Concrete Still Wet after a Month

[maradcliff]

I poured concrete in a barn, about a month ago. The weather has been cool, and it took forever to dry. One corner still has water on the surface. That corner is furthest away from any air flow. I have even dried it with an old towel, several times, and run a large fan for several days, but it is still "sweating". It's plenty hard, I can walk on it, but it just seems to never dry. The slab is 4" thick.

My concern is that the weather has begun to freeze at night in the past week. I dont think it froze inside the barn, but it soon will. If that cement still contains water in it, (which it must), wont the freeze cause the concrete to fail?

Any suggestions?

PS. There is only one window in the shed, and its a tin sided building, so not much ventilation.

Thanks

Mark

[Roger]

Concrete needs neither air nor dryness to set. Your concrete likely reached nearly full strength weeks ago, a few days to a week after you poured it. The water on top is likely condensation from the ground being cooler than the dewpoint of the confined air above the concrete. Water on concrete is therefore "new" water and unrelated to the setting process, which is a chemical process, unrelated to humidity or ventilation.

[JerryMouse]

Yep. Concrete doesn't "dry" - it "sets." This is a chemical reaction. Concrete can harden/set under water.