Transport

Inside the UK project that hopes to put an end to potholes

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Potholes cost billions of dollars to repair, and cause a ton of accidents
Potholes cost billions of dollars to repair, and cause a ton of accidents
Cao's solution places coils of pipe across the road every 5-10 meters, connected via a heat pump to a loop of underground pipes 5-10 meters down, surrounded by soil that's been impregnated with phase-change microcapsules designed to store and release heat
Benyi Cao

An ambitious project out of the University of Surrey aims to stop potholes from developing, using super-efficient ground source heat pumps and phase change microcapsules. We spoke to team leader Dr. Benji Cao to find out how it works.

In 2022, England spent £1.2 billion (about US$1.5 billion) repairing potholes. That's no insignificant sum of money – and lord knows what they've cost the country as a result of an estimated 5,000 pothole-related accident injuries that have happened since 2018.

Dr. Benyi Cao of the University of Surrey has taken on the challenge of coming up with a solution – and indeed, he's been awarded a £625,000 ($780,000) research fellowship to pursue, develop and test a system designed to stop potholes from developing in the first place.

"You need basically three elements for pothole formation," Dr. Cao told us over a video call. "The first is a surface crack – these form and expand over time due to traffic, we can't avoid that. The second is water, and the third is the freeze/thaw cycling. We get these small cracks, and then water seeps into the cracks. In winter, it gets down to about -10 °C (14 °F) in the UK, so that water freezes and expands, pushing open those cracks. In spring, when the temperature rises again, that water thaws and contracts."

"This repeated freezing and thawing, and subsequent expansion and contraction, can weaken the asphalt binder – the glue of the road surface," he continued. "This causes all kinds of deterioration; potholes is just one problem, but it's a major one. So I started thinking about how to warm up the road surface in winter, so no freezing happens."

This has been attempted before in other demonstration projects, but typically with heating elements embedded in the road surface. Cao was looking for a much more efficient and lower-carbon solution.

"So I'm thinking," said Cao. "We have a road here, and there's a huge amount of ground underneath the road – why don't we just use this ground itself as a collector and storage for heat in summer, and extract that heat again in winter?"

The system Cao has designed works roughly like this: during road construction, workers will lay a series of slim, 10-mm-diameter plastic pipes across the road, maybe every 5-10 m (16-32 ft). Beside or below the road, they'll dig down maybe 5-10 m into the subgrade soil, and create more loops of piping down there. The surface loops and the underground loops will interface at a heat pump.

Cao's solution places coils of pipe across the road every 5-10 meters, connected via a heat pump to a loop of underground pipes 5-10 meters down, surrounded by soil that's been impregnated with phase-change microcapsules designed to store and release heat
Benyi Cao

The subgrade soil around the underground loops will be impregnated with tiny microcapsules, explained Cao: "These capsules are made of a phase-change material, perhaps like paraffin or wax, that can store a lot of heat. The shells are going to be graphite or graphene based materials, to transfer heat quickly."

All the heat pumps really need to do is gently circulate water, with an antifreeze mixture, around the loops. And not continuously, either; once enough heat is stored underground, they can be switched off, and they won't need to be switched back on until the road temperature drops to a couple of degrees above freezing.

Cao says a single set of underground coils and heat pump could likely handle more than a 100 m (330 ft) length of road. "Every unit of electricity you use to run that heat pump, moves four units of thermal heat," he said. "So it's quite efficient – way more energy efficient than the electric road heater systems."

Throughout summer, when the road surface gets nice and hot, the heat pumps will transfer that heat into the phase change capsules in the soil, and then in winter, when temperatures get close to or below freezing, the pumps will switch on in reverse. "We just need to avoid freezing of the road, so we only need to keep the temperature above zero," said Cao. "It shouldn't be that difficult here in the UK."

With funding on board, Cao says the first step is to design and produce the phase change microcapsules. "That's a big part of the project," he told us. "Secondly, we're going to create a model road in the lab, probably about three meters (10 ft) long, in a very controlled environment in a big soil chamber. Thirdly, we'll do a numerical simulation to see the long-term effects and overall performance and resilience of the system."

And then it'll be time to test it in the real world. "The last task is to do a full scale field trial with the Transport Agency," Cao said. "In that field trial, we'll embed some of these pipes and a pump under a road segment of maybe 20 meters (66 ft). We'll monitor the performance for a whole year, and that'll tell us if we've captured enough heat through summer and warmed the road properly in winter. The critical things we'll be looking at are whether we can keep the road surface from freezing, whether our ground loops are deep enough, do we need more phase-change material... Or maybe we're storing too much heat, and we can look at reducing pipe depth or using fewer microcapsules, or serving a longer piece of road... We'll be looking for the optimum approach."

Will it be economically viable to roll out across the United Kingdom? Well, that depends on a number of factors that'll be examined through the project. "We haven't done a cost analysis and I feel like we couldn't do one until the field trial," added Cao. "It'll be an additional cost to transport infrastructure, but we think there'll be benefits in terms of carbon emissions from pothole repairs, which are not insignificant – some 700 tons per year, and also in the lifespan of the new roads."

Fascinating stuff, we look forward to the results.

Source: University of Surrey

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9 comments
cjeam
Presumably some proportion of potholes are entirely due to road wear, without any freezing action which is the component this system solves, and thus those potholes will continue. The usefulness of the system in colder climates, where snow clearing is a significant financial and carbon cost, might be more relevant, especially if it can be tied into district scale heating and cooling loops using heatpumps to get different temperatures where they are needed.

"but we think there'll be benefits in terms of carbon emissions from pothole repairs, which are not insignificant – some 700 tons per year"

700 tons of CO2eq per year actually is completely insignificant in terms of the whole of England.
CSPK
I can think of few things more ridiculous. Using energy - mostly from fossil fuels - to heat roads, however 'efficiently', is barmy. Since there is no mention of retro-fitting, all affected roads would need to be dug up anyway, so one may as well build them out of frost-proof surfacing. Probably much cheaper per mile than having heat pumps and all the plumbing installed, not to mention the electricity infrastructure needed. As for saving 700 tons of CO2 - whoop de doo!
windykites
How about periodically detecting cracks in the road, and applying heat to soften the asphalt, and seal the cracks? Quick and easy.
pbethel
For most of my life I lived where it rained 160 to200 inches of rain per year and now I live where it rains 8 to 12 inches per year and yet observe the same mode of damage.
Hydraulic forces when a vehicle runs over a crack filled with water are enormous and require no freeze thaw cycle. Pavement cracks happen regardless.
This seems to be a expensive partial solution.
TechGazer
There would probably a future disaster from all that buried phase-change material, which would turn out to poison groundwater, make the soil unstable, or some other problem that isn't immediately obvious.

This is one of those ideas that is best dealt with by saying "Go ahead and develop this scheme with _your_ own money".
vince
I think it will be surprisingly difficult once the Atlantic flow is disrupted due to global warming and the greenland ice sheet melts and then Europe and UK will be 20 degrees colder year round. That will mess up their pothole plans sadly.
Jinpa
The description of the construction doesn't reflect knowledge of what already is under a lot of roads. It isn't just dirt. It is a lot of piping and wiring for all sorts of things. Also, this description assumes the roads are asphalt, which many are. Don't concrete roads last longer? And isn't a lot of the pothole problem due to poor-quality filling of prior potholes?
martinwinlow
Who on Earth makes the decision to spend such a huge amount of money on such a perfectly stupid idea? This scheme would increase the cost of road building by an order of magnitude, shifting all that soil away and then bringing it back again let alone adding all the ancillary stuff to make it work. Just repair the bally potholes *before* they get so big to cause problems. How hard is it, FCOL!
Sergius
I live in Brazil and the rainfall here is high.
There is no freezing of the ground or roads, but water enters through cracks in the asphalt and creates pockets beneath.
When a car passes, the hydraulic pressure exerted causes the water to act as a high-pressure hydraulic blade, expanding the area where the asphalt detaches from the ground below.
Therefore, freezing can also represent a problem for the enlargement of potholes, however, those pockets of water below the asphalt layer and the hydraulic pressure that traffic exerts seem to me to be the big villain.
Perhaps a drainage system for this water that accumulates between the asphalt and the ground could result in an effective solution.