3 ms·

If concrete is reinforced, even with proper care, physics will get you eventually. It'll happen faster if you're near a coast. It'll take longer if you're inlan

If concrete is reinforced, even with proper care, physics will get you eventually. It'll happen faster if you're near a coast. It'll take longer if you're inland. But eventually, the inevitable will happen. Our reinforced concrete structures will never last as long as, say, the Pyramids. Wood will last longer [than reinforced concrete], again, with proper care. But in the end, entropy wins against wood as well. [And again, wood will never outlast the Pyramids]. In civil engineering, there really is no such thing as a free lunch. All materials come with drawbacks. EDIT: To clarify wording.

maayank 5y ago
What timespans are we talking about here? 30 years until reinforced concrete starts failing? 100?
- ska 5y ago
  As usual "it depends". Basically rust is the problem, so if you are scrupulous on upkeep (read, spend money) it will last much longer than if not. How long is also enviroment dependents (temperature swings, salt air, emiisions etc. can make it worse)
- stonemetal12 5y ago
  About 100 years is the max life span of reinforced concrete. If not done to a high standard half that.
  - renw0rp 5y ago
    What about prefabricated houses in post-communist countries? You definitely can't accuse them of using highest quality materials nor spending loads of money on maintenance, but I haven't heard about major failures and there are probably millions of such blocks of flats out there, built mostly between '60-'80 using a couple of different variations of the technology (some involving pre fabricated pieces of reinforced concrete connected with steel joints). I think they were estimated to last 50 years or so, but there is still large proportion of the population living in such houses in some countries nowadays.
    - stonemetal12 5y ago
      Sorry, I only got curious and started looking into it after the condo collapse in Florida. Every reference I can find on the subject says 100 years is the max life span of reinforced concrete. Not being a structural engineer I took it at face value.
- pmontra 5y ago
  That bridge in Italy collapsed after 51 years. https://en.wikipedia.org/wiki/Ponte_Morandi https://en.wikipedia.org/wiki/Ponte_Morandi
  - afiori 5y ago
    51 years and criminal care. But if we are comparing concrete and wood as construction material we should use buildings that can be built with either.
lolsal 5y ago
> Our reinforced concrete structures will never last as long as, say, the Pyramids. > Wood will last longer, again, with proper care. I'm curious to understand why as this seems completely counter-intuitive to me (someone with no expertise in materials science or building things!). Can you elaborate? What does the caveat of "with proper care" actually mean? Isolation from all the elements? Does routine maintenance count (replacing deteriorating materials? replacing fasteners? reinforcing?)? A wood structure properly taken care of does not seem like it would last longer than a pyramid or a reinforced concrete structure, if each of those is taken proper care of. But this is a hunch, not data, and based on nothing remotely scientific. I'm fascinated by this kind of thing; I appreciate any tidbits you can share!
- bilbo0s 5y ago
  Sorry. Perhaps my wording was poor. I meant that wood will last longer than reinforced concrete, even when you are properly caring for both. Neither will outlast the Pyramids. I'll reword my comment so that people understand it better.
- wongarsu 5y ago
  Concrete is strong in compression, but weak in tension or shear forces. To solve that you reinforce it with rebar (basically steel bars). But concrete is porous to water, and steel rusts. When it rusts it expands, which damages the concrete. The only ways to escape that is with coating the rebar (hard to do well) or reinforcing with something else (not many options we know of). You can try to prevent or patch cracks in the concrete to slow down the process, and you can use more rust resistant steel. Both of them prolong the lifetime a lot, but they only delay the inevitable. Wood is simpler, because it isn't a composite material. You have to prevent it from rotting and from being eaten, but on a timescale of a couple decades we can do that quite well. Also with wood structures it's often easier to replace small parts as soon as damage occurs, which prolongs the overall lifetime (similar to steel structures, but unlike reinforced concrete).
chongli 5y ago
As iconic as the pyramids are, they're not very useful. A better comparison may be the Pantheon in Rome. Nearly two thousand years old and in continuous use throughout its life. There are a number of other Roman structures that have seen continuous, heavy use for over a thousand years. There are actually quite a number of ancient temples, churches, bridges, castles, and roads still in use throughout Europe, Asia, and the Middle East. Hōryū-ji [1] in Japan is a 1300-year-old wooden Buddhist temple that's still in use today! [1] https://en.wikipedia.org/wiki/Hōryū-ji https://en.wikipedia.org/wiki/Hōryū-ji

maayank 5y ago

What timespans are we talking about here? 30 years until reinforced concrete starts failing? 100?

ska 5y ago
As usual "it depends". Basically rust is the problem, so if you are scrupulous on upkeep (read, spend money) it will last much longer than if not. How long is also enviroment dependents (temperature swings, salt air, emiisions etc. can make it worse)
stonemetal12 5y ago
About 100 years is the max life span of reinforced concrete. If not done to a high standard half that.
- renw0rp 5y ago
  What about prefabricated houses in post-communist countries? You definitely can't accuse them of using highest quality materials nor spending loads of money on maintenance, but I haven't heard about major failures and there are probably millions of such blocks of flats out there, built mostly between '60-'80 using a couple of different variations of the technology (some involving pre fabricated pieces of reinforced concrete connected with steel joints). I think they were estimated to last 50 years or so, but there is still large proportion of the population living in such houses in some countries nowadays.
  - stonemetal12 5y ago
    Sorry, I only got curious and started looking into it after the condo collapse in Florida. Every reference I can find on the subject says 100 years is the max life span of reinforced concrete. Not being a structural engineer I took it at face value.
pmontra 5y ago
That bridge in Italy collapsed after 51 years. https://en.wikipedia.org/wiki/Ponte_Morandi https://en.wikipedia.org/wiki/Ponte_Morandi
- afiori 5y ago
  51 years and criminal care. But if we are comparing concrete and wood as construction material we should use buildings that can be built with either.

lolsal 5y ago

> Our reinforced concrete structures will never last as long as, say, the Pyramids. > Wood will last longer, again, with proper care. I'm curious to understand why as this seems completely counter-intuitive to me (someone with no expertise in materials science or building things!). Can you elaborate? What does the caveat of "with proper care" actually mean? Isolation from all the elements? Does routine maintenance count (replacing deteriorating materials? replacing fasteners? reinforcing?)? A wood structure properly taken care of does not seem like it would last longer than a pyramid or a reinforced concrete structure, if each of those is taken proper care of. But this is a hunch, not data, and based on nothing remotely scientific. I'm fascinated by this kind of thing; I appreciate any tidbits you can share!

bilbo0s 5y ago
Sorry. Perhaps my wording was poor. I meant that wood will last longer than reinforced concrete, even when you are properly caring for both. Neither will outlast the Pyramids. I'll reword my comment so that people understand it better.
wongarsu 5y ago
Concrete is strong in compression, but weak in tension or shear forces. To solve that you reinforce it with rebar (basically steel bars). But concrete is porous to water, and steel rusts. When it rusts it expands, which damages the concrete. The only ways to escape that is with coating the rebar (hard to do well) or reinforcing with something else (not many options we know of). You can try to prevent or patch cracks in the concrete to slow down the process, and you can use more rust resistant steel. Both of them prolong the lifetime a lot, but they only delay the inevitable. Wood is simpler, because it isn't a composite material. You have to prevent it from rotting and from being eaten, but on a timescale of a couple decades we can do that quite well. Also with wood structures it's often easier to replace small parts as soon as damage occurs, which prolongs the overall lifetime (similar to steel structures, but unlike reinforced concrete).

chongli 5y ago

As iconic as the pyramids are, they're not very useful. A better comparison may be the Pantheon in Rome. Nearly two thousand years old and in continuous use throughout its life. There are a number of other Roman structures that have seen continuous, heavy use for over a thousand years. There are actually quite a number of ancient temples, churches, bridges, castles, and roads still in use throughout Europe, Asia, and the Middle East. Hōryū-ji [1] in Japan is a 1300-year-old wooden Buddhist temple that's still in use today! [1] https://en.wikipedia.org/wiki/Hōryū-ji https://en.wikipedia.org/wiki/Hōryū-ji