Pouring concrete in the cold weather can cause severe complications, and if you haven’t taken the necessary precautions then you could end up with concrete that is unusable.
As the winter draws ever nearer, it pays to be aware of the effects that colder temperatures have on concrete. This month, we’re taking a look at the things you should consider when tackling a concrete pour in the cold, so you can give your project the best possible chance of success.
How the cold affects concrete
The main danger of pouring concrete in the cold is the chance of the concrete freezing before it sets. If this were to happen, the concrete would lose strength, likely becoming unfit for its purpose. Once the concrete has set to a certain strength, it will be able to resist the effects of freezing, no longer being malleable enough to be influenced by the expansion of freezing water.
As with every concrete pour the strength of the mix should be suited to the needs of your project, and if this is reduced in any way then what you will end up with is weak concrete which is prone to cracking and collapse. This can be dangerous, as well as time consuming and costly to repair. Whether it’s decorative concrete like a garden patio, or load bearing concrete for beams or walls, you should take precautions to ensure that the cold temperature doesn’t impede on the integrity of your pour.
Before the pour
For concrete, the ambient temperature should be over 5ºC. At this temperature the concrete will be able to set without freezing, though it will take longer to reach its proper strength. If you’re expecting the temperature to be 5ºC or lower at the time of delivery and the pour itself, you will need to take measures to keep it warm.
It’s wise to prepare the pour site well in advance of delivery, and this is especially true in the winter. Take the time to insulate your formwork. Frost blankets will help prevent the subgrade from freezing, so your concrete won’t end up cracking once the subgrade has thawed. You can also use frost blankets once the pour is complete, to help keep the heat in the concrete as it sets.
You might also need to use a space heater for interior projects. This will keep the pour site heated, maintaining an acceptable air temperature before delivery, during and after the pour.
If you’ve kept the pour site insulated in preparation of the concrete, you should look to pour the concrete as soon as possible. This is common practice, usually to avoid premature setting of the mix. In the cold, pouring it quickly after delivery means the mix won’t naturally lose more heat than expected, helping it maintain a comfortable temperature for longer.
You should never pour concrete on frozen ground. If the pour site has frozen in advance of delivery, make sure it is properly thawed and brought to an acceptable temperature before pouring your concrete. This may mean delaying the pour until the temperatures have risen, but this is definitely preferable to dealing with weak, damaged and unworkable concrete later on.
After the pour
Once the concrete is in place, the period directly after the pour becomes critical. As we’ve said, at around 5ºC, the concrete will take longer to set to a suitable strength. This makes it more important to keep the ambient temperature warm, and not let it drop close to freezing. There will be more chance for the mix to freeze the longer it takes to set, so preventing this is paramount.
For the following two days after the pour, closely monitor the ambient temperature and keep the concrete covered with a frost blanket. The concrete will develop its strength during this time, so keeping it warm gives it the best opportunity to do so unimpeded. Fresh concrete which has frozen during this time will lose significant strength, rendering the pour a failure, so keep exposed surfaces covered and insulated where necessary.
The curing process is the final step in the concrete’s strength development. You should try to maintain a warm temperature without the concrete drying too rapidly. It’s wise to leave insulated forms in place for as long as possible, and make use of insulated sheets which help keep the concrete at an optimal temperature so as to prevent freezing.
EKA Concrete are experienced suppliers of high quality concrete for domestic and commercial customers throughout the South and South East of England. Our highly skilled and knowledgeable team can help you find the perfect mix for your project, no matter the size or scale, and will advise you on pouring techniques in extreme conditions. For more information on all of our services, don’t hesitate to get in touch today.