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“Reversible Concrete” May Revolutionize Temporary Architecture (vice.com)
61 points by bemmu on Oct 10, 2015 | hide | past | web | favorite | 20 comments

That's a deadly mass of material. In the video, when they're taking the mold off, the trajectory from the top of any falling chunks is super sketchy, too.

Would be interesting to see destructive tests. They obviously have digital designs, but could those be accurately used for simulation?

I'm sure they know what they're doing, they've wearing matching overalls. Those are just some concerns I'd have about constructing and exhibiting such a thing.

I've held those rocks - the material is porous and super light, almost like styrofoam.

You're right. It's not gneiss as the article says, either.


When I saw the title, my immediate question was “Reversible by who?” The answer seems to be: everybody. With such a structure, anybody could come along and knock it over by simply pulling out the loose string. I’m not sure I’d want to use this for anything important.

Or giving it a solid shove, by the looks of it. It seems stable against only its own weight.

A similar effect can already be done by entirely conventional means.


Gabion: https://en.wikipedia.org/wiki/Gabion

I don't know how useful this will be. I think being made from crushed gneiss in a jammed configuration, it should be fairly strong in pure compression. Bending stress would probably cause failure quite rapidly, and I think it would steadily weaken with vibrations of sufficient amplitude, especially if it wasn't loaded.

That said, I really don't care just how useful or practical this is because it's already so damn cool. That trick with the string is very clever and I would love to see the mathematical model they use for planning its path.

I'm not a materials scientist, but I bet this has a good deal of vertical strength, but almost no lateral strength. Probably limits its utility quite a bit.

But, still really interesting.

Concrete is awesome because you just pour it into a mold and it dries. With this technology it appears that you still need a mold and you have to take the time to layer it.

Expanding on what x3n0ph3n3 said, concrete doesn't harden because the water in it evaporates away. Rather, the water is consumed in a chemical reaction. In fact, you have to be careful that the water doesn't evaporate too much during the curing process. It's very common to hose down a curing sidewalk and keep it covered for 30 days.

Incidentally, the chemical reaction is exothermic. That's one of the reasons why you can't pour a concrete dam all at once: the heat generated would be enormous.

Concrete cures. Drying is a misnomer.

Now now, let's not get all prescriptive-linguistics up in here.

Poured concrete is wet. Cured concrete is dry. Sounds like drying to me.

The water doesn't evaporate, it is consumed in a chemical reaction. It's a fundamentally different process, not an arbitrary linguistic rule. In fact, you have to be careful that the concrete doesn't dry out during the curing process.

Also, cured concrete isn't necessarily dry. For structures like bridge piers, concrete can, and often does, cure underwater.

That said, if x3n0ph3n3's intent was to enlighten rather than score points, he could have explained this more clearly.

Does the reaction not require oxygen? I was wondering what happened to concrete underwater.

Nope. Some plasters, mortars, cements, and similar substances require exposure to air (actually it's usually carbon dioxide they need rather than oxygen) but others, including modern Portland cement, do not.

Classic Roman concrete would also set under water.

In a conversation about structural integrity, the distinction between drying and curing is meaningful, not pedantic. http://www.cement.org/for-concrete-books-learning/concrete-t...

Impressive, they use a 3d printer but it seems like it could be done by hand. Which would make for a fun craft project. "Today we will knit an scarf, tomorrow a wall!"

Still, it does seem like it would erode quickly and the article doesn't says if it could withstand a platform on top.

I bet it could support a great deal of weight. Right by my coffee shop one year the side of a creek collapsed, they built a huge retaining wall with exactly this kind of gravel. They would dump it in 10x8x8 wire crates and stack the crates on top of each other. The article said it was gneiss gravel, that stuff takes awhile to erode. It's not like concrete at all, much much stronger.

This is interesting, and the technique is certainly surprising to me, but I don't think "reversible concrete" is a reasonable way to describe what has been produced. Perhaps it is a lot more stable than it looks, but what about compression loads?

What about a good rainstorm and an overnight freeze?

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