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.

snow covered street

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

Construction site

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.

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Curing Cold Concrete: Electric vs. Insulated Blankets

Electric concrete blankets versus insulated blankets. Which one is best and why is it Powerblanket?

Not All Concrete Insulated Blankets Are Created Equal

If you happen to read almost any do-it-yourself guide, you will likely see a sentence that says, “If temperatures are below 40°F, use insulated blankets or straw to keep your freshly-poured concrete from freezing.” Well, that sounds nice and easy, but simply keeping concrete from freezing isn’t enough.

Why Heat Concrete?

The optimum range for proper concrete curing is between 65° – 85° F. When concrete dips below that range, ice crystals can form, cure strength will be compromised, and several temperature based defects can occur. Concrete pouring is a critical stage in any construction project and problems derail progress when it needs to be repaired or re-poured. Solely insulating concrete during curing seems appealing and money-saving, but can lead to costly time delays and expensive re-works.

What is Thermal Insulation?

Simply put, thermal insulation reduces the transfer of heat between objects. There are a myriad of both natural and synthetic materials used to insulate objects in different industries. When thermal insulation is placed on something that is already warm, it will prevent heat from escaping.

The chemical reaction of concrete formation is exothermic and does create some heat. This heat can be trapped (to some degree) with the use of insulating blankets or straw. But if it’s cold enough outside, insulating blankets won’t keep the temperature at an ideal level for maximum curing.

Insulation + Heating

When pouring concrete in cold weather, providing thermal insulation is only half the battle. Most insulated blankets will not provide enough surface contact to effectively insulate your concrete on really cold days. Combining the protective power of insulation plus even heat distribution gives you an advantage over mother nature.

Electric concrete heating blankets provide the protective layer of insulation and an extra boost of heating power to keep your concrete between 65° and 85° F. Concrete blankets have 10x more surface contact than other blankets. They efficiently transfer heat down into your concrete while heavy-duty weather-proof insulation protects it from the elements and heat-loss.

Thaw Before Your Pour

No insulating blanket on its own will thaw frozen ground, and pouring concrete on frozen ground can have serious repercussions.

electric ground thawing blankets

Electric ground thawing blankets are the best way to ensure your concrete pour gets off on the right foot. Using an electric ground thawing blanket prepares the ground before you pour so ambient temperatures above and below your concrete are at ideal levels.

Concrete Curing BlanketsMany factors have an effect on concrete cure time, such as the type of mix used, the size and shape of the slab, and the ambient weather. Of all these factors, weather and temperature is the most unpredictable. The colder the temperature, the longer concrete will take to set and reach its proper strength. During cold weather, a conventional insulated blanket will cause the concrete to take longer to cure and will result in a weaker concrete.

For example, concrete kept at 70°F will set in approximately 6 hours, whereas concrete kept at 40°F will take 14 hours to set. Concrete maintained at 70° F will reach a compression strength of 2,700 psi in 3 days; concrete maintained at 40° F will only reach a strength of 1,200 psi in 3 days.

This disparity in strengths makes a huge difference in whether your construction project can proceed. If concrete takes too long to set, cure, and strengthen, your project can be significantly delayed. Some concrete manufacturers find it too problematic to operate during the winter, creating a costly off season.

Concrete Solutions From Powerblanket

With Powerblanket, there is no off season. The difference between conventional insulating concrete blankets and electric concrete curing blankets is clear, and our electric blankets are a cut above the rest. By combining heavy weatherproof insulation with electric heating components, Powerblanket can cure concrete 2.8 x faster than conventional insulated blankets.

Our ground thawing blankets melt ice and snow and prepare the ground before your concrete is even poured. Our concrete curing blankets then maintain the temperatures you need to more quickly cure your slab to a strong finish. Powerblanket can eliminate costly weather delays, ensure your project proceeds on schedule and that your concrete will be long-lasting and durable. Contact us to find the right concrete solution for your needs 855.440.0208 or [email protected]

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Massman Construction Co. teams up with Powerblanket on the Christopher S. Bond Bridge

Christopher S. Bond Bridge in Kansas City Missouri

As motorists travel their daily commute, they appreciate infrastructure upgrades such a freshly paved roads, smoother drives, and improved routes. However, they often don’t realize the skill, effort, and creative problem solving that goes into the construction itself. 

In April 2008, Kansas City embarked upon a $245 million project that included the renovation of more than 4 miles of Interstates 29 and 35, and the construction of the Christopher S. Bond Bridge. The Bond bridge would replace the Paseo Bridge, which had spanned the Missouri River since 1954. The Missouri Department of Transportation (MoDOT) estimated that the project would require 7,000 tons of steel and 50,000 cubic yards of concrete. 3 contractors (Clarkson Construction Co., Massman Construction Co., and Kiewit Construction) formed a joint venture partnership known as Paseo Corridor Constructors (PCC) to bid on the project. The PCC partnership won the contract, and construction began in April 2008. 

Bridging The Gap

In late 2009, Massman Construction, a century-old company with a reputation as one of the country’s most successful bridge builders, encountered a unique challenge during a critical portion of the new bridge. The bridge deck would be comprised of precast concrete panels, each weighing about 60,000 pounds. These panels were formed in a precast yard offsite and then transported to the bridge. Once the panels were placed, Massman was left with an 18 inch wide, 12 inch deep void that would need to be filled in with poured concrete in order to solidify and connect the bridge deck. Unfortunately, to stay on schedule, this concrete pour would have to be accomplished in the dead of a mid-west winter.

Dale Helmig, Massman project manager, said that in order for the concrete to cure properly, “we had to maintain our concrete pour at a minimum temperature of 46° F for 7 consecutive days. We were on a tight schedule and looking at outdoor temperatures at or below 0° F, we had to find a way to keep the concrete warm.” Massman contemplated concrete heating methods and realized heating the top layer of concrete was not the problem. They needed a way to protect the bottom of the fresh concrete from constant exposure to the winter elements below the bridge.

The crew decided the only way to keep the bottom layer of concrete warm, was to completely enclose it. A river barge would float underneath the bridge, hoist a plywood enclosure, and force heated air at the bottom of the bridge. This solution would be excessively expensive, time-consuming, and there was no guarantee radiant heating would be efficient enough to work.

A Powerful Solution

Fortunately, Massman connected with a local equipment dealer that had an alternative solution; electric-powered concrete curing blankets from Powerblanket. Unlike the radiant heat from the barge proposal, Powerblanket products use conduction to deliver direct, even heat. 

Powerblanket diagram on conduction for concrete curing

These electric concrete blankets help cure within a desired temperature range. This seals in the concrete’s hydration reaction, and protects it from thermal cracking and surface defects.

“We gave Powerblanket’s engineers the boundary conditions we had to keep the concrete pour within — at least 46° F at the bottom but no warmer than 82° F at the top,” said Helmig. “They performed the calculations and determined the appropriate blankets needed to get the job done.” In order to heat the entire 12 inch deep slab, Powerblanket recommended our EH0612 blankets to counteract the extremely cold conditions beneath the bridge deck. For all 34 heating blankets, Powerblanket also created custom external digital thermostats so that Massman could constantly monitor their temperatures. 

Pouring fresh concrete in direct contact with the freezing cold precast panels also presented a challenge. Rapid temperature change in concrete will cause it to thermally crack. To protect the structural integrity of the bridge, Powerblanket provided 6 foot x 12 foot concrete curing blankets that easily exceeded the 18 inch trough. The additional blanket width pre-heated the precast concrete panels, making it safe to pour the fresh concrete.

concrete

A Strong Finish

Massman began the week-long concrete cure, during which the outdoor air temperature hit a low of -5° F. Crew members used probes to take temperature readings several times a day. “It was awfully cold, but the blankets did their job keeping the concrete temperatures within spec,” said Helmig. “We achieved the PSI levels we had targeted, and it turned out to be a successful operation. We didn’t have the time to wait out the winter for the temperatures to become more moderate. The Powerblanket products certainly played an important role in keeping us on schedule and not having to postpone the pour.”

Helmig has since moved on to another ongoing Massman project in St. Louis, and says he may be using the blankets again there. “We were committed to doing something to stay on track,” said Helmig. “Using Powerblanket products turned out to be the fastest, simplest means of getting the job done correctly.” Work progressed so well that by late October 2010, the Christopher S. Bond Bridge had already opened to traffic crossing the Missouri River.

Thanks to partnership and ingenuity, 102,000 daily motorists can rely upon the Paseo Corridor and Christopher S. Bond Bridge. Powerblanket is proud of our part in the construction of a strong and stunning work of American infrastructure. 

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