The temperature is dropping, the days start to get shorter, and frost covers the ground. While the cold weather may be exciting to imagine a festive winter season, that is not what comes to mind when working in the construction industry. Especially, when you have a project to complete, a schedule to maintain, and a desired concrete temperature and strength to achieve; the pressure is on when dealing with factors like freezing of concrete at an early age, rapid temperature changes, all while trying to meet the required strength.
The American Concrete Institute (ACI), as stated in ACI 306 defines cold weather concreting is,
“a period when for more than three successive days the average daily air temperature drops below 40 degrees Fahrenheit (4.5 ℃) and stays below 50 degrees Fahrenheit (10 ℃) for more than one-half of any 24-hour period.”
In simpler words, cold-weather concreting is the process of placement, finishing, curing, and protection of concrete during winter as per ACI 306. This definition mainly addresses the problems with freezing of concrete at an early age.
How To Protect Concrete during Winter?
Protection itself here is a broad term. It is one of the major challenges commonly faced in cold-weather concreting. When proper steps are taken during concrete production to its placement and protecting in cold weather, it will enable the development of sufficient strength. This will therefore increase durability to satisfy the intended service requirements as prescribed by ACI.
During cold-weather conditions, the temperature can be extremely low, let’s say around -40℉ (-40℃), which could affect the hydration process and result in slowing down the hydration reaction affecting the strength growth. Notably, when the concrete is in the plastic state, the freezing temperature within the first 24 hours can reduce the strength by more than 50%.
Some common protection steps:
- Removal of Snow and Ice
- Heating of Water and/or Aggregates
- Warming up of formwork before concrete placement
- Protection in the forms of heated enclosures, coverings, and insulations.
- Controlled temperature gradient
- Avoiding Wet Curing
- Reshoring if necessary
- Protection against contact with salts
Source: Giatec.
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