We all know that when the weather turns cold we want to wrap up warm and we may need more energy to keep going. The same goes for concrete, it is affected by changes in the ambient environment as well as its own temperature, which could have major effects on performance and strength.
If the core temperature of concrete is at 0°C or below, the water within the mix freezes. When water freezes it expands by an extra 10%, creating pressure that can cause cracking. This in turn could mean it’s no longer suitable for the job and have to be removed, which is time consuming and expensive! It is therefore strongly advised that concrete should not be laid until the temperature has risen above 2°C.
Equally, expanding ice will push aggregates and other materials apart, meaning the bonds between them will be weakened. Only a partial reaction will take place between the cement and the water and this also weakens the concrete.
Have no fear, we can tackle the winter weather once the ambient temperature is sufficient for pouring.
- We can use heated mixing water, below 80 degrees. This will keep the concrete mix warmer for longer during the initial setting stage, and reduce the likelihood of freezing.
- We can also keep the aggregates covered and dry before putting them into the mix, as the concrete mix would need additional energy to thaw them.
- If the aggregates have already frozen and this is too late, they can be blasted with hot air to melt the ice before use.
- When it comes to designing concrete specifically for lower temperatures it is best to use CEM I, rather than using an additive of GGBS or Fly Ash.
- Air entrainer can tackle ice freezing by creating spaces for the water to expand into.
There are a couple things that you can do too! One of them is to wrap your concrete up with a wool insulated blanket straight onto the concrete freshly placed. There are also alternatives such as polythene sheets, straw or other lightweight insulation materials, or to have heaters near to the slab.
If you need any further help deciding what kind of concrete you need in the winter months, give us a call on 0330 123 2065 and we can advise you further.