If you’re planning to build a new construction building or remodel the structure, then you might be concerned about the concrete’s curing process as it can become more challenging in cold weather.
Adding concrete additives in concrete can help enhance its properties and performance and help slow down or accelerate its curing process, but pouring concrete at lower temperatures can result in a much slower hardening or setting time and higher chances of cracking due to the formation of ice crystals.
In this article, you’ll learn about the different types of concrete additives and their purpose to help you decide which ones are best used during cold weather.
What is a Concrete Additive and its Purpose?
Concrete admixtures, also known as concrete additives, are natural or artificial materials added during the concrete mixing, along with cement, aggregates, and water, to enhance the properties of the fresh or hardened state of concrete.
The specific concrete properties include durability, workability, permeability, strength, dispersion, air entrainment, rate of hydration, and setting time. They are commonly added during the placing, laying, or casting stage.
Concrete admixtures are also used to improve the concrete’s behavior in various conditions, accelerate the initial set of concrete, speed up the rate of concrete’s strength at early stages, reduce the heat of evaluation, enhance the resistance to freezing/thawing, and control the expansion of concrete.
They are also used to change the speed for bleedings, ensure a good quality of concrete in less-than-ideal conditions, and fix emergencies during the concrete process.
The effectiveness of concrete admixtures may depend on different factors, including the quality and ratio of materials, mixing and curing time, concrete and ambient temperatures.
Types of Concrete Admixtures or Additives
Concrete admixtures are divided into two main types: Chemical Admixtures and Mineral Admixtures.
Chemical admixtures are used to reduce the cost of construction, guarantee a good quality of concrete during mixing, placing, curing, and transporting, and overcome concrete operation emergencies.
They are available in six main categories, including air-entraining admixtures, water-reducing admixtures, retarding admixtures, accelerating admixtures, plasticizers or superplasticizers, and specialty admixtures.
Air entraining admixtures increase the concrete’s durability under thawing and freezing conditions by forming non-coalescent air bubbles when added to the concrete mixture. The bubbles act as a buffer or barrier against cracking caused by freezing temperatures.
Air entraining mixtures will also enhance the workability of the concrete, reduce the unit weight, prevent bleeding and segregation, and improve the concrete’s resistance to freeze o thaw cycles. Other benefits of using this type of chemical admixture are high resistance to drying and wetting cycles and higher durability.
Water-reducing admixtures are used to reduce the required amount of water by about 5 to 10 percent for the concrete mixture to create a desired lump. Using this type of mixture on concrete will increase the strength without putting too much cement, and water, meaning the concrete will have lower water to cement ratio
Retarding admixtures, also known as retarders, are used to slow down the chemical reaction called cement hydration that happens during the initial stage or setting process of concrete. They are used to decrease the effects of the accelerating hardening effect of high temperatures and enhance the resistance to cracking, which can make finishing more difficult.
This type of chemical admixture is commonly used in high-temperature areas where concrete sets or hardens more quickly.
Accelerating admixtures, also called accelerators, are used to speed up the early hydration or the process of hardening concrete and reduce the initial time for curing. They are also used to improve the concrete’s strength and modify its properties.
This type of admixture is most efficient to use in cold weather because the curing process of the concrete takes much longer in lower temperatures.
Superplasticizers are also called plasticizers or high-range water reducers (HRWR), which are chemical admixtures used to reduce the amount of water by about 12 to 30 percent. They are added to the concrete mixture with a low-to-normal slump or low water to cement ratio to create highly fluid and workable concrete.
The effect of superplasticizers can only last about 30 to 60 minutes, depending on the dosage rate and brand of admixture. After that time, the workability of the concrete decreases. That’s why they are recommended to use at the job site.
One example of a specialty admixture is a corrosion-inhibiting admixture, which is a concrete admixture that helps slow down the rate of corrosion of steel in concrete. It is used when there are chloride salts present, which can result in rust in steel reinforcements.
Corrosion inhibitors are commonly used in concrete structures exposed to high concentrations of chloride, such as parking garages, marine facilities, and highway bridges.
Other examples of specialty admixtures are alkali-silica reactivity inhibitors and shrinkage-reducing admixtures.
Mineral Admixtures are used or added to increase the workability and strength of fresh concrete, enhance the resistance to thermal cracking, reduce the level of permeability and alkali-aggregate expansion, and reduce the amount of cement in the mixture.
Popular mineral admixtures are Fly ash, Silica fume, and Ground granulated blast furnace slag (GGBFS).
Fly Ash is a fine powder that is a byproduct of coal-burning power plants and is added to reduce the slump loss under hot weather conditions and replace the portions of cement in the concrete mixture. Replacing the cement by using fly ash helps reduce the rise of temperature, which helps avoid cracking.
Adding fly ash to the concrete mixture can also increase the setting time of hardening and reduce the bleeding and segregation of concrete.
Silica Fume is a powder of amorphous silica that is a byproduct of silicon metal or other silicon metal production. It is used to replace cement of about 5 to 10 %, which can help increase the concrete’s strength and reduce its permeability.
But adding too much silica fume to the concrete can cause plastic shrinkage, which can cause cracking, so it’s best to add this type of mineral admixture moderately.
Ground granulated blast furnace slag (GGBFS) can be used to replace cement to the concrete mix of about 30 to 70%. Adding GGBFS improves the workability and strength of the concrete. It also increases the setting time, sulfate resistance and helps reduce permeability and temperature rise during the curing process.
So, What is the Best Concrete Additive for Cold Weather?
Since cold weather can result in a slower curing process and weaker concrete, adding concrete additives or admixtures will help improve the workability, durability, and strength of the concrete at lower temperatures.
The best additives you can use when cold weather is present are air-entraining admixtures, accelerators, and superplasticizers.
Air entraining admixtures improve the resistance of concrete to damages caused by freezing and thawing. Accelerating admixtures or accelerators speed up the curing process and hardening time of the concrete by increasing the hydration rate.
Superplasticizers reduce the amount of water needed in the concrete mixture, which can lessen the formation of ice crystals during the curing process.