Concrete Work in Cold Weather: how to do it?

Are you planning a concrete project soon, but the temperatures are dropping? Do you have concrete to pour for the summer, but would like to get a head start before the warm season? If you are in such a situation and have questions about the use of concrete in cold weather, you are at the right place!!

Find out how concrete interacts with sub-normal temperatures, precautions to take, benefits of this practice and our expert advice.

How does concrete react to cold temperatures?

The reason why concrete is strongly affected by the ambient outdoors temperature is its water composition. Fresh concrete contains 15% to 18% of water. When the ambient temperature is too cold, or the objects on which the concrete rests are too cold, water in the concrete is likely to freeze. Freezing and thawing action in concrete can reduce its strength by 50%.

What are the temperatures (in Celsius degrees) to be respected?

According to CSA A23.1/.2, special measures must be taken when the ambient temperature is 5 ºC and below or when a drop below this value is expected within the next 24 hours.

Elements in contact with the freshly placed concrete (foundation materials, reinforcement, etc.) must be at an above freezing point temperature, i.e., about 2 °C. Obviously, all ice or snow must be removed.

Once the concrete is in place, it is essential to keep it at a temperature above 10 °C for a period of three to seven days. It is this important period of a few days that allows the concrete to gain enough strength to resist the cold afterwards.

What is the setting time of concrete in cold weather?

A temperature drop increases concrete setting time. Here is a table created by l’Association béton Québec (ABQ) (Quebec Concrete Association) to illustrate variations in setting times according to the ambient temperature.

Preventive Measures for using concrete in Cold Weather

It is important to note that all elements related to the protection of concrete (special measures and equipment) must be present from the first hours of the process (when the concrete is most vulnerable).

Use of Entrained Air

This technique, recommended for cold weather concreting, consists of inserting air bubbles into the concrete mix. This protects it from freezing-thawing by reducing the amount of water in the mix by 5% to 15%.

Use of Set Accelerating Admixtures

Concrete admixtures are highly recommended for use in cold weather. They help concrete reach full strength more quickly, but do not prevent the concrete from freezing. It is important to follow all preventive measures even when using set accelerating admixtures.

Protective and Heating Equipment

Equipment frequently used on construction sites, such as portable heaters, insulated forms, covers, shelters and screens are effective in protecting concrete during cold weather.

Safety precautions associated with these types of equipment must always be followed. Failure to exercise caution could lead to overheating of concrete, fire or carbon monoxide poisoning.

Increase in Formwork Time

Since cold temperatures increase the setting time and attainment of full strength of the concrete, the formwork must be held in place longer.

Pros of Concreting in Cold Weather

Although cold weather concreting requires more care and planning, it also has benefits.

Availability of Building Contractors

Cold weather is often the least busy time of the year for many contractors. This can make it easier for you to find the contractor that best suits your needs. This increased availability also has a positive impact on meeting deadlines.

Suppliers generally have more materials during these periods and stock-outs are less frequent.

More Free Time for Summer Vacations

Doing your work during the colder periods (fall, winter and spring) gives you more time to enjoy the summer! Ask your building contractor if the work you need to do in the summer can be done in cold weather and make sure you follow all preventive measures.

Expert Advice for Concreting in Cold Weather

Now that you know the rules and benefits of cold weather concreting, let’s zoom through a few more expert tips on the subject:

• Avoid concreting altogether when the temperature reaches -18 °C. Under these extreme conditions, concrete will not be able to set.
• Schedule a meeting with your building contractor to discuss the concrete protection measures that will be put in place. This is important to ensure that the work goes smoothly.
• Remember to remove any snow or ice that may come in contact with the formwork, concrete or surfaces touching the concrete.
• Keep a close eye on the concrete when it is heated. It should not be overheated, as concrete that dries too quickly is less resistant.
• When concrete is kept hot and the difference with the ambient temperature is high, it must be cooled slowly. Too much thermal shock can damage it.

Can my house foundation be poured in winter?

This is a question we regularly receive! Should all the rules of concreting in cold weather be respected, a house built in winter will be of as good quality as a house built in summer.

For example, it is important to insulate the house’s formwork during construction. To achieve this, it is recommended to use insulating blankets, a concrete mix adapted to cold temperatures and an accelerating admixture.

You have a house to build? Here’s everything you need to know about house foundations!

Contact Our Experts

Groupe Bellemare has been working in the concrete industry for over 50 years. With this expertise, we are able to answer all your questions regarding your small and large projects.

For more information, talk to one of our experts or consult the ABQ official document (French only) on concrete work in cold weather.