Why does concrete harden slowly in winter?

In this article, we discuss why concrete hardens slowly in winter. To buy and know the price of super lubricant, tile adhesive, anti-acid mortar, rebar planting adhesive, concrete restorer, epoxy and antifreeze grout, etc., you can contact Shimi Abadgaran company.

Why does concrete harden slowly in winter?

When carrying out construction work using concrete, it should be borne in mind that the hardening process, which required only a few hours in the summer, is now at a temperature of +5 degrees and takes several days. As the temperature drops to 0°C, its rate decreases significantly. If the thermometer drops to -3-6 degrees Celsius, hydration and freezing practically stop.

This feature of mortar behavior is explained by the presence of water in it, which solidifies with a decrease in temperature and thus disrupts the hydration process. And so on. Setting and hardening of concrete. In view of this, it is recommended to resort to winter construction methods when the thermometer drops to + 10 degrees Celsius and add antifreeze additives for concrete to the solution.

What are antifreeze additives for concrete?

The main construction methods in winter include electric heating of concrete, concreting in a greenhouse, heating form and other similar methods. Unfortunately, it is not always possible to use such technologies. In this case, the optimal solution is to introduce special antifreeze additives into the composition of concrete mixtures, which significantly accelerate the process of setting and hardening of mortar at low temperatures.

What are antifreeze additives?

Next, we look at the most popular antifreeze additives available today and discuss their pros and cons.

• Calcium chloride

The undisputed leader, the most popular and effective concrete accelerator. Its unique properties were discovered and used at the end of the 19th century.

Benefits of calcium chloride

1. Calcium chloride is non-flammable and non-toxic.
2. It exhibits softening properties by reducing water separation
3. Calcium chloride increases the resistance of concrete against moisture penetration and at the same time increases its strength and performance.
4. The introduction of this frost-resistant additive in concrete mixes makes it possible to obtain an excellent material for pouring floors, paving and creating other road surfaces.
5. Another advantage of this admixture is its cost-effectiveness, as a small dosage of CaCl2 is required in the concrete mix.

• Sodium formate or sodium formate

A little below the leader, but quite effective as an antifreeze additive. Sodium formate is similar in properties to sodium nitrite, but has significant advantages over it.

Sodium formic acid is non-toxic, anti-explosion and fire, does not cause corrosion of steel structures and embedded elements. The antifreeze additive HCO2Na allows you to carry out construction work using concrete mixtures until the temperature drops to -15 degrees Celsius.

• Potash – potassium carbonate, K2CO3

Irreplaceable in Siberia, in the construction of residential buildings and agricultural buildings at a significantly reduced temperature.

Among the advantages of this antifreeze additive in the concrete mix is ​​high acceleration in the setting and curing process of concrete. As well as the ability to maintain efficiency at a temperature of 30-32 degrees Celsius and the absence of a corrosive effect on reinforcement. Moreover, unflammable And it is non-toxic. In addition, potash on the surface of concrete stone does not cause salt to bloom and does not weaken the grip of concrete with reinforced reinforcements under tension.

The disadvantages of potassium carbonate are:

1. Tends to form a caustic alkaline compound during cooking. Therefore, its use in solution with activated silica is not recommended.
2. Also, do not use this antifreeze additive to work at temperatures close to 0 degrees Celsius and above. This is because the concrete mixture under its influence thickens and sets very quickly.
3. Potassium carbonate is very wet, it “expands” in the air, which is why it should not be used in high humidity conditions.
4. It should be remembered that potash is added to concrete mixes containing lime and is used near high voltage sources.

Regarding potassium carbonate entering the solution, it can be added dry and dissolved. Since potassium carbonate causes an alkaline reaction, all work must be carried out using personal protective equipment: Goggles, gloves, respirator and clothing.

Sodium sulfate or sodium sulfate Na2SO4

It can be used as an independent antifreeze additive or as part of plasticizers for concrete mixtures, which significantly increases their performance.

At the same time, sodium sulfate is slightly soluble in water. In some types of cement, if its amount exceeds 1% in the total composition of the mixture, it can cause corrosion. And in a concentration of more than 2 percent by weight of cement, it causes a strong efflorescence on the surface of concrete stone. In addition, sodium sulfate is prone to weathering if stored for a long time.

Calcium nitrate, otherwise calcium nitrate, calcium nitrate Ca(NO3) 2

As in the previous case, calcium nitrate, an antifreeze additive in concrete solutions, can be used both independently and in combination with other materials. For example, such as urea, nitrite, nitrate and calcium chloride.

Among the advantages of calcium nitrate as an antifreeze additive in concrete mixtures, it is possible to use it when working with reinforcement, increasing the resistance against moisture of concrete structures, increasing the resistance against freezing of concrete up to -20 degrees Celsius. Grad pointed out. Also, a significant reduction in the setting and hardening time of the concrete mixture – up to 14-20 hours.

Among the disadvantages of calcium nitrate, it should be noted the risk of fire, high hygrometry, the tendency to blur in the air and the high price of calcium nitrate as an independent additive.

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