Amazing! Can Concrete Be Poured In The Winter? What Temp. is too Cold?
Information about Can Concrete Be Poured In The Winter? What Temp. is too Cold?
It is possible to pour concrete in winter if you take the proper precautions. First, protect the base from freezing. Second, use a cold weather concrete mix that contains warm to hot mixing water. Third, cover the concrete with curing blankets to keep the concrete from freezing.
I have poured concrete in very cold winter weather for many years. If we live in Maine our winters are from December 1st to the end of March.
As a concrete contractor, I have to pour concrete when temperatures are 40°F, 30°F, 20°F and even 10°F.
In the video below we’re pouring this concrete floor with temperatures below freezing.
will harden concrete in cold weather
Concrete hardens in cold weather. It will even harden in freezing temperatures if you protect it.
Heat is generated when concrete hardens. This is referred to as “heat of hydration”. When cement and water are mixed together (two components of concrete), a chemical reaction takes place.
It is this chemical reaction that generates heat and initiates the curing process. When the outside temperature is cold, the chemical reaction slows down and less heat is generated. This can dramatically slow down the curing process, but the concrete will still cure.
Being able to use warm or hot mixing water will greatly increase the curing time and reduce the chance of the concrete freezing.
If you can somehow warm the room by building a tent over it or pouring heat into a building, it will help the concrete harden better.
Finally, if the concrete is exposed to temperatures around or below freezing, you will need to cover the concrete with curing mats or poly with hay on it to protect the concrete from freezing.
What I’ve experienced with pouring many concrete floors in the winter is that you don’t need to protect the concrete when temperatures are above freezing and will remain above freezing for the next week.
The concrete will harden from heat of hydration, it will just be much slower.
Personally, I still like to cover the concrete to cure. Covering with poly, a tarp, or blankets keeps some of the heat of hydration in the concrete and cures better.
Once the concrete reaches 500psi. it can withstand sub-freezing temperatures at this time.
If temperatures are at or below freezing on the day of pouring and the days thereafter (for the next week), I cover the concrete with insulated curing blankets and leave them on for at least a week.
What temperature is too cold to pour concrete?
I don’t know if there’s an exact temperature at which it’s too cold to pour concrete. What I do know is if you protect the subfloor from freezing and your concrete mix has hot water in it, you can pour it when it’s below freezing.
When we pour concrete floors in freezing temperatures, the subfloor is protected with insulated curing blankets, styrofoam, and sometimes poly and hay. Either one or a combination of these to keep the ground from freezing. Never pour concrete on frozen ground.
My concrete mix is typically a 4000psi mix with 150F water and we always use an accelerator in the mix. Either flaky calcium chloride or a liquid accelerator from the batch plant.
As you will see in the video below, we started watering at 7am when it was 15°F. The daily high was 30°F. The concrete temp was very warm (68°F) and cured very well, we finished smoothing at 2pm.
After machine smoothing, we sawed our contraction joints and covered the slab with insulated curing blankets, which we left on for a week. The concrete slab hardened perfectly.
Pouring onto styrofoam in cold or sub-freezing temperatures helps keep the concrete temperature warm and speeds up curing significantly.
Unless the concrete mix contains warm or hot water, I would not pour concrete in temperatures below 35 to 40 degrees Fahrenheit for safety reasons.
If morning temperatures are at or around 35F and temperatures are expected to rise into the 50s and then drop to 35 – 40 that night, you should be able to water with cold mixed water as well. I would use an accelerator in the mix so it hardens faster in this case.
What happens when new concrete freezes?
When new, freshly poured concrete freezes before it reaches 500 psi. Strength, some damage will be done to the concrete.
The extent of the damage is not immediately apparent. It can take days or even months to determine what type of damage has occurred.
What I’ve found when a concrete floor or slab is left unprotected and exposed to freezing temperatures the day of pouring, or even a few days after:
- The concrete does not reach its full strength
- The concrete develops more cracks
- The surface begins to peel, scale, or flake
- The concrete is “softer” and more prone to wear
- There is internal damage that is not visible to the eye
Freshly poured concrete contains a lot of mixing water. As the concrete hardens, much of this moisture evaporates. In cold temperatures, this takes significantly longer than in summer.
When the moisture in the concrete freezes, it expands and causes damage. The concrete is not “strong” enough to take the pressure of the expanding moisture within it.
The extent of damage done to the concrete depends on how far below freezing the temperature was and how long the concrete was exposed to freezing temperatures.
Tips for pouring concrete in winter
Here are a few tips I use when planning a concrete pour in the winter.
- Protect the ground from freezing with insulated blankets or poly & hay
- Do not pour on frozen ground, snow or ice (otherwise the concrete will settle and crack).
- Thaw any frozen areas of subsoil with underfloor heating
- Use a higher psi value. Mix for more cement (this increases heat of hydration)
- Ask the batch facility to use warm or hot water in the mix
- Use an accelerator additive in the concrete mix (most Ready-Mix Co. have these)
- Plan how you will protect the concrete afterwards (insulated ceilings work really well)
- Have some wood handy to “hold down” the insulated blankets (the wind will blow them away)
- Leave on all molds for a few days
- If inclement weather is forecast after you complete the slab, add a layer of poly over the blankets to protect the slab from rain, snow, and freezing rain.
specifically cures at 30°f
Above is a basic chart of how long it takes concrete to cure at different temperatures.
These are estimated times only so you can visually see how long it will take for the concrete to set as temperatures drop.
When outside temperatures reach freezing and less than 30°F, the concrete needs some help to properly cure.
Plan for the concrete to cure by warming the room, covering with insulating blankets, covering with poly and straw or hay, or laying underground heating pipes on and around the concrete and covering with a tarp.
The concrete needs heat to set properly, without heat the concrete may not reach its full strength.
For more information on pouring concrete in the winter, see my cold weather concrete page.
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