rejection for what reason? I would have to believe that rejection due to poor workmanship or materials is quite low, however, finding those numbers may be tricky. Contact the DOT for each state and ask the construction guys. You might get lucky.
I think that you would have to get a consensus from individual suppliers. Some concrete may be rejected at the time of placement due to slump/air etc., some due to low strength, some due to finishing, some due to environmental factors (plastic shrinkage, etc.). And the list could go on. The Portland Cement Association or American Concrete Institute may have some facts and figures.