When fresh concrete is exposed to freezing temperatures, its strength can be reduced by 20 to 40 percent. To address this issue, antifreeze admixtures are used in concrete to improve its resistance to freezing. These admixtures have specific properties that make them effective in cold weather concreting.
One important factor to consider in cold weather concreting is the durability of the concrete against the freeze and thaw cycle. The durability factor is used to measure the resistance of fresh concrete against this cycle, and it can be lowered by 40 to 60 percent in cold weather conditions.
Another concern in cold weather concreting is the bond between the reinforcement and the concrete. When concrete is not properly cured in cold weather conditions, there can be a 70 percent decrease in this bond. Therefore, it is crucial to ensure that fresh concrete does not undergo freezing in its plastic state during concreting in cold weather conditions.
Overall, using antifreeze admixtures in concrete and taking proper precautions during cold weather concreting are essential to maintain the strength and durability of the concrete. By addressing these concerns, the quality of the concrete can be maintained even in cold weather conditions.
When it comes to carrying out concreting in cold weather conditions, there are two primary approaches that can be utilized. The first method involves ensuring that the concrete is exposed to normal ambient temperatures, which can be achieved through the heating of the concrete ingredients or by providing heating enclosures.
To implement the first approach, the concrete ingredients are typically preheated before they are mixed together. This can involve heating the aggregates, cement, and water to a temperature that is suitable for concrete placement in cold weather. Alternatively, heating enclosures can be erected around the construction site to provide a warm and sheltered environment for the concrete to cure properly.
The second approach to cold weather concreting involves the use of chemical admixtures. These admixtures are added to the concrete mix to improve its properties and allow it to set and harden at lower temperatures. By modifying the hydration process, these admixtures can help to prevent freezing and ensure that the concrete reaches its required strength and durability.
While both of these approaches can be effective for cold weather concreting, they each have their own unique advantages and limitations. Choosing the best method will depend on a variety of factors, including the specific project requirements, the local climate conditions, and the available resources and equipment. Ultimately, careful planning and execution are key to ensuring the success of any cold weather concrete placement project.
Conventional Chemical Admixtures in Cold Weather Concrete
The use of calcium chloride as an accelerating admixture in conventional concrete is a common practice to counteract the slow hydration of concrete in low temperatures. However, this method becomes ineffective in freezing temperatures, making it a drawback in the conventional form of admixtures. To address this issue, special admixtures are needed for arctic weather conditions.
Antifreeze admixtures are a type of special admixture that can be used in arctic weather conditions. These admixtures are specifically designed to work in low temperatures where traditional admixtures fail. Antifreeze admixtures provide a solution to the problem of concrete’s slow hydration process in freezing conditions.
The use of antifreeze admixtures in concrete provides an effective solution to offset the retarding effects of slow hydration in freezing temperatures. This approach enhances the durability of concrete in arctic weather conditions. Antifreeze admixtures have become an essential part of concrete production in areas with harsh winter conditions. The use of these admixtures ensures the proper setting of concrete, even in extremely low temperatures, leading to improved performance and strength.
Antifreeze Admixtures for Concrete
Antifreeze admixtures have a significant impact on the physical properties of the mix water that is utilized in the process of concreting. By reducing the freezing point of the water to a considerable degree, these admixtures can prove to be beneficial in extremely low temperatures, even below -30 degrees Celsius. This can be especially advantageous in construction projects where the temperature drops below freezing, as it allows for a longer construction period.
The use of antifreeze admixtures can help to overcome the challenges posed by extremely low temperatures, which would typically halt or delay construction activities. By lowering the freezing point of the mix water, the concrete mixture can be kept from freezing, enabling the continuation of the construction process even in harsh weather conditions.
Furthermore, antifreeze admixtures can be used to extend the duration of the construction activity. This can be especially beneficial in situations where the construction timeline is tight, and any delay would be detrimental. By reducing the impact of cold weather on construction activities, antifreeze admixtures can help to ensure that the project is completed within the designated time frame, without any unforeseen delays due to weather-related factors.
Chemical Composition and Action of Antifreeze Admixtures
Antifreeze admixtures can provide both antifreeze properties and accelerate the setting and hardening of concrete. There are two groups of these admixtures. The first group includes chemicals like weak electrolytes, sodium nitrite, sodium chloride, and non-electrolytic organic compounds. These chemicals lower the freezing point of the water used in concrete and act as weak accelerators for setting and hardening. The second group includes binary and ternary admixtures containing potash and additives like calcium chloride, sodium nitrite, calcium chloride with sodium nitrite, and calcium nitrite-nitrate-urea. These admixtures have effective antifreeze properties and accelerating properties for setting and hardening. They are used in larger dosages than conventional admixtures. For instance, 8% sodium nitrite can be used to keep liquid at -15 degrees Celsius. These admixtures work by lowering the freezing point of the liquid phase and accelerating cement hydration at freezing temperatures.
By adjusting the dosage in the mixture, non-chloride admixtures can enable the placement of concrete or mortar at sub-freezing temperatures, reducing the need for protective measures during cold weather. This improves the quality of the concrete and facilitates early setting, allowing for early stripping of formworks. This, in turn, enables the reuse of the form within a short time, speeding up construction.
Table-1 illustrates the significant difference in strength gain at 3, 7, and 28 days for plain concrete and antifreeze admixture used concrete.
Table.1: Concrete Compressive strength with and without antifreeze admixture
(As per Ratinov and Rosenburg)
| Property | Plain Concrete | Freeze-protection Admixture |
| Set time (-4 degree Celsius) | – | – |
| Compressive strength (MPa) | ||
| -4 degree Celsius (3 days) | 3.4 | 9.24 |
| -10 degree Celsius (7 days) | 8.3 | 39.3 |
| -10 degree Celsius (28 days) | 18.1 | 49.9 |
It is feasible to combine antifreeze admixtures with other admixtures containing superplasticizers. The primary benefit of such a combination is a decrease in water content overall. By reducing the amount of water in the mix, the amount of freezable water content is also reduced. This freezable water content typically serves as a heat sink for the heat generated by the initial hydration reactions. Consequently, the need for antifreeze admixtures is also reduced, resulting in a more efficient mixture.
Selection of Antifreeze admixtures
When selecting antifreeze admixtures for cold weather concreting, several factors must be taken into consideration. These factors include the type of structure being constructed, the operating conditions of the environment, and the protective methods being employed during winter concreting. Additionally, the type of cement brand and aggregate types used must also be considered.
To ensure the effectiveness of the antifreeze admixtures being used, laboratory tests must be conducted using the materials that will be used in the actual construction site. This is necessary in determining the proper dosage of antifreeze admixtures that should be used in the field.
The use of other admixtures, such as retarders and superplasticizers, in conjunction with antifreeze admixtures is allowed in cold weather concreting. However, the dosage of all admixtures being used must be established experimentally to ensure optimal results.
Application and Advantages of Antifreeze admixtures
Antifreeze admixtures are a useful tool for cold weather concreting, providing a simple and effective way to improve the cohesiveness, plasticity, and overall quality of the concrete. These admixtures can also help to minimize issues such as cold joints and sand streaking, making them a popular choice among builders and engineers.
One of the key benefits of antifreeze admixtures is their ability to provide significant cost savings compared to other methods such as steam curing or concrete enclosures. This makes them a highly attractive option for those looking to reduce costs while still achieving high-quality results.
When combined with water reducing agents or air-entraining agents, antifreeze agents can also help to increase the resistance of concrete to frost action and corrosion. This can be particularly important in areas where cold weather and exposure to harsh conditions are common, as it can help to prolong the lifespan of the concrete and prevent damage or deterioration over time.
Overall, antifreeze admixtures are a valuable tool for those working in the construction industry, offering a range of benefits that can help to improve the quality and durability of concrete in cold weather conditions.