Ann: CDOT Central 70 Project Update, page-89

It could happen that a new concrete mix raw materials were discharged to the mixer not cleaned properly from the previous concrete batch. In this case the new mix can start hardening in the mixer and operators will add more water to maintain liquidity of concrete. The concrete will exhibit poor properties in testing. The same can happen in the lab. I am not sure if all lawyers and salesmen are aware of this phenomenon.