Our national mandatory concrete standard CSA A23.1-2014 states that Cold Weather Concreting protection must be provided to ensure that the concrete materials do not fall below 10°C otherwise an abnormal set and problems can result (eg: delaminations). It is essential that the supporting granular base temperature is also at least 10°C to ensure that concrete materials are not reduced below this 10°C minimum temperature. Please note that recent testing has shown that concrete materials retain excess mix bleed water abnormally in cold temperatures. As such, it is critical that ambient and supporting temperatures are at least 10°C before placing concrete. Concrete mixes being supplied in air and granular base temperatures of less than 10°C will require a concrete mix review for cementitious material type (GU) and the use of non-chloride accelerators. Note that accelerators may change the colour of the concrete from that of conventional concrete (aesthetic concern).
Excerpt from CSA A23.1-2014:
“18.104.22.168 Cold Weather Concreting Job preparation:
When there is a probability of the air temperature falling below 5°C within 24 h of placing (as forecast by the nearest official meteorological office), all materials and equipment needed for adequate protection and curing shall be on hand and ready for use before concrete placement is started. If the temperature of the concrete is expected to drop below 5 °C then protection is required. All snow and ice shall be removed before concrete is deposited on any surface. Calcium chloride or other de-icing salts shall not be used as a de-icing agent in the forms. Concrete shall not be placed on or against any surface that will lower the temperature of the concrete in place below the minimum value shown in Table 14 or below 10 °C for slabs less than 1 m thick or 5 °C for slabs more than 1 m thick, except when non-chloride, non-corrosive accelerators are used (see also notes).”
Please see our 2014 Cold Temperature Study for more information on the difference between concrete construction in cold weather and in hot weather.