concrete floor

I had a concrete floor poured for my garage and cracked the next day and continues to crack. The footings are 24 wide 27 deep, base was 4" of compacked sand #4 rebar 24 oc. I could fine nothing wrong with preperation. they use large rock with fiber added. The weather was about 72 degee. I kept it damp for 5 days. The contractor wanted to cut control joints the nex day. But I didn't want them I wanted a smooth floor it was crack the next day anyway. When I showed the contractor the problem he had no explanation for the cracking and suggest he could cut some control joints in and that might help.I think something is wrong with the mix. What do you think?:furious: