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.
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.
But, still really interesting.
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.
Poured concrete is wet. Cured concrete is dry. Sounds like drying to me.
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.
Classic Roman concrete would also set under water.
Still, it does seem like it would erode quickly and the article doesn't says if it could withstand a platform on top.