It is all acid as far as I know, but it's much easier on steel than muriatic (hydrochloric) acid. The concrete cleaner is for removing the haze and splatter on the outside of the drum. The inside should stay polished if it's used and cleaned right every time. If not it builds up and sucks the moisture out of the new stuff and builds up faster, then it's jack hammer time.
I don't think acid is going to do anything for you in this case. Maybe soak it with water and let it freeze, thaw repeatedly, then attack it in the spring? Unless it was poured in there intentionally, I really can't see how this could be very well cured mortar.