not_of_this_world wrote:
I hope this isn't OT, but I am doing it myself.
I have been asked to transport a block of reinforced concrete.
It is approx. 20 cu. metres and is supposedly 80 tonnes.
This seems a bit on the heavy side to me, I had thought reinforced concrete
was
approx. 3 t/m which would give a weight of 60 tonnes (ish).
I suppose it is a 'piece of string' question as I don't know the
specification
of the materials used. OTOH, could different mixes cause a weight increase
of 25/30%?

Yes.
IIRC, there are concretes made from lead-bearing minerals that are double
the weight of ordinary.
(used for radiation shielding)