Three observations of using ICFs and CMU

Thad points out three huge observations that communicate cold weather benefits of insulated concrete forms in relation to CMU.

1. The General Contractor has to pay for any cold weather material that is used for CMU construction- including heaters, plastic tenting, blankets etc .  If it is windy they will have to repair all of those elements as they whip around and become damaged due to the weather. The GC spends more money in order to continue to keep the job on schedule and for safety of the workers. The tent is heated so that they can grout the walls, which ICFs no grout is needed so tenting is eliminated.
2. The mason contractor can bid both ICF and CMU packages.
3. The masonry workers had to shut down the day Thad was there because it was too cold and the tent was destroyed throughout the day by high winds.  Generally the crew would have to be sent home and a day of work is wasted.  The ICF portion of the building was not effected by the cold or the wind and construction was still moving forward.

For more information on cold weather and concrete see our previous posts or access our insulating concrete form product manual where you can see all of the research and testing done on our product lines:

Insulating Concrete Forms and Cold Weather Concrete Part I
Insulating Concrete Forms and Cold Weather Concrete Part II
Insulating Concrete Forms and Cold Weather Concrete Part III

Insulating Concrete Forms in sub-freezing temperatures

In order to keep the concrete at the desired temperature for the protection period, the concrete must be covered or insulated. This is where ICF construction in cold climates becomes an obvious benefit. The R-value of one panel of Reward iForm EPS is R-10. Assuming a cement content of 500 pounds per cubic yard and a wall thickness of 6 inches and interpolating from the graph below for R-10, the minimum ambient temperature for placing concrete would be around 10º F.

Thermal resistance (R) of insulation required to maintain the concrete surface temperature of walls and slabs aboveground at 50º F or above for 3 days. Concrete temperature as placed 50º F. Maximum wind velocity: 15 mph.

Insulating Concrete Forms
Using ICF construction in cold weather means that vulnerable corners and edges are consistently covered and protected. Forms are left in place to keep moisture and heat contained for an extended period of time, improving the curing condition of the concrete. Additionally, the consistent insulation from ICFs allows for even heat distribution.

Not only is it important to insulate the top of the Reward ICF wall after concrete placement in cold weather, there are three other areas to be concerned with. These include footings, bulkheads and embedment steel. Placing concrete on top of a cold footing and around cold steel embedments can affect the concrete temperatures in those local areas. Precautions should be considered or taken for these areas. Bulkheads, much like the top of the ICF wall must be insulated as well.

Tips for strong concrete

• Keep forms covered before concrete placement if any precipitation is expected. This will prevent snow and ice from forming inside the cavity of the ICFs.

• Cover the top course after concrete placement in order to contain the heat produced and to insulate the top of the concrete wall. Rigid or batt insulation blankets of R-10 or greater work well for both covering the forms before concrete placement and for insulating the top of the wall after concrete placement.

• Work closely with a local ready mix supplier to determine concrete mix requirements for the specific project and climate.

• Do not rush a concrete pour late in the day or if bad weather is approaching. This can lead to problems.

CMU vs. ICFs during Cold Weather

Next week we will highlight a specific ICF school job we were at about a week ago, where they used CMU for a portion of the building and ICFs for the other. The pictures will tell the story.

insulating concrete forms

Heat of Hydration

Concrete generates heat as it hydrates through a chemical reaction of the cement reacting to the water. The heat generated is affected by the dimensions or mass of the concrete, the air temperature, the initial concrete temperature, the water-cement ratio, the cement composition, the amount of cement and admixtures. The heat of hydration sometimes generates enough heat to provide adequate curing in cold weather.

Concrete Mixture

Concrete mixtures may be adjusted in cold weather to accelerate the curing time by using one or a combination of 1) Type III Portland cement – high-early strength cement; 2) additional Portland cement of 100 to 200 pounds per cubic yard; 3) chemical accelerators such as a maximum of 2% by weight of calcium chloride and 4) air-entrained concrete to help the concrete absorb stresses due to ice formation.

Temperature of Concrete

The recommended temperature of the concrete as mixed and as placed should be not less than what is shown in the table below. Mixing concrete to temperatures higher than 70º F can have adverse effects of shrinkage and cracking.



In order to get the proper concrete mix temperature you are trying to achieve, the aggregate, cement and water temperatures must be known and accounted for.

The concrete should be placed into the forms before the concrete temperature drops below 55º F as indicated in the table above. That temperature should be maintained for the duration of the protection period indicated in the table below. This maintains durability against exposure to freezing and thawing.

For Thursday part III we’ll address how the insulation effects the temperature of the concrete and explain exactly why ICFs are ideal for cold weather applications.

ACI 306 is the standard used for placing concrete in cold weather. ACI 306 defines cold weather as a period when for more than 3 successive days the mean daily temperature drops below 40º Fahrenheit (F). Normal concreting can resume once the ambient temperature is above 50º F for more than half a day. Fresh concrete that begins to freeze can reduce the strength gain and its durability.

The next few posts in this series will look a cold weather concreting form a technical standpoint, showing pictures and proejct examples in the field, and will highlight the extra steps needed to do CMU construction during cold weather.

Cold Weather Concreting

The concrete mixture and its temperature must be adapted to the construction procedure during cold weather. This means making preparations to protect the concrete’s temperature from the cold air. The insulating concrete forms, reinforcing steel and concrete embedments must be clear of snow and ice when the concrete is placed.

Concrete strength gain is a function of the temperature at which it cures. Typical concrete compressive strengths are based upon the concrete curing at an ideal temperature of 72º F the entire 28 days. Temperatures higher than 72º F will shorten the curing time and temperatures lower than 72º F will increase the curing time. Concrete gains very little strength at low temperatures.

The concrete must be protected against freezing effects until the degree of saturation of the concrete has been sufficiently reduced by the process of hydration. This time corresponds to the time that it takes the concrete to attain a compressive strength of 500 psi. During normal temperatures, this time is usually within the first 24 hours of concrete placement. Significant strength loss of up to 50% can occur if concrete is frozen shortly after placement or before it reaches a strength of 500 psi.

Yes that it snow, not a white sand beach. This is an Air Force Base Reward did a few years ago in Alaska.

For Tuesday Part II we will talk about the chemical reactions and properties of concrete that play a role curing concrete in  cold weather.

During the Waterside Towers project, Parks ICF participated in a study that helped scientifically prove that concrete curing times are greatly accelerated in cold weather when placed in ICF forms versus when left exposed.  The field tests showed the concrete reached the required 2,000 psi compressive strength in just 2 days versus 4-5 days with exposed concrete.  Mr. Petersburg of Shield Engineering worked hand-in-hand with us on the project as a third-party engineering representative as we continued with sample testing on each floor before the flooring system was placed.  Through this testing, Parks ICF was able to accelerate the project schedule by 10 to 15 days and help keep the other crews continuing with minimal down time.

“The incredible thing about working with ICF wall systems was its workability in cold temperatures and inclement weather.  Working through what turned out to be one of the coldest and wettest winters in recent memory, we’ve experienced minimal lost days versus a potential of several weeks or months with traditional construction methods.”  -Ted Kuerschen, Project Manager, Waterside Condos

“One of the great benefits we found working with ICF, especially in the winter, is that weather does not slow down construction as it does on standard job sites. Rain and snow did not affect placement of ICF block or of concrete. Being insulated with the foam, the concrete was able to retain its temperature even on the coldest of days of placement. Both laboratory and field cured cylinders were cast during the construction process. It was found that standard field cured cylinders broke considerably lower than core samples obtained from the poured wall. The strength of ICF cured test cylinders, giving a more realistic indication of on-site conditions, were more closely correlated to the laboratory cured specimens.”  -Nathan Petersburg, Shield Engineering

Waterside Towers at Norris Lakes is one of the more recent projects that have been completed, especially of this size and significance. It was a sizable project, unique not just for the building materials and the location, set in in a peaceful getaway spot, but unique for the construction techniques and concrete testing the builder, Parks ICF Wall Systems, LLC performed.

The Waterside Towers, located North of Knoxville, Tennessee, presented many architectural challenges that were overcome by the strength properties of Reward ICFs. Designed to withstand seismic loads, the Waterside Towers utilized ICFs to provide extreme strength and resistance to environmental changes such as earthquakes and high winds that develop on the adjacent lake. The architect also used the noise reduction properties of ICFs for the interior unit, separation walls in order to keep noisy neighbors silent to condo owners. ICFs were also used in the elevator shaft to reduce noise transmission to the adjacent units.

Cold Weather Challenges Met

One of the greatest challenges faced by the crews of Parks ICF, on this project, was the weather. Having begun the project in October, their crews worked through the cold winter months to finish the tower in just over 3 months. The temperature dropped to just 22 degrees Fahrenheit during the project. Through the use of concrete accelerators and extensive compressing strength testing, our crews were able to finish ahead of schedule. (More on testing measures of concrete in later posts)

Waterside Towers Impact on Environment

Parks ICF Wall Systems, LLC is dedicated to protecting the environment and reducing the environmental impact of construction. The fragile ecosystems and undeveloped woodlands surrounding the Waterside at Norris Lake, sustains many different types of wildlife that can be greatly impacted by traditional construction methods. The profitability of the Waterside Towers depends on the the surrounding environment to bring in customers and tenants to the multi-hundred thousand dollar condos. Reward ICFs helped to minimize the effects on the environment and thus increase profitability. Also, in order to reduce emissions, the Towers minimized the size of their HVAC systems because of the energy efficiency of the ICF.