What precautions do I have to take during cold-weather concreting?
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.
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Question and answer courtesy of Portland Cement Association (PCA). More information is available at: http://www.cement.org/tech/cct_faqs.asp.