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Comment by russfink | Hacker News Reader

My question - how does the composition of the surface compare with that in other parts of the world that are hotter - Dubai, Saudi Arabia, Australia, the American southwest? Is there some code or regulation that helps these hotter places avoid this problem, and if so, should the UK government adopt them?

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"the American southwest"

Here in Denver, at least, our runways are all made of cement instead of tarmac. I knew one of the civil engineers who worked on the special blend of cement the used, and from what I remember of what he told me, it is much thicker than I expected, and has other stuff in it compared even to highway-grade cement to make it more durable. The freeze-thaw cycle is still rough on the cement, in 2007 $11 million of cement slabs had to be replaced due to that. The airport as a whole has 15,000 20-square-foot slabs across its multiple runways.

Of course, one could still have buckling with cement if the expansion joints are too close together for the expansion of adjoining slabs over a certain temperature. Perhaps this is what actually happened here?

> Here in Denver, at least, our runways are all made of cement instead of tarmac. [...] has other stuff in it compared even to highway-grade cement

That's something that looks so different about (some/many?) American roads that I never twigged about until you said that. Roads are tarmac here too, not just runways. For some reason it didn't occur to me reading other comments about hotter places not using tarmac that it'd effect roads for cars too.

I am from the Denver region and from personal experience I know the area has a lot of Bentonite clays [0] which can expand as water is absorbed and contract as it dries. My neighborhood was built on land with a lot of this clay and our streets are wavy and our driveways are cracked to hell. I imagine they deal with similar issues at DIA.

[0]: https://en.wikipedia.org/wiki/Bentonite

My neighborhood is the same. The ground and site prep out at DIA the Civil Engineer friend told me about took things like that into account.

I for one have had much of the cement replaced around my house (some more than once) and when I had the driveway redone, explicitly asked them to mitigate against the clay with whatever they had that made sense. I forget what all they had extra in the proposal that I approved (it was 10+ yrs ago) but my new driveway isn't having any issue while some neighbor's new ones are already cracked again.

I'm guessing the composition is dictated by local average conditions. It rains a lot in the UK and freezing ground temperatures are common in the winter too.

I lived in Spain for a while and non-average weather such as a day of heavy rainfall can result in disaster movie-style scenarios. It's all relative.

I would have guessed local outlier conditions with a bit of padding rather than averages, but I suppose those latent optimizations get progressively more expensive.

Which part of Spain? On the Atlantic Spain, heavy rainfall can just be "Thursday".

Alicante/Valencia mainly but, yeah, I lived in Galicia for a while also. Two different worlds in many ways.

The article mentioned a section "buckled" - this is the more likely outcome. When designing roads/runways, engineers design for the most likely thermal range. This is then used to determine how much expansion to account for. You'll see this most commonly on bridges, with sections of "teeth" that allow for large expansion/contraction ranges, since the bridge can't expand in the same way a ground road can.

In this case, its likely more a matter of runways needing more precision, and therefore the design allowance on the range of extreme temps being much lower. I'm sure a civil engineer could explain better.

Aha, so perhaps the press got it wrong by saying it "melted" - maybe it actually buckled. They might have it confused with common roads that are actually softening and "melting" rather than buckling.

Growing up in a very country part of Texas, the road in front of my house changed over the years as the county would upgrade it. One upgrade in the 80s was a tar base with gravel rocks. During the summer when it would get 100+, the tar would melt and get stuck to everything. It is the primary reason I quit running around barefoot as a kid. I ran along the road with the melted tar, and learned a life lesson. Not only was the hot tar painful, it was extremely unpleasant to remove.

Maybe in the 40 years since, people have figured things out like don't pour gravel covered tar roads in the heat?

Chip seal is still very common. I suspect that the reason you may have seen it evolve at a particular location is that the usage pattern of the road changed. Everything from gravel to asphalt to tarmac to concrete makes sense depending on what kind (and volume) of traffic a particular road sees.

This is exactly what happened. When my parents built the house and moved in, there were only a handful of houses. As more houses built and more traffic came from that, the county went through the upgrade process much like in Sims games.

That tar was often waste product, perhaps for processes that aren’t happening.

Not sure about your area, but in mine GE “donated” waste oil to counties for use on roads. Much of it was contaminated with nasty stuff and there are cancer clusters along these roads as the crushed stone and dust would get ground down and become airborne.

Thaks for that. Now that's a thought that's going to fester. None of the neighbors that I knew from back then nor anyone in my family got cancer, so probably shouldn't let it fester too long though. Phew

Pouring them in the heat is the best time because it's easier to melt the tar.

I didn't mean the physical act of pouring hot tar when making the road. I meany don't pour as in don't use that material in places where it regularly, almost set a calendar to it, getting hot enough to melt the material.

I misread your comment and thought you were chasing the road crew and burning yourself on freshly laid tar. After re-reading I see that it was melted by the sun.

Nope!

It's still the cheapest way to resurface a road.

As well as making concrete runways the best thing the UK government could do is adopt a "war footing" where it comes to climate change.

I use the term war footing because the impact of climate change is going to be on the order of a major war. And also because the response required for the decarbonisation required is going to be a significant portion of GDP.

Or they could keep their heads in the sand.

The whole world needs to.

I've flown through Dubai a few times, and I think most of their flights are early in the morning or at night. I don't know if that's for the runway or for the tires (or just heat in general), but I wonder if those factors played into things in the UK?

It's for air temperature. Warm air is considerably less dense, which raises the takeoff and landing speed of planes (for a given weight), up to unsafe levels, in addition to requiring a longer runway.

Mmm, density altitude... (https://www.faasafety.gov/files/gslac/library/documents/2011...)

Indeed!

I didn't want to call altitude into play since it tends not to vary too much between day and night in the same place :)

Or requiring weight reductions on the aircraft itself (fewer pax, lower fuel, less cargo).

This definitely isn’t the case, flights go all day at DXB.

I don't know if that's for the runway or for the tires (or just heat in general), but I wonder if those factors played into things in the UK?

Some afternoon and evening flights are sometimes cancelled at LAS if it's over 110°. Something to do with the expansion of the fuel due to the heat, and long-distance jets can't get enough on board.

It's in the local newspaper there occasionally, and should be Googleable.

Not takeoff needing longer runways at higher temp due to less engine power?

That's a factor for canceling flights on smaller, lower range jets. The big long-distance jets have the problem I mentioned.

And the runway is packed away into a hangar rest of the times?

If you use a cold weather composition in hot weather, you get melting asphault like this. If you use a warm weather composition in cold weather, you get cracks and potholes earlier than normal. Your composition is typically defined by climate conditions, not weather extremes.

Thank you - good explanation - the problem, then, is that there is no "one <type> fits all" solution for tarmac. It's just a case of the runway being built for different conditions. In other words, mother nature (global warming) violated the design requirements.

American highways use a PG rating system for the bitumen in the asphalt. You can read about it here: https://ftp.dot.state.tx.us/pub/txdot-info/cst/tips/faq_pg.p.... Short story is yes, places where it is expected to become very hot do use asphalt that doesn't rut under higher temperatures. The only exception I know of it Death Valley, which technically requires PG 76-10, but uses 70-10 just because California deemed it wouldn't be worth it to manufacture the extra grade just for one place that doesn't see much traffic. So I guess the highways just sometimes melt in Death Valley, too.

I do recall being a kid going on road trips through these deserts and noticing some of the highways were red and seemed to be made of something different. This was before the switch to the PG rating system. My dad claimed it had something to do with not melting the tire rubber of the vehicles on those roads, but I have no clue what his source was and I can't find any information about these highways, if they even still exist.

Its about building a surface that will also survive the winter and the summer. Its a tricky problem to solve. We could probably replace this with tarmac that could survive much hotter temps, but would just crack and break in the winter when its gets too cold.

Thank you - good explanation. There is no "one <type> fits all," then, for tarmac.

There's a similar story happening with our rail lines. The story seems to be that the materials we used in the UK are not stressed to deal with 40 degree heat. They never thought it would be an issue in the UK. Whereas many European railway lines were made to deal with 40-45 degree heat. I'm guessing it's the same for runway tarmac or whatever it is ...

Climate change is here ...

It's not so much the materials - modern rail, especially for high speed trains is laid in long continuously welded sections. The track is pre-tensioned so that at cold temperatures as it tries to shrink it is under significant tension and as it warms it becomes less tensioned. The question is what temperature to tension it to - at some temperature it is no longer under tension and above that it becomes in compression and then you have risk of the rails buckling. If I recall correctly, in England the track is tensioned for 27C (a typical hot summers day temperatures). They could tension for a higher temperature, but then you risk rails cracking in very cold weather. So in the end it's a compromise, but one that was made without expecting the current 40C temperatures.

> at some temperature it is no longer under tension and above that it becomes in compression and then you have risk of the rails buckling. If I recall correctly, in England the track is tensioned for 27C (a typical hot summers day temperatures)

While the basic gist is correct, a certain amount of compression is fine, too, because the trackbed can resist a certain amount of sideways buckling force, especially once the track has settled in a bit. It's only when the buckling forces caused by the temperature expansion and resultant compression exceed the sideways resistance of the trackbed that you get buckling.

Besides, rail temperatures on a hot summer day in the sun will definitively be higher than 27 °C – that value just happens to be the neutral temperature between maximum allowable compression and maximum allowable tension, whatever those temperatures exactly are.

https://www.networkrail.co.uk/stories/why-rails-buckle-in-br... says “rail can actually be up to 20 degrees higher.” and “For some of our track, such high temperatures are more than our track is designed to cope with”, so it depends on the track, but can be around 50°C.

A rail that’s in the shade for most of the day will get less hot, so I expect location also influences at what air temperature track will buckle.

Yes, exactly. And once it's in compression even at higher temperatures it will often be fine if left alone. This is why railway companies impose speed restrictions when it gets hot - they don't want the dynamic load of a passing train to exceed the ability of the track bed to resist buckling. Running at low speeds helps in this respect.

The relevant HN thread, a few days ago:

https://news.ycombinator.com/item?id=32118818

> There's a similar story happening with our rail lines

No, there's a similar story happening with everyone's rail lines. There's a curious thing bout Britain where the British press love a hysterical "here's an example of Broken Britain!" headline, and Europe and America quite enjoy seeing the UK getting any sort of comeuppance (and normally I wouldn't begrudge them this, there have been a lot of insane goings on in the UK of late).

But the only instance I've seen of this - not announcements of restricted services or reduced speeds as a precaution or due to reduce damage in overhead lines, actual buckling - today has been in Spain:

- https://twitter.com/rail_arri/status/1549039421525458945

- https://twitter.com/rail_arri/status/1549034924010655745

edit: and just minutes after I post this, I spot an instance in England from the weekend! https://twitter.com/networkrail/status/1548760985246261249/p...

Britain is broken.

This isn't the place to debate it, but we're currently a rudderless, borderline second world country.

It's going to take a generation to recover (let alone thrive) from what the last decade of flagshagging idiots have done to this once great country.

> This isn't the place to debate it, but we're currently a rudderless, borderline second world country.

You are teetering on the brink of alliance with the Soviet Union? (The first/second/third world thing originally referred to cold war alignment: first and second were US and Soviet spheres, third non-aligned; later first- and third-world got adopted as synonyms for “developed“ and “less developed”, but second-world is never used in that economic sense.)

Well, I'm using it in an economic and social sense.

Glad I could clarify.

Edit: and now my annoyance has settled down, I accept your correction. Thank you. Second division is more appropriate.

That may be, but by and large the loudest voices who make those complaints are usually just whining about immigrants, things being "too woke", the colour of their passport or whatever the flavour of the month target of hate is. They've little interest in looking at making people's lives better, they only seem interested in personal grievances

They put more gravel inside the tarmac or use concrete.

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