First, the classification of antifreeze: according to the different modes of action of antifreeze, it can be divided into three categories.

(1), can reduce the freezing point of water and make concrete hydrate at negative temperature, such as sodium nitrite (NaNo2). However, once the dosage of this antifreeze is insufficient or the temperature is lower than the specified temperature, it will still cause freezing damage and reduce the final strength of concrete.

② It can not only lower the freezing point of water, but also severely deform the lattice structure of ice crystals containing such substances, such as urea and methanol (CH3OH). When the content is insufficient, the concrete stops hardening at negative temperature, but continues to hydrate at positive temperature, which has little effect on the formation of final strength.

(3), can't reduce the freezing point of water, just directly react with cement, accelerate the setting and hardening of concrete. Such as calcium chloride.

Second, the choice of antifreeze

(1), the curing process of negative temperature concrete in each unit adopts comprehensive heat storage method, and the addition of antifreeze is basically prevention, so its dosage can be determined according to the product manual or through experiments;

(2) As the comprehensive high heat storage mode is adopted, the specified temperature of "-15℃" can be selected as the antifreeze;

(3) Try to choose a compound antifreeze with water reducing and early strength components. Sodium nitrite and methanol have better antifreeze effect;

(4) antifreeze has strong "local characteristics", and the contents of antifreeze, water reducing and other components change with the temperature characteristics of the use area. When selecting, the tester should fully communicate with the technical personnel of the manufacturer, rather than simply "using it".