[TowerTalk] Using old concrete in new pour

[David Gallatin via TowerTalk]

Hello everyone,
A ham friend today suggested using concrete from an old pad that's broken into small (maybe fist size or a bit smaller) pieces and using it in
a new pour, specifically for my new 30 foot aluminum tower. He said you make the new mix "a little soupy" and toss the old chunks in as you go, the idea being less new concrete is used (and paid for) and when it dries you can't tell a difference "concrete being concrete". He did not specify what kind of ratio of old to new is used but he does have two pads of his own he has done this with that hold 60' steel self supporting towers. 
I have tried to research this and come up with nothing. I did find reference to concrete being recycled (crushed) into aggregate size and used as such in new pours but what he is talking about does not seem to be the same thing. 

 Obviously I am a tad concerned about doing this. Has anyone heard of this technique before?
 
73, 
David, AA9G 

ex W5DCG and KC9EEV