section_path: Construction with concrete/Placement/Cold weather placement
section_name: Cold weather placement
paragraph_text: Cold weather placement
  
  Extreme weather conditions (extreme heat or cold; windy conditions, and humidity variations) can significantly alter the quality of concrete. Many precautions are observed in cold weather placement. Low temperatures significantly slow the chemical reactions involved in hydration of cement, thus affecting the strength development. Preventing freezing is the most important precaution, as formation of ice crystals can cause damage to the crystalline structure of the hydrated cement paste. If the surface of the concrete pour is insulated from the outside temperatures, the heat of hydration will prevent freezing.
  
  The American Concrete Institute (ACI) definition of cold weather placement, ACI 306, is:
  
  In Canada, where temperatures tend to be much lower during the cold season, the following criteria are used by CSA A23.1:
  
  The minimum strength before exposing concrete to extreme cold is 500 psi (3.4 MPa). CSA A 23.1 specified a compressive strength of 7.0 MPa to be considered safe for exposure to freezing.