It has been really, extremely, record-setting hot here on the US East Coast and in the Midwest. (After the past few weeks, 90 degrees fahrenheit now seems “cool” to me.)
It was so hot that the tarmac melted at Washington’s Reagan National Airport on Saturday. So much for asphalt tarmac, the “foundation of our mighty air network,” being sturdy and stable stuff to plant your feet, let alone an airplane, on, as Megan Garber writes in The Atlantic.
The US Airways plane was taxiing to take off when it was stuck on the tarmac for three hours. Then it became stuck in the tarmac which had softened from the heat. A groove had formed, the airplane sunk into it and at first it could not be removed.
It was 100 degrees Fahrenheit on Saturday which is certainly hot but not the hottest. Garber explains why a “semi-solid surface” like tarmac became “ever-so-slightly less solid” while also pointing out that “our current common surface might not be fully suited to its new, excessively heated environment.”
What is tarmac?
Tarmac, Garber explains, is “an abbreviation for “tarmacadam,” which is itself an abbreviation for “tar-penetration macadam.” Macadamization is a method of road construction in which stones are broken down into smaller chunks that are bound together with a cementing agent (often stone dust mixed with water) and placed atop bare soil. Tarmac contains not only the pulverized stones (which generate a lot of dust) but also coal tar, cement, resin, pitch, and ironworks slag, all smoothed flat by a steamroller.
In the US, petroleum-based pitch is used as a binding agent. The pitch makes the tarmac not quite a solid so repairs are relatively efficient. But, as Garber writes:
Viscoelasticity means that the asphalt is — rather frighteningly — always capable of liquifying. Heat the stuff to around 250 degrees F, and it will become liquid. Cool it back to room temperature, and it will become relatively solid. Again, that’s what’s great about it — and, normally, outdoor temperature is close enough to room temperature that asphalt’s latent meltiness isn’t an issue. Normally, tarmac can function pretty much like concrete. Normally.
The extreme heat this past weekend, after over a week of higher-than-average temperatures, meant that even the tarmac was not the same — was not as solid as it usually is
Climate change means that what seemed solid and stable (airport runways) is not exactly so. So, assuming if — regrettably — hotter temperatures are here to stay, we will need to start rethinking how such changes affect the materials of the things we use and not only for roads and runways: What about bridges and buildings?
Global warming, the melting tarmac at the Reagan Airport shows, is changing our world and its very properties in ways seen and unseen and certainly much felt.
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Photo by James Cridland