1. When should you treat a pothole?
Before it even exists. As soon as cracks begin to appear, consider applying some form of surface treatment.
Surface dressing, where a bitumen binder is sprayed onto the road and then stone chippings spread on top, is better for busy urban or rural roads. Micro surfacing (also called micro asphalt or thin surfacing) involves the application of a base and top layer of slurry – a water-based mix of stones and bitumen – onto the road surface. It is best for less-busy roads.
2. What is a pothole?
There’s no formal definition of a pothole. They are usually between 40mm and 60mm deep and cover an average area of 0.35m2. Most treatments are effective up to these depths. (Shameless plug: Thermal Road Repairs technology is effective up to 100mm deep).
Any defect in the road should be treated because it is only going to get bigger and bigger. Cold joints over reinstated utility trenches and infills around utility covers are commonly occurring weak spots which some councils choose to treat early.
3. What causes potholes?
Over time, the bitumen that holds the aggregate in a road surface becomes less elastic which means that it is more susceptible to cracking. The higher the volume of traffic and the heavier that traffic, the sooner this point will be reached. Once a defect has formed, as described above, water can get into it. When water freezes, it expands, pushing the crack further open (freeze-thaw action).
Sometime freeze-thaw can attack from below as well. For instance, if a thinnish layer of asphalt has been laid over cobbles or compacted stone in a country road. In these cases, larger areas of asphalt may delaminate.
4. What are the methods of repairing potholes and which one is best?
i. Patch with hot asphalt
Traditional method which involves squaring up the edges of the pothole, taking loose material away, bringing in hot asphalt to fill the hole and compacting.
- Where: any road
- Pros: quick, familiar
- Cons: joint between old and new material is a weak point, high carbon, risk of HAVS
ii. Thermal road repairs
Heat the loose material in the pothole and the surrounding area with a specialist heater, top up and mix with new asphalt, compact.
- Where: any road, but most cost effective for clusters of potholes
- Pros: long-lasting, no waste, low carbon, no HAVS risk
- Cons: requires specialist unit
(Shameless plug: not all systems are created equal. Thermal Road Repairs’ patented system heats the road in a very controlled way to optimise the bond at the perimeter of the pothole. It also uses solar energy to partially power the heater, further lowering the carbon footprint of the repair).
iii. In-situ thermal recycling
Loose material is removed from the road, heated and mixed in a purpose-made vehicle with new material before being returned to the pothole and compacted.
- Where: anywhere, needs high volume to be cost effective
- Pros: reduced waste, lower carbon
- Cons: specialist operation, cold joint remains a weak spot, significant space and traffic management required
iv. Spray injection patching
A specialist machine applied cold emulsion asphalt into potholes under high pressure. The same machine is used to prepare the pothole by blowing out any loose material and then to apply a bitumen emulsion before aggregate is added to the stream to fill up the pothole. It is self-compacting.
- Where: rural roads
- Pros: fast, lower cost, no waste, no HAVS risk
- Cons: specialist unit, durability may be a problem
v. Cold-applied instant material
Pothole is prepared by squaring up the edges and applying a primer to the bottom and primer. The material is then applied and compacted, possibly in layers, and a primer applied around the edges.
- Where: ideal for lower trafficked roads
- Pros: fast, good for temporary repairs, lower carbon
- Cons: durability not great for trafficked roads
5. How can I lower the carbon footprint of my pothole repair?
There are six questions to consider when looking at ways to reduce the carbon footprint of a pothole repair.
- Is there any waste material to be taken away?
- Does the patching medium contain recycled material?
- How much heat is used in the process?
- Does energy come from a renewable source?
- How many vehicle movements are needed?
- What is the patch’s longevity? This is perhaps one of the most important aspects. Mending a pothole twice is spending the carbon twice.
(Shameless plug: Thermal Road Repairs’ system ticks all these boxes)
6. What are the other considerations when repairing a pothole?
The responsible authority has a statutory responsibility to keep its roads as safe as possible, under Section 41 of the Highways Act 1980. It may be that speed of repair is the number one consideration due to concerns about the safety of car users or cyclists. Some councils are also facing hefty claims from motorists looking to recoup the cost of damage to their vehicles.
Access and width of the road will also dictate what methods are possible, and what aren’t. Residential streets with parked vehicles will require a different approach to main roads, country lanes demand a different approach again.
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. We invest significantly in R&D, to create new technologies and to continuously improve our existing ones.
High output. Low emission. Permanent solution.
Potholes – a repair guide, Department for Transport and ADEPT, March 2019