Bricks, Masonry, Asphalt and Concrete - Discoloration On Slab

I recently poured a 30x30 thickened edge slab,about two months ago. There is still a large area of the slab that is dark in color, a dark gray almost black. I have been told it is moisture bleeding through, and nothing to worry about.I live where it is very cold in the winter, im afraid of cracking . Should I be concerned, and any suggestions on fixing this problem. Thanks for any advice.

If the slab was poured with expansion joints I wouldn't worry about the temporary discoloration. Concrete cures differently depending on the composition, temperature, moisture, etc. - there's a lot of variables.

Also, if the concrete was air-entrained, it will handle the cold weather much better.

How was the slab cured? Under plastic sheeting, cure-n-seal compound, air dry? Were items left laying on the slab for an extended period soon after finishing? Were the dark spots in the shade more than the light spots? Many times discoloration can occur because of the method of curing. A slab cured under plastic or in shade will stay darker for a very long time. You will see lighter streaks where the plastic wasn't in contact with the slab (wrinkles). Applying cure and seal thicker in some spots and thinner in others can produce the same problem. All of the things I mentioned can cause darkening of the slab. I wouldn't worry about cracking due to moisture freezing though, unless you just poured the slab yesterday and there was a deep freeze last night.

Pecos

Another thought: Was the slab burnished with a trowel machine or hand finished? If it was burnished (trowelled until it was very shiny and almost black) then it will stay that way. The darkening in this case is not moisture.

Pecos