It would work within reason for low accuracy machines like cutting wood etc but Because concrete takes an age to settle down and will slowly change shape it's not a good idea for higher accuracy machines.

I built a Granite shaping/cutting/polishing gantry for my mate which ran on 6ft high concrete block walls with 10x8ft bed which was made using concrete floor beams with concrete block in fills then levelled with Epoxy..!!

If I was building a wood only machine and had the room with no desire to move it then I would probably take this route has it's easy and cheap using concrete blocks and epoxy.!!