On Saturday, February 18, 2012 8:59:17 AM UTC-8, rangerssuck wrote:
I was watching a concrete delivery yesterday and got to wondering -
what happens with the concrete that is left over in the truck? I
suppose they keep the truck turning with some extra water

The usual deal, is that the readymix operator delivers it all, and
the customer can have the 'extra' dumped onto his shoes.

The truck driver knows how hard it is to clean out of the truck,
and usually does NOT have his own dumpsite nearby, so it's the
customer's problem if the forms won't hold the whole order.

Water alone doesn't stop it from hardening. Inside the truck.