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I have 2 6000 sq ft slabs. The 1st was poured 3 years ago it was 6 sack with no flyash. The second one was poured 10 months ago and it also was 6 sack with flyash. They are 30' apart. This winter I noticed in the newer slab a gray powder type substance started coming thru the surface along with these wet slimy patches. Is anybody familiar with this issue? Also, I have had no issues with the older slab.
 

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I have 2 6000 sq ft slabs. The 1st was poured 3 years ago it was 6 sack with no flyash. The second one was poured 10 months ago and it also was 6 sack with flyash. They are 30' apart. This winter I noticed in the newer slab a gray powder type substance started coming thru the surface along with these wet slimy patches. Is anybody familiar with this issue? Also, I have had no issues with the older slab.
Dusting could mean a few things

Premature finishing, this will bring excess water to surface which weakens the paste.

It could be carbonation due to open salamanders, heaters or engines give off carbon dioxide, inhibiting the normal hydration process.

Condensation due to temp of concrete on an inside floor rises slower than surrounding, more humid air which is common in the spring and fall.

Inadequate curing (another word is Dry-out) it happens when there is not sufficient moisture to continue the hydration process of Portland cement paste and because of that it produces a soft weakened material.

I hope it helps...
 
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