When fresh concrete is exposed to freezing, the strength of the concrete is reduced by 20 to 40%. The properties of antifreeze admixtures in concrete, as well as their applications in cold weather concrete, are discussed. The durability factor, which is also reduced by 40 to 60%, determines the resistance of fresh concrete to the freeze-thaw cycle. The link between the reinforcement and the usually cured concrete is reduced by 70 percent. As a result, it is critical to guarantee that the concrete does not freeze in its plastic state while concreting in cold weather circumstances. Concrete Antifreeze Admixtures for Cold Weather Concreting Cold weather concreting can be accomplished in two ways:
Chemical admixtures are added to the mix
The concrete will be kept at normal atmospheric temperatures. This can be accomplished by heating the concrete materials or by constructing heating enclosures. Chemical admixtures are added to the mix.Chemical Admixtures Used in Cold-Weather Concrete Calcium chloride was employed as an accelerating additive in traditional concrete to compensate for the sluggish hydration of concrete at low temperatures. This admixture is ineffective at temperatures below freezing. In the traditional form of admixtures, this is proven to be a disadvantage. As a result, particular admixtures are required for arctic climatic conditions. Antifreeze admixtures are one example. Concrete Antifreeze Admixtures Antifreeze admixtures have an effect on the physical condition of the concrete mix water. These can significantly lower the freezing point of water.
There are two types of antifreeze admixtures that give antifreeze properties as well as faster setting and hardening. They are as follows: The first group includes: Chemicals, weak electrolytes, sodium nitrite, sodium chloride, and non-electrolytic organic substances that lower the freezing point of the concrete’s water are examples of this. However, these individuals operate as weak accelerators in the setting and hardening process. The Secondary Group Inset and ternary admixtures with potash and additions based on calcium chloride, sodium nitrite, calcium chloride with sodium nitrite, calcium nitrite-nitrate-urea, and other compounds are among them. These have antifreeze qualities as well as an accelerating property that helps the setting and hardening process. When compared to traditional admixtures, these are utilised in higher dosages.
Selection of Antifreeze admixtures
One example is the use of 8% sodium nitrite to maintain a temperature of -15 degrees Celsius in a liquid. These admixtures work by reducing the freezing point of the liquid phase and speeding up cement hydration at freezing conditions. The non-chloride additive, depending on the dose in the mix, allows the mix (concrete or mortar) to be laid at sub-freezing temperatures. As a result, the requirement for preventive measures during the cold weathering process is reduced. The approach increases the quality of the concrete and allows for early formwork stripping since it allows for early setting. This allows the form to be reused in a short period of time, speeding up the construction process. The significant difference is seen.
It is feasible to combine antifreeze admixtures with other admixtures that contain super plasticizers. The key benefit of such a combination is that it will save water in the long run. The freezable free water content in the mix will be reduced as a result of the water reduction. The heat released by the early hydration reactions is absorbed by this freezable water content, which acts as a heat sink. As a result, the number of antifreeze admixtures will be reduced. Antifreeze admixture selection The selection of antifreeze admixtures is dependent on the following factors: The structure’s kind The Operating Environment Methods of protection used during winter concreting Types of aggregates and cement brands It is necessary to do a laboratory test with the.
Antifreeze Admixtures: Their Use and Benefits
Other admixtures, such as retarders and superplasticizers, can be mixed with antifreeze admixtures in cold weather concrete. All of the admixture dosages must be determined by experimentation. Antifreeze admixtures are low-tech and useful for cold-weather concrete. Cohesiveness, cold joint minimization, sand streaking, and plasticity are all improved by the admixture. These are expected to save a significant amount of money over existing methods of steam curing or concrete enclosures. The use of antifreeze chemicals in conjunction with water decreasing or air-entraining agents will help to improve concrete’s resistance to frost and corrosion.
For example, if the concrete element is not susceptible to load or the atmosphere, the protection period is 2 days for normal-set concrete without any admixtures. For partially loaded and exposed conditions, however, it can take up to 6 days. Concrete may only develop appropriate and required strength and durability if it is correctly proportioned, put, and protected during cold weather. Concrete’s final compressive strength will be reduced by early thawing and freezing cycles. Admixtures are used during concrete mixing to improve the qualities and performance of fresh concrete to overcome these challenges during Cold Weather Concreting. Antifreeze admixtures are chemical substances added to concrete mixing water to lower the freezing point of the aqueous solution.
Problems in Cold Weather Concreting:
ACI specifies the minimum temperatures that must be maintained while mixing, pouring, and curing concrete. This is mostly determined by the stage of concreting, ambient temperature, and concrete element thickness. Because the temperature difference across depth is not considerable, thinner members require a higher level of control. ACI 306-R Concrete Temperatures for Cold Weather Concreting ACI 306-R Concrete Temperatures for Cold Weather Concreting Recommendations The Protection Period is also defined in the code, during which the recommended concrete temperature must be maintained. As previously stated, the duration of the protection time is determined by the service condition after concreting until the concrete reaches the necessary strength. The removal of formwork requires temperature management since the strength growth is different in cold weather.
To accelerate the hydration reaction, use warm water or heated aggregates. By boosting the cement content. Because the exothermic reaction of the concrete mixture generates heat during hydration, adding more cement will generate more heat.Using a cement with a high early strength. It has a high concentration of C3S and C3A, resulting in speedier setting. Type III Portland cement has a high early Portland content. By ensuring that sufficient insulation is in place, heat may be maintained in concrete. Blankets and boards are suitable for use. By making use of hot formwork. Heated formwork will prevent freezing since fresh concrete cannot connect with frozen concrete.
Chemical Composition of Antifreeze Admixture:
Antifreeze admixtures serve two purposes: they lower the freezing point of aqueous solutions and they speed up the setting and hardening of concrete in cold temperatures. Antifreeze admixtures are divided into two categories: Chemicals, weak electrolytes, sodium nitrite, sodium chloride, and non-electrolytic organic molecules make up the first group. Potash and additions based on calcium chloride, sodium nitrite, calcium chloride with sodium nitrite, calcium nitrite-nitrate-urea, and other compounds are included in the second group. The first group has poor qualities for accelerating setting and hardening. The second group, on the other hand, possesses effective accelerating qualities. However, the admixtures must be applied in the proper proportions. Calcium chloride, for example, works as accelerates at 2%, but raising the amount to 9% can operate as retarders and lengthen the setting time.
The freezing and boiling points of a liquid are mutually exclusive. It implies that they are reliant on the concentration of solutes. When a liquid freezes, it forms a solid crystalline structure. It’s tough to slow down the molecules in their subsequent freezing point when an antifreeze is applied. The attraction forces of solution are blocked by several types of molecules. As a result, the freezing point drops. How to Use Admixtures in Concrete for Cold Weather Powder or liquid antifreeze admixtures are available. It’s blended with water or pre-made cement mortar first. The doses are determined by the admixture’s chemical type. The mixture is then homogenised for at least 60 seconds. The time will vary depending on the mixing device. Fresh concrete must be placed after the old one has been removed.
Sikament HE200 is a new technology admixture that provides an effective superplasticising .
Superplasticizers- These are high range water reducers.
Calcium chloride is the most effective and least expensive cold weather accelerator for concrete.