Dark Edge on Concrete Patch

See --> http://www.dropbox.com/gallery/20192720/1/ConcretePatch?hk41d6
Had the slab dug up and patched where the shower drain pierces it. Was done about 10 days ago. The feathered edge of the patch remains dark (doesn't seem to be damp). Is this dampness rising through the seam with existing concrete, or just aesthetics?
Thanks.
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Dark concrete is usually damp concrete. Tape down three separate 1' square pieces of clear plastic over three spots - inside the patch, on the old existing concrete adjacent to the patch, and a piece straddling the existing concrete/patch seam. Wait 24 hours and report back.
R
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Never had much luck with the plastic test in the past. Usually lose the seal due to powdery top layer of concrete. But, since it could be a lack of skill (?) instead of bad luck, I have applied the 3 squares and will check tomorrow.
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It doesn't have to be perfectly air tight. Or is that airtight? In any event, it don't. ;)
R
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FWIW, this morning's check showed no obvious differences under the three pieces of plastic. Supposed to rain later today, maybe that will make a difference.
Tried a pin-type moisture meter (WetChec by Drieaz). It didn't detect anything on new/light, new/dark or old concrete. Did detect a bit of saliva rubbed on the concrete. Don't know if that tells me anything.
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Okay, so far, so good. Let's see what happens with the rain. If things remain constant after the rain, then there's probably nothing to worry about. If you wanted to step up the sensitivity of the test, but a few folded squares of toilet tissue under the plastic to absorb whatever moisture is there.

That unit doesn't appear to be listed for concrete, but if it works for plaster, then it should work fairly well for concrete. At least on the gross scale we're talking about.
R
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Before and After pix added ---> http://www.dropbox.com/gallery/20192720/1/ConcretePatch?h=6b41d6
I can't see any difference after yesterday's rain. I'll keep an eye on it for a day or two to allow for slow percolation, but I'm going to assume (yuck!) everything is okay and proceed with the restoration. Maybe the new concrete picked up some sort of colorant from the flood damage and/or excavated material.
Thanks for your help.
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