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For anyone else that's curious, cement is mixed with water and some sort of aggregate to make concrete.

Don't forget the sand, which is technically an aggregate[1]. Using the wrong sand is a classic mistake being rediscovered in China:

[1]-The concrete recipes I remember always had sand and rocks, gravel and/or pebbles (depending on local availability)

Yes, you want coarsely crushed ('sharp') sand, not sand that has better decorative qualities.