- Cold Weather Concreting

- Cold Weather Concreting

WHAT is Cold Weather?
HOW to Place Concrete in Cold Weather?
Figure 1 Effect of Temperature on Set Time (1a)
Cold weather is defined as a period when the average daily
temperature falls below 40°F [4°C] for more than three successive
days. These conditions warrant special precautions
when placing, finishing, curing and protecting concrete against
the effects of cold weather. Since weather conditions can
change rapidly in the winter months, good concrete practices
and proper planning are critical.


WHY Consider Cold Weather?

Successful cold-weather concreting requires an understanding
of the various factors that affect concrete properties.
In its plastic state, concrete will freeze if its temperature falls
below about 25°F [-4°C]. If plastic concrete freezes, its potential
strength can be reduced by more than 50% and its durability
will be adversely affected. Concrete should be protected
from freezing until it attains a minimum compressive
strength of 500 psi [3.5 MPa], which is about two days after
placement for most concrete maintained at 50°F [10°C].
Low concrete temperature has a major effect on the rate of
cement hydration, which results in slower setting and rate
of strength gain. A good rule of thumb is that a drop in concrete
temperature by 20°F [10°C] will approximately double
the setting time. The slower rate of setting and strength gain
should be accounted for when scheduling construction operations,
such as form removal.
Concrete in contact with water and exposed to cycles of
freezing and thawing, even if only during construction,
should be air-entrained. Newly placed concrete is saturated
with water and should be protected from cycles of freezing
and thawing until it has attained a compressive strength of
at least 3500 psi [24.0 MPa].
Cement hydration is a chemical reaction that generates heat.
Newly placed concrete should be adequately insulated to retain
this heat and thereby maintain favorable curing temperatures.
Large temperature differences between the surface and
the interior of the concrete mass should be prevented as cracking
may result when this difference exceeds about 35°F [20°C].
Insulation or protective measures should be gradually removed
to avoid thermal shock.


Cold Weather Concreting Guidelines
1. Use air-entrained concrete when exposure to moisture and freezing and thawing conditions are expected.
2. Keep surfaces in contact with concrete free of ice and snow and at a temperature above freezing prior
to placement.
3. Place and maintain concrete at the recommended temperature.
4. Place concrete at the lowest practical slump.
5. Protect plastic concrete from freezing or drying.
6. Protect concrete from early-age freezing and thawing cycles until it has attained adequate strength.
7. Limit rapid temperature changes when protective measures are removed.