Dave,
I agree he may of been shorted but...
You may get them to take pity on you and get the finish batch for free. but otherwise how would you prove how deep the footings were, dig under every linear foot?...
I think I could easily make the case for being seriously shorted on concrete by merely digging down to the bottom of the footer (next to the footer) in a few places. Then average the depths found.
As I understand it, the one he didn't try to pour at all is almost a yard, so the one that should have been 4 yards took over 5. No pictures, but that seems like a lot of bowing.
Now I agree that ordering an extra yard is good practice, and when I pour I have about 5-10% of the pour available as sacks, so I can make up shortages in an emergency, in addition to the extra yard.
It really depends on the situation, but if we are looking at a 2" overlay with a cold joint, I would be asking the concrete supplier to pick up the cost of jackhammering and cleaning out the footings to a depth where an 6" overlay would be poured. Jackhammering should be easy in a fresh pour, and if enough rebar was added to the initial concrete, a nice rough surface should give a much better bond. Add one of the acrylic bonding agents, and it would be a lot better.
Depending on how many suppliers are in the area, I might even growl something about small claims court. But if this is is the only practical supplier, then that is not a good idea -- just suck it up and absorb the cost.
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My best friend, who passed a few years back, was a mechanical/structural engineer who supervised concrete pours on a weekly basis. He knew geometry and how to measure, and he felt that he was shorted on 50-75% of the times he poured. Of course he had enough experience to order extra, and was a good enough customer that they would always send out an extra truck if necessary.