Concrete laying in sub-zero temperatures. At what temperature are antifreeze additives used? The principle of operation and types of frost-resistant compounds

Features of concreting are that the concrete base does not instantly become strong, but gains this indicator gradually. The process of curing is considered optimal if the concrete has reached the design indicator in 28 days. But this time indicator depends on some factors. And the most influential is the temperature and humidity indicators. Moreover, there is an opinion that it is impossible to pour concrete into a minus.

Features of concrete hardening

How does the strength of concrete take place? The simplest explanation is the loss of moisture from the concrete mixture. The moisture content must be distributed evenly, in accordance with regulatory requirements. And if the temperature is not optimal, but is approaching minus or negative?

In this case, the concrete will begin to harden within a few hours only due to recoil own heat and then there are two options:

• water in microcracks and pores will freeze and begin to expand, which will lead not to hardening of the monolith, but to its cracking;
• at very low temperatures the concrete itself will freeze and the process of curing will stop until it is completely thawed. Strength after thawing usually decreases, and the life of the entire structure becomes shorter.

Neither the first nor the second version of the builders are satisfied. Therefore, it is worth weighing the pros and cons of pouring concrete at sub-zero temperatures.

The organization of work depends on the grade of concrete being worked with. For different brands there is an indicator of critical strength, which sets the percentage of the design value at which freezing of concrete will not disrupt its structure so much as to affect the final strength value. For example, for the M300 concrete grade, this percentage is 40%, and for grades lower than M200 - 50%.

The task of the builders is to provide such conditions for concrete solidification so that it has time to reach critical strength before the moment of complete freezing.

There are several options for laying concrete at sub-zero temperatures, when the requirements for critical strength can be met:

• the use of electric heating;
• thermos method;
• the introduction of antifreeze additives;
• creation of shelters with the maintenance of a certain regime or a convective method.

Stage of production and transportation in winter

If you do not comply with all technological requirements at each stage of creating a concrete structure in winter, you can lose quality even at the stage of mixture formation or its transportation.

The temperature of the transported mixture must be such that, at the time of its unloading at the construction site, it corresponds to the design temperature for a given brand and installation method. When using heating or additives, the concrete mixture can have a temperature of about 5 0 C, and if the thermos option is used, then it is necessary to provide a temperature of 25 0 C.

Note! High temperature reduces the mobility of concrete.

In order for the final product to have the required temperature, several technologies can be applied:

• use warmed up high temperature water;
• heat the aggregate - sand, crushed stone, gravel;
• steam heating of all components during mixing in a concrete mixer.

Note! In the manufacture of concrete on a construction site, the procedure is as follows: hot water is first combined with aggregate, and then only cement is introduced.

To maintain the temperature of the resulting concrete, the body is insulated in the machines or warm containers are used. But the most profitable way is to use truck mixers, when hot water right on the construction site.

In conditions when the mixture has cooled down during transportation, but has not begun to set, it is heated by electrodes to the required temperature.

Operation at sub-zero temperatures

It is impossible to avoid concreting at sub-zero temperatures, which means that it is necessary to reduce the time to reach the critical strength of the composition. In addition to the methods already listed, they often follow a simpler path and increase the grade of concrete, but this option requires careful calculations and selection of components.

With any method of concreting in winter, make sure that the temperature inside the entire structure is above 0 0 C during the entire time of gaining the required percentage of strength.

Creating an insulated protective structure or covering with a thermal film with a flooring of heat-insulating materials is considered the simplest. Sawdust, snow, peat serve as a material for flooring. They provide the necessary temperature, and only humidity control is required.

If necessary, bring the pouring of concrete at minus 5 0 C, insulation alone may not be enough. An effective option may become use electric current which will provide isothermal heating. In this case, the concrete mix itself becomes part of the electrical circuit like resistance. In her Electric Energy will turn into heat. Used as electrodes steel reinforcement. The electrodes themselves can be located inside the mixture and on its surface.

Electric heating is carried out not only with the help of electrodes. To do this, use several more methods and devices, such as:

• thermoactive formwork;
• electric reverberatory furnaces;
• infrared heaters;
• cylindrical resistance devices.

Any electrical appliance, steam generator, induction field can act as a heating device. The choice of instrument and heating method depends on the following factors:

• structure design, its geometrical parameters;
• index of critical strength of the composition;
• the presence of the required electric power.

Antifreeze additives

From the point of view of energy resources, the introduction of additives that increase the frost resistance of the concrete mixture is considered less expensive. Antifreeze additives can be up to 10% of the total volume of cement in the concrete mixture. They do not allow concrete to freeze and contribute to its strength development at temperatures below 0 0 С.

The most common chemical additives in concrete at sub-zero temperatures it is calcium or sodium chloride, sodium nitrate and sulfate, potash. AT reinforced concrete potash is used as an additive, which allows the mixture to harden at a temperature of -25 0 C. Sometimes you can use the so-called cold concrete. In it, the amount of additives reaches 15% by weight of cement. Such concrete is protected by a thermal cushion from all sides to ensure the same temperature throughout the structure.

Cannot be applied antifreeze additives if the structure itself will be operated at a temperature of more than 60 0 C or in an aggressive environment.

Concreting works in winter period it is possible, but it is quite a costly and energy-intensive event. It may be worth waiting a bit to be able to comply with all technological requirements.

Optimal temperature range for the device concrete foundations on traditional technologies– from 15 to 25 °С. Therefore, in the vast majority of cases, these works are carried out in the warm season. But what if you need to continue or start construction in the fall or in the middle of winter, when it's freezing outside? To answer this question, we propose to understand under what minimum temperature you can pour concrete and what it is fraught with for the developer.

Is it possible to concrete in frost

After filling with favorable conditions the hydration process begins in concrete, which takes place in 2 stages:

1. The water enters chemical reaction with cement, which causes bonds between the particles and the solution begins to thicken. The setting stage lasts 10-20 hours and is accompanied by heat release.
2. The second stage is the hardening (hardening) of the concrete mixture, which lasts up to 4 weeks. During this period, the monolithic structure gains maximum strength.

The lower the temperature environment the longer it takes to hydrate. For clarity, we give an example in the form of a table reflecting the behavior of standard M250 concrete based on Portland cement grade 400 at different temperatures.

Reference. According to building codes, the formwork is removed after reaching 50% strength, and further work- not earlier than at 70%.

At negative temperature water freezes and practically does not react with cement. If ice crystals are formed, then the monolith that has not had time to harden begins to collapse. From the above table it is clearly seen that even at zero temperature your construction will stretch for an indefinite period.

To avoid this, you need to prevent the water from freezing, and ideally, heat it to the required condition in order to accelerate hydration. There are several methods for organizing the concreting of the foundation for a house in the autumn and winter:

• Introduction to concrete mix antifreeze additives;
• heating of a monolithic structure from the inside and outside;
• covering and insulating concrete after pouring.

Construction experience shows that correct application of these methods, singly or in combination, allows you to safely build foundations down to -15 ° C on the street. If you live in major city, then they probably noted that in winter, work at large facilities does not stop. AT equally these technologies are also applicable to the construction of small bases for a house or a bath.

Use of additives

These chemical substances are divided into groups according to the method of impact on the concrete mixture:

1. Additives that prevent water from freezing at sub-zero temperatures and allow cement hydration to proceed. They are best used in combination with heating to shorten setting and curing times.
2. Additives - accelerators with antifreeze properties. Their function is to sharply increase the activity of the cement and thus force the concrete to gain design strength regardless of the ambient temperature. Successfully used without heating structures.
3. Substances that accelerate the setting of the solution and cause maximum heat release, which is why the monolith is heated independently at first.

Reference. From a financial point of view, the introduction of additives is considered the most profitable way, since electric or air heating of concrete is more expensive.

A feature of the use of any additives is the observance of the exact dosage in accordance with the conditions of concreting, especially when combining substances. The fact is that some of the compositions initiate the appearance of rust of the reinforcing cage, but give the water antifreeze properties. Others are corrosion inhibitors, so both groups are used together.

Hence the conclusion: do not try to make a solution for winter construction yourself by adding additives, such material must be ordered at the factory and delivered by a concrete truck (in jargon - a mixer). Contact the specialists of the enterprise and find out at what temperature it will be possible to use their products in order to pour the foundation without consequences. In case of emergency, correctly combined and accurately dosed admixtures can reduce the mortar laying threshold to minus 25 °C.

The following substances most often act as antifreeze and accelerating additives:

• potassium carbonate (potash);
• various calcium and sodium salts;
• urea (otherwise - carbamide);
• sodium formate.

You will learn more details about chemical impurities - modifiers from the following video:

Structure heating

This method is widely used for pouring reinforced concrete foundations small buildings and is implemented in two ways:

1. The entire area of ​​the future house is covered with a film tent mounted on a frame made of wooden beams. Inside are electric or gas heat guns supporting a certain temperature regime throughout the curing time of the concrete.
2. Before pouring, the reinforcement cage of the foundation is wrapped with a heating cable, which is connected to the network after laying the mortar into the formwork. There are other types of electric heaters - heating elements, nichrome spirals and so on.

Note. Both options are usually used without the introduction of antifreeze additives into the concrete mixture. But at too low temperatures (-15 ° C and less), additives are indispensable.

Device concrete base followed by air heating - not too effective technique in severe frosts and frozen soils. The injection of heat into the space under the tent allows you to increase the air temperature by 15-20 ° C, which is not enough. In turn, the heating cable can burn out inside the monolith and then part of the foundation will remain without heating.

Unloading concrete from the machine into the heated shelter

The main disadvantage of these methods is high energy consumption and large initial investments for the construction of a canopy or the purchase of a cable (heat guns can be rented). Again, heaters or cable operation must be monitored and kept on site at all times. To understand the process, we suggest watching the video

Construction in modern world you can start not only in spring, summer and early autumn, but now late autumn and even in winter.

And this became possible with the invention of antifreeze additives. We will talk about this interesting additive later.

Application conditions

Such additives make it possible to use low-quality instead of expensive high-quality ones, and this makes it possible to reduce the cost of concrete products. Due to this, it is also possible to reduce the thickness of the product, for example, floor slabs, moreover, without compromising quality.

About the use of antifreeze additives

How to use

How to cook containing special additive?

An antifreeze additive is added to concrete along with other ingredients (sand, water, plasticizer). Better supplement add along with water, because the additive can replace water. Everything must be mixed well with a concrete mixer for an hour, until a homogeneous mass.

The additive is introduced into the mixture according to the instructions on the package. This amount is approximately 0.2% of the amount of cement at an air temperature not exceeding or decreasing the value indicated on the package.

In the event of a decrease in temperature, the dosage of the additive should be increased at the rate of 0.05% per degree. On the packaging, the dosage is indicated in grams.

In the event that the dosage of the additive is indicated in milliliters, then in order to determine the amount of the substance, its mass is divided by 1.45. The result obtained will be the volume in milliliters. Then we measure right amount and add to the mixture.

Antifreeze additives are used only at sub-zero ambient temperatures. They cannot be used under other conditions! After pouring concrete, structures made of this material are moistened for about two days.

Construction objects

The use of antifreeze additives makes it possible to build at any time of the year and under any weather conditions. Due to this, the construction time of facilities is reduced, as well as the cost is reduced due to rational operation. construction equipment and labor force.

Antifreeze additives are used:

• in the manufacture of heavy and light iron concrete structures,
• in the construction of monolithic reinforced concrete structures,
• it is added to
• when laying pavement and production of road elements,
• build bridges, oil and gas platforms, various buildings, dams, dams and much more.

Antifreeze additives are applicable at air temperatures from -15 to approximately -25 ° C, depending on the substance used.

Antifreeze additives are delivered to stores and retail chains in containers with a volume of 1 m3 or 5 liters each.

If you are thinking of building in the cold season, we recommend that you use antifreeze additives and be sure to carefully read the instructions on the packaging of additives.

We hope that this article was useful to you. We wish you good luck in your endeavors!

The maturation of concrete slows down significantly at temperatures below +5°C, and completely stops at minus. This is due to the freezing and crystallization of water entering the solution. But builders are often forced to continue work in the cold season. The problem with freezing under adverse conditions is solved by introducing special antifreeze additives. When using this method, it must be taken into account that the strength of a material with such impurities at low temperature is no more than 30% of the design one, it will gain full strength after thawing.

Benefits offered by the use of antifreeze components:

• the ability to perform work related to mixing concrete at any time of the year;
• many important characteristics material - density, moisture and frost resistance;
• the plasticity, mobility and stability of the solution increase, cracks do not appear after it hardens;
• mixture separation is prevented;
• lower cost compared to alternative ways combating the delay in maturation;
• the risk of shrinkage is reduced.

Disadvantages of using antifreeze additives:

• more consumption of the binder component (cement) - due to this, and also because of the need to spend on the additives themselves, concrete is more expensive;
• some substances that accelerate hardening at low temperatures are poisonous;
• maturation is accelerated, but strength development may be slowed down.

Types of antifreeze

According to the effect on concrete, antifreeze additives are distinguished:

• antifreezes and accelerators - help to lower the freezing point of water in solution;
• sulfates - warm the mixture due to the release of heat during the reaction;
• complex - are at the same time antifreeze components, hardening accelerators, plasticizers for concrete, as well as masonry and plaster compositions.

PMDs are classified according to the lowest temperature level at which they are effective: down to -10, -15, -20 or -30°C.

List of substances that accelerate the maturation of concrete at low temperatures

In pure form or as part of ready-made complex mixtures, as antifreeze additives, the following are used:

1. Sodium nitrite. At temperatures from 0 to -25°C, the inscription Poison should be on the container. It is flammable, the use of this component in combination with lignosulfonic acids is prohibited, since as a result of their reaction poisonous gaseous nitrogen compounds are formed. Sodium nitrite is sold in powder form or solution. Consumption: 4-10% of the weight of the cement in the mixture.

2. Sodium tetraborate (borax, sulfate-yeast brew) and calcium carbonate (potash). These substances are recommended to be used together, since calcium carbonate without borax reduces the strength of the finished concrete (up to 30%), provokes its cracking. Potash is harmful, be sure to take precautions. Requires a plasticizer, consumption: 5-10% by weight of cement.

3. Sodium formate. It goes on sale in the form of a white crystalline powder, it dissolves well in water. When using it, a plasticizer is required. Sodium formate is usually added together with powdered or liquid naphthalene lignosulfonate, which is a mixture thinner. Due to the content of phenol and formaldehyde, it is classified as dangerous substances. Consumption of sodium formate: 2-3% by weight of cement.

4. Ammonia water. It is sold as a 25% aqueous solution suitable for use at the lowest temperatures (theoretically ammonia water can be used even at -100°C). Positive properties - not only does not provoke corrosion, but, on the contrary, creates an effect on the reinforcement protective film, significantly increases frost resistance finished construction. In the warm season, ammonia in the form of a gas evaporates from concrete and it becomes the same as mixed with ordinary water.

Complex means

Complex additives suitable for use at temperatures down to -20°C:

• calcium nitrite and nitrate (NNK);
• calcium nitrite with urea (NKM);
• nitrite and calcium nitrate with urea (NNKM).

Complex frost-resistant additives for concrete, suitable up to -30°C:

• nitrite, nitrate and calcium chloride (NNHK);
• nitrite, nitrate and calcium chloride with urea (NNHKM).

Subject to the ratio between salts and urea in a mixture of 3:1, the listed antifreeze additives do not contribute to the oxidation of reinforcement, do not reduce frost resistance. They are not used in the manufacture of:

• span structures made of reinforced concrete, if their length is more than 6000 mm;
• products on the surface of which the appearance of efflorescence is not allowed;
• structures exposed to sulfate type corrosion;
• structures located at a distance of less than 100 m from sources direct current high voltage.

Complex PMD can be made from individual components with your own hands or purchased ready-made in liquid form with already selected proportions. It is more profitable to use professional complex solutions due to lower consumption. Several options for such additives:

• Ivitek - up to -10°C.
• Frieze De Lux - up to -15°C, during masonry, plastering work, as well as pouring screeds.
• Hermes - up to -30°C, optional positive properties- reduces cement consumption by 10%, increases strength characteristics by 14%.
• Establishes Safescreen SN1 - during the construction of monolithic and prefabricated monolithic structures and products made of concrete or reinforced concrete, it is also suitable for adding to masonry, insulating and assembly mortars.

For efficient and safe use antifreeze liquids, you must follow the rules:

1. Added to concrete with the last third portion of water, which must be heated.

2. It is undesirable to make a dry mix.

3. To obtain the effect, you should wait for some time (up to 15 minutes). This is necessary for uniform distribution of the substance.

4. The temperature of the mixture at the outlet of the mixer should be in the range from +15 to +25C.

5. During snowfall, it is imperative to install a canopy over the tank. Otherwise, the snow, getting into the mixture, will worsen its properties, as it will change the ratio of the components. Laying during precipitation is not possible. If the snowfall begins during pouring, then the already laid concrete is covered with a layer of waterproofing.

6. When working with the addition of anti-frost ingredients, as well as when mixing, be sure to use protective equipment: gloves, goggles. In case of contact with skin - wash with soapy water, in eyes - rinse abundantly clean water and see a doctor.

7. Never pour PMD residues onto the ground, into sewers or waterways.

Despite the introduction of anti-frost components into the composition of the mixture, concrete in winter time it is recommended to cover and warm.

Do-it-yourself antifreeze additive

If for some reason it is not possible to purchase PMD professional quality, then it is permissible to use the usual technical salt - sodium chloride. An additional advantage of this tool is that it reduces the consumption of cement. The disadvantage is that it increases the corrosion of the metal, therefore it is impossible to use salt for concrete used for the manufacture of reinforced products and structures, as this leads to peeling of the frame, deterioration of performance. Salt consumption depending on the air temperature at the construction site:

• not lower than -5°C - no more than 2% by weight of the solution;
• from -5 to -15°C - up to 4%.

When using technical salt instead of ready-made PMD, concrete strength development is worse - 100% of the design will be only three months after pouring a solution with a 2% salt concentration. If sodium chloride is poured up to 4%, then during the same time the concrete will gain only 50% strength. It is acceptable to use it as an independent additive, but best effect can be achieved in combination with calcium chloride. It is administered in an amount of 0.5% by weight of the mixture at temperatures up to -5 ° C and up to 2% if it is from -5 to -15 ° C outside.

Price

The price depends on the composition and volume of the party. They can be bought as powders, packaged in 25 and 50 kg bags, or liquids in 10 or 20 liter cans.

Minimum prices for large batches of antifreeze additives in concrete:

Via various formulations you can solve the problem of slowing down and completely stopping the maturation of concrete at low air temperatures (below + 5 ° C) on your own. The need for their application arises if for some reason it is necessary to continue construction in the winter period.

This measure is forced and may lead to deterioration specifications. Many of the components of PMD are themselves toxic or are capable of releasing them over time. Therefore, it is recommended, if possible, to avoid introducing these agents into the solution, to supplement them with plasticizers.

In winter, when the temperature outside drops below zero, the construction of reinforced concrete, monolithic and concrete structures becomes more complicated. The liquid included cement mortar, begins to crystallize, as a result, the process of concrete hardening almost completely stops.

As soon as the warm season sets in, the hydration of the cement resumes, and the mortar that has frozen during the construction phases has a high thermal conductivity and low strength. This is due to the fact that the frozen water expands, making the concrete loose. In order to eliminate such consequences, it is customary to use antifreeze additives. They resist liquid crystallization at sub-zero temperatures.

Additives in concrete

Having visited hardware store, you can find concrete additives in large assortment. For example, sodium nitrite is in the form of a liquid or white crystals. Carbamide is known by its second name - urea - and is produced in the form of colorless crystals. You can find compounds of calcium nitrate and urea. The kind of white powder is sodium formate.

The dark brown liquid is a compound that suggests the presence of:

• acetylacetone;
• nitrochloractinide;
• acetoacetic ether.

It is noteworthy that this composition is used at temperatures up to -25 ° C. Asol-K is made from special modifiers and potash solution. It is able to withstand temperatures down to -10 °C, while when the temperature changes above 0 °C, concrete hardening is accelerated. High-quality antifreeze for mixtures is Hydrozim, which provides hydration at temperatures below -15 ° C. From NH3 gas and ordinary water, a composition is made that can withstand frosts down to -30 ° C. Hydroconcrete has plasticizing properties, which can be used at temperatures not lower than -15 °C.

Additives for cement slurries

The antifreeze additive in the solution allows the latter to be used in the construction of monolithic structures, buildings and the manufacture of reinforced concrete elements. Today, such additives are presented in a wide range, but the most popular are electrolyte compositions and their compounds. They provide antifreeze effect and accelerate the hardening of the solution. Among the most common are:

• HK, HH1.
• NNHC.

sodium formate

Formate is an antifreeze additive that has the appearance of a crystallized white powder that dissolves well in water. An additive is made from sodium salts of formic acid. The main actions are aimed at reducing the temperature of the water in the solution and prolonging the hydration of the concrete.

The additive does not have plasticizing properties and is capable of creating tension in the structure due to salt crystallization. In order to avoid this, you should additionally use the C-3 plasticizer, which is available in liquid and powder form.

Consumption

The consumption of an antifreeze additive must be known in order to purchase the right amount of the product. In the manufacture of a solution with an antifreeze additive FN + S-3, warm water, into which sodium formate and a plasticizer should be poured. The amount of additive is determined depending on weather conditions. If the temperature varies from 0 to -5 ° C, then the consumption will be 3% of the total mass of cement.

When the temperature changes in the range from 0 to -10 ° C, an additive in the amount of 4% by weight of cement should be used. The amount of additive increases to 6% if the ambient temperature drops to -15 °C. The volume of C-3 plasticizer always remains at the level of 0.8-1% by weight of cement, which does not depend on air temperature. For an antifreeze substance, the consumption will be different. This parameter will be influenced by the properties of the additive and the air temperature.

Application of additives

Antifreeze additives must be added to the solution along with the liquid. It is desirable to do this with the last third of the water. Additives should not be added to the dry mix. As soon as the additive is added, you should wait a certain time, which is necessary for the distribution of the components. Antifreeze additives are used at sub-zero temperatures according to certain rules.

If you have to work in snowy conditions, then it is important to take care of shelter. When the solution leaves the mixer, it is important to keep its temperature in the range from +15 to +25 °C. The working mixture should be prepared using heated water. Aggregates are heated before direct use.

Application restrictions

Antifreeze additives of some types can be used subject to restrictions. They apply to prestressed structures and products that will be subjected to dynamic loads. It is not allowed to use solutions of chloride salts when embedding the joints of reinforced concrete structures. This applies to products that have embedded parts and fittings. The rule is relevant if chemical protection has not been carried out.

Mixtures of antifreeze additives should be applied after preliminary testing of the samples for corrosive attack. The described means can cause efflorescence on the concrete surface, as well as reduce the strength characteristics of structures. Concrete with additives must have a positive temperature by the beginning of curing.

This parameter should be higher than the outside air temperature by 5 °C or more with a plus sign. For example, if the air temperature is -13 °C, then the concrete temperature should be +18 °C. Unburied surfaces of structures should be thermally insulated to prevent freezing of water from these areas.

The use of antifreeze additives requires compliance with the outside air temperature limits. If chloride salts (sodium nitrate) are used, the temperature should be -15°C or higher. As for potash, this limit will be -25 ° C. The technology of using the described additives has one important virtues, which consists in the minimum material and physical costs for implementation. The disadvantage of technology is a long period acquisition of critical strength by the structure. If the rules for using additives are violated, some problems may arise, such as efflorescence on the surface and corrosion of the reinforcement.

When an antifreeze additive is used in concrete, complex methods of maintaining structures are often used. Thermos technology is used to reduce the hardening time. To do this, the mixture is prepared on the heated components of the liquid with the thermal insulation of concrete.

Why You Should Use a Chloride-Based Supplement and When You Should Avoid It

Antifreeze additives made on the basis of chlorides have many advantages, among them should be highlighted:

• low cost;
• no effect on the structure of the solution;
• no effect on the rate of solidification, so that the solution can be prepared in advance;
• an increase in the mobility of the particles, due to which it is possible to give the solution the desired shape.

The above additive has a minus, which is expressed in high level corrosive activity. As a result, such a tool can be used only for those structures that do not have reinforcement and metal in the structure. The latter begins to oxidize, exfoliate from the structure, thereby violating the integrity.

Precautions for use

Wear protective gloves when handling additives. If the product got on open areas skin, they should be washed with soap and water. The additive should not get into the eyes, but if this could not be avoided, then they should be rinsed large quantity water and see a doctor. Additives must be disposed of in accordance with local regulations, as these formulations contain harmful components. This indicates that the mixture must not be poured onto the soil, discharged into sewers or water bodies.

Conclusion

Using antifreeze additives, it is possible to increase the structural strength by almost 2 times. These ingredients allow you to save on cement, because it can be of a lower class, which means it will cost less. Structures can be made of less impressive thickness, while strength and other properties will not be lost.