Precautions for Cold-Weather Concrete

Cold weather in concrete construction is defined as a period when the average daily temperature falls below 40 F [4 C] for more than three successive days. In Oklahoma we not only can have these conditions but also dramatic weather changes that can adversely affect concrete and concrete finishing.

Since weather conditions can change rapidly in the winter months, good concrete practices and proper planning are critical. Cold weather just as hot weather can affect concrete properties and the finshed product.

In Its plastic state, concrete will freeze if the material temperature falls below 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 [3.5MPa], which is about two days after placement for most concrete maintained at 50 F [10C].

Lower tempertures have a dramatic affect on set times and the strength gain. A good rule of thumb is that a drop in concrete temperture by 20 F [10 C] will approximately double the setting time. contractors should allow for the slower rate of setting and strength gain when scheduling construction operations, such as form removal.

Exterior concrete should always be air-entrained, but expecially during cold weather placement. But even air-entrained concrete that is placed during cold weather should be protected from cycles of freezing and thawing until has attained a compressive strength of at least 3500psi [24.0 MPa].

Even when precautions are made to protect concrete in cold weather, it should be noted that large temperture 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]. Insulation or protective measures should be gradually removed to avoid thermal stock.

There is lots of information available to those placing concrete in Cold Weather and our firm would be happy to provide you or assist you on any projects to be placed during the winter months in Oklahoma.

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 temperture 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.