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+38 (067) 55-999-07 Features of construction work in the winter.
Construction work using concrete in the autumn-winter period places special demands on both the methods of their implementation and the composition of building materials.
How to do construction work in winter?
The latter are regulated by the use of special building antifreeze additives.
Why does concrete harden slowly in winter?
When carrying out construction work using concrete, it should be borne in mind that the process of its hardening, which required only a few hours in summer, is already at a temperature of +5° It takes several days. With a decrease in temperature to 0 ° C, it slows down significantly. If the thermometer drops to -3-6°С, hydration and solidification will practically stop.
This feature of the mortar behavior is explained by the presence of water in it, which solidifies when the temperature drops, thereby disrupting the hydration process. And correspondingly. setting and hardening of concrete. Given this, it is advisable to resort to the use of winter construction methods when the thermometer drops to + 10 ° C, introducing anti-frost additives for concrete into the solution.
What are antifreeze additives for concrete?
The main construction methods in winter include electric heating of concrete, concreting in greenhouses, heating formwork and other similar methods. Unfortunately, it is not always possible to use such technologies. In this case, the optimal solution is the introduction of special antifreeze additives into the composition of concrete mixtures, which significantly accelerate the process of setting and hardening of the mortar at low temperatures.
What are antifreeze additives?
Next, we will look at the most popular antifreeze additives that exist today, dwell on their advantages and disadvantages.
The undisputed leader, the most popular and effective concrete accelerator. Its unique properties were discovered and adopted at the end of the 19th century.
The benefits of calcium chloride.
- Calcium chloride is non-toxic and non-flammable,
- Demonstrates plasticizer properties by reducing water separation
- Calcium chloride increases the resistance of concrete to moisture penetration, while increasing its strength and performance.
- The introduction of this frost-resistant additive into concrete mixtures makes it possible to obtain an excellent material for pouring floors, laying sidewalks and creating other road surfaces.
- Another advantage of this admixture is its cost-effectiveness, since a small dose of CaCl2 is required in the concrete mixture.
However, it has a significant drawback – the tendency to corrode the reinforcement in case of moisture, and, as a result, is prohibited for use in prestressed reinforced concrete.
At the same time, calcium chloride in an amount of 2% increases the electrical conductivity of fresh concrete pouring by 4-5 times, which should be taken into account when applying voltage .
If the work is carried out in accordance with the recommendations, with strict observing the concrete preparation technology, with careful isolation of the reinforcement from moisture penetration, calcium chloride will be the best solution as an anti-frost additive.
Slightly inferior to the leader, but quite effective as an antifreeze additive. Sodium formate is similar in its properties to sodium nitrite, but has a number of significant advantages over it.
Sodium formic acid is non-toxic, explosion and fire safe, does not cause corrosion of steel structures and embedded elements. The antifreeze additive HCO2Na allows you to perform construction work using concrete mixtures when the temperature drops to -15 ° C.
Irreplaceable in Siberia, in the construction of residential buildings and agricultural buildings at significantly reduced temperatures.
Among the advantages of this anti-frost admixture in concrete mixtures is a high degree of acceleration of the concrete setting and curing process. As well as the ability to maintain efficiency at temperatures up to -30-32 ° C and the absence of a corrosive effect on reinforcement. Moreover, it is non-toxic and non-flammable. In addition, potash does not cause salt efflorescence on the surface of concrete stone and does not weaken the setting of concrete with stressed reinforcement.
Disadvantages of potassium carbonate include:
- Tends to form a caustic alkaline compound during curing. Therefore, it is not recommended to use it in a solution with active silica.
- Also, do not use this antifreeze additive for working at temperatures close to 0°C and above. This is due to the fact that the concrete mixture thickens and sets very quickly under its influence.
- Potassium carbonate is very hygroscopic, it “spreads” in air, which is why it should not be used in high humidity conditions.
- It should be remembered that potash is added to concrete mixtures containing lime and used near high voltage sources.< /li>
As for the introduction of potassium carbonate into the solution, it can be added both in dry and dissolved form. And the amount of anti-frost additive introduced depends on the ambient temperature and the mass of cement used. Since potassium carbonate causes an alkaline reaction, all work should be carried out using personal protective equipment: goggles, gloves, respirators and overalls.
Not used as a stand-alone substance for concrete mixtures, but included in complex antifreeze additives, for example with nitrite , nitrate and calcium chloride, nitrite and calcium nitrate, with calcium nitrate and in other combinations. Acts as a plasticizer and salt removal regulator. In addition, carbamide is able to lower the temperature of the liquid in the pores of concrete and regulate the rate of hardening of the concrete mixture.
Sodium Sulphate or sodium sulfate Na2SO4
Can be used as an independent anti-frost additive, or as part of plasticizers for concrete mixes, significantly enhancing their effectiveness.
Sodium sulfate increases the strength of concrete by 3-4 times and accelerates its hardening at low temperatures up to 24 hours, depending on the mineral composition of cements . At the same time, sodium sulfate is poorly soluble in water. In some types of cements, it can cause corrosion if its amount exceeds 1% in the total composition of the mixture. And at a concentration of more than 2% by weight of cement causes strong efflorescence on the surface of the concrete stone. In addition, in the case of long-term storage, sodium sulfate is prone to weathering.
Calcium nitrate, otherwisecalcium nitrate, calcium nitrate Ca(NO3) 2
Similarly to the previous one, calcium nitrate, an anti-frost additive in concrete solutions, can be used both independently and in combination with other substances. For example, such as urea, nitrite, nitrate and calcium chloride.
The advantages of calcium nitrate as an antifreeze additive in concrete mixtures include the possibility of its use when performing work using reinforcement, increasing the moisture resistance of concrete structures, increase of frost resistance of concrete up to -20°C. As well as a significant reduction in the setting and hardening time of the concrete mix – up to 14-20 hours.
Among the disadvantages of calcium nitrate, one should indicate its fire hazard, high hygroscopicity, up to a tendency to blur in air and the high price of calcium nitrate as an independent additive .
Ammonia water or ammonia water NH4OH
The most budget-friendly of all products in this class. This antifreeze additive for concrete mixtures does not cause corrosion of metals and forms efflorescence on the surface of the concrete coating, it is approved for use in stressed reinforced concrete structures.
At the same time, ammonia water has a number of significant drawbacks. First of all, it is a pungent smell, which implies the presence of powerful ventilation and the need to monitor the concentration of ammonia in the air. For the same reason, it is prohibited for use in the construction of residential buildings and livestock complexes. Another disadvantage of aqueous ammonia is the inadmissibility of early operational loads. In addition, ammonia water, when introduced into the composition of concrete, evaporates very quickly. Accordingly, the surface poured with concrete must be covered with a film and kept to a technologically necessary minimum in order to avoid delamination of the upper layers of the coating.
Sodium chloride, otherwise called technical salt, NaCl
Another inexpensive antifreeze concrete admixture that is readily available and non-toxic. However, it should be remembered that technical salt causes severe corrosion of reinforcement, efflorescence and efflorescence on the surface. It also forms wet spots on plaster.
When choosing the optimal antifreeze additive for concrete mortar, remember that its action directly depends on the components of the building mixture with which it enters into a chemical reaction. And also from the brand of cement, its manufacturer, concrete mix modifier components and the type of cement used.filler: gravel, sand, limestone and other materials.
It should be noted that some imported anti-frost additives, which have proven themselves well in construction work abroad, no longer work when interacting with domestic materials so effective. To get a really good result, it is necessary that all the components of the concrete mixture are produced by the same manufacturer as the antifreeze additive. And this option is unacceptable for budget construction.
Using anti-frost additives for concrete mortars during construction, the recommended dosages should be strictly observed, since their excess can adversely affect the quality of the concrete structure: worsen the physical and chemical properties of concrete, shrink, and so on.
Dosage of antifreeze additives.
For convenience, here is a table of average dosages of antifreeze additives that can be used as a guide when preparing a solution.
| Anti-frost additive | Number of additives in % relative to the mass of cement used at an average temperature, ˚С | ||
| 0 to -5< /strong> | -5 to -10 | -10 to -15 | |
| Potassium carbonate (potash)< /td> | 6 | 9 | 12 |
| Calcium nitrate (calcium nitrate) | 6 | 8 | 10 |
| Calcium chloride | 2 | 4 | 7 |
| Sodium formic acid (sodium formate ) | 5 | 8 | 10 |
A method of introducing antifreeze additives into concrete.
To obtain a high-quality concrete mortar, you must first dissolve the anti-frost additive in water. Then the resulting solution is introduced into the concrete, bringing it to the required percentage of the mass of cement. This percentage directly depends on the air temperature and the type of additive used.
It should be remembered that no additive is a panacea for winter building work. This is just one of the methods of an integrated approach to accomplishing such a task, and in some cases, heating the concrete with the use of an anti-frost additive is mandatory.
We must not forget that all additives are different, have different properties and behave differently from each other even in the same weather conditions. Therefore, before making a decision in favor of one of them, you should carefully study its characteristics and recommendations for use. In addition, conduct experimental studies in the conditions of the upcoming construction project.
Safety precautions.
We must not forget that working with anti-frost additives for concrete requires strict adherence to safety measures. Because some of them are toxic or flammable, such as urea and sodium nitrite.
The warehouse for storing these additives must be equipped with fire fighting equipment and have access to a fire hydrant. Workers should be instructed on which chemicals they will work with. We recommend equipping places for storing personal belongings and eating in a room isolated from these substances.
When working with antifreeze additives, it is necessary to use overalls and personal protective equipment: goggles, gloves, respirators and special clothing.