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Concrete slab problem

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Seasons Greetings.

There once was a concrete slab, 8 inch thick, unreinforced, placed on November 4, 1999 which has irregular areas of delamination ranging from 1/4 to approx. ½" below the top of slab surface.

I'm in the process of trying to determine two things.  First, due to project schedule, I need to find an appropriate repair.  I think the three options are slab removal/replacement, delam removal/patching, and epoxy injection.  I'm leaning toward epoxy injection because it looks like it would provide an adequate repair and have good post-repair aesthetics (what?? I'm an engineer.. did I type aesthetics or just think it?) without the expense of a tearout.

Question 1:  Any thoughts?

The second determination to make is the cause.  The problem seems to be somewhat rare.  The mix, as modified by the supplier without my input or knowledge, as far as I have been able to learn so far, is 4500 psi, 4 % air, accelerating admixure, mid-range (although the testing agency log did not indicate this). 

Evidently, the concrete installer had scheduled 5 trucks to show up at 5 am ready to place.  But, around a dozen trucks showed up before 5 am (some were actually eventually dumped before the concrete began to set).  The contractor also had to remove placed concrete because it was chuted too late.  (Keeps getting worse and worse, doesn't it?)

The air temperature in the morning was above freezing.  I am having trouble finding historical temperature info on the night time temp(any ideas).  The subgrade was at least cold, maybe frozen.. I don't know yet.

My thinking is that it is probably mix and temp related.  We are having a petrographic analysis performed on a core, above and below the delam.. should give a pretty good picture of the material placed. ( the concrete suppliers rep said ,"Shoot, if you want the w/c ratio, I can give you that from the batch tickets".. no really, he said that, I'm not making that up).

Question 2:  Any thoughts?

Sorry for the lengthy message.. thought a few of you would be interested in this one.

John Schwarz, P.E.