Types of antifreeze and their mechanism of action

Antifreeze is an admixture that can make concrete harden under negative temperature and achieve sufficient antifreeze strength within a specified time. China's commonly used antifreeze agent is a multi-component composite, its main components are antifreeze components, water-reducing components, air-entraining components, early strength components.

1. Commonly used antifreeze agent

Antifreeze component is an important component of the composite antifreeze agent, according to its composition can be divided into three categories:

(1) chloride salts

Commonly used for calcium chloride, sodium chloride. As calcium chloride is involved in the hydration reaction of cement, can not effectively reduce the freezing point of the liquid phase of concrete, so often used in combination with sodium chloride, usually using a ratio of calcium chloride: sodium chloride a 2:1.

(2) Chlorine salt rust inhibitor

Chlorine salt is compounded with rust inhibitor. Rust inhibitor has sodium nitrite, chromate, phosphate, polyphosphate, etc. Among them, sodium nitrite has the best rust inhibiting effect, so it is widely used.

(3) Non-chlorine salts

There are nitrate, nitrite, urea, acetate, etc. The above types of antifreeze components applicable temperature range is generally: sodium chloride alone for -5 ℃; nitrate (sodium nitrate, calcium nitrate salt), urea type for -10 ℃; nitrite (sodium nitrite salt) for -15 ℃; compound antifreeze in the water-reducing components, air-entraining components, early strength components are used in the previous types of water-reducing agents, air-entraining agents, early strength agents.

2. Mechanism of action of antifreeze agent

The role of the components of the antifreeze agent on the concrete are: change the concentration of the liquid phase in the concrete, reduce the freezing point of the liquid phase, so that the cement can continue to hydrate at negative temperatures; reduce the amount of water used in concrete mixing, reduce the amount of water in the concrete can become ice. At the same time to make the concrete in the most can be a few pore size becomes smaller, further reduce the liquid phase freezing temperature, change the shape of ice crystals; the introduction of a certain amount of tiny closed bubbles to slow down the freezing stress; improve the early strength of concrete, enhance the ability of concrete to resist freezing damage. The combined effect of the above-mentioned effects is to make the concrete frost resistance to obtain a significant increase. Various types of antifreeze agent has different characteristics, so the choice of antifreeze agent species is very important. Chlorine salt antifreeze agent is suitable for unreinforced concrete. Chlorine salt antifreeze class antifreeze agent can be used for reinforced concrete. Chlorine-free salt antifreeze agent, can be used for reinforced concrete and prestressed reinforced concrete, but nitrate, nitrite class shall not be used for prestressed concrete and reinforced concrete with galvanized steel or contact with aluminum and iron parts. Containing hexavalent chromium salts, nitrites and other toxic antifreeze, is strictly prohibited for drinking water projects and contact with food parts. The amount of antifreeze should be determined according to the ambient temperature at the time of construction; the content of the antifreeze component must be controlled, too much and too little can lead to adverse consequences.