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How to choose antifreeze for a construction site when temperatures drop?

The function of antifreeze

Antifreeze is a type of concrete that can harden at negative temperatures without the need for heating, ultimately achieving the same quality level as concrete cured at room temperature. The main function of antifreeze is to improve early strength and prevent freezing damage.

Introduction to the main components of commonly used antifreeze agents

Antifreeze ingredients

Generally used are sodium chloride, calcium chloride, sodium nitrite, sodium nitrate, calcium nitrate, potassium nitrate, sodium thiosulfate, sodium acetate, urea, ammonia water, methanol, etc. Its main function is to lower the freezing point of water, so that cement can continue to hydrate at negative temperatures.

Early strength ingredients

Generally used are sodium chloride, calcium chloride, calcium nitrate, calcium nitrite, triethanolamine, sodium thiosulfate, sodium sulfate, etc. Their main function is to improve early concrete strength, resist expansion stress caused by freezing water, and lower the freezing point so the concrete can reach or exceed its critical strength for freezing as soon as possible.

Water-reducing ingredients

Generally used are calcium lignosulfonate, sodium lignosulfonate, naphthalene-based superplasticiser, melamine, aminosulfonate, coal tar-based superplasticiser, etc.

Its main function is to:

reduce the amount of mixing water, refine the capillary tube, increase the concentration of antifreeze in the capillary tube, and lower the freezing point;
Reduce the content of ice in concrete and make the ice crystals small and evenly dispersed, reducing the destructive stress on concrete;
Improve the workability of fresh concrete and enhance the strength and durability of hardened concrete.

Air-entraining ingredients

Generally used are rosin thermal polymer, soapberry-based water-reducing agent, calcium lignosulfonate, sodium lignosulfonate, anthracene-based water-reducing agent, etc. Its main function is to introduce a suitable amount of enclosed microbubbles into concrete to alleviate ice swelling stress.

Carrier

Generally, fly ash, ground slag, brick powder, etc. are selected as carriers for antifreeze agents.

Its main functions are to:

make it easy to add some liquid or trace components and evenly disperse them;
avoid moisture and clumping;
make it easy to mix and use.

Antifreeze classification

According to the negative temperature maintenance temperature, it is divided into three categories: -5 ℃, -10 ℃, and -15 ℃. No standard exists for antifreeze agents with lower negative temperatures.

According to the composition materials, it can be divided into three categories, namely:

Chloride antifreeze: Refers to antifreeze agents composed mainly of chloride salts (calcium chloride, sodium chloride) or a combination of chloride salts with other early strength agents, air-entraining agents, water-reducing agents, etc.

Chloride salt rust inhibitor antifreeze: refers to antifreeze agents mainly composed of chloride salt and rust inhibitor (sodium nitrite), or antifreeze agents composed of chloride salt, rust inhibitor, early strength agent, air entraining agent, and water reducer.

Chlorine-free salt antifreeze: refers to an antifreeze agent composed of nitrite, carbonate, sodium acetate or urea as the main raw materials, and chlorine-free early strength agents, air-entraining agents, water-reducing agents, etc.

Application scope and maintenance measures of antifreeze

1.Dosage

At present, the temperature range suitable for antifreeze products is generally 0-20 ℃. When construction is carried out at lower temperatures, take other winter construction measures, such as the greenhouse method, comprehensive heat storage method, etc.

When using one layer of plastic film, two layers of straw bags or other substitutes for covering and curing: under the condition of alternating positive and negative temperatures of -5 ℃ to 5 ℃ on the same day, early strength agent or early strength water reducer can be used; When the lower temperature of the day is -10 ℃, antifreeze with a specified temperature of -5 ℃ can be used; When the lower temperature of the day is -15 ℃, antifreeze with a specified temperature of -10 ℃ can be used; When the lower temperature of the day is -20 ℃, antifreeze with a specified temperature of -15 ℃ can be used.

Conclusion: How to choose antifreeze for a construction site when temperatures drop?

Generally, when temperatures alternate between -5 ℃ and 5 ℃ on the same day, use early strength agents or early strength water reducers. If the daily temperature reaches or falls below -10 ℃, use antifreeze with a specified temperature of -5 ℃. If the daily low temperature is -15 ℃ or -20 ℃, use antifreeze agents with specified temperatures of -10 ℃ and -15 ℃, respectively.