Reinforced concrete structures are known to have a relatively short lifespan. Wood easily lasts several times as long with proper care.
Regular reminder that stainless steel reinforcement exists, is used bridges and it's use outside is growing, and it will last a thousand years.
Also there is Basalt, carbon fiber and even reinforcement out of used wind turbine blades, which is used in Britain for HS2, and other non-steel reinforcements, which can give you a structure nearly impervious to weathering.
On wood: In Europe we've been using Mass Timber for decides, and it's really good from Carbon perspective and outperforms RCC for small to medium residential and office buildings. Probably not going to replace RCC in infrastructure and industry, but what do I know
This has been a big issue with stainless steel climbing anchors and hangars, as it leads to sudden catastrophic failure with little warning, as you don’t get rust like normal steel. Some areas near the ocean have had failures in as little as 5 years - faster than if they’d used normal steel.
Even 316 rusts and corrodes, and that should be fairly obvious to most users if they actually look at the bolts before trusting them.
Not what you want in rebar (or climbing anchors!)
Large dry laid stone can easily last thousands of years as long as the foundation is solid. Consider the pyramids both in Egypt and South America plus a host of other very old structures. However, you need to avoid tension, earthquakes, and unstable ground, can’t build very tall etc. High construction costs, slow build times, and serious limitations in what structures are viable shows just why we mostly abandoned the technology.
Mortar is basically indefinitely replaceable with constant maintenance and has lower upfront costs. So it’s generally a much better option.
The only way to fix it is to remove existing rebar and replace it which isn’t viable on most structures.
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.
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.
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.
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 believe there is a very unfortunate example of this in Miami in the recent condominium collapse.
A bridge recently collapsed in Italy.
Etc.
So the problem of failing concrete structures is not 'theoretical' but a very real issue. Even though most concrete construction does seem to last pretty well.
If you keep the water out, there's no reason why 2x4 and sheetrock shouldn't last a good long time.
I live in New England, and there's plenty of old post-and-beam construction that's held up for a couple of hundred years. Some houses still have their original interior trim and softwood floors, and if that holds up, I can't think of any reason why 2x4s shouldn't.
But old New England construction lasts because it's maintained. New roofs, new clapboards every 50 years, regular painting, interior repairs and renovations. With land costs what they are in many regions, it's cheaper to take care of a good house rather than just letting it fall apart over 50 years.
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.
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)
But if we are comparing concrete and wood as construction material we should use buildings that can be built with either.
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!
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.
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).
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!
Non-reinforced concrete has to be built bigger, but can last a long time. The coliseum is still up - Hoover Dam will also probably last awhile. And that's without much maintenance.
Smaller non-reinforced structures are harder to build. You have to use the concrete to hold itself up which requires a larger structure.
So you're left with reinforcement. There are options for non-rusting rebar, and non-rusting coatings, but I believe they're expensive. Also, any nick or scratch in a coating ruins it. There's also unique and novel research for non-rebar reinforcement - again expensive.
Here in US most buildings are built to last X years. So long as the rebar lasts longer than X, they'll use rebar. Increase X via regulations, and the quality (and cost) of the buildings in that area increases. Otherwise the bidder with the lowest cost of materials is most competitive. Anyone know what it's like in China?
Galvanised rebar is omnipresent around the world. I believe even mandatory in some countries.
> Otherwise the bidder with the lowest cost of materials is most competitive. Anyone know what it's like in China?
Just as you said. Construction companies save on everything. GFRP rebar got adopted in China not so much because of advantages, but because of code allowing for lower concrete cover with it, as I heard.