WS has good advice (strong mix) with reinforcing fibres saves rebar would be well mixed from S. Morris Ltd. by the time it got to you though
Do you need to insulate the slab to make it dry ?
I'll tell you what I did...
I had to dig into the hill side to get a level base to build my garage, so I get a lot of water coming out of the hill side after it's been raining. So prior to pouring my concrete base I installed a field drain all the way around the outside of the garage and the water was draining from the garage base for days.
So now when it rains my field drain keeps my garage floor perfectly dry. It's never ever been damp in there. Mind you my field drain is shifting up to 100 Tons of water a day away from my garage (sad I know but I timed/measured the flow). The longest it ever ran for was 6 weeks after it had stopped raining
Sooner or later that tend to fail but tanking has come a long way of late so the cure is easily at hand. I am not a believer in insulating a shop floor to answer your starting question. I mean as soon as the doors are left open you start holding in the cold. I build a few kennels and some insist on this and its dumb - I mean under an open run even, total waste of time and money
Well, 1st quote for grinding the floor came back at £4.5k I will be cheaper buying the machine, doing the job myself then flogging it again!