Making the wrong choice of pothole repair system can be very costly indeed – in terms of cash, carbon and reputation. The potholes will reform, the budget to fix them must be found again and the original good-news story about splashing out on pothole repair turns into a PR nightmare.
However, it’s difficult to make the right decision without the right information. We hope that our Q and A on pothole repair will help. Let’s start at the beginning.
Why do potholes form?
The source of a pothole is usually a crack or some other small defect. Cracks can form due to repeated loading of the road. It may be that the road is taking more traffic, and heavier traffic than it was designed for. Or the bitumen in the road may be old and oxidised which means it is more brittle and hence more likely to crack.
Utility trench reinstatements are another common source of potholes. The joint between the existing road and the asphalt used to top off the reinstatement widens over time to become a pothole.
Some cracks form in the lower layers of a road and travel up. It could be that the ground beneath a road becomes unstable. This sometimes happens to country roads where intense rainfall causes movement or even the ground to wash away.
Cracks widen due to the action of vehicles driving over them. When there is wet weather, tyres can force water into the cracks at pressure, widening them. Freezing spells further increase damage as water seeps into cracks and down into lower layers, expands as it turns into ice and causes more havoc.
Why do potholes come back so quickly?
Often potholes reform quickly because the joint between the pothole repair material and the existing road is a weak point, effectively a tiny crack. Although a treatment such as a tack coat may have been applied around onto the edges of the existing road, there may still be some small areas where the bond between old and new is not 100%. So, there are little cracks and the whole process starts again.
Sometimes pothole repairs are only supposed to be short lived. For example, on a busy road, the authority may choose to use a fast fix method such as cold repair material so that the danger of vehicle damage or even an accident is removed before a more permanent solution can take place. Cold repair techniques don’t generally last due again to the weak joint between old and new, even when a cold-spray sealant is used.
What is the traditional way to repair potholes?
A traditional repair would involve cutting out the asphalt around a pothole, using a saw and breaker, to cut away damaged material at the edge of the hole and to create a nice vertical face for the tack coat to be applied to so that the bond can be good.
Waste material, together with any other loose material, is transported to a processing plant. Hot asphalt, perhaps held in a hot box, is then placed in the hole and compacted.
What about quicker methods?
On country roads, where road closures or restrictions are difficult, spray injection techniques may be a good solution. A high-pressure blower blasts out loose material, a bitumen emulsion is then applied to seal cracks and then the asphalt is sprayed into the hole at pressure, compacting itself as it goes.
Mastic asphalts can be a quick pothole fix. These consist of bitumen, often modified with a polymer to make them more flexible, fillers and sometimes fine aggregate. Versions which use waste tyre rubber as a form of modifier are also under trial.
Although there will be some bonding between the existing material around a pothole and the new, flowable or sprayable asphalt, there is still the risk of weak points at joints. If the material around the edge of the pothole is not cut out and carted away, there could be weak material which again will fail and form into potholes over time.
What about all-in-one machines?
These deploy the same principal as traditional pothole repair methods with a Swiss-army-knife approach which puts all the tools required in one piece of plant, usually an excavator, which has been adapted for the task. It has many of the downsides of the traditional method, creating waste material that must be carted away and with the same risk of weaknesses at joints.
There are health benefits since using attachments on a mechanical arm, rather than held by a human, removes the risk of hand arm vibration syndrome (HAVS) and they can be very quick at preparing the pothole for filling.
However, the carbon benefits are questionable, given this process doesn’t actually fill the holes. A whole new vehicle is required to transport the asphalt and potentially additional team members to fill the prepared holes. If the excavator has to travel some distance to site, it may also need an additional vehicle such as a low loader to transport it. And there are still the same risks of failure and waste material to be accounted for.
What is different about thermal techniques?
The big idea behind thermal techniques is that they heat up the road so that you are basically making the existing bitumen in a road sticky and flowable, so that when new, hot material is added everything blends together and there is no joint or weak point.
Some systems simply use a flame, others use heaters that are positioned over a pothole or defect. Thermal Road Repairs went a step further to develop a patented system that monitors the temperature to which the road is heated and then automatically switches off. This is to avoid overheating which can lead to oxidisation of the bitumen which increases the risk of cracking.
Because there is no need to cut a straight edge for the pothole repair, there is no waste material to be carted away and less new material is needed, lowering the use of resources and the carbon footprint. Thermal Road Repair also uses solar energy to top up its heaters and bio fuel, further lowering the carbon footprint of any repair. Again, no HAVS risk here and no noise pollution either.
What about carbon?
When considering the carbon footprint of a pothole repair, it is important to look at the bigger picture – especially as it will be audited further down the line. It isn’t enough to compare the carbon emissions per kg of different repair materials. The relative volumes of new material needed for different repair types, carbon emissions due to vehicle movements for both new material and waste, and the longevity of the repair should all be taken into consideration.
There is nothing low carbon about a pothole repair that fails and needs doing again in a few months. The longer the repair lasts, and the fewer return visits that are required, the lower the lifetime carbon footprint.
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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.
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