[barbacoa]

>concrete and cement production are quite bad.

Modern concrete construction uses iron rebar liberally. That means every concrete structure built today will crack and crumble in a few hundred years at most, as the iron absorbs oxygen, it swells from the rust. Which is a shame, roman concrete buildings without rebar will still be standing 1000s of years from now.

[foxglacier]

Roman construction was also much less efficient because they had no material (besides wood) capable of carrying load in tension. Rebar allows us to make cheap practical structures that are impossible with just concrete - roman style or not.

[bdamm]

It would be quite fascinating to see what kind of structure we could produce if we decided to make the longest lasting cement structures we could create with modern technology, and assuming minimal maintenance over the lifetime of the building. A one-and-done kind of structure.

I bet we could do fairly well. Hundreds, maybe even thousands of years. We've learned a lot about how to form exceptionally long lasting cement. We just choose not to do it that way, most of the time.

[nashashmi]

How about petrified wood? Would that also crack and crumble in the long run?

[dredmorbius]

Petrified wood is stone. The stone matrix has formed around a wood structure, but the properties which remain are those of stone, not wood.

Wood is a composite material, strong under both compression and tension. It's the fibres in wood (lignans) which provide the latter. Stone (and unreinforced concrete) lack such fibre elements, and are strong only under compression.

With stone it's necessary to build compression structures such as arches and domes for heavy load-bearing, and taller structures must be significantly flared out at the base (or utilise buttresses, as with gothic cathedrals) for stability. Structures under tension can be far more lightweight and compact.

Steel-box construction and reinforced concrete both offer tension-based strength, but are also susceptible to metallic oxidation (rust), which limits the life of such structures. A nonmetallic fibre (natural or synthetic) might offer an alternative to this, and I've seen some work investigating this, though there may be other issues (e.g., depolymerisation of plastics over long periods of time).