5 ms·

Reinforced concrete is easier to maintain indefinitely than wood, because it's easier to seal against moisture, especially in harsh environments. Just because t

by ak217 5y ago

Reinforced concrete is easier to maintain indefinitely than wood, because it's easier to seal against moisture, especially in harsh environments. Just because there are plenty of poorly built/maintained reinforced concrete structures, doesn't mean that it can't be built for longevity.

jazzyjackson 5y ago
I wonder if wood construction is more forgiving than concrete once you get to a point where it was neglected for some time. Wood will rot and need replacing, but if your concrete is ignored and the rebar starts crumbling, you can’t just slap fresh concrete over it and call it a day, right?
- iratewizard 5y ago
  I'm no expert, but repointing concrete is essentially doing just that
  - Retric 5y ago
    Not for reinforced concrete, the rusted rebar is still rusted after repointing. Which causes ever increasing internal stress and lower strength over time. The only way to fix it is to remove existing rebar and replace it which isn’t viable on most structures.
  - deleted 5y ago
    [deleted]
- mcguire 5y ago
  Steel rebar doesn't crumble. Rusting steel expands, causing more cracks, which then allow more water intrusion and more rust.
  - Retric 5y ago
    Rust isn’t load baring, it’s effectively replacing steel with a powder which is a huge issue if you needed the steel in the first place. Cracks from expansion make both this worse and make it obvious, but even without that it would still be a critical failure.
majormajor 5y ago
Why is reinforced concrete easier to seal? Why couldn't you apply the same sealant to wood? And why wouldn't you have the same issues, such as when you punch a hole in the exterior to mount something, or run wires, etc, you now have to make sure that sealant stays in good shape? Or expansion joints?
ohazi 5y ago
Maintenance of steel reinforced concrete is an all-or-nothing affair. You either get it right and seal everything perfectly and monitor everything perfectly and repair tiny cracks before they allow moisture to get in, or you're sunk. If surveillance is lax for a few years you can easily end up with damage that can't be repaired. Wood construction, on the other hand, is extremely easy to repair. You can cut away sections and replace them piecemeal, essentially forever. Wood gives you the ability to continuously build a Ship of Theseus, while structurally compromised concrete structures often require you to tear them down and build them again from scratch.
- ak217 5y ago
  It's relatively straightforward to overengineer concrete to the point where it will take many decades, not just years, of neglect for damage to become unrepairable. A lot of this discussion is comparing apples to oranges. Reinforced concrete often serves applications that wood is simply unable to perform in (bridges, heavy duty foundations, dams, retaining walls). And yes, poorly maintained, especially prestressed concrete in those applications will deteriorate and fail - but the structure would be impossible with wood in the first place. In more light duty applications wood and concrete can both serve well, but good luck protecting a foundation made of wood from water intrusion. For light duty applications there is no argument that concrete can be overkill and wood can be very appealing.
  - ohazi 5y ago
    > A lot of this discussion is comparing apples to oranges. I agree that wooden houses are not comparable to reinforced concrete bridges. But the part I'm trying to highlight is that being able to easily inspect a structure is a critically important aspect of maintenance, and that most reinforced concrete is inherently difficult or impossible to inspect. The fact that exterior waterproofing is relatively cheap is only incidental. It's not enough to overengineer a bridge and say it'll last a hundred years if you don't have a reliable way to determine when the bridge is no longer safe beyond year 70. Kicking the can down the road is not a viable long-term strategy. We're about 100 years into widespread use of reinforced concrete and are now starting to see the occasional catastrophic results. Potting steel in concrete is done because it's cheap and easy, not because it's particularly maintainable. It's inherently difficult to inspect the structure when you build things this way. > especially prestressed concrete Agree. Unbonded, post-tensioned concrete (where you can replace individual strands) seems like the only reasonable approach to me, but building this way and doing all of the inspection and maintenance is way more expensive than the "do almost nothing" approach for rebar concrete. But the benefits are only realized after 100 years, so nobody has the incentive to design this way.

by ak217 5y ago

jazzyjackson 5y ago

I wonder if wood construction is more forgiving than concrete once you get to a point where it was neglected for some time. Wood will rot and need replacing, but if your concrete is ignored and the rebar starts crumbling, you can’t just slap fresh concrete over it and call it a day, right?

iratewizard 5y ago
I'm no expert, but repointing concrete is essentially doing just that
- Retric 5y ago
  Not for reinforced concrete, the rusted rebar is still rusted after repointing. Which causes ever increasing internal stress and lower strength over time. The only way to fix it is to remove existing rebar and replace it which isn’t viable on most structures.
- deleted 5y ago
  [deleted]
mcguire 5y ago
Steel rebar doesn't crumble. Rusting steel expands, causing more cracks, which then allow more water intrusion and more rust.
- Retric 5y ago
  Rust isn’t load baring, it’s effectively replacing steel with a powder which is a huge issue if you needed the steel in the first place. Cracks from expansion make both this worse and make it obvious, but even without that it would still be a critical failure.

majormajor 5y ago

Why is reinforced concrete easier to seal? Why couldn't you apply the same sealant to wood? And why wouldn't you have the same issues, such as when you punch a hole in the exterior to mount something, or run wires, etc, you now have to make sure that sealant stays in good shape? Or expansion joints?

ohazi 5y ago

Maintenance of steel reinforced concrete is an all-or-nothing affair. You either get it right and seal everything perfectly and monitor everything perfectly and repair tiny cracks before they allow moisture to get in, or you're sunk. If surveillance is lax for a few years you can easily end up with damage that can't be repaired. Wood construction, on the other hand, is extremely easy to repair. You can cut away sections and replace them piecemeal, essentially forever. Wood gives you the ability to continuously build a Ship of Theseus, while structurally compromised concrete structures often require you to tear them down and build them again from scratch.

ak217 5y ago
It's relatively straightforward to overengineer concrete to the point where it will take many decades, not just years, of neglect for damage to become unrepairable. A lot of this discussion is comparing apples to oranges. Reinforced concrete often serves applications that wood is simply unable to perform in (bridges, heavy duty foundations, dams, retaining walls). And yes, poorly maintained, especially prestressed concrete in those applications will deteriorate and fail - but the structure would be impossible with wood in the first place. In more light duty applications wood and concrete can both serve well, but good luck protecting a foundation made of wood from water intrusion. For light duty applications there is no argument that concrete can be overkill and wood can be very appealing.
- ohazi 5y ago
  > A lot of this discussion is comparing apples to oranges. I agree that wooden houses are not comparable to reinforced concrete bridges. But the part I'm trying to highlight is that being able to easily inspect a structure is a critically important aspect of maintenance, and that most reinforced concrete is inherently difficult or impossible to inspect. The fact that exterior waterproofing is relatively cheap is only incidental. It's not enough to overengineer a bridge and say it'll last a hundred years if you don't have a reliable way to determine when the bridge is no longer safe beyond year 70. Kicking the can down the road is not a viable long-term strategy. We're about 100 years into widespread use of reinforced concrete and are now starting to see the occasional catastrophic results. Potting steel in concrete is done because it's cheap and easy, not because it's particularly maintainable. It's inherently difficult to inspect the structure when you build things this way. > especially prestressed concrete Agree. Unbonded, post-tensioned concrete (where you can replace individual strands) seems like the only reasonable approach to me, but building this way and doing all of the inspection and maintenance is way more expensive than the "do almost nothing" approach for rebar concrete. But the benefits are only realized after 100 years, so nobody has the incentive to design this way.