When the ambient temperature is low, the hydration reaction of cement is slow, which affects the growth of concrete strength. The test shows that every time the temperature decreases by 1°C, the hydration of cement decreases by about 5% to 7%. In the range of 1°C to 0°C, the hydration activity of cement decreases drastically and the hydration is slow. Generally, when the temperature is below a certain range of 0℃, free water will begin to freeze. When the temperature reaches about -15℃, almost all free water will freeze into ice, causing the hydration and hardening of cement to completely stop.
When water is converted into solid ice, its volume increases by about 9%, causing internal stress in the concrete, causing relative displacement of aggregates and cement particles and internal Moisture migrates to the negative temperature surface and forms ice aggregates in the concrete body, causing local structural damage. Premature freezing of newly poured concrete will greatly reduce the ultimate strength, and the strength loss rate may reach 50% of the design mark, and even cause damage to the overall structure; but when the concrete reaches the critical strength and is frozen, the ultimate strength loss of the concrete is small, and the concrete is frozen. No overall structural damage will occur.
A certain amount of antifreeze added to the concrete mixing water will lower the freezing point of the aqueous solution. The degree of reduction in the freezing point depends on the type and dosage of the antifreeze or solution. related to the concentration. The effectiveness of antifreeze depends largely on the concentration of the solution and the negative temperatures to which the concrete is subjected during hardening. The main purpose of adding antifreeze to concrete is to maintain a sufficient liquid phase at negative temperatures so that the hydration of cement can continue; after switching to positive temperatures, the strength of the concrete can further increase and reach or exceed the design label.
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