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You're both correct. Building grade sand is scarce and its extraction is environmentally catastrophic.

Yes, but concrete does not use this grade. It's crushed granite and limestone, i.e. the most sustainable. -- https://www.builderspace.com/types-of-sand-used-in-construct...

Sand is cheaper per kilo than used coffee grounds.

"Building-grade sand" is sharp sand. It is the cheapest sand you can buy. Roman's built things out of their concrete which was full of random bits of rubble, and some of these structures still stand today.

Correction: they used lime mortar. Modern concrete was created about a century and a half ago. The random bits were chunks of lime which increased the building's hydraulic qualities - lime self heals, concrete doesn't

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