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.