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Cold Weather Concrete Guide
Special care must be taken when placing concrete in cold weather, If early age concrete is allowed to cool below freezing point it can be damaged and rendered unfit for use. It should also be understood that even in cooler temperatures above freezing strength will develop at a much slower rate.
Using Concrete in Cold Weathers
When using concrete, two different temperatures should be taken into consideration. These are ambient air temperatures and actual concrete temperatures. It’s important not to confuse the two. If freshly placed concrete is exposed to temperatures of 0°C and declining, the water in the mix can freeze and expand, causing cracks and potential spalling. This would make the concrete useless and unsafe. Thermal blankets should be used to hold the concrete temperature above 5°C for a minimum of 24 hours, allowing the concrete to achieve a minimum strength of 2 N/mm². The severity of weather determines the procedures that need to be put in place. For the purposes of concrete placement, this can be divided into two separate categories.
Ambient temperatures below 5C but no frost
When the air temperature is low but does not drop below 0°C, there is no danger that the concrete can be permanently damaged; however, it will take more time to gain compressive strength. It’s important that formwork striking times are considered and not removed too early. It’s impossible to guess when formwork should be struck due to different cement contents, mixes, and ambient air temperatures. If needed, this process can be expedited by using higher cement content mix designs or with additions like accelerators to speed up the hydration process.
Frost Overnight and Daytime
Concrete must be 5°C or above. There will be occasions where the supplier cannot achieve this, and a decision must be made whereby the customer either takes responsibility for the concrete and its aftercare or cancels the concrete pour. Protection should include frost blankets, insulated formwork, or the erection of temporary covers, with ambient temperatures increased using space heaters. Prior to concrete placement, ensure that sub-bases, formwork, reinforcement, and placing equipment are free from ice and snow.
