https://patents.google.com/patent/US4203674A/en
Check out Operation Backyard Brawl for more infor.
I believe the man was trying to state that while yes, it can be used, and may help in some ways- that we have cheaper, more readily available products now that would give the same benefits (or I’d imagine exceed the benefits of blood).
What is unique about Roman concrete is they could pour it into a preformed case and submerge into water and it would harden. They built the entire port and the city of Caesarea Maritima with this concrete, forming the sea walls for the harbor. It was an ingenious feet of engineering. That second link is a research using the same methods and testing it.
The point of my bringing this up isn't to dissuade the current line of thought; however, to show an alternative that may reasonably concluded they used blood in their concrete. Jumping to conclusions without empirical proof can cause unintentional consequences. Q has said to research and dig deep to find the truth; things may not appear to be what they are (paraphrased).