1) Concrete strength is reduced by 50% if freshly mixed concrete freezes due to exposure to low temperatures below 5°C for three days. Freezing and thawing cycles also increase porosity and reduce strength. 2) Several methods can be used to maintain the temperature of freshly poured concrete in cold weather, including enclosures, insulating materials, and heaters to protect the concrete and allow proper curing. 3) Specifically, polyethylene sheets or insulating blankets made of fiberglass or sponge rubber can be used as insulating materials, while direct-fired or indirect-fired heaters supply heated air to keep the concrete warm.

1. 08/01/2015
References available upon request
CONCRETING IN COLD WEATHER
Curing Concrete can be made in different weather conditions; In each condition, it has to insure that the
concrete will attain its desirable strength to resist construction works and the applied loads. This article will
highlight on the influence of cold weather on fresh concrete and the methods used to reduce its negative
effects. The temperature is considered to be low if it falls below 5°C for three consecutive days.
The concrete strength of concrete will be reduced
dramatically (up to 50%) if the freshly mixed concrete
freezes due to its exposure to a low temperature.
Therefore, a sufficient hydration time must be insured
before the concrete is exposed to repeated cycles of
freezing and thawing. These incidents will reduce the
strength of concrete and increase its porosity. At a
temperature less than minus 10°C the hydration and
strength gain will stop.
During the hardening process, the concrete will generate heat resulting from the chemical reaction between
cement and water, this heat is called heat of hydration. The heat of hydration helps the concrete gaining the
suitable temperature needed for hydration process.
Several factors affect the amount of heat generated:
€ Amount of cement
€ Dimension of the concrete placement
€ Ambient temperature
€ Initial concrete temperature
€ Water-cement ratio
€ Admixtures
While concreting in cold environment, ready mixed concrete must be delivered at a suitable temperature, the
steel bars and forms must be free of snow and at a proper temperature. Thermometer can be used to evaluate
the temperature of each material.
Figure 1: Ice impressions of Frozen fresh concrete
Figure 3: Effect OF Temperature on Compressive
StrengthFigure 2: Effects of temperature on Concrete

2. 08/01/2015
References available upon request
In order to obtain a high concrete strength at
an early age during cold season, one of the
following solutions can be used:
1) Type III or HE high-early-strength cement
2) Additional Portland cement (60 to 120
Kg/m3
or 200lb/yd3
)
3) Chemical accelerators (ex: calcium
chloride). Chemical accelerators are not
recommended in areas containing steel
reinforcement bars or aluminum or
galvanized inserts, or surfaces exposed
directly to soil or water.
4) Air-entrained concrete which is a perfect
solution to reduce the effect of freezing
and thawing on the concrete and hence
reduces the cracks induced by this
phenomenon since the ice will be formed
within the air bubbles so no additional
stress will be created within the concrete.
The temperature of the fresh concrete mixture is one of the factors that affect the strength of the
hardening concrete. Figure 4 below shows the recommended concrete temperature under several conditions.
In order to obtain the desired temperature of fresh concrete it is practical to heat the water used in the
mixture. The fresh concrete should be placed in forms before getting to a temperature lower than the values
shown in the table below (Figure 4).
The maximum allowable temperature drop for the cast-in-place concrete during the first 24 hours is given in
figure 5 below.
Figure 4: Recommended Concrete Temperature for cold-weather construction – Air-entrained concrete
Figure 5: Maximum allowable temperature drop during the first 24 hours after end of protection, at surface
In order to maintain the temperature of the newly poured concrete and eliminate the cracks produced
under the effect of large temperature difference several methods can be used:
1) Enclosures: heated enclosures are considered to be the most effective way for protecting concrete from
cold weather but it is at the same time the most expensive method. Enclosures can be made of several
materials such as wood, canvas or polyethylene film.
Figure 6: Polyethylene Plastic Sheets

3. 08/01/2015
References available upon request
2) Insulating materials: Insulating materials such as commercial insulating blankets made of fiber glass,
sponge rubber or batt insulation. Their effectiveness can be measured by placing a thermometer between
the insulating material and the concrete surface. Several layers can be used in order to obtain the desired
temperature. Figures 7 and 8 below show some examples of insulating materials.
3) Heaters: there are three types of heaters that can be used:
A) Direct- fired heater which is not recommended because it supplies hot air directly with CO2 which
produce a weak layer at the concrete surface
B) Indirect-fired heater which removes the product of the combustion and supply clean heated air
C) Hydronic system which transmits heat through glycol water solution circulating in a closed system of
pipes. This technique can be used to defrost the soil or to heat the forms when pouring the fresh
concrete.
Pouring concrete can be made under several weather conditions as long as a suitable procedure will be
followed to isolate the fresh concrete from the factors that affect its strength and threaten its durability and
serviceability.
Sally Al Alam
Civil Engineer
Figure 7: Insulating Concrete Forms Figure 8: Stack of insulting blankets