7 ms·

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 Americ

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?

dazc 4y ago
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.
- brailsafe 4y ago
  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.
- anthk 4y ago
  Which part of Spain? On the Atlantic Spain, heavy rainfall can just be "Thursday".
  - dazc 4y ago
    Alicante/Valencia mainly but, yeah, I lived in Galicia for a while also. Two different worlds in many ways.
darksaints 4y ago
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.
- russfink 4y ago
  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.
LightG 4y ago
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 ...
- mhandley 4y ago
  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.
  - jaclaz 4y ago
    The relevant HN thread, a few days ago: https://news.ycombinator.com/item?id=32118818 https://news.ycombinator.com/item?id=32118818
  - iggldiggl 4y ago
    > 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.
wiremine 4y ago
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?
- ycombinete 4y ago
  This definitely isn’t the case, flights go all day at DXB.
- gruturo 4y ago
  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.
  - mcguire 4y ago
    Mmm, density altitude... (https://www.faasafety.gov/files/gslac/library/documents/2011/Aug/56396/FAA%20P-8740-02%20DensityAltitude%5Bhi-res%5D%20branded.pdf https://www.faasafety.gov/files/gslac/library/documents/2011...)
    - gruturo 4y ago
      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 :)
  - Scoundreller 4y ago
    Or requiring weight reductions on the aircraft itself (fewer pax, lower fuel, less cargo).
- manojlds 4y ago
  And the runway is packed away into a hangar rest of the times?
- reaperducer 4y ago
digdugdirk 4y ago
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.
- russfink 4y ago
  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.
dylan604 4y ago
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?
- mulmen 4y ago
  Pouring them in the heat is the best time because it's easier to melt the tar.
  - dylan604 4y ago
    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.
    - mulmen 4y ago
      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.
- rootusrootus 4y ago
  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.
  - dylan604 4y ago
    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.
peapicker 4y ago
"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?
- macinjosh 4y ago
  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 https://en.wikipedia.org/wiki/Bentonite
  - peapicker 4y ago
    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.
- OJFord 4y ago
  > 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.
petre 4y ago
They put more gravel inside the tarmac or use concrete.
Milner08 4y ago
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.
- russfink 4y ago
  Thank you - good explanation. There is no "one <type> fits all," then, for tarmac.
badcppdev 4y ago
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.
- Synaesthesia 4y ago
  The whole world needs to.
nonameiguess 4y ago
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.pdf 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.

dazc 4y ago

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.

brailsafe 4y ago
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.
anthk 4y ago
Which part of Spain? On the Atlantic Spain, heavy rainfall can just be "Thursday".
- dazc 4y ago
  Alicante/Valencia mainly but, yeah, I lived in Galicia for a while also. Two different worlds in many ways.

darksaints 4y ago

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.

russfink 4y ago
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.

LightG 4y ago

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 ...

mhandley 4y ago
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.
- jaclaz 4y ago
  The relevant HN thread, a few days ago: https://news.ycombinator.com/item?id=32118818 https://news.ycombinator.com/item?id=32118818
- iggldiggl 4y ago
  > 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.

wiremine 4y ago

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?

ycombinete 4y ago
This definitely isn’t the case, flights go all day at DXB.
gruturo 4y ago
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.
- mcguire 4y ago
  Mmm, density altitude... (https://www.faasafety.gov/files/gslac/library/documents/2011/Aug/56396/FAA%20P-8740-02%20DensityAltitude%5Bhi-res%5D%20branded.pdf https://www.faasafety.gov/files/gslac/library/documents/2011...)
  - gruturo 4y ago
    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 :)
- Scoundreller 4y ago
  Or requiring weight reductions on the aircraft itself (fewer pax, lower fuel, less cargo).
manojlds 4y ago
And the runway is packed away into a hangar rest of the times?
reaperducer 4y ago

digdugdirk 4y ago

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.

russfink 4y ago
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.

dylan604 4y ago

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?

mulmen 4y ago
Pouring them in the heat is the best time because it's easier to melt the tar.
- dylan604 4y ago
  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.
  - mulmen 4y ago
    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.
rootusrootus 4y ago
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.
- dylan604 4y ago
  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.

peapicker 4y ago

"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?

macinjosh 4y ago
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 https://en.wikipedia.org/wiki/Bentonite
- peapicker 4y ago
  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.
OJFord 4y ago
> 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.

petre 4y ago

They put more gravel inside the tarmac or use concrete.

Milner08 4y ago

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.

russfink 4y ago
Thank you - good explanation. There is no "one <type> fits all," then, for tarmac.

badcppdev 4y ago

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.

Synaesthesia 4y ago
The whole world needs to.

nonameiguess 4y ago

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.pdf 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.