How Cold is Too Cold to Pour Concrete?

 Ground heating electrical blanket for curing 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.

Things to Consider with Cold Weather Concreting

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.

Maintaining Ideal Temperature

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. 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.

Powerblanket Concrete Blankets

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.

 

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!

Temperature makes all the difference when pouring concrete. Check out our article on how temperature affects concrete that is still curing inside the Hoover Dam!

The Effects of Pouring Concrete in Cold Weather

concrete pouring temperature graphic
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 undesirably 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 Weatherpouring a concrete foundation at a jobsite

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.

Learn More

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 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.

Learn More

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 should. Inclement weather can delay the curing of concrete considerably.

Heated concrete blanket

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.

For more about Powerblanket’s concrete curing blankets, click here.

 

PCA

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

 

Laying Bricks and Block in Cold Weather

House construction in winterEven with the onset of winter, construction must continue. Problems from working in cold weather can include slowing the hydration of cement in mortar mix, lengthening cement curing time.
Mortar mixed during cold weather often has lower water content, increased air content, and reduced early strength compared with those mixed during normal temperatures. Mortar is often mixed with heated materials to produce performance characteristics associated with mortar mixed at normal temperatures, or with admixtures which may improve the early strength and plasticity of the mix. Water, sand, or both are often heated for use in mortar in cold weather. However, heating prepackaged materials such as cement and hydrated lime has long been a problem for brick masons.

Frozen Mortar Will Not Work

Mortar freezing should not be allowed to freeze. Mortar that freezes is not as weather-resistant or as brick mortar freeze protection guide graphicwatertight as mortar that has not frozen. Significant reductions in compressive and bond strength may occur. Mortar with water content over 6-8% of total volume will experience disruptive expansive forces if frozen due to the increase in volume of water when it is converted to ice, and the bond between the brick or block and the mortar can be damaged or destroyed.

The Benefits of Concrete Curing Blankets

Experts recommend covering newly-laid brick or block with insulating blankets when temperatures are below 40°F, and using heated enclosures when the temperature is below approximately 25°F. Powerblanket® concrete curing blankets eliminate the need for heated enclosures and are the best option when it comes to insulating blankets. They maintain the proper curing temperature no matter what changes in weather occur, keeping the mortar bond strong and lasting. Instead of building enclosures, concrete curing blankets can be easily hung on newly-laid walls, eliminating the need for constructing enclosures or other temporary structures.

Concrete curing blankets can:

Laying Bricks and Block in Cold Weather

  • Keep the sand pile and dry mix bags warm and dry
  • Ensure that crews can lay brick or block in any temperature
  • Achieve durable and long-lasting walls, with predictable scheduling and minimal crew downtime caused by poor conditions
  • Maintain proper curing temperature regardless of external conditions
  • Hang easily

Hot Boxes are Problem Solvers 

Whether you need a means for protecting temperature-sensitive materials in storage, or you need a heating solution for onsite temperature maintenance, consider the Powerblanket Hot Box. This versatile heating solution accommodates remote-location use, job site heating, the transporting of temperature sensitive materials. Imagine transporting materials from job to job, knowing that your mortar, sand, and/or dry mixes will be ready for use when you arrive and well into the day. The revolutionary design of Powerblanket Hot Boxes provides uniform heat to all materials stored inside. This reduces the chance of having any hot and cold spots. If stored properly, masonry materials, chemicals, industrial products, and temperature sensitive materials will last longer and be more effective.

Hot boxes are:

  • Versatile and easy to use for many different applications
  • Easily transported
  • Provide even heating
  • Reliable
  • Time, material, and money saving

 

Laying Bricks and Block in Cold Weather

Pouring Concrete on Frozen Ground

 heated blanket versus open flame to thaw groundWhen temperatures are cold, it’s tough to schedule your jobs because you can’t control the weather. You can lose time and money, and it’s extremely hard to schedule your sub-contractors. If you wait for the weather to break, you might find yourself waiting a long time. Powerblanket® concrete curing blankets eliminate the weather variable and keeps your downtime to a minimum.

Unlike normal insulated blankets, Powerblanket Multi-Duty curing and thawing blankets allow you to unthaw frozen ground prior to pouring. Simply place them ahead of time and when your crew is onsite the ground will be ready for pouring – and on your schedule, not the weather’s.

Once you’ve poured, the same blankets will allow you to maintain the optimal curing temperature, ensuring a strong, durable slab, within a predictable time-frame that keeps your job moving.

For rapid thawing, use Powerblanket Extra-Hot Thawing blankets, which provide a number of advantages over other ground-thawing methods:

  • No open flames
  • Faster & more economical
  • No carbon monoxide discharge
  • No noxious fumes
  • Safe, energy-efficient, and environmentally friendly

electric blanket thawing ground with snow on itPowerblanket frozen ground thawing and concrete curing blankets allow concrete work to continue through the winter: you can efficiently schedule your crews and equipment and maintain a steady work schedule throughout the year.  

A final tip: NEVER POUR FRESH CONCRETE ON FROZEN GROUND. You now have a solution for thawing frozen ground and curing concrete in any weather condition. Keep your jobs and your crews on schedule with Powerblanket.

 

To learn more about the cure for common cold concrete, click here.

 

 

Placing Concrete in Cold Weather – An Overview

TITLE
0
access_time

Placing Concrete in Cold Weather - An OverviewThe 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.

Hard, gray Jell-O

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.

Crystals in Concrete

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.

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.

Hot Stuff

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.

Temperature is one of the most influential factors in determining the strength of concrete. For more information on that subject, click here.