This article will answer the above questions.
It’s better to avoid concreting in cold weather. But, for our tight project schedule, it’s often not possible to avoid cold weather concreting.
On large commercial projects we can use expensive heated enclosures to protect concrete from cold weathering damage.
But, on many residential projects it can’t be possible to use such expensive protections. So we’ll use some alternate ways to protect our concrete from cold weathering affects.
What is cold weather for concreting?
First we need to know what is cold weather for concreting.
When the average daily temperature drops below 5°C (40°F) for more than three consecutive days and stays below 10°C (50°F) for more than one-half of any 24 hour period then that period is defined as cold weather for concreting. – [Reference: ACI 306]
Affects of cold weather on concreting:
Cold weather mostly affects the freshly placed concrete. Following are the affects of cold weather on concreting –
Cold weather increases the setting time of concrete.
It reduces the rate of strength gain of concrete.
In this situation, concrete can be freezed during first few days of curing.
Early freezing can reduce up to 50% ultimate strength of concrete.
As a result, concrete will loss its strength and weather resistance capability and thus it will loss its durability as well as the quality of structure.
The purpose of precaution is to protect concrete from freezing untill it has gained its minimum strength of 3.5 MPa (500 psi). This strength gain typically happens within first 24 hours.
Following actions can be taken to protect concrete from cold weathering affects –
- Reduce the water content in concrete mix. That means, the slump of concrete should be less than 100 mm for slab and other flatworks.
- Add air-entraining admixture to concrete mix. You can use air-entraining cement (See Types of cement).
- Using windbreaks to protect concrete from cold winds. Because, cold winds cause for temperature drops and excessive evaporation from concrete.
- During hydration process of cement, it produces heat on its own. Protect that heat from escaping by using polythene sheets.
- If you mix concrete with mixture machine at site then store concrete ingredients somewhere in hot place.
- If you order concrete from ready-mix plant then give them instruction to control concrete temperature.
- Place concrete as early as possible after mixing to reduce heat loss.
- Increase cement content in concrete mix or use high early strength cement (see: Types of Cement).
- Do not strip concrete-form as long as possible to reduce evaporation.
If it’s not possible to avoid cold weather concreting, yet we shouldn’t sacrifice our concrete quality. So, take essential precautions to protect concrete from cold weather affects.
Have you ever concreted during cold weather?
How did you protect then?