Concrete placing and Finishing in Cold Weather
When deciding on placing concrete in a cold weather environment it can be done successfully but there are a few things you should should know and understand to have a long lasting concrete slab.
The negative impact of cold temperatures on concrete can be avoided if done correctly.
Newly, fresh and recently poured concrete slabs lose moisture and heat rapidly in cold weather conditions. It is important to keep concrete that has been placed in cold weather from early freezing to ensure the concrete develops its early strength while curing.
Cold weather concrete requires special planning. To achieve a long life from your concrete placed during cold weather the production of aggregates, proper design of the mix, adequate mixing and the transporting to the jobsite, as well as proper placing and finishing practices with special care in its protection must be followed.
Here are some ways that will help ensure your cold weather concreting will be a success:
* Planning
* Pre-placement
* Placement
* Post-placement
Planning
Have ready the proper equipment as well as manpower to be in place prior to the pour.
Have weather protection ready to help maintain a consistent working environment and to help the concrete maintain the proper temperature for its placement and finishing.
Consider using a lower slump concrete especially for flat work in cold weather this will reduce the setting time and cut bleed water since cold air retards the evaporation rate and setting time of the concrete.
Consider the use of concrete mixes that have accelerating admixtures or Type III Hi Early cement that will require a shorter protection time from freezing.
Consider using concrete mixes that contain flyash only if your project will be able to be protected from freezing for a longer period of time.
From your readymix company request a heated mix or you can order 100 pounds of extra cement in each cubic yard of concrete to help it develop early strength.
Pre-placement
Remove all of the snow and ice from the concrete forms and the sub-base before placing the concrete.
Make sure the sub-base temperature is not below 32° F and if it is heat up the sub-base with torches or other heating devices.
Placement
Make sure the minimum concrete temperature, is maintained or exceeds 55°F.
Don’t let the concretes temperature rise above 75° Fahrenheit.
Post-placement
Do not start the final finishing operations while the bleed water is present.
Make sure to properly finish the concrete with no extra water or excess bleed water worked into the surface and do not over-finish.
Don’t over work a cooled slab that shows delayed setting characteristics.
Make sure that the cold weather concrete has properly cured and don’t allow hardened concrete to dry out.
Keep ice from forming on the concrete – When ice has formed, hydration stops and the strength development is seriously impaired. Newly placed concrete that has frozen during the first 24 hours can lose up to 50% of its full 28 day cured strength!
You should maintain a temperature above 50° with insulation blankets or heated enclosures for three to seven days after the pour.
Use a high quality curing compound if you feel you will be unable to keep the concrete temperatures above 50° degrees F for the three days to a week time.
Maintain the concrete temperature above 40° degrees Fahrenheit for at least four more days after the use of the insulation blankets or heated enclosures.
Do not apply a sealer to freshly placed concrete in cold weather.
Remove the heat protection in a way that keeps the temperature of the concrete from dropping more than 40° F in the next 24 hours.
With these tips and advise Concrete can be successfully placed, finished, and cured to its proper strength in cold weather conditions. Just make sure proper planning and care is taken prior to and after the concrete has been placed.
Happy cold weather concreting.