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> 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

by 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).

by lolsal 5y ago

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).