Tips for Pouring Concrete in Winter

When it comes to pouring concrete in winter, weather can pose significant challenges. Concrete sets best at 50-60°F; pouring concrete in winter means the ambient temperature will likely fall well below this range. Fortunately, there are steps you can take to effectively tackle cold weather concrete curing.

Concrete Pouring Temperature Limits

As mentioned above, concrete prefers a mild temperature between around 50 and 60°F to set. Below this, the exothermic reactions that cause wet cement to transform into strong concrete will slow significantly. This could mean long delays in work while you wait for concrete to set and strengthen before continuing with a project. Additionally, If concrete reaches freezing temperatures during the setting process, the water in the cement mix will freeze and expand. This will cause concrete to become weak, brittle and even flaky when it sets.

 

Successfully Pouring Concrete in Winter

Fortunately, strategies can be implemented to increase the temperature of cement mixtures. Here are some tricks you can use to keep the cement flowing all winter long:

  • Use heaters or heated blankets to thaw surfaces where concrete will be poured. Pouring concrete on frozen ground will quickly cool concrete well below ideal temperatures. Using a heater to prep surfaces will prevent too-quick cooling or freezing and help keep the necessary reactions going.
  • Mix cement using hot water to help increase the temperature of the concrete.
  • Store materials in a warm location.
  • Use quick-set cement; during cold weather. It may set more slowly than the instructions indicate, but will still harden more quickly than traditional cement mix.
  • Mix in additives that accelerate set time.
  • Use extra cement (typically 100 lb/ cubic yard) to make the reaction hotter and cause concrete to hydrate more rapidly.
  • Utilize squeegees or a vacuum to remove bleed water that has a difficult time evaporating during colder weather.

Cold Weather Concrete Curing

After the concrete has been poured, it needs to be kept at the correct temperature to cure. Most importantly, it needs to be kept from freezing. Ideal temperatures (50-60°F) should be maintained for about 48 hours for the concrete to reach optimal strength as it sets. This can be tricky during the winter; even if temperatures are optimal during the day, they can plummet at nighttime. Maintaining warmer temperature will require some sort of external heat source. One option is a heated enclosure. These are effective but can be time-consuming to install. If you choose to use an enclosure, be aware that excess carbon dioxide from the heater can cause bubbling in the surface of concrete. This can typically be avoided with proper ventilation.

Concrete Blankets

Another option for temperature maintenance during cold weather concrete setting is concrete blankets. Concrete blankets can be used to thaw ground before pouring concrete and again after finishing to keep concrete from freezing. They are easy to install and transport and require only an outlet to use. This means no time wasted setting up complex heating mechanisms. If you’re interested in minimizing downtime involved pouring concrete in winter, these blankets are an excellent heating option to look into.

What Temperature is Too Cold to Pour Concrete?

What Temperature is Too Cold to Pour Concrete?
What Temperature is Too Cold to Pour Concrete?

What Temperature is Too Cold to Pour Concrete?

Experts agree that the best temperature to pour concrete is between 50-60 °F. The necessary chemical reactions that set and strengthen concrete slow significantly below 50 °F and are almost non-existent below 40 °F. Even when daytime temperatures are within the satisfactory range, winter concrete setting creates risks that could result in weak, inadequate concrete. If nighttime temperatures are below freezing, the water in the concrete will freeze and expand, causing cracks. Additionally, if temperatures reach below 40 °F (but not freezing) during set time, concrete will take much longer to reach required strength. However, if the correct measures are taken, concrete can still be successfully placed during even the coldest months of the year.

Before embarking on a cold weather concrete project, it’s important to determine any special strength requirements or considerations. This will help as you schedule your pouring and determine which strategies you will use to keep your surroundings and materials warm. The predominant challenge you will face during a winter concrete project is ensuring that the concrete sets before it is exposed to freezing temperatures. You might take the following suggestions into consideration as you plan your upcoming project:

  • Use heaters to thaw frozen ground, snow or ice.
  • Use hot water to mix cement.
  • Keep dry materials in a dry, warm location.
  • Use products designed to set quickly. During cold weather, these products will not set as quickly as the instructions may indicate, but will set faster than conventional materials.
  • Use additives that accelerate set time. Use caution; if additives contain calcium chloride, any rebar or metal wire mesh in concrete will rust and cause concrete to crack.
  • Use extra cement (typically 100 lb/cubic yard) to make the reaction hotter and cause concrete to hydrate more rapidly.
  • Remember that you still need to wait for bleed water to evaporate. Incorporating the water into the surface during finishing will weaken the surface. Bleeding starts later and takes longer during cold weather; you can use squeegees or a vacuum to remove water quickly.
  • Wait until concrete has reached desired strength to remove any framework. If the framework is removed too early, the concrete will be damaged and the surface could collapse.

After implementing the above suggestions, It’s important to consider how you will keep concrete at the correct temperature during the curing process. Concrete must maintain a temperature above 50 °F for approximately 48 hours for the correct chemical reactions to take place, allowing the concrete to eventually settle at 4000 psi. Two popular options used during cold weather concrete curing are heated enclosures and insulated blankets. If using an enclosure, ensure that the structure is both wind and waterproof. Additionally, ensure that there is proper ventilation for the space heater. Heaters cause an increase in carbon dioxide that could cause carbonation in the surface of the concrete, not to mention a work hazard for employees.

Powerblanket® concrete blankets are an extremely effective option for attaining and maintaining the correct temperatures for concrete pouring and setting. Powerblanket® concrete blankets can be used to thaw ground before pouring concrete and again after finishing to keep concrete from freezing. Utilizing Powerblanket concrete blankets will ensure that concrete is kept at the correct temperature for the necessary reactions to happen quickly and the desired strength to be reached. With Powerblanket, it’s almost never too cold to pour concrete!

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The Effects of Pouring Concrete in Cold Weather

Effects of Pouring Concrete in Cold WeatherEffects of Pouring Concrete in Cold Weather

First, let’s define cold weather with respect to pouring concrete. Any time you have three 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 three days–that is unpleasantly cold for concrete. Pouring concrete in cold weather will have a detrimental affect on concrete curing for several reasons.

How Does Concrete Cure?

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.

Slower Chemical Reactions

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.

Read how Powerblanket solved concrete issues at the Statue of Liberty.

 

Concrete Can Be Successfully Poured in Cold WeatherThe Effects of Pouring Concrete in Cold Weather

How to avoid a bad concrete pour:

  • Never pour concrete on frozen ground, snow, or ice. 
  • 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 concrete curing blanket. The heated concrete blanket will prevent freezing and keep the concrete at an optimal curing temperature.
  • After about three days, remove heated concrete blankets to allow the concrete to air dry.

Powerblanket Concrete Curing Blankets

If you use Powerblanket Concrete Curing Blankets to pour in cold weather, your cement will cure 2.8 times faster than with conventional insulated blankets. Time and convenience are critical factors when planning out a project in the winter, and Powerblanket has you covered.  Our goal is to provide solutions to problems, and give you total temperature control over every process and aspect of your business.

We Solve Problems

From drum and barrel heaters to pipe wraps and snow melting mats, Powerblanket is dedicated to helping your business grow, saving jobs, and improving your bottom line.   Whether you need to extend the pouring season, or you are trying to survive an early winter, know that you have total temperature control with Powerblanket.

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

Powerblanket at the World of Concrete—A Demo in Concrete Curing

Earlier this month, Powerblanket attended the 2015 edition of the World of Concrete at the Las Vegas Convention Center. This year’s exhibition attracted 55,779 registered professionals. In addition, the event drew in 1,459 companies exhibiting their products and services. For Powerblanket and its concrete curing demo, the event proved to be a great way to engage with those in need of the company’s products.

 

Powerblanket at the World of Concrete—A Demo in Concrete Curing

Powerblanket and the World of Concrete

For Powerblanket, this year’s World of Concrete was an exciting investment of company time and resources. Powerblanket ran a concrete curing demo to demonstrate the effectiveness of Powerblanket® curing blankets on the set times and structural integrity of concrete pours. Those who were present were able to witness for themselves how much efficiency the curing blankets added to the curing process. Not only were the blankets able to cure the concrete nearly three times as fast, but they were also able to increase the strength of the concrete by 50%.

The slab used for the demonstration was 8” thick with a mix design that was formulated to provide a minimal PSI of 4,000 in only two days.  The slab was poured two days prior to the demonstration, and for the purposes of the demonstration, one portion remained unheated while the other section was covered in an MD series Powerblanket® curing blanket. At the beginning of the demonstration, the unheated portion of the concrete measured close to the 4,000 PSI that was required for the minimal target. Then the Powerblanket was added, and the portion of the slab that was heated by the Powerblanket MD Series concrete curing blanket measured a consistent 6,000 PSI after only 16 hours in place. That’s a PSI strength increase of 50% over the unheated portion of the concrete slab.

Powerblanket® curing blankets allow for such efficiency through the company’s patented technological approach to concrete curing and many other heating solutions. Not only do Powerblanket® curing blankets insulate the chemical reactions responsible for concrete heat exchange, but they also add heat to the equation—making them far more efficient than the common curing blanket.  Through the Powerblanket design, electrical heat is evenly distributed through the entire application, allowing for quicker set times and stronger concrete.

“Seeing people’s reactions to the demonstration was exciting,” said Ryan Jensen, Marketing Director for Powerblanket. “It was clear that everyone was impressed with the outcome.”

As a result, Powerblanket has engaged with more customers in an industry they already heavily serve.

 

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A Concrete Curing Solution

If you live in the North American Mountain West, or any region where it gets cold during the winter months, chances are you’ve seen chipping concrete. Have you ever stopped to think what causes concrete to chip? Improper curing is what causes it, but with a good concrete curing blanket, this problem can be completely avoided.

 

A Concrete Curing Solution 1

Not All Concrete Curing Blankets Are The Same

If you’ve ever seen chipped concrete before, it’s likely due to cold weather. But we’re not talking about cold weather after the pour. No, chipping concrete often results from it being poured when it was too cold. This means the concrete never fully cured. Thus, it became brittle and flaky. The simple solution to this dilemma is either to wait until its warm enough outside, or else apply a concrete curing blanket.

If you did a search on Google for concrete curing blankets, you’re likely to find a myriad of options. But not all these options are the same. A good majority of the curing blankets out there are merely insulation blankets. Now insulation is a good thing to have in a curing solution, but it’s only half of the equation. The problem with simply insulating the concrete is twofold.

If you have a concrete blanket that only acts as an insulator then it’s not likely to help in the extreme weather. This is the first problem with an insulation blanket. The second is this: with only insulation on your side, you’re not going to be speeding up the curing process at all. When concrete cures, a chemical reaction occurs. This reaction causes the concrete to put off heat. With this in mind, placing an insulated blanket over the concrete will help to keep some of this heat in, but the amount of heat it will trap isn’t substantial enough to help cure concrete in really cold weather, or to speed up the curing process much either.

 

A Concrete Curing Solution 2

The Real Solution is Electric

This is why you need an electric curing blanket, or a heated curing blanket, to get the job done right. Electric curing blankets will both insulate and heat the concrete to an ideal temperature for curing. With the characteristics of a heated blanket at play, you can properly cure concrete in very cold temperatures. What’s more, even if the weather isn’t that bad, you can apply such a solution to speed up the curing process by leaps and bounds.

When it comes to picking the best electric curing blanket, there are a few major aspects to be concerned with. Number one, you want to make sure you get a blanket that will evenly distribute the heat throughout the entire application area. If the blanket is hotter in some places than others, you’re not going to get an even cure. Number two, you want to make sure you get a product that is properly certified for safety and efficiency. And number three, you want to make certain you purchase a blanket that can regulate its own heat. A blanket with a thermostatic controller will enable you to apply the heat and walk away without worrying whether it will keep consistent heat for the whole time you’re curing.

 

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The Cure for the Common Cold Concrete

If you’ve ever had to lay concrete in the cold, then you can attest to the fact that it doesn’t set up as fast as it aught too. Actually, inclement weather can delay the curing of concrete considerably.

 

Heating Mortar Ingredients for Cold Concrete Weather Masonry

The Cure

When it comes to curing concrete, the optimal temperature is easy to obtain most of the time…if it’s summer. But what about all the other months of the year? What do you do when winter rolls around? More often than not, winter will put a screeching halt on the progress of temperature-sensitive construction projects, and concrete is one such example.

When concrete is subjected to cold weather, the time is takes to adequately cure increases significantly. According to the Portland Cement Association (PCA), “compression strength of concrete cured at 50 degrees Fahrenheit is expected is expected to gain strength half as quickly as concrete cured at 73 degrees Fahrenheit,” (PCA). So how do you speed up the process?

 

Insulation or Heat Application

A long standing-tradition for protecting concrete against the cold is to apply insulation to the concrete after it is hard enough to maintain its form under the weight of an insulation blanket. While this helps to keep the concrete from dropping in temperature drastically, it does nothing to bring the cement to an ideal temperature. However, there is an option that does this very thing.

Along with insulation blankets, there are concrete curing blankets.Concrete curing blankets not only help to insulate concrete against the cold, but they also help to raise its temperature and that of the ambient air around it. Done right, concrete curing blankets can be dialed in to a certain temperature and left to do the job without monitoring.

 

PCA

http://www.cement.org/for-concrete-books-learning/concrete-technology/concrete-construction/curing-in-construction   

See all the details of the Powerblanket® concrete curing blanket by downloading the free product spec sheet!

 

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