4 ms·
The very first sentence of this article is a giant red flag, the comparison between the Pantheon in Rome and modern concrete is deeply misleading -- Roman concr
by reidacdc 10y ago
The very first sentence of this article is a giant red flag, the comparison between the Pantheon in Rome and modern concrete is deeply misleading -- Roman concrete was a different material than modern Portland-cement/sand/gravel scheme, it had better resistance to cracking and could set under water. [1]
The rest of the article seems to be, if you think on different time-scales and use different cost-benefit criteria (e.g. include or exclude environmental effects), you get different answers about the suitability of various materials. This is indisputably true.
[1] https://en.wikipedia.org/wiki/Roman_concrete https://en.wikipedia.org/wiki/Roman_concrete
- wiredfool 10y agoModern concrete can set underwater, and, at least for concrete where you care about the results, you want to keep the surface wet until the concrete cures appropriately. (IANAPE, but I took a grad level concrete course in school) addition/edit: Quick primer. When concrete cures, it's a chemical process that converts free water into an electrostatic gel in the cement crystals. That interlocks the small and large aggregate to make a solid. If concrete dries rather than cures, then that gel doesn't form and you don't get the gel holding it together. If you heat up cured concrete enough, you'll drive out the water and make it a powder again. If you cure something under water, it can technically continue to cure for a very long time. Normally you keep it moist for 24-48 hours, and standard testing is done at 28 days. That will get you something like 90% of the final strength, if it can continue to cure indefinitely. I've tested concrete that was semi-submerged for 40 years where the design strength was 4ksi, and it tested out at 14ksi.