The main action mechanisms of antifreeze in concrete are as follows.
(1) Ice crystal distortion theory
When pure water freezes at 0℃, due to The effect of hydrogen bonds will cause water molecules to gather to form molecular aggregates with strong frost heaving force. After adding antifreeze to water, ice will slowly precipitate when the temperature drops below its freezing point. However, the hydrogen bonds between water molecules will be interfered by the antifreeze molecules and will precipitate into a flocculent structure, which is very soft macroscopically. Small ice crystals that significantly reduce frost heave stress. For example, NaNO2, Na2SO4, Ca(NO3)2, etc. have strong ability to reduce frost heave force.
(2) Ural's Law
The concentration of antifreeze has a significant impact on reducing the The freezing point of the liquid phase plays a certain role. Only by lowering the freezing point of the liquid phase can the concrete have liquid water to participate in cement hydration under negative temperature conditions. This is concrete that uses antifreeze. The concrete can still hydrate under negative temperature conditions and improve the strength of the concrete.
(3) Liquid-cement ratio balance theory
When the temperature drops to the liquid phase in concrete At the freezing point, the concrete mixture containing antifreeze will gradually begin to freeze. In the liquid phase under a negative temperature environment, the freezing point decreases as the concentration of ice precipitation increases, and then reaches a state of coexistence of ice and liquid under this negative temperature condition. , which is the new dynamic balance. At this time, the liquid water in the concrete can ensure that the cement continues to hydrate, the antifreeze concentration remains unchanged, and the liquid phase concentration remains unchanged. The water generated by melting ice supplements the water needed for cement hydration, which is the liquid-cement ratio balance.
(4) Maturity theory
The influence of temperature on cement hydration is extremely significant. For concrete with a certain mix ratio, as the curing temperature decreases, the cement hydration rate slows down and the growth rate of concrete strength gradually decreases. Therefore, the development of concrete strength is not only related to curing time, but also has a great relationship with curing temperature. For example, the maturity coefficient is 1 at 20°C, but only 0.12 at -10°C. The concrete maturity during winter concrete construction acceptance is calculated based on 600℃·d, and is stipulated not to exceed 60 days. For many projects that do not take insulation measures, it is still difficult to reach the specified maturity of 600℃·d even if it exceeds 60 days. Springback detection The intensity is often low.
