt a seamless approach to avoid this in the first place?
Thermal Road Repairs is a green technology company which supplies systems to improve the quality, cost and time efficiency of road repairs and paving – at a far lower environmental cost than traditional methods. It invests significantly in R&D, to create new technologies and to continuously improve existing ones.
Thermal Road Repairs: Decarbonising the asphalt repair industry.
High output. Low emission. Zero waste. Permanent solution.