You can use it like giant solid concrete block but not as a filler to reduce the concrete volume. I am not certain how you would tie all of the reinforcement together. If you were planning on stacking it with a really cement rich mortar it would be ok but I agree the biggest problem is cold joints.
"When there is no life in the soil it is just dirt."
Rototillers convert rich soil into dirt. Please note that this tiny ad is not a rototiller: