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The performance of many building and remodeling materials is deeply rooted in basic chemistry and physics. Concrete seems like a simple product… but in reality it’s a highly sophisticated chemical compound. Due to its sophistication, care must be taken in its application to ensure proper curing and strength.

In some ways concrete is like Jell-O. You take a powdered mixture, mix it with water, stir it up, and before long you have a semi-solid compound.

There is a difference, however, between concrete and Jell-O. The cold temperatures in your refrigerator speed up the transition of the liquid mixture into a semi-solid material. With concrete, cold temperatures slow this transition. In the case of concrete, cold temperatures can be disastrous.

Concrete is a strong material because of its chemistry. When you mix water with the cement powder, you start an irreversible chemical reaction. Tiny crystals begin to grow. These crystals attach to one another, the sand and the gravel in the mixture. When everything goes right, you’ve created a compound hard as rock.

Let’s take a step back and talk about crystals in concrete. When water freezes it also turns into ice crystals. This transition would normally be no problem, but as the ice forms the volume of the water grows by nine percent. (That’s why ice cubes end up larger than the volume of water that produced them.) The ice tends to push or break things that get in its way.

In the case of freshly poured concrete, ice can destroy your slab. Enough cement crystals must be allowed to grow within the concrete to withstand the forces of growing ice crystals. Depending on the outside temperature, it can be a race against time. Most concrete chemists and engineers agree that if the concrete can attain a minimum strength of 500 pounds per square inch (PSI), it can resist ice damage.

The chemical reaction of concrete formation creates heat. This heat can be trapped by the use of insulating blankets. But if it’s cold enough, insulating blankets won’t keep the temperature at an optimum level for maximum curing efficiency. No insulating blanket will keep concrete at a temperature between 65 – 85°F, the optimum temperature range for proper concrete curing.

To ensure the concrete maintains the optimum temperature range, use Powerblanket® concrete curing blankets. Powerblanket® concrete curing blankets are heated blankets that not only insulate the concrete, holding in heat it naturally produces as it forms, but they also produce additional heat to keep the concrete within the desired temperature range.

Powerblanket® | The Ultimate Concrete Curing Blanket – The ONLY Concrete Curing Blanket!

Concrete placed in cold weather can result in insufficient strength and durability. The amount of protection concrete needs from cold weather increases dramatically as ambient (outside) temperatures decrease.

Concrete setting times vary greatly depending on the temperature. In general, setting times go up approximately 33 percent for every 10°F decrease in temperature.

Here’s a breakdown of setting times at various temperatures:

Temperature Approximate Concrete Setting Time

70°F – 6 hours

60°F – 8 hours

50°F – 11 hours

40°F – 14 hours

30°F – 19 hours

20°F – Concrete will freeze

As you can see, setting time increases dramatically as the outside temperature decreases. In order to maintain optimal curing temperatures of 65 – 85°F, use Powerblanket® concrete curing blankets. Powerblanket® concrete curing blankets create a consistent temperature regardless of daily or hourly changes in outside temperature. The sooner concrete sets and cures, the sooner you can continue the construction process, saving valuable time and cost.

To ensure optimal setting time, here are some tips for cold weather placements:

• Use a heated Powerblanket® or warm concrete mix.
• Don’t allow the concrete to freeze – use Powerblanket® concrete curing blankets to control temperature.
• Don’t place concrete on a frozen sub-grade – use Powerblanket® thawing blankets to control temperature.
• Protect concrete from excessive drying.
• Incorporate accelerators to maintain strength and normal set time.
• Avoid rapid changes in concrete temperature with Powerblanket® concrete curing blankets.

Powerblanket® | The Ultimate Ground Thawing & Concrete Curing Blanket – The ONLY Concrete Curing Blanket!

First, let’s define cold weather with respect to concrete. Any time you have 3 consecutive days where the average daily temperature is less than 40°F or if the temperature is lower than 50°F for less than half of any of the 3 days, concrete thinks it’s cold. Cold weather can have a detrimental affect on concrete curing for several reasons.

Concrete transforms from a liquid to a solid material through a chemical reaction. The speed of the reaction depends upon the temperature of the concrete. When the weather is warm, the reaction proceeds quickly. When it’s cold and the ground hasn’t been thawed, the reaction slows down. That’s the problem: the concrete needs to harden as rapidly as possible to resist pressures caused by water freezing within the concrete.

If the temperature is too cold, the concrete may not have reached a minimum strength of 500 psi soon enough to resist the effects of freezing temperatures. If your concrete isn’t protected with concrete curing blankets after it’s poured, it may cool too rapidly, slowing the chemical reaction.

Poor finishing techniques can also doom your slabs. Freshly poured concrete often bleeds. The water in the mix floats to the top, since it’s the lightest ingredient. Floating or troweling this water into the concrete weakens the top layer. Troweling the concrete too early can seal this bleed water just below the surface as well. If your slab is then exposed to freezing temperatures several days later, this water can freeze and fracture the top layer. Using a concrete curing blanket can eliminate the potential of freezing.

Concrete can be successfully poured in cold weather.

Several precautions need to be taken:

• Never pour concrete on frozen ground, snow, or ice. Use Powerblanket® concrete curing blankets for ground thawing ahead of time.
• Be sure to order air-entrained concrete. Request a heated mix or order 100 lbs of extra cement for each cubic yard of concrete. This extra cement helps develop early strength.
• Be sure the concrete is ordered with a low slump (drier mix). This minimizes bleed water.
• After the final finish is completed, cover the concrete with a Powerblanket® concrete curing blanket. The Powerblanket® concrete curing blankets will prevent freezing and keep the concrete at optimal curing temperature.
• After about 3 days, remove Powerblanket® curing blankets to allow the concrete to air dry.

Powerblanket® | The Ultimate Concrete Curing Blanket -

The ONLY Concrete Curing Blanket!

Ideally, concrete should cure for 7 days at temperatures between 65-85°F, with humidity levels under 100%. Due to seasonal weather changes, ideal conditions rarely occur naturally.

Use Powerblanket® Concrete Curing Blankets

Pouring concrete slabs in concrete slabs can be a challenge. The cold temperatures can increase the risk that your concrete will not cure properly. Proper concrete curing is a key to a strong, long-lasting concrete slab.

Never pour concrete on frozen ground. Use Powerblanket® concrete curing blankets to thaw the ground and bring the temperature up to at least 65°F. Why? Not only can the ground freeze the concrete from the bottom up, cracking can occur when the ground thaws. Hollow spots under the concrete may also be created – and driving over the hollow spots will create tension which in turn creates cracks.

Likewise, never pour concrete over snow – you’ll simply add unnecessary water to the concrete.

If you’re pouring a foundation slab, temperature control is even more critical. A foundation wall is simply a vertical slab – but it’s exposed on three sides once the forms are pulled. Foundation forms should be protected with Powerblanket® concrete curing blankets for at least three days, depending on weather conditions.

If you remove forms too quickly, your foundation walls will have less protection, especially if you also remove the Powerblanket® concrete curing blankets. Temperatures below 14°F completely stop the hydration (crystal growing) process.

If the walls are backfilled before proper curing has taken place, the concrete may not be strong enough to withstand the pressure. Once temperatures rise above that point, the chemical reaction resumes, but very slowly. It could take a long time for your foundation walls to gain enough strength to resist the pressure of backfill dirt.

Use Low Slump Concrete

Low slump concrete is hard to work with, but in cold weather it can mean the difference between success and failure. While labor costs can be higher, you’ll have less water bleed problems, and you can place the Powerblanket® concrete curing blankets on the slab more quickly, reducing the effects of cold weather.

Powerblanket® | The Ultimate Concrete Curing Blanket – The ONLY Concrete Curing Blanket!