When pouring concrete in cold weather, because the cold environment has a dramatic effect on the early strength development, frost resistance, and durability of the concrete, measures must be taken, including the use of specific concrete admixtures. The following are a few commonly used additives for cold-weather concrete construction:
The main function of early-strength additives is to accelerate the rate of cement hydration reaction, shorten the setting time of concrete, and enhance early strength growth. Under cold conditions, the rate of cement hydration reaction is significantly reduced, and the use of early strengthening agents such as sodium sulfate, triethanolamine, etc., can help the concrete in the low-temperature environment to achieve faster demolding and load-bearing strength, reducing the risk of frost damage.
Antifreeze is an important additive for concrete construction in cold climates. Their main components contain chloride salts, nitrates, nitrites, etc., which can lower the freezing point of the liquid phase of concrete over a range of temperatures, preventing water from freezing and causing ice crystal damage within the concrete. However, it should be noted that over-reliance on chloride salt antifreeze may have a corrosive effect on the steel reinforcement, so the new environmentally friendly antifreeze, the
Therefore, new environmentally friendly antifreeze antifreezes, such as calcium formate, urea, and other organic compounds, have gradually replaced the traditional chlorinated salt antifreeze.
An air-entraining agent can cause the internal formation of a large number of tiny closed air bubbles in concrete, increasing its porosity and thus improving its freeze-thaw resistance. In winter construction, the appropriate amount of air can be introduced into the concrete to relieve the internal freezing pressure and reduce frost damage. Commonly used air-entraining agents are rosin soap, alkyl sulfonate, and so on.
Under extreme cold conditions, in addition to accelerating the rate of setting and preventing freezing, the maintenance of concrete also needs to be considered. Thermal insulation and moisturizing agents can form a layer of film on the surface of the concrete, reduce heat loss, and maintain the internal temperature of the concrete while preventing rapid evaporation of water to ensure that the concrete is fully hydrated. For example, certain polymer-containing curing agents not only can play a moisturizing effect but also improve the crack resistance of the concrete surface.
In recent years, many composite admixtures have appeared on the market for the complex needs of concrete construction in cold areas. These, such as early strength antifreeze, antifreeze early strength air-entraining agent, etc., set a variety of functions in one, which can not only ensure the normal construction and hardening of concrete at low temperatures but also improve its frost resistance and durability.
In general, when pouring concrete in cold weather, according to the specific conditions and project requirements, reasonable selection of the above types of additives, combined with appropriate construction methods and technical measures, such as covering thermal insulation, steam curing, and other means, ensures the quality of concrete and structural safety. At the same time, it is also necessary to pay close attention to the temperature monitoring and quality inspection of concrete to adapt to the challenges of construction in cold weather.
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