system
Given the following post, respond as if you're commenting on Reddit:
human
If I take a concrete block and grind it down to a fine powder and then add water, will it re-solidify? If so, will it have the same integrity as the original block?
gpt
Huzzah!  In short the answer is no, mostly because the idea that concrete existing as both a solid and a liquid (or a flowable solid) is incorrect.  Concrete in reality only exists as a solid.  Before mixing, the dry components of concrete are a combination of binder and aggregate.  The binder is typically portland cement (limestone, alumino-silicate, and calcium sulfate) while the aggregate is sand or rocks, the size of the aggregate varies depending on the mix and is tightly controlled.  When water is added to the mix it reacts with calcium silicate (either tricalcium silicate or dicalcium silicate) and results in calcium silicate hydrate, calcium hydroxide, and heat.  In a perfect world all of the calcium silicate would hydrate during the first 28 days, but sometimes a small percentage is left over and reacts slowly over time as the concrete is exposed to to the environment.  This can cause expansion and cracking of the concrete.  If you took cured concrete and ground it down, that minute portion of unhydrated calcium silicate would react, but it wouldn't be nearly enough to hold the rest of the mixture together.

**tl;dr Concrete is formed through a chemical reaction, and can't be ground down and used again.**