Cold Weather Working

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 with 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.

The problem

If the core temperature of concrete is at 0’C or below, the water within the mix will freeze. 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 at hand and have to be removed, which is a long, time consuming and expensive job! It is therefore strongly advised 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 less strong. Only a partial reaction will take place between the cement and the water, so this also weakens the concrete.

Our job

Have no fear, we can tackle the wintery 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 alone, 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.

Your job

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 with the winter drawing in, give us a call on 0330 123 2065 and we can advise you further.