7 ms·

I learned recently that reinforced concrete buildings only last about 50 years. Moisture and oxygen seeps into concrete and corrodes the rebar.

karolist 6y ago
Many WW2 era German bunkers and coastal batteries seem fine with no maintenance and erosive sea climate doing it's thing so not sure about that. https://www.tracesofwar.com/sights/12168/German-Coastal-Battery-Klaipeda.htm https://www.tracesofwar.com/sights/12168/German-Coastal-Batt...
- medium_burrito 6y ago
  Yeah, German reinforced concrete structures like those and the flak towers are basically gonna last longer than the pyramids. They are the honey badger of architecture.
- hoseja 6y ago
  There's difference between engineering for lowest possible cost and engineering to win a war.
  - warmwaffles 6y ago
    Uh no, axis and allies produced the cheapest/most effective means to win the war. Take for instance the Stg44, mostly stamped sheet metal. Russian PPSH, stamped sheet metal.
    - labster 6y ago
      I think GP was trying to say that fortified buildings last longer than shoddy McMansions. Which seems true given the survival ratio of castles to hovels over a millennium or so. Of course to win a war you may want to fortify cheaply... but given the modern system armies we have now I’d have to say that part of the grand strategy is to simply outspend rival nations.
hulitu 6y ago
I think 50 years is a very pessimistic (and journalistic) value. There are whole towns in eastern europe build with reinforced concrete and they are still ok.
- Mediterraneo10 6y ago
  They often aren’t OK. In many of those whole towns in Eastern Europe, the municipality is gradually pushing to move people out of the socialist-era concrete buildings and into newer ones. Their design means that, even if the structure itself does remain physically sound, they often struggle with ventilation, so mold forms.
  - lucian1900 6y ago
    That’s not universally true. In my home city the socialist-era blocks tend to be the ones without mould, when compared to some of the under-regulated new builds. If anything they’re sought after.
  - dtgriscom 6y ago
    True, but unrelated to the point being made.
  - PeterisP 6y ago
    This seems to be mostly a construction quality issue of the time - in my corner of Eastern Europe, the 1960s buildings often are so bad to need reconstruction or replacement, but the 1900s/1910s/1920s/1930s buildings are structurally fine (with some exceptions due to total neglect) despite being twice as old. It's more of an indicator if you intentionally build mass cheap sloppy housing intended to be temporary just to allow faster urbanization ASAP (as arguably was the goal of 1960s soviet housing projects), then you're not getting proper long-term buildings - IIRC it was expected already when being built, the planned design lifetime of those buildings without major repair was just 30 years or so, and they've certainly met that bar.
    - Quenty 6y ago
WJW 6y ago
That seems super unlikely to be true. Easy counterexample: the Ingalls building in Manhattan was the first skyscraper to be built out of reinforced concrete and it was built in 1903. It still stands today. https://en.wikipedia.org/wiki/Ingalls_Building https://en.wikipedia.org/wiki/Ingalls_Building
- s_dev 6y ago
  It's been maintained with constant supervision. Probably regular inspections and fixes. Watch what happens in as little as ten years once it has no human intervention at all.
  - tokai 6y ago
    Ten years of no-maintenance is unhealthy for any type of building.
    - bruce343434 6y ago
      What does the maintenance look like? Try to spray wd40 in between the concrete cracks? I can't really find anything about this anywhere.
      - Red_Leaves_Flyy 6y ago
        The eli15 answer is that concrete is repaired by excising the damage and replacing what was removed. If you're really interested check out Sikas brochures.0 if you prefer video form I found this [1] that seems to cover a good variety of applications and can probably be comfortably watched at 2x speed. Maintaining concrete is a matter of having routine structural inspectors come out to poke and prod the concrete. Worn traffic areas get patches and sealants. Areas with a lot of runoff get seals to direct water in ideal ways. Etc. 0. https://www.sika.com/en/construction/structural-strengthening.html https://www.sika.com/en/construction/structural-strengthenin... 1. https://youtu.be/c0Pj5Qdy9IU https://youtu.be/c0Pj5Qdy9IU
      - mr_overalls 6y ago
todorstoyanov 6y ago
This can be the period the construction engineers are responsible or the worst possible exploitation conditions. My estimate is 200 - 300 years if roof is maintained well and no pipe leaks inside.
- lazide 6y ago
  Worst possible conditions usually involve seawater, acidic conditions, and/or moisture. Even without those factors it’s rare for reinforced concrete to last more than 50 years. The more protection from the elements, the better of course. Most concrete structures with long design lifetimes made of concrete (some dams, levees, bridges - but not all by any stretch) will use design techniques to minimize or remove the use of rebar, such as compression only designs , or ‘overbuilding’ so expected corrosion still leaves the structure strong enough over it’s design life. Generally, concrete is a strongly base compound and protects rebar from corrosion. Over time however it can be influenced by the environment, with those base compounds reacting and leaving a less protective environment. Some environments do it faster than others. If the covering concrete is strong enough/thick enough, the pressure caused by the rebar turning to rust inside the concrete won’t crack it - if the rebar was structurally important (pretty much always or why use it?) it still weakens the structure though, sometimes dangerously. Attempts to mitigate the risk where weatherproofing is not an option and rebar is essential for structural reasons like concrete roadways and bridges have had their share of disasters. epoxy coated rebar for instance can lead to unpredictable and sometimes rapid failures in exactly the types of environments it was expected to help in [https://www.fhwa.dot.gov/publications/publicroads/99novdec/rebars.cfm https://www.fhwa.dot.gov/publications/publicroads/99novdec/r...] https://partridge.com.au/concrete-cancer-what-is-it-and-what-does-it-mean/ https://partridge.com.au/concrete-cancer-what-is-it-and-what... Some other failure modes include the Alkali-Silica reaction (sometimes confusingly named concrete cancer too, though fundamentally different) [https://en.m.wikipedia.org/wiki/Alkali–silica_reaction https://en.m.wikipedia.org/wiki/Alkali–silica_reaction] The more dependent a design is on an element that can corrode, and the tighter it’s design tolerances, the more fragile it is. The more overbuilt it is, and more conservative the design, the more expensive it is. Taking a low margin design and then not maintaining it is a recipe for this kind of disaster [https://www.google.com/amp/s/www.independent.co.uk/news/world/europe/genoa-bridge-collapse-engineer-riccardo-morandi-warning-corrosion-rust-concrete-a8498716.html%3famp https://www.google.com/amp/s/www.independent.co.uk/news/worl...] and lots of dead people.
marcosdumay 6y ago
Steel does not corrode when embedded in concrete. The failure mode of reinforced concrete is when the rebar loses contact with the concrete. This condition can be detected and fixed before failure.
- refurb 6y ago
  Apparently it depends on the climate. In Singapore, you need to maintain the surface of the concrete to keep water out or the rebar corrodes and the concrete spalls. Buildings only last 50 years or so before being torn down and rebuilt. https://www.mynicehome.gov.sg/article/dealing-with-spalling-concrete-in-your-flat https://www.mynicehome.gov.sg/article/dealing-with-spalling-...
  - marcosdumay 6y ago
    It doesn't depend on the climate, but it does depend on the concrete chemistry (that does vary geographically). Anyway, the sequence is that micro cracks form on the concrete and expose the steel, then the exposed steel rusts and pushes more concrete away, exposing more steel. This too can be fixed before it becomes a problem.
    - bilbo0s 6y ago
      I think the material point is that, as engineers, we have to all concede that modern concrete has that fatal flaw. People are being hyperbolic here when they are saying these buildings won't last 60 years. In my opinion, most will definitely last 60 years, even with no maintenance. At the same time, I'm intellectually honest enough to concede that few reinforced concrete structures will last 500 years with no maintenance. And I'm confident that zero reinforced structures will last 1000 without maintenance. People on this thread claiming a collapse in 60 years are probably not civil engineers. People claiming that reinforced structures will outlast the Pyramids at Giza are definitely not civil engineers.
      - marcosdumay 6y ago

karolist 6y ago

Many WW2 era German bunkers and coastal batteries seem fine with no maintenance and erosive sea climate doing it's thing so not sure about that. https://www.tracesofwar.com/sights/12168/German-Coastal-Battery-Klaipeda.htm https://www.tracesofwar.com/sights/12168/German-Coastal-Batt...

medium_burrito 6y ago
Yeah, German reinforced concrete structures like those and the flak towers are basically gonna last longer than the pyramids. They are the honey badger of architecture.
hoseja 6y ago
There's difference between engineering for lowest possible cost and engineering to win a war.
- warmwaffles 6y ago
  Uh no, axis and allies produced the cheapest/most effective means to win the war. Take for instance the Stg44, mostly stamped sheet metal. Russian PPSH, stamped sheet metal.
  - labster 6y ago
    I think GP was trying to say that fortified buildings last longer than shoddy McMansions. Which seems true given the survival ratio of castles to hovels over a millennium or so. Of course to win a war you may want to fortify cheaply... but given the modern system armies we have now I’d have to say that part of the grand strategy is to simply outspend rival nations.

hulitu 6y ago

I think 50 years is a very pessimistic (and journalistic) value. There are whole towns in eastern europe build with reinforced concrete and they are still ok.

Mediterraneo10 6y ago
They often aren’t OK. In many of those whole towns in Eastern Europe, the municipality is gradually pushing to move people out of the socialist-era concrete buildings and into newer ones. Their design means that, even if the structure itself does remain physically sound, they often struggle with ventilation, so mold forms.
- lucian1900 6y ago
  That’s not universally true. In my home city the socialist-era blocks tend to be the ones without mould, when compared to some of the under-regulated new builds. If anything they’re sought after.
- dtgriscom 6y ago
  True, but unrelated to the point being made.
- PeterisP 6y ago
  This seems to be mostly a construction quality issue of the time - in my corner of Eastern Europe, the 1960s buildings often are so bad to need reconstruction or replacement, but the 1900s/1910s/1920s/1930s buildings are structurally fine (with some exceptions due to total neglect) despite being twice as old. It's more of an indicator if you intentionally build mass cheap sloppy housing intended to be temporary just to allow faster urbanization ASAP (as arguably was the goal of 1960s soviet housing projects), then you're not getting proper long-term buildings - IIRC it was expected already when being built, the planned design lifetime of those buildings without major repair was just 30 years or so, and they've certainly met that bar.
  - Quenty 6y ago

WJW 6y ago

That seems super unlikely to be true. Easy counterexample: the Ingalls building in Manhattan was the first skyscraper to be built out of reinforced concrete and it was built in 1903. It still stands today. https://en.wikipedia.org/wiki/Ingalls_Building https://en.wikipedia.org/wiki/Ingalls_Building

s_dev 6y ago
It's been maintained with constant supervision. Probably regular inspections and fixes. Watch what happens in as little as ten years once it has no human intervention at all.
- tokai 6y ago
  Ten years of no-maintenance is unhealthy for any type of building.
  - bruce343434 6y ago
    What does the maintenance look like? Try to spray wd40 in between the concrete cracks? I can't really find anything about this anywhere.
    - Red_Leaves_Flyy 6y ago
      The eli15 answer is that concrete is repaired by excising the damage and replacing what was removed. If you're really interested check out Sikas brochures.0 if you prefer video form I found this [1] that seems to cover a good variety of applications and can probably be comfortably watched at 2x speed. Maintaining concrete is a matter of having routine structural inspectors come out to poke and prod the concrete. Worn traffic areas get patches and sealants. Areas with a lot of runoff get seals to direct water in ideal ways. Etc. 0. https://www.sika.com/en/construction/structural-strengthening.html https://www.sika.com/en/construction/structural-strengthenin... 1. https://youtu.be/c0Pj5Qdy9IU https://youtu.be/c0Pj5Qdy9IU
    - mr_overalls 6y ago

todorstoyanov 6y ago

This can be the period the construction engineers are responsible or the worst possible exploitation conditions. My estimate is 200 - 300 years if roof is maintained well and no pipe leaks inside.

lazide 6y ago
Worst possible conditions usually involve seawater, acidic conditions, and/or moisture. Even without those factors it’s rare for reinforced concrete to last more than 50 years. The more protection from the elements, the better of course. Most concrete structures with long design lifetimes made of concrete (some dams, levees, bridges - but not all by any stretch) will use design techniques to minimize or remove the use of rebar, such as compression only designs , or ‘overbuilding’ so expected corrosion still leaves the structure strong enough over it’s design life. Generally, concrete is a strongly base compound and protects rebar from corrosion. Over time however it can be influenced by the environment, with those base compounds reacting and leaving a less protective environment. Some environments do it faster than others. If the covering concrete is strong enough/thick enough, the pressure caused by the rebar turning to rust inside the concrete won’t crack it - if the rebar was structurally important (pretty much always or why use it?) it still weakens the structure though, sometimes dangerously. Attempts to mitigate the risk where weatherproofing is not an option and rebar is essential for structural reasons like concrete roadways and bridges have had their share of disasters. epoxy coated rebar for instance can lead to unpredictable and sometimes rapid failures in exactly the types of environments it was expected to help in [https://www.fhwa.dot.gov/publications/publicroads/99novdec/rebars.cfm https://www.fhwa.dot.gov/publications/publicroads/99novdec/r...] https://partridge.com.au/concrete-cancer-what-is-it-and-what-does-it-mean/ https://partridge.com.au/concrete-cancer-what-is-it-and-what... Some other failure modes include the Alkali-Silica reaction (sometimes confusingly named concrete cancer too, though fundamentally different) [https://en.m.wikipedia.org/wiki/Alkali–silica_reaction https://en.m.wikipedia.org/wiki/Alkali–silica_reaction] The more dependent a design is on an element that can corrode, and the tighter it’s design tolerances, the more fragile it is. The more overbuilt it is, and more conservative the design, the more expensive it is. Taking a low margin design and then not maintaining it is a recipe for this kind of disaster [https://www.google.com/amp/s/www.independent.co.uk/news/world/europe/genoa-bridge-collapse-engineer-riccardo-morandi-warning-corrosion-rust-concrete-a8498716.html%3famp https://www.google.com/amp/s/www.independent.co.uk/news/worl...] and lots of dead people.

marcosdumay 6y ago

Steel does not corrode when embedded in concrete. The failure mode of reinforced concrete is when the rebar loses contact with the concrete. This condition can be detected and fixed before failure.

refurb 6y ago
Apparently it depends on the climate. In Singapore, you need to maintain the surface of the concrete to keep water out or the rebar corrodes and the concrete spalls. Buildings only last 50 years or so before being torn down and rebuilt. https://www.mynicehome.gov.sg/article/dealing-with-spalling-concrete-in-your-flat https://www.mynicehome.gov.sg/article/dealing-with-spalling-...
- marcosdumay 6y ago
  It doesn't depend on the climate, but it does depend on the concrete chemistry (that does vary geographically). Anyway, the sequence is that micro cracks form on the concrete and expose the steel, then the exposed steel rusts and pushes more concrete away, exposing more steel. This too can be fixed before it becomes a problem.
  - bilbo0s 6y ago
    I think the material point is that, as engineers, we have to all concede that modern concrete has that fatal flaw. People are being hyperbolic here when they are saying these buildings won't last 60 years. In my opinion, most will definitely last 60 years, even with no maintenance. At the same time, I'm intellectually honest enough to concede that few reinforced concrete structures will last 500 years with no maintenance. And I'm confident that zero reinforced structures will last 1000 without maintenance. People on this thread claiming a collapse in 60 years are probably not civil engineers. People claiming that reinforced structures will outlast the Pyramids at Giza are definitely not civil engineers.
    - marcosdumay 6y ago