> 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.
> you don't have a reliable way to determine when the bridge is no longer safe
I have a hard time believing this. Despite the ridiculous claims of another poster in this thread (that rebar just spontaneously and completely turns into rust) properly formulated and surfaced concrete and steel don't just rot on the inside with no external signs of decay. If you have repeated water intrusion, you will see seeping and cracks. If you have increasing stress, you'll see spalling. You can core concrete, drill out and patch rebar if you have spot damage.
In general I find the sentiments in this thread bizarre since the vast majority of long-lasting buildings now and in the past century are made of concrete (many of the more modern ones have a concrete foundation and wood or steel superstructure). You don't see many old wood structures because most of them decayed and were torn down - there's a reason why you don't see many wooden bridges standing. Concrete is the closest thing that we have structurally to something that can last forever, and we're learning more about how to make it last longer all the time.
Let me know if you have links that discuss maintainability of concrete in this context. Would be glad to learn more.
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.