Frequently Asked Questions
Cement & Concrete
Technology Home > FAQs > Cold-Weather Concreting.
Q: What precautions do I have to take during cold-weather
concreting?
I am a contractor involved with a variety of concrete projects including commercial
buildings, residential foundations and flatwork, as well as pavement
and curb and gutter. The projects are located in a northern climate.
I must ensure that provisions taken for cold weather conditions
follow acceptable industry practice to assure a quality finished
product. When should I be concerned about cold weather placement
conditions and what practices should be used to achieve quality
results?
A: Cold weather concreting is a common
and necessary practice, and every cold weather application must
be considered carefully to accommodate its unique requirements.
The current American Concrete Institute definition of cold-weather
concreting, as stated in ACI 306 is, “a period when for more than
3 successive days the average daily air temperature drops below
5°C (40°F) and stays below 10°C (50°F) for more than one-half of
any 24 hour period.” This definition can potentially lead to problems
with freezing at early age of the concrete.
 Rule
number ONE is that ALL concrete must be protected from freezing
until it has reached a minimum strength of 3.5 MPa (500 psi), which typically happens
within the first 24 hours. In addition, whenever air temperature
at the time of concrete placement is below 5°C (40°F) and freezing
temperatures within the first 24 hours after placement are expected,
the following general issues should be considered:
(1) Adjustment of construction schedule regarding loads imposed
on the new concrete structure.
(2) Placing and curing temperatures to produce quality concrete.
The exposure of concrete to cold weather will extend the time required
for it to gain strength. In structures that will carry large loads
at an early age, concrete must be maintained at a minimum of 10°C
(50°F) to accommodate stripping of forms and shoring and to permit
loading of the structure. In many cases, achieving the required
durability will require a protection period of more than 24 hours.
This may not be an issue with residential applications where applied
loads are typically small and may be applied in small increments
over several days or weeks.
In no case should concrete be allowed to freeze during the first
24 hours after it has been placed. Since cement hydration is an
exothermic reaction, the concrete mixture produces some heat on
its own. Protecting that heat from escaping the system may be all
that is required for good concrete quality, while more severe temperatures
may require supplemental heat.
More information is available from the following references:
1) ACI Committee 306, Cold-Weather
Concreting, ACI 306-88, reapproved
2002, American Concrete Institute, 2002, 23 pages.
2) Cold-Weather
Concreting, IS154, reprinted from Chapter 14 of Design
and Control of Concrete Mixtures, EB001.14, Portland Cement Association,
2002, 20 pages.
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