basement floor crack

My builder poured the basement floor on Friday. I went to check it out on Sunday and there are already some fairly long hairline cracks in the concrete. Should this be expected this early after the concrete has been poured? Should I be worried about the longevity of this floor?

 

[Ron]

Cracks appearing that early are a result of poor control and placement practices. The concrete was likely high slump (wet) and there were apparently no control joints in the slab.

Make the contractor repair the cracks at least. You will likely see more cracks and the ones that are there will get wider.

 

[dirtsqueezer]

The structural engineer must concede that concrete cracks whichever way you slice it. Concrete cracks, that is a fact that no one can change.
The question is, how big are the cracks? If, in 6 months, they are hairline, that is common. If, in 6 months, they are on the order of 1/8 inch, you could have a problem.

Another common cause of major cracking I have seen is uneven ground under the concrete.
Even if the concrete was poured with a low slump (dry), if the supporting ground was potholed or otherwise uneven, this will cause the concrete to shrink sporatically on curing, and will almost always cause cracking.
You might want to also research who prepared your grade. Good luck!