Nature has her own charms and curses. We have seasons like Spring, summer, autumn, winter, monsoon etc. All season has different humidity, temperature, day hours etc. If you want to work in such varying whether you have to take precautions. Here we are going to describe the cold weather concreting. The knowledge about cold weather concreting is most essential where the climate is cold in countries like America, Russia, Canada, etc. and in India in the Himalayan regions. The concreting procedure in cold weather is different and difficult than in warmer weather.
By the word concreting itself, you can understand that, it is the procedure of concrete batching, mixing, transporting, placing, compacting and finishing etc. and which is the most essential procedure for the each and every construction. The particular procedure such as batching of concrete, mixing of concrete, transportation of concrete, placing of concrete, are already described in our previous articles.
What Temperature is too Cold for Concreting?
According to “The American Concrete Institute under ACI 306R- 16”, The conditions of cold weather concreting exist when the air temperature has fallen to or is expected to fall below, 40°F (4°C) during the protection period. The protection period is defined as the amount of time recommended to prevent concrete from being adversely affected by exposure to cold weather during construction.
Cold Weather Concreting Image
How the Low Temperature Can Affect the Concrete?
As one knows concrete gets transformed from semiliquid to a solid or plastic state to hardened state due to a chemical reaction known as hydration. The rate of hydration depends on the temperature. When temperature increases the rate of hydration increases and when temperature decreases the rate of hydration also decreases. If hydration is low then the process of transforming from semiliquid to a solid is delayed and it affects the quality of concrete as well as the economy of construction. Thus, this is essential that the temperature is maintained during the placing of concrete and it should be above 4°C or 40°F. Cold weather can have a detrimental effect on concrete for various reasons.
Also Read: Do’s & Don’ts While Concreting
Effects of Cold Weather on Concrete
(a) Delay in Setting and Hardening of Concrete
The setting of concrete is a stage in which concrete gets stiff to acquire the shape and hardening of concrete is a stage of development of strength and after which concrete can carry the intended loads. Both depend on the rate of hydration and the rate of hydration depends upon the temperature. If the temperature is low, concrete takes a long time to set as well as longer time to harden. The delay in setting time makes concrete vulnerable to frost attack and other disruptions and delay in the hardening period does not allow removal of formwork in a short time period. Due to this rate of work progress will be very slow and overall it affects the economy.
(b) Freezing of Concrete at an Early Age
Freezing of concrete is the development of solid water i.e. ice within the paste that disrupts the paste, causing frost lenses to develop in the paste.
In the fresh concrete, pores are filled with water. When the temperature goes below freezing point, the free water contained in the plastic concrete freezes. When water freezes to ice it occupies almost 9% more volume than the water. Freezing of water also prevents the hydration of cement and also makes the concrete expand. This expansion causes deterioration of concrete.
(c) Repeated Freezing and Thawing of Concrete
Climatic condition varies in the cold weather regions due to which fresh concrete or hardened concrete gets exposed to freezing and thawing cycles and will continue throughout successive winter seasons resulting in repeated loss of concrete surface and other qualities. Due to this durability of concrete gets greatly impaired. Freezing and thawing may also exert fatigue in the concrete.
Freezing and Thawing Effect Image
(c) Stresses Due to Temperature Differentials
In the cold weather, large temperature differentials are likely to occur at the time of removal of form insulations. Such temperature differentials within the concrete member may promote cracking and have a harmful effect on the durability.
Also Read: How to Avoid Cracks in Concrete?
Points to be Remember While Cold Weather Concreting
General precautions and recommendations are given below which may help you in the cold weather concreting:
01. Pre-Preparation of Cold Weather Concreting
- Prior preparation of the concreting and as precautions for cold weather concreting work strategies shall be completed well in advance such as windbreakers shall be erected to protect the mixing and batching plant, materials, forms, plastic sheets and other covering and insulating materials shall be made available at the site.
- Well-defined temperature record chart including concrete temperature and exterior temperature should be kept on site.
- Before placing of concrete, all frozen material like ice, snow, and frost should be cleaned from the ground and never place concrete over frozen subgrade or on something that contains frozen materials.
- Freshly excavated earth should be covered with insulated blankets to preserve the natural warmth of the subsoil and don’t remove the blankets until you begin to pour the concrete.
02. Ingredients Used for Cold Weather Concrete
- Concrete in cold weather is recommended to have a low slump, and nominal water-cement ratio, to reduce bleeding and decreases setting time. Low-slump concrete minimizes bleeding. Don’t seal freshly placed concrete until it has bleed and the setting process has begun.
- Air entraining admixtures can also be used in cold weather concrete and it should have the correct amount of air entrained voids that will resist freezing and thawing effects.
- Accelerating admixtures may also help to reduce the effect of freezing and thawing.
- High-early-strength cement can also be used.
- When there is no other option, adding cement to the mix will help not much but to a certain level for maintaining the concrete temperature.
03. Concrete Covering Material
- During cold weather, surfaces of all concrete should be covered to preserve the heat and to help freezing prevention. You can use concrete covering material such as expanded polystyrene, plastic sheets, and waterproof paper etc.
- Heated enclosures or insulation blankets are commonly used for protecting concrete when air temperatures are near or below freezing and be sure that enclosures or insulation blankets must be windproof and weatherproof.
- Enclosures may be heated by steam, steam pipes and other types of heaters and it may be made of wood, canvas, fiber insulation board, plywood etc.
Also Read: Plywood: All You Would Like to Know!
- Insulating material should be placed against any formwork before concreting and the same can be used as protection after the formwork has been stripped.
- Forms should not be released until the concrete has achieved the strength of at least twice the stress to which the concrete may be subjected at the time of removal of formwork.
05. Cold Weather Concrete Curing
- In cold weather concrete curing, water curing is not necessary because of the loss of moisture from the concrete by evaporation is greatly reduced in cold air conditions.
- You can use concrete curing blankets in cold weather concrete curing to prevent freezing and keep the concrete at an optimum curing temperature.
Curing Blanket Image
06. Inspection During Cold Weather Concreting
- During cold weather concreting, keep some personnel inspection data such as a record of the date, time, outside air temperature, a temperature of concrete at the time of placing and general weather (calm, windy, clear, cloudy, etc.).
This knowledge is helpful and essential to homeowners and businesses who hire concrete contractors and deal with such kind of weather condition. Because, In the cold weather concreting, concrete will develop sufficient strength and durability to satisfy the proposed service recommendations only when it is properly proportioned, produced, placed, and protected. Thus, it’s essential to increase the degree of protection as the ambient temperature decreases.