That 24000 rpm spindle would be able to make very shallow surface cuts in steel using a very small cutter. So engraving-type operations would probably work okay. But it would be pretty useless for most of what we think of as machining in that material. For that you'd need a much slower spindle with lots of low-speed torque.

I'm not sure what you mean by a mix of epoxy-granite and concrete. These are entirely separate materials which don't mix together well. Were you talking about using e-g for some parts and concrete for others?