[toxik]

IIRC concrete aggregate should be jagged so that it interlocks with itself. You actually can't just use any old sand, you need sharp sand, which is an increasingly scarce resource.

[defrost]

My bad .. mentally insert more commas and juggle the clauses :-)

The tumbling was only meant to be applied to application requiring rounded grit, you're correct that concrete and other uses might prefer jagged.

[inglor_cz]

"you need sharp sand"

Hmm, practical concerns about acquisition aside, would lunar dust work?

[jasomill]

Yes:

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