For the first time in the recorded history of the United Kingdom, temperatures exceeded 40 degrees Celsius – equivalent to 104 degrees Fahrenheit.
The heat wave has put British infrastructure to the test, and it hasn’t always passed. London Luton Airport briefly had to shut down a runway because of heat-related damage, and British press reported a Royal Air Force runway had “melted.”
The reports came as a surprise to many Brits, especially since such high temperatures aren’t uncommon in other parts of the world, where runways nonetheless seem to remain intact. Some wondered how it was possible runways could melt at all, others why it was happening in Britain and not elsewhere.
Can hot weather damage asphalt runways?
Yes, hot weather can damage asphalt surfaces such as airport runways.
WHAT WE FOUND
Asphalt is made up of a mixture of sand, rock, and a binder known as bitumen, a sort of oil-based tar.
Sand and rock don’t melt unless heated to 1,000 degrees Fahrenheit or more. But the binder melts at much lower temperatures, allowing asphalt to be spread and paved.
For the paving process, asphalt typically gets heated to 270 F or higher, turning the binder into a liquid. Once it cools, it becomes a solid that can support the weight of large vehicles like airplanes.
Hot weather alone won’t heat asphalt to 270 F and liquify it. But because asphalt is dark and retains heat, air temperatures of 100 F can cause an asphalt surface to reach 150 F or hotter, which is enough to soften the bitumen and cause the sort of damage that forces runways to shut down.
“Basically we are talking about a softening,” said Manik Barman, a civil engineering professor at the University of Minnesota who specializes in pavement infrastructure. “It becomes soft enough so that if a little amount of load is applied, you can see an imprint – or we technically we call it plastic deformation, a deformation that doesn't rebound back.”
This is something that London Luton Airport itself recognized as a potential issue, in a 2019 environmental report analyzing possible impacts of climate change on its infrastructure. The report stated “increased summer temperature and increased winter temperature variability has the potential to cause damage to the tarmac and asphalt.”
But why did this happen in London and not, for instance, Phoenix – where temperatures regularly far exceed what Britain is seeing? According to Barman, there are different grades of asphalt binder that are able to withstand different temperatures. The Federal Aviation Administration (FAA) told VERIFY that American runways typically use pavement that can withstand temps up to 169 F.
But it’s simply never gotten that hot in the U.K. before.
“Maybe 10 years down the line, what is happening this week, we will not say these are record temperatures, so we should be prepared in every infrastructure,” said Barman. “If we want to [have a long-term] fix and if you want to be visionary… select the grade based on the peak [temperatures] you're going to see in the next 30 years.”
Barman says typically, pavement grades are selected based on historical temperature data, but the effects of climate change mean those data may now be unreliable predictors.
London Luton Airport did not respond to VERIFY’s questions about the grade of asphalt it uses, but sent a statement reading in part, “Our runway is built to the same specification as any other in the UK, meeting all industry safety standards and regulations. Our maintenance and inspection regime also follows industry best practice and all requirements set out in our operating license.”