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The other day I asked if a skyscraper could be built from modern or mildly futuristic materials that would last 10'000 years (and still make good economic sense). The (many) answers were a resounding "No", but this got me thinking...

Ok, so a regular (or mildly futuristic) skyscraper just isn't going to cut it but... what would it take to build a 10'000 year skyscraper? Carbon nanotubes? Graphene? Nanocrystalline cellulose? Titanium? Fiberglass? Laminated Quartz? Or something else entirely?

And by "skyscraper" I mean a tall slender building on the order of a hundred+ meters (pyramids might be tall and long lasting, but when was the last time you saw someone actually build one?).

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    $\begingroup$ Don't be so quick with discarding pyramids en.wikipedia.org/wiki/Shimizu_Mega-City_Pyramid $\endgroup$ – Mithoron Nov 1 '16 at 22:40
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    $\begingroup$ Why you hating on my pyramids! They got like 40 upvotes! $\endgroup$ – kingledion Nov 1 '16 at 23:12
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    $\begingroup$ archdaily.com/588430/… $\endgroup$ – ApproachingDarknessFish Nov 1 '16 at 23:22
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    $\begingroup$ 1984. That's the last time I can recall someone built a pyramid. Practically the Dark Ages. But I would bet you they have since then. SUCH a classic. $\endgroup$ – Erin Thursby Nov 1 '16 at 23:53
  • $\begingroup$ It's not that I've got anything against pyramids per se, it's just that a pyramid is not a towering skyscraper and is not a type of building that is likely to become popular with the construction industry anytime soon... a modern civilization is unlikely to build a whole city out of them $\endgroup$ – Samwise Nov 3 '16 at 22:27
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When you get to be 10,000, it's not about material at that point. It's about design and environment. Things last when in an environment that doesn't have extremes in temperature, which are maintained.

A building could perhaps last 10,000 years if it was occupied and maintained. That means that you couldn't just build it, and never add to it for 10,000 years. There would have to additions, replacements & upgrades as you went.

This engineer on reddit says:

Concrete will (if in the right environment) continue to strengthen with time. It can be susceptible to attack by chlorides and other chemicals though (e.g. in an environment where the road is salted in the winter) and this can reduce the lifespan of highway bridges if they don't have sufficient cover depth or the right admixtures in the concrete. Steel in buildings is generally mild steel with bolted connections - and therefore not very susceptible to fatigue. For a skyscraper the main source of fatigue would be vortex shedding - in the case of the empire state building the construction of walls with cinder blocks and the weight of the structure damps this out. So in theory you could maintain the chrysler building and empire state building indefinitely.

With maintenance, the future is NOW!! As to the materials, many of the ones you mention are more resistant to wear and tear, but they aren't immune. Titanium CAN rust, it's just more resistant to it than regular steel.

From the same thread on building lifespan:

Buildings don't really have a lifespan - they have a continuous cost-benefit analysis between cost to maintain and cost to rebuild and value of use/inhabitation. Sometimes with increasing age the cost to maintain also increases, but this isn't necessarily the case, nor is it linear.

10,000 is such a large figure in terms of years. Our oldest occupied structures are at best three thousand years old, and you are talking about pushing that with a design that does not, frankly, lend itself to longevity. Gravity is a thing. The higher up you build, the more stresses on a building.

It's about design, maintenance, and a lack of natural disasters rather than material. You don't like pyramids but hey, that's what stands the test of time. There are some Indian temples which have some of the height you want, but are built in more of a triangle shape.

We don't use materials that stand the test of millennia in modern structures because we value the ability to push buildings to their extremes (in the case of the skyscrapers, that's height). So things that we know can last, like stone, simply can't be used because they lack flexibility for the design. And we like glass.

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I don't see why you can't build a building to last 10,000 years.

As far as I know, there are 2 major issues. Earthquakes and Wind and rain wearing it down over time.

Earth Quake can be handled with with some modern tech which I'm sure if they wanted to increase the safety range on those wouldn't be that hard with modifications that are either too expensive or big for your normal building. So i don't see that as real problem.

The degredation over time issue I think can be handled with things that we'd normally not put in building, like covering it in carbon nanotubes, which would be very expensive and I'm not sure it can be done yet. You could also have a layer between the Carbon Nanotubes (we really need a better word for those) and the inside building made of that substance that fills holes automatically, just in case the nanotubes broke down.

The main issue after that then is Oxidation of the Steel. This can be solved with a coating of some kind that exists, but I don't know what it is. You can also make the inside of the bulding sealed off from the outside so that you have minimal corrosive air and further you can adjust the air inside to be lower in oxygen and higher in some other elements that will slow oxidation even more.

So I think it's possible, but it would be extra-ordinarily expensive and for us, not very worth it. We aren't really building them to last an extraordinary amount of time for a number of reasons and doing so, beyond what we're doing just to get them up, really doesn't serve much purpose.

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