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Were pouring a small 15 x40 slab here in alabama, its unusually cold here in the mornings (15 deg). I want to have the concrete truck here at 8 am so I know i will have plenty of time for it to set. How do you figure how much calcium to add, I dont want to leave it to the cement guys there idiots. You say a 4 in slump with these guys and its running out the shoot like white water rapids:no: Does the calcium effect finishing quality? Any help will be appreciated, I'm a concrete newbie.
 

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I try not to put any chemicals in concrete , if its too cold to pour or if the ground is frozen you should try to put the pour off till a better day.

You should also cover the ground with some blankets or salt hay to keep it from freezing.
 

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You could add 1/2% - 2% calcium and this will increase the setting speed. You said you're a newbie at concrete so be forewarned. It can get away from you if you aren't prepared. I think the most I have ever added was 1% for some footings. The beginng pour was setting up as we were finishing the last part. This was something that didn't require any hand troweling.
Another option would be to add air-entrainment. I'm not that familiar with it, but you could ask the ready-mix company. They add tiny air bubbles and this displaces the water content. Less water means less chance of freezing.
I would cover it with concrete blankets though, after its finished and set. We can buy or even rent them here.
Good luck,
rj
 

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Project Superintendent
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Most engineers and architect don't allow calcium in concrete these days. It causes corrosion of wire mesh and rebar. There are non- chloride accelerators that your batch plant can add, but these are pricey, and again, they don't keep it from freezing, the just make it set up faster. Hot water helps as well. If it's 15 degrees there it's too cold in my opinion. The ground is probably frozen, and you don't want to pour on frozen subgrade. Wait for warmer weather, 40 and rising is my rule of thumb. If your forecast is similar to Middle Tennessee, I would say forget it this week!
 

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Concrete Mike
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Were pouring a small 15 x40 slab here in alabama, its unusually cold here in the mornings (15 deg). I want to have the concrete truck here at 8 am so I know i will have plenty of time for it to set. How do you figure how much calcium to add, I dont want to leave it to the cement guys there idiots. You say a 4 in slump with these guys and its running out the shoot like white water rapids:no: Does the calcium effect finishing quality? Any help will be appreciated, I'm a concrete newbie.
1 make sure that you have people that know how to place the concrete first.
2 make sure the base is not frozen.
3 if u have people that know how to place it use 1% or 2% Nonchloride
4 u can pour below 32 but the rule of thumb is 32 and rising
5 cal or nonchloride will not affect finish but will affect set, it will go fast.
6 cover with blankets after finished or cover with straw and black plastic
7 leave on for 7 days
8 hire a cement contractor that knows what he is doing
You can make the slum up to a 7" with super.
 
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