Human corpses must be first cremated into a powder where they can be easily added to concrete. Need to be mindful that too much can affect curing and/or impact the strength of the cured concrete. A massive consistent supply of concrete would be needed to accommodate the added "powder". My guess is no more than 5-7% maximum loading of the dry blend with powder. Secondly, bodies can be ground into and blended with meat:
http://kfor.com/2016/05/15/human-and-rat-dna-found-in-burgers-according-to-lab-report/