Fox Blocks
Airlite Plastics Co.
6110 Abbott Street
Omaha, NE 68110
877.369.2562
www.FoxBlocks.com
Cold Weather Concreting
If certain precautions are taken when building with insulating concrete forms (ICFs), concrete can be placed properly
throughout the winter months even in cold climates. 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 Farenheit (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 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.
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.
Fox Blocks
Airlite Plastics Co.
6110 Abbott Street
Omaha, NE 68110
877.369.2562
www.FoxBlocks.com
Line
In order
proper
mix
Condition
Thickness of Sections:
Less than 12"
1
Above 30° F
60
2
0° F to 30° F
65
3
Below 0° F
70
4
5
Minimum temperature of fresh
concrete as mixed for weather
indicated, ° F
Minimum temperature of fresh concrete as placed and
maintained, ° F
to get the
concrete
55
Maximum allowable gradual drop in temperature in first 24
hours after end of protection, ° F
50
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 durability
In
to
the
Service category
Conventional concrete, days
High-early-strength concrete, days
No load, not exposed, favorable
moist-curing
2
1
No load, not exposed, but later
has favorable moist curing
3
2
Partial load, exposed
3
2
Fully stressed, exposed
3
2
order
keep
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 Fox Blocks EPS is R-10.8.
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.
Fox Blocks
Airlite Plastics Co.
6110 Abbott Street
Omaha, NE 68110
877.369.2562
www.FoxBlocks.com
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.
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 Fox Block 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.
Images courtesy of the Portland Cement Association