When is it Too Cold to Pour Concrete?
by TRP Ready Mix on October 11, 2019
Tips for Pouring Concrete in Cold Weather
Construction doesn’t stop when the temperatures drop. But pouring concrete in winter conditions does pose some unique challenges you must be prepared for.
The ideal temperature to pour concrete is between 10˚C and 15˚C (50˚F and 60˚F). When the temperature drops below 10˚C, the chemical reactions needed to set and strengthen concrete slow down significantly. And when the temperature drops below freezing, the setting and strengthening stops.
When it’s too cold, concrete won’t develop its desired strength. And when freshly poured concrete freezes during the first 24 hours, it can lose 50 percent of its potential 28-day strength.
On top of not strengthening, concrete can freeze and expand in freezing temperatures, resulting in cracks. But with the right precautions, you can still pour concrete in cold weather and protect it from cold weather damage.
Things to Consider with Cold Weather Concrete Pouring
If there are specific strength requirements for the concrete, make sure to protect the concrete at the required temperatures. You will also need to make sure the concrete sets before it is exposed to freezing temperatures.
Consider using the following to ensure your concrete is protected:
- Hot water to mix cement.
- Extra cement to make the reaction hotter and cause faster hydration.
- A squeegee or a shop vac to remove bleed water quickly.
- Warm, dry materials that have been kept in a warm, dry location.
- Concrete mixes that set quickly—additives (accelerators) that speed up the setting time. But avoid additives with calcium chloride if using steel-reinforcements since it can cause rusting and lead to cracks in the concrete.
- Heated enclosures that are windproof and weatherproof to protect concrete in cold weather. And if you use combustion heaters, vent these outside to prevent carbonation.
- Insulated forms and temporary covers to provide sufficient insulation in beams, walls, and columns.
Things to Avoid When Working with Concrete in The Winter
When pouring concrete in winter, do not:
Let Fresh Concrete Get Cold/Freeze
Concrete needs warm temperatures (minimum 10˚C) to cure and reach its desired compressive strength. And it will freeze at -4˚C.
If it’s too cold, the concrete won’t cure at all. So be sure to keep the concrete warm with heaters while curing in winter.
Pour Concrete on Frozen Ground
Fresh concrete closest to the frozen ground will cure slower than the concrete surface, so the bottom will stay soft and the top will set. Also, when frozen ground thaws and settles, it will cause concrete to crack.
To avoid pouring concrete on frozen ground, use heaters to warm up the ground first, or place concrete blankets or black plastic on the ground for a few days before pouring.
Use Cold Tools
Cold tools, especially cold forms, can alter the strength and quality of concrete. So be sure to keep your tools warm and out of the cold by storing them inside when not in use.
Remove Formwork Early On
Avoid removing formwork when concrete is too cold and hasn’t reached its desired strength. Otherwise, the concrete might collapse.
Seal Concrete Below 10˚C
Since concrete needs to be kept at a minimum temperature of 10˚C to cure properly, avoid sealing the concrete until it has fully cured. If the temperature is below 10˚C, take precautions and consult with a concrete supplier about the best practice for sealing.
Ignore the Temperature of the Concrete
You must monitor the temperature of concrete in cold weather to prevent freezing, slow curing, and poor-quality concrete.
Tips for Pouring Concrete in The Winter
Use these tips to ensure you have a quality pour in cold weather:
- Schedule and determine the cold weather protection measurement of the concrete mix.
- Keep record of the concrete temperature and the exterior temperature.
- Do not pour concrete on snow, ice, or frozen ground.
- Use heaters to thaw frozen ground before pouring concrete.
- Keep dry concrete mix and tools inside and warm until the concrete is mixed and ready to pour.
- Use a concrete mix with the right amount of air entrained voids to prevent damage from freezing and thawing.
- Use accelerating additives in the concrete mix to make concrete cure faster.
- Use a concrete mix with a water reducer or a low slump and minimal water-to-cement ratio to limit bleeding and reduce the setting time.
- Request heated ready mixed concrete from your local concrete suppliers to help the concrete develop early strength. Or, request 100 lbs of extra cement for each cubic yard of concrete.
- Place concrete as soon as possible after mixing.
- Use concrete curing blankets or heated enclosures to maintain concrete temperatures above 10˚C (50˚F) for three to seven days.
- Do not finish the concrete if bleed water is present.
Maintaining Ideal Temperature
To protect concrete in cold weather, the concrete should be kept warm during the curing process—over 5˚C for the first 48 hours. Concrete strength development is critical during the first 48 hours. But if it is below 5˚C, concrete will take longer to develop its required strength.
Ideally, you will maintain concrete temperatures above 10˚C (50˚F) for the first three to seven days. And for at least four more days after, maintain the concrete temperature above 4˚C (40˚F). Be careful not to let the concrete temperature drop more than 4˚C in 24 hours.
Frost blankets and insulated formwork can help keep concrete warm enough and protect it from the cold. So be sure to cover the concrete slab with a plastic sheet, and then cover the plastic sheet with insulating blankets.
Concrete pouring in winter is possible. You just need to take the necessary precautions to ensure the concrete isn’t at risk of freezing, cracking, and not curing to its desired strength.
For help pouring concrete in cold weather, contact your local ready mixed concrete suppliers.