Cold weather concreting-Practices and Principles
Concrete can be implemented in cold weather or during the winter, but it requires an understanding of the impact of cold weather on the process of creating long-lasting concrete. Hereafter are important recommended practices and basic principles for cold weather concreting.
Planning for concrete placing
Prior to the pour, clearly define the cold weather concreting methods that will be used. A pre-placement meeting with the contractor, specifier, producer, laboratory and other interested parties is highly recommended.
Pre-placement
Remove all snow and ice from all concrete forms and the subbase before placing the concrete.
Check the temperature of, and heat up if necessary, the subbase and any other surfaces that come in contact with the concrete to ensure they are not below 32° Fahrenheit.
Concrete Curing and Protection
Where a specified concrete strength must be attained in a few days or weeks, protection at temperatures above 10°C (50°F) is required.
Temperature Records
Temperature of the concrete determines the effectiveness of protection, regardless of air temperature. Maintaining temperature records of concrete in place is essential.
Heated Enclosures
Must be strong enough to be windproof and weatherproof. Combustion heaters must be vented to the outside to prevent carbonation.
Exposure to Freezing and Thawing
Concrete should be properly air entrained if it will be saturated and exposed to freezing and thawing cycles during construction.
Slump
All else being equal, lower slump and/or lower water/cement ratio mixes are particularly desirable in cold weather for flatwork. This reduces bleeding and decreases setting time.
Truck Travel Time
The distance from the plant to the point of placement can have a severe effect on the temperature of concrete.
Hot Water
While hot water improves setting time of cold weather concrete, after the first few batches of concrete hot water heaters may not be able to maintain hot water temperature. Later in the pour, concrete may be cooler than at the beginning of the pour.
Temperatures for Placement and Protection in Concrete Weather
ACI 306 provides recommended temperatures for placement and protection of concrete.
Additional Accelerator Toward the End of the Pour
Adding more accelerating admixture at the end of the pour will offset the effects of cooler mixing water and provide a more consistent set. Another reason to add more accelerating admixture as the pour progresses is to speed up the setting of the latter mixes and have all the concrete in the pour reach set at about the same time in order to facilitate the finishing operation.
Concrete can be placed, finished, and cured to its proper strength in cold weather conditions if sufficient planning and care are taken. Following the above practices and principles will ensure your cold weather concrete project is implemented successfully.
PRE-PLACEMENT
- Remove all snow and ice from all concrete forms and the subbase before placing the concrete.
- Check the temperature of, and heat up if necessary, the subbase and any other surfaces that come in contact with the concrete to ensure they are not below 32° Fahrenheit.