Concrete Curing in Freezers

Curing concrete in a deep freezer is a unique experience. Walk-in freezers are crucial to any organization that handles temperature sensitive material. The ability to store mass amounts of cold product in a controlled environment allows for meat, ice cream, cadavers, liquid oxygen and more to be used nearly anywhere in the world, so long as there is a freezer to put it in.

Most often, these freezers have a concrete flooring that is specially cured to handle the frozen environment around it, while keeping the heat from nearby room temperatures out. On top of all this, concrete flooring also needs to be able to withstand everything from footsteps to forklifts in ways that mitigate as much repair as possible.

Image taken from www.garonproducts.com

When preparing and pouring cement for freezer floors, there are several steps that one should consider, especially since this isn’t your usual concrete constructing picnic:

  • Maintain the mix: Be sure that your mix of concrete doesn’t contain too much water. Not only is it likely to cause cracking due to shrinkage, but it can also lead to water freezing within the concrete if it’s not cured enough by the time the freezer begins operating.
  • Seal the deal: The United States Dairy Association has a zero-tolerance policy regarding leaks in the freezer space. Frozen food should be stored at 0°F (-18°), as “freezing to 0° F inactivates any microbes — bacteria, yeasts and molds — present in food.” Any leakage would lead to moisture invading the freezer, potentially allowing mold and other harmful bacteria to grow. Any concrete installed as part of a walk-in freezer must be properly set and sealed to prevent leaks from happening.

Restoring Concrete Freezer Floors

With that in mind, you might be wondering how to repair concrete floors in freezers. Damage to the concrete floor like cracking or chipping can happen via forklift accident, replacing glycol heating systems, or subsoil moisture freezing.

Cracking occurs naturally in concrete, and there’s virtually no way to prevent it from ever happening. The best tools for repairing concrete freezer floors are low-temperature grade epoxy seals and additional concrete.

Equally important of what to use is what not to use. Repair product manufacturers like Polycote advocate against hard repair mortar when fixing floor joints. Doing so will create an inflexible bond that will not allow for any concrete movement, increasing the chances of additional concrete cracking.

Things to Keep an Eye Out For

Our friends at Concrete Mender offer several challenges that pose a problem when repairing concrete, which include frost, working conditions, and curing:

  • Frost: Frozen moisture in the concrete will act as a barrier between the repair material and the pores of the concrete. Most repair materials will try to bond to the frost coated concrete. When the temperature increases, the frost melts and so does the bond.
  • Working conditions: Working with materials in the cold is challenging to both man and materials. Mixing epoxies or mortars in the cold is especially challenging. As the temperature decreases, the viscosity and flow rate of these materials increase making them harder to mix and much more difficult to work with. Drum heaters are an excellent solution to keeping epoxy and mortar warm while waiting to use on a freezer job.
  • Curing: With most materials, cure times in cold environments are extended significantly. A product that normally cures in an hour at room temperature may take as much as 12 hours in a cold environment. Some materials may not cure at all before actually freezing solid. Use a concrete curing blanket to help the concrete cure for maximum strength.

If You’re Gonna Do a Job, You’d Better Do It Right

Fixing a freezer is a job you only want to do once. Making crack repairs can be tedious and have to be done exactly to specifications in meeting safety requirements. After all, keeping that freezer sealed tight with a good concrete job will keep the cadavers cold and food frozen.

The best tools to help with a quick, clean concrete repair job are drum heaters and curing blankets. For more information on these items, check out Powerblanket’s concrete solutions.

All About Concrete Cracking Repair

Concrete gets old with age, just like we do. When laid correctly, concrete doesn’t really pose any problems until the cracking and wearing part of the life cycle begins. Concrete cracking happens naturally, but that doesn’t mean you can’t do anything about it. 

Stock Image

Cracking is a constant in concrete. Nearly every slab of concrete ever laid will feature cracking at some point. This can lead to a series of important questions:

  • What is causing the cracking?
  • Is the structural integrity of my concrete compromised due to cracking?
  • Can cracking be repaired without replacing the concrete?
  • What can be done next time to help mitigate cracking?

Concrete Cracking Causes

The Concrete Network lists five causes of concrete cracking: excess water in concrete mix, rapid drying of concrete, improper strength concrete poured, lack of control joints, and poor ground conditions before pouring.

  1. Excess water in concrete mix: Concrete shrinks as it dries thanks to the water within the concrete mix evaporating. Though water is an important part of the concrete mixture, too much water will create a “soupy” concrete mix. When the water evaporates, the remaining concrete shrinks to maintain its strength. According to the Concrete Network, “concrete slabs can shrink as much as 1/2 inch per 100 feet. This shrinkage causes forces in the concrete which literally pull the slab apart. Cracks are the end result of these forces.”

    The best way to mitigate cracking of this type from happening is to be careful with how much water is added to your concrete mix. A low water-to-cement ratio will go a long way in preventing cracking.
  2. Rapid drying of concrete: Concrete will often not be able to achieve its maximum strength if it cures too fast. Hydration is the chemical reaction that allows the cement mixture to absorb water, changing from a liquid mixture into a solid slab. This process can take days, even weeks to become stiff enough to achieve desired strengths. Using a concrete curing blanket can allow less impact from external variables that affect concrete drying.

    Powerblanket image
  3. Improper strength of concrete poured: Not all cement mixes are created equally. Different mixes suit different purposes. You can bet that the concrete slab you poured to make the kids’ basketball court is a different strength than the Normandy bunkers stormed by the Allies on D-Day. Pouring the wrong strength of concrete can set you up for cracking. Check with your concrete provider to ensure you’re using the right strength of concrete for your project.
  4. Lack of control joints: Control joints let you choose where the cracking occurs. By allowing for spacing between concrete slabs, you can make sure cracks happen in straight lines and don’t spread due to temperature fluctuations and movement.

    Image taken from Concrete Construction Magazine

    When control joints aren’t used, cracking will happen in the most natural way possible with no direction from you. Cutting control joints must be done within 12 hours of pouring concrete, or as soon as the concrete has hardened.

  5. Poor ground conditions: Do not pour concrete on frozen ground. The poured concrete will bind to the ice inside of the frozen soil, and will become unbound once the ice melts. If you have to pour concrete in cold weather conditions, use a ground thawing blanket to get ground surfaces to the right temperature. This will ensure proper joining of ground and cement layers. The ground should also be dry, so make sure you’re not pouring concrete into a puddle or saturated soil.

Cracking Impacts Concrete

Structural integrity is what concrete is all about. Properly evaluating the impact of cracking can help you decide if your structure is sustainable, or if you need to replace that part of the project with another concrete pour. Opting to repair your concrete is feasible only once it’s been confirmed there are no structural issues.

Image taken from www.nextstartech.com

Repairing Cracks

Concrete Construction says that if you’ve noticed cracking in your concrete, you’ll want to follow several steps before taking any repair measures:

“Before repairing your next crack, perform a crack evaluation and establish the repair objectives. Decide what type of repair is needed. Choices include a structural repair using epoxy, a route and seal repair using a flexible sealant to accommodate future crack movements, and a hard or semi-rigid filler repair to support crack edges, with or without routing. Also, establish the cosmetic requirements. After choosing the repair material and procedure, follow the manufacturer’s recommendations.”

Stock Image

After completing the crack repair, reassess the area to see how you can blend the look of the repair back into the concrete, giving your project a smoother look.

Cracking: It’s Going to Happen

Though repairing cracking will allow for longer-lasting strength for your concrete, mitigating excessive cracking from happening in the first place is best. It can’t be stopped, but it can be controlled. Refer to the above guide next time you’re on a concrete job to make sure you have all your concrete cracking bases covered.

Check out Powerblanket’s concrete solutions here.

Concrete Curing Time

concrete pouring down the chute

Waiting for the curing of concrete can easily test patience, especially when you’re ready to move on to the next step of a project. However, it’s important to remember that quality is the end goal, not quickness. Rushing ahead and not allowing enough time for concrete to properly cure before allowing foot traffic or heavy machinery to travel across your newly placed cement can seriously compromise the integrity of a concrete slab.

 

Cement Curing Factors

Several factors influence concrete slab cure time, including:

  • Mixture proportions- Increasing cement to water ratio will decrease setting time but may compromise long-term strength.
  • Type of mix used- Some fast curing concrete mixes and add-ins  are available
  • Specified strength
  • Size and shape of slab
  • Ambient weather/temperature- Higher temperatures decrease initial concrete setting time, but may decrease long-term strength.

 

Typical Concrete Setting Time

Typically, concrete is recognized to have reached full strength 28 days after placement; however, this does not mean you need to wait 28 days to walk, or even continue construction on newly placed concrete. After placement, concrete increases in strength very quickly for 3-7 days, then gradually for the next 3 weeks. This means that concrete hardening time is typically 24-48 hours, at which point it’s safe for normal foot traffic. After one week, concrete is typically cured enough to handle continued construction including heavy machinery.

concrete curing time

The “70 in 7” Rule

When in doubt, remember the “70 in 7” rule: Most concrete mixes will have reached 70% of specified compressive strength after 7 days. At this point, it’s ready for exposure to normal traffic.

concrete curing blanket on ground

Concrete Curing Blankets

Unfortunately, cold weather during winter months can seriously slow down concrete cure time and significantly hold up construction projects. The best temperature to cure concrete is above 5o°F, which can be difficult to replicate if the air is below freezing.

Luckily, solutions, such as concrete curing blankets that maintain optimum temperatures during cure time, are available. Concrete Blankets are an effective option that cure concrete 2.8 times faster than a typical insulated blanket and properly maintain moisture throughout the hydrating process. Concrete Blankets are easily transported and installed and maintain ACI compliance for cold-weather concreting. If you’re looking for a solution to maintaining optimum concrete cure time during cold winter, using a Concrete Blanket is the best method for drying and curing concrete.

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!

 

How long does concrete take to set?

If you really want to know the truth, concrete never stops curing; it continually hardens forever. However, for practical purposes, it reaches a point where further hardening will be so slow it becomes unnoticeable. In this article, we cover the basics of what you need to know if you’re asking the question, “how long does concrete take to set?”

Concrete Never Stops Curinghow long does it take concrete to set

The continual hardening occurs because cement particles react with the water in the mix (hydration), and as long as cement is in contact with moisture, even miniscule bubbles, it will continue to form bonds. This is minimal after “full strength” is achieved, but it is continual.

Curing Time for Concrete

In standard industrial cases, full strength concrete is recognized at 28 days. At seven days, you should have concrete that is cured to 70% full strength or greater. But to answer the question of, “How long does concrete take to set?” concrete setting time is generally 24 to 48 hours. At this point the neighborhood dog will not leave his footprints in it, but you should keep it clear of heavy equipment during this time period. Most mixes are cured at 28 days.

Factors Affecting Concrete Setting Time

  • MMoisture's Effect on Concrete Settingoisture plays a critical role in curing time for concrete. If there is not sufficient water in the mix, the concrete will cure too fast, resulting in weaker overall strength. Too much moisture, often used in the finishing step will weaken the top layer and cause flaking.
  • Hot ambient temperatures and wind accelerate the evaporation of moisture–speeding concrete setting time.
  • The mix design has a lot to do with concrete setting time. Some jobs will require accelerants because the area needs to be usable as soon as possible. The accelerant will do its job and speed up the concrete setting time. Accelerant mixes will show a weaker overall strength in the end, but will still meet strength requirements.

Concrete Blankets

If you are wondering about how long concrete takes to set, a solution for your concrete setting needs is a concrete heating or cooling blanket. If you are dealing with HOT conditions and your concrete setting too quickly, consider  FluxWrap.

The FluxWrap from North Slope Chillers is portable cooling equipment that will keep newly poured concrete safe from heat, regulating concrete setting time in both regular and hot conditions.

The FluxWrap is combined with either a cooler or chiller to achieve optimum results. The Circulation Blanket draws heat to the blanket in order to cool the concrete.

  • Use Powerblanket’s patented heat-spreading technology in reverse–the cooling blanket draws heat away and lowers the temperature of the concrete.
  • Take it with you on every jog.  It is easily portable.
  • Blanket cover and insulation are the same as the robust system used in Powerblanket heating products
  • Control the curing speed of newly poured concrete even in hot conditions

If conditions are cold, concrete curing blankets provide a manageable way to cure concrete effectively and confidently. Powerblanket curing blankets increase production by rapidly curing with consistent, even heat.

  •  Cure concrete 2.8 times faster than conventional, insulated blankets
  •  Maintain moisture throughout hydrating process
  •  Easily installed and removed
  •  Produce cold weather concreting strength of up to 3,925 psi in 72 hours
  •  Prevent a freeze cycle
  •  Thaw ground and frost from job site before you pour
  •  Reduce downtime & increase profitability
  •  Maintain ACI compliance for cold weather concreting

 

Concrete Curing Temperature Makes a Difference

How Warm Does it Have To Be To Pour Concrete?

Whether the conditions are hot or freezing, the ideal concrete curing temperature should be maintained at about 55°F to achieve the optimum concrete strength.

Curing the Hoover Dam

At its completion in 1935, the Hoover Dam was the largest dam in the world and a marvel of labor and engineering.  The first pour began on June 6, 1933. Rather than being a single block of concrete, they built the dam as a series of individual columns. The trapezoidal columns rose in five foot lifts. This method allowed the tremendous heat produced by the curing concrete to dissipate. If the dam were built in a single continuous pour, the concrete would have gotten so hot that it would have taken 125 years for the concrete to cool to ambient temperatures. The resulting stresses would have caused the dam to crack and crumble away (The Story).  

The heat and dryness of Nevada posed additional complex problems with the pour and concrete curing temperature.  When the concrete was first poured, river water circulated through cooling coils of 1″ thin-walled steel pipes. Once the concrete had received a first initial cooling, chilled water from a refrigeration plant on the lower cofferdam circulated through the coils to finish the cooling (The Story).

Concrete Curing is an Art

We live in a world where faster always seems better; however, concrete that cures too quickly or under hot concrete curing conditions can actually result in weak or unstable concrete.  If concrete is cured in cooler ambient  temperatures (32°F to 50°F) with moisture continually present, strength gain will be slow but the concrete will eventually reach a high strength. Concrete should not be allowed to get hotter than 90°F or to dry out during the curing period.

Best Concrete Curing Temperature

By “best” we mean “most thoroughly,” not the fastest.  High temperatures mean faster curing, but fast curing equates to weaker strength in the end.  The following study by Paul Klieger in the Portland Cement Association Research Bulletin 103 illustrates this concept.

concrete cure time chart with concrete curing temperature

Concrete Cure Time Chart with Temperature

At an age of 1 day the 120°F concrete was strongest and the 25°F concrete was weakest. By 7 days the high-temperature cured concretes had no more strength than the 73°F concrete or even less. By the age of 28 days the high-temperature concretes were weaker than the 73°F concrete. From 28 days to 1 year the 55°F concrete was considerably stronger than the 73°F concrete. All of this suggests that, provided there is continuous curing, concrete cured at about 55°F for the first 28 days ultimately reaches the highest strength (Concrete).

Hot Weather Concrete Temperature Limits

Hot weather concreting doesn’t simply involve temperature.  High ambient temperatures, winds, and relative humidity all play a role in “hot weather.”  Under hot heather conditions, the primary curing issue is having the top of the slab of concrete dry much faster than the bottom. As concrete dries it shrinks. This means that the top will be shrinking while the bottom is not. This creates internal problems with the concrete that will result in a damaged slab. The top and the bottom of the pour need to cure at the same rate (Placing).

Concrete Curing Temperature Solutions

Is it too HOT?

Powerblanket ICE is portable cooling equipment that will keep newly poured concrete safe from heat. Portable, insulated, and efficient, Powerblanket ICE effectively regulates the temperature of concrete under both regular and hot conditions.

The Powerblanket ICE Circulation Blanket is combined with either a cooler or chiller to achieve optimum results. The Circulation Blanket draws heat to the blanket in order to cool the concrete.

  • Use Powerblanket’s patented heat-spreading technology in reverse–the cooling blanket draws heat away and lowers the temperature of the concrete.
  • Blanket cover and insulation are the same as the robust system used in Powerblanket heating products
  • Portable
  • Control the curing speed of newly poured concrete even in hot conditions

Is it too COLD?

Can you pour and cure concrete in the winter? Powerblanket concrete curing blankets provide a manageable way to cure concrete effectively and confidently in the cold weather months. Even in warm weather, Powerblanket curing blankets increase production by rapidly curing with consistent, even heat.

  •   Cure concrete 2.8 times faster than conventional, insulated blankets
  •   Produce cold weather concreting strength of up to 3,925 psi in 72 hours
  •   Maintain moisture throughout hydrating process
  •   Easily installed and removed
  •   Prevent a freeze cycle
  •   Thaw ground and frost from job site prior to pour
  •   Reduce downtime & increase profitability
  •   Maintain ACI compliance for cold weather concreting

Works Cited

“Placing Concrete in hot or cold weather”. Sakrete Blog. 16 May 2017. http://www.sakrete.com/media-center/blog-detail.cfm/bp_alias/Placing-Concrete-in-hot-or-cold-weather

“The Story of Hoover Dam – Essays”. Bureau of Reclamation. 16 May 2017. https://www.usbr.gov/lc/hooverdam/history/essays/concrete.html

Hot Weather Concreting Made Easier

Hot Weather ConcretingHot weather concreting

Hot weather concreting problems are most often encountered in the summer; however, any condition that increases curing rates and strips the concrete of moisture is considered hot weather concreting.

Pouring Concrete in Hot Weather

With temperatures rising and summer approaching, attentions shift from protecting concrete from the cold to concreting in hot conditions.  When pouring concrete in hot weather, special procedures should be followed for proper mixing, placing, finishing, and curing.  High ambient temperatures, high concrete temperatures, low relative humidity, and/or high winds impair the quality of freshly mixed and recently placed concrete (Hot).  Pouring concrete in hot weather affects laboratory test results, showing that higher temperatures affect the compressive strength gain of hardened concrete. Even though concrete poured in hot weather will produce higher early strength but as time goes by, the ultimate strength will be lower than expected (Rodriguez).

Water Loss

Hot weather concreting causes increased setting rates and rapid water loss.  Shrinkage and cracking are usually associated with hot windy weather.   The major side effect of faster curing and water loss is decreased overall concrete strength.  It is critical to prevent moisture from evaporating from the concrete surface. The evaporation rate removes surface water necessary for hydration , and thermal cracking may result from rapid changes in temperature, ie. pouring concrete on a hot day followed by a cool night (CIP 12). Proper mix design can compensate for these conditions, and in combination with protective measures to prevent rapid evaporation, quality concrete can be poured in hot temperatures (Rodriquez).

Adding water can increase concrete workability. However, adding water beyond the amount required by the approved mix design increases the water to cement ratio. This, in turn, can result in decreased compressive strength and an increased chance of cracking (Hot).

Recommendations for Hot Weather Concreting

Preparation is key and there are several basic precautions that can reduce the damaging effects of hot weather on concrete:

  • Use mix designs that are less susceptible to the effects of hot weather. The use of low-heat-of-hydration cement and certain admixtures (such as hydration retarding and/or water-reducing admixtures) are two standard approaches.
  • Keep concrete as cool as reasonably possible. ACI 305R does not state a maximum “as-placed” or “as-delivered” concrete temperature, but 90° F is commonly used. Substituting chilled water or shaved ice for a portion of the required mix water can help.
  • Limit the amount of time between loading the concrete at the plant and placement/finishing at the site.
  • Limit water addition at the job site, except to adjust slump upon arrival (when permitted by mix design).
  • Avoid or limit hydration accelerating admixture use.
  • Schedule large concrete pours in the early morning or evening when temperatures are cooler and have the manpower available to complete the job as quickly as possible.
  • Use temporary wind screens and water misting nozzles to reduce surface moisture loss (Hot).
  • Consider using a concrete cooling blanket to both retain moisture and protect the concrete’s surface from high ambient temperatures.

Powerblanket ICE Concrete Cooling

Powerblanket ICE® is portable cooling equipment that will keep newly poured concrete safe from heat.  Portable, insulated, and efficient, Powerblanket ICE effectively regulates the temperature of concrete under both regular and hot conditions.

The Powerblanket Ice Circulation Blanket is combined with either a cooler or chiller to achieve optimum results. The Circulation Blanket draws heat to the blanket while also cooling the concrete.

  • Blankets use Powerblanket’s patented heat-spreading technology in reverse–the cooling blanket draws heat away from the drum and lowers the temperature of the concrete.
  • Blanket cover and insulation are the same as the robust system used in the Powerblanket heating products
  • Powerblanket Ice industrial cooling systems are portable (120VAC required)
  • Control the curing speed of newly poured concrete even in hot conditions

 

Works Cited

“CIP 12 Hot Weather Concreting”. NRMCA. 5 May 2017. www.nrmca.org/aboutconcrete/cips/12pr.pdf

“Hot Weather Concrete”. Engineering Consulting Services.  5 May 2017. www.ecslimited.com/blog/hot-weather-concrete

Rodriguez, Juan. “Pouring Concrete in Hot Weather: Tips and Tricks”. The Balance.  5 May 2017. 

https://www.thebalancesmb.com/pouring-concrete-in-hot-weather-845030

 

Process Heating Engineering: Heat Tape

Process Heating Engineering:  Heat Tape

Powerblanket makes industrial heating blankets; however, for this process heating project, we skipped the outer jacket and went straight for the heat tape on the inside.

Upgrade Your Security Clearance

For the third installment of Powerblanket Engineer Favorites, we delve (really only dip our toes) into the world of defense contracting.  

The Heating Dilemma

This company needed to cure carbon fiber reinforced polymer composites.  They were on a very tight timeline and their current suppliers were unable to react quickly enough to meet their needs. This became a custom project because the composites had a complex geometry that could not be evenly heated/covered with a standard industrial heating blanket.

The Powerblanket Custom Solution

Powerblanket recognized that a standard blanket could not meet the process heating needs of these complicated composites.  So we offered them the electrical heating tape normally used inside PB400 blankets that would adhere directly to the surfaces they wanted to heat.  In addition, we built them a custom power cord and wiring harness to power several pieces of heat tape at once.  

They had their own temperature control system, so our offering was incredibly simple: a plug, a cord, and a wiring harness used to power several pieces of adhesive-backed high-temperature heat tape (300 F°/149°C rated).  We designed the heat tape to be one-time-use disposable and the power cord and wiring harness to be reusable and easily be disconnected.

Powerblanket Custom Team

Powerblanket’s custom engineering team prides itself on creativity and out-of-the-box thinking, quickly dreaming up a solution that met all of the customer’s technical requirements.  Despite this being a new product category for Powerblanket, we provided a quote within 24 hours of the initial conversation, and built and shipped the process heating product within a week of receiving the PO.

When you purchase a Powerblanket custom process heating solution, you will enjoy quick turn-around times and the ability to choose from varying levels of customization. Our products are certified to universal safety standards and are easy to install, use, and store.

So whether you need a heat solution for complicated composite curing, tank heaters for your three phase horizontal separator used during drilling operations, or process heating temperature control on your assembly line, our custom approach can provide you with the perfect custom process heating solution. Powerblanket has you covered.

 

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.

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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.

 

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.

 

PCA

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