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Crushing rock is very energy intensive (Griffith theory of fracture mechanics).

It's much better to let Mother Nature crush the rocks through stream action. (Sort of hydroelectric, without the electric parts.) Your suggestion would only replace one environmental cost with a different one.

TANSTAAFL.

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So is digging it up and transporting it...

You would have to transport it regardless. Whether it's crushed rock or sand.

But how far?

If you use old concrete from a building project in the city, crush it, then truck it 10 Miles to the new build site.

If you get it from far away you could be trucking it thousands of Miles

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