Winter additives in concrete and mortar. Technological features of pouring concrete at sub-zero temperatures. How to pour a concrete foundation in winter

The optimal temperature range for the construction of concrete foundations using traditional technologies is from 15 to 25 °C. 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:

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.
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 ambient temperature, the longer the hydration takes. 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 temperatures, 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 autumn and winter period:

introduction of antifreeze additives into the concrete mixture;
warming up monolithic construction 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 chemicals are divided into groups according to the way they affect the concrete mixture:

Additives that prevent water from freezing sub-zero temperature and allowing the hydration of the cement to proceed. They are best used in combination with heating to shorten setting and curing times.
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.
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:

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.
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 when too low temperatures(-15 ° C and less) additives are indispensable.

The device of a 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

In winter, when the temperature outside drops below zero, the construction of reinforced concrete, monolithic and concrete structures becomes more complicated. The liquid, which is part of the 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 right amount funds. 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. Use when sealing joints reinforced concrete structures solutions of chloride salts are not allowed. 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 used after preliminary testing of 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 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 advantage, which is 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.

Undoubtedly, to engage in construction in winter time harder than in summer. Most often, the weather conditions are not too conducive to the performance of high-quality work. Usually work in severe frosts continue either professional construction teams, or craftsmen who want to move into their own homes as soon as possible. invaluable help for those and others there will be specialized antifreeze additives. The use of the latter helps to prevent premature hardening of the cement.

What is an antifreeze additive in the solution?

As a rule, with a significant decrease in ambient temperature, builders begin to experience additional difficulties in working with concrete and all kinds of solutions. This is because cement-based compounds cannot stand frost. So, at a temperature of -5 o C, it would seem that high-quality solutions cease to gain strength.

AT last years craftsmen are increasingly using antifreeze additives that can withstand temperatures down to -35 ° C or more. Specialized formulations for contain chemicals, active ingredients which are reduced As a result, the concrete sets in the masonry even in extreme cold.

The problem of organizing brickwork in cold weather

When building in winter, it becomes most problematic to provide the structures with the necessary strength. When the temperature drops below zero, the liquid in the solution crystallizes. Thus, the process of cement hydration is stopped.

With an increase in air temperature, the ice formed inside the masonry and on the surface of the building material begins to melt, which necessarily causes a decrease in the adhesion of the solution. Another negative effect is the formation of small cavities in the concrete structure, which can subsequently lead to a rather rapid destruction of walls and ceilings.

Features of the preparation of the solution

In spite of difficult conditions work, can be no less qualitative than in the warm season. However, in order to obtain the expected result, it is necessary to prepare a special solution, which must contain antifreeze additives.

Starting to prepare the building mixture, you need to take care of personal safety. It should be borne in mind that almost all antifreeze additives differ in composition based on rather aggressive chemicals that can be harmful to health. Therefore, during the preparation of concrete, it is necessary to work in tight gloves, goggles, rubber boots and, if possible, in overalls.

With a more serious cooling down to -30 ° C, it is advisable to use potash. The advantage of this solution is protection against corrosion manifestations in case of construction reinforced floors. The use of potash also prevents the appearance of efflorescence on the hardened mortar. As for chlorine-containing additives, the latter do not slow down the destruction of the reinforcing parts of building structures.

Antifreeze additive: consumption

In the manufacture of formulations for brickwork it is important to observe the necessary proportions. They depend primarily on the ambient temperature.

Let's look at the average norms typical for the use of the most popular "antifreeze" in the table. It reflects the consumption of antifreeze additives in percentage to the mass of cement.

Air temperature	sodium formate	Potash	sodium nitrite

plasticizers

Can be replaced with special plasticizers, which increase the elasticity of the mortar and reduce the need for liquid. Thanks to the use of the latter for several days, there are practically no changes in the laid composition. Thus, the solution has time to seize even with significant frosts.

In addition to masonry, such a specific anti-frost additive can be used for glue, preparing mixtures for arranging self-leveling floors, and when performing concrete work. Plasticizers are mixed with a minimum amount of water. Their content in the solution is about 5% by weight of the cement. Compliance with this proportion is sufficient to perform reliable masonry at low temperatures.

What you need to know about masonry work in the winter?

In order not to be disappointed in the results of construction activities that are carried out at negative air temperatures, it is enough to pay attention to the following recommendations:

For masonry, it is forbidden to use building materials covered with snow, frost or ice.
All components of the future solution, including antifreeze additives and plasticizers, should be stored in dry, ventilated areas at room temperature.
Regardless of the composition of the solution and temperature conditions laying in winter is recommended to be done as soon as possible. The lack of delay allows the substances to seize faster.
Going on a break, the rows of masonry must be insulated with plastic wrap or other suitable material suitable for the role of an effective temporary insulator.
As a basis for preparing the solution, it is worth using cement of a grade not lower than M-50. Mixing the components, even in the case of the use of "antifreeze" should be carried out in a warm room.
If necessary, work with low temperatures it is better to give preference to the purchase of ready-made solutions, in which antifreeze agents are added in optimal proportions even at the production stage.

Eventually

While doing construction works in winter, the main thing is not to forget to add special antifreeze additives to the solution. However, the introduction of "antifreeze" in cement composition looks appropriate only if the ambient temperature drops to -5 o C.

During the preparation of the solution, it is absolutely not recommended to use long-stored, old antifreeze additives with a questionable shelf life. Otherwise, you will have to pay with the formation of abundant smudges and efflorescence on the surface of the structures.

The construction of prefabricated concrete and reinforced concrete structures, as well as the construction of monolithic structures, does not cease to increase its pace, but often the craftsmen have to face the rush due to the approaching end of the construction season. This is explained operational characteristics cement slurry, one of which is the presence of a liquid phase, which contributes to the continuous process of hydration and maturation of the composition. If the temperature drops below 5 degrees, the concrete maturation phase slows down, and if negative values it stops, which is due to the crystallization of water, which is part of the cement slurry. This leads to the destruction of the concrete structure, which becomes unusable. Despite this, most craftsmen with experience in the field monolithic construction, are faced with the need to continue the cycle of concrete work in the winter, and therefore, they face the question: “How to extend the liquid phase of concrete, and, consequently, its life. To solve this problem, experts suggest using antifreeze additives in concrete, specifications and the main varieties of which will be discussed in this article.

Antifreeze additives in concrete: main varieties

Antifreeze additives in concrete are a chemical substance in the form of a dry mixture or solution, which, through involvement in the process of concrete crystallization maximum number water, accelerate the process of hydration of the concrete mixture, contributing to the hardening of concrete in conditions of negative temperatures. However, the main purpose of the antifreeze additive is to maintain liquid state concrete mortar and the subsequent acceleration of its hydration, which significantly slows down when negative temperatures.

Important! When using antifreeze additives in concrete, it is important to remember that the strength of concrete with antifreeze additives in conditions of negative temperatures does not exceed 30% of the maximum possible design strength, the remaining 70% of the strength of the concrete is gaining in the process of thawing. In this regard, structures, the concreting of which took place in the winter period, should not be subjected to high loads.

In accordance with the chemical basis, the following types of antifreeze additives in concrete are distinguished:

Antifreeze;
sulfates;
Antifreeze additives-accelerators.

Let us consider in more detail the characteristics of each presented variety.

Antifreeze is an antifreeze additive in concrete, which helps to reduce the crystallization temperature of the liquid that is part of the solution, and also increases or slightly reduces the setting rate of the solution. However, it does not have any effect on the rate of formation of structures.
Sulfate based concrete additives are another popular antifreeze component that provides top speed formation of a dense solution. characteristic feature antifreeze additives based on sulfates is the active release of heat, which begins after they are added to the solution and is accompanied by the interaction of the concrete solution with hydration products. Due to the fact that sulfate-based additives are characterized by strong binding to sparingly soluble compounds, they cannot be used to lower the freezing point of the working mixture.
At the heart of the action antifreeze additives-accelerators lies in the increase in the degree of solubility of the silicate components of cement, which, reacting with the products of its hydration, form double and basic salts, which reduce the freezing point of the liquid component of the concrete mortar.

Important! Modern complex antifreeze additives for concrete not only regulate the kinetics of its strength gain, but also correct its rheological properties. By lowering the crystallization temperature of the liquid component of the solution, they reduce the time of its initial setting, influencing the hardening of the cement stone and increasing its grade strength.

There are several types of accelerator additives, each of which has a certain set of chemical and operational properties. Let's consider them in more detail.

Potash or calcium carbonate, which is a crystalline substance, is a strong antifreeze component, significantly accelerating the process of setting and subsequent hardening of concrete. Like any antifreeze additive, calcium carbonate reduces strength concrete structure, and in order to minimize this Negative influence for construction, experts recommend combining potash with sodium tetraborate or sulfide-yeast mash, the concentration of which should not exceed 30%. Due to the fact that calcium carbonate is a potential dangerous substance, during its operation it is necessary to observe certain safety measures;

Sodium tetraborate, also called brown or sulfate-yeast mash, is a mixture of sodium, calcium, ammonium or lignosulfonic acid salts. Experts recommend adding this substance as an admixture when using calcium carbonate, which helps prevent the loss of strength characteristics of concrete structures after they are thawed. Otherwise, one can observe not only the appearance of cracks in the structures, but also a decrease in their water resistance and frost resistance. Thus, the use of potash as an antifreeze additive without the addition of sodium tetraborate will reduce the strength characteristics of the structure by 20-30%;

sodium nitrite- crystalline powder used as an antifreeze additive to concrete mortar. Given that sodium nitrite is a flammable poisonous substance, during its operation it is important to observe the maximum permissible concentration of the substance, which is determined empirically and usually does not go beyond 0.1 - 0.42 l / kg of cement mortar, provided that ambient temperature will be from 0 to -25 degrees. At the enterprise, in the process of working with sodium nitrite, the maximum permissible concentration of the substance in the workplace should not exceed 0.005 mg/l. In accordance with the requirements of the Research Institute of Concrete and Reinforced Concrete, the container that was used for the transportation, storage and manufacture of sodium nitrite must be marked "POISON". The joint use of sodium nitrite and lignosulfonic acids is prohibited, since their interaction is accompanied by the formation of toxic gases;

sodium formate- white crystalline powder, which also acts as an antifreeze accelerator. In most cases, it is used in conjunction with naphthalene lignosulfonate to improve water-reducing and plasticizing characteristics. Sodium formate is an antifreeze additive in concrete, the consumption of which does not exceed 2-6% of the total mass of cement.

Important! In addition to the above substances, sodium formate on alcohol, calcium chloride, ammonia water and urea.

Advantages and disadvantages of antifreeze additives in concrete mortar

Advantages of antifreeze additives in concrete

Using antifreeze additives in concrete, you will be able to carry out concrete works on the construction site even in winter;
Due to the fact that antifreeze additives increase the degree of adhesion of the mortar components, they significantly increase the strength of the monolith;
Thanks to high strength products made using antifreeze additives in concrete, they can be used for industrial purposes;
They have a positive effect on the durability of the mixture, extending the life of the building;
Increases plasticizing and stabilizing characteristics cement mixture- the use of concrete with increased plasticity makes it possible to manufacture structures that will not crack after the working composition has solidified;
Increases the frost resistance of the concrete mixture. This indicator is especially important for concrete intended for the construction of critical structures, for example, bridge supports. In most cases, it is directly dependent on the density of concrete. More dense grades of concrete are characterized by a large number of possible freeze and thaw cycles;
Unlike alternative methods increasing the frost resistance of concrete, the use of antifreeze additives is characterized by a relatively low cost;
Using antifreeze additives, you will significantly reduce the risk of shrinkage deformations of a concrete monolithic structure;
Improving the moisture resistance of concrete structures by filling the pores with plasticizers that prevent the penetration of water;
The acceleration of the process of hardening of the concrete mortar is the main point due to which the mortar can "not be afraid" of the cold;
By opting for an antifreeze additive in concrete, you will reliably protect the reinforcement used from corrosion processes that occur due to the water that is part of the concrete solution.

Disadvantages of antifreeze additives in concrete

The desire to increase the reliability of the strength characteristics of concrete, it is necessary to increase the consumption of cement;
The individual components that make up the additives are poisonous;
In some cases, the declared power of concrete is reduced;
In the case of using antifreeze additives in concrete, the speed of the set of strength characteristics of the concrete structure is reduced.

Experts advise introducing an antifreeze additive into the concrete solution along with water. It is important to note that it is desirable to do this with the last third of the liquid. It is not recommended to add additives to the dry mix. By adding to the solution antifreeze additive, wait a certain period of time, during which there will be a uniform distribution of the components.

When carrying out installation activities in conditions of negative temperatures, follow the instructions below:

If you are working in snowy conditions, take care to organize appropriate shelters;
The temperature of the solution that came out of the mixer should not go beyond the recommended range from +15 to +25 degrees;
To prepare the working mixture, experts recommend using heated water;
As for the heating of aggregates, it is recommended to do it before direct use.

Important! Specialists in the construction industry recommend paying attention to SNIP 3.03.01, according to which, in order to achieve the necessary strength characteristics of the concrete solution, it is necessary to comply with the requirements for the care of concrete in the winter. In the process of performing these measures, by the time the temperature for which the additive dosage was calculated was reached, it is not recommended to achieve a structural strength exceeding 20% of the declared design strength.

Dosage and consumption of antifreeze additive in concrete

The dosage of the antifreeze additive in concrete, the consumption of which is an extremely variable parameter, is selected taking into account each specific situation through tests in production and laboratory conditions.

The consumption of antifreeze additive depends on the following factors:

Ambient temperature under which installation activities will be carried out;
Declared grade strength of the cement used;
Chemical-mineralogical and material composition of the cement used in the process of work, as well as its estimated rate of curing;
The temperature of the solution, which it will reach at the outlet of the mixer;
Maintenance conditions for concrete structures.

Important! In the case of long-term use or storage of a solution in which additives were added, it is necessary to check its homogenization by periodically stirring. Calculation required amount antifreeze additive is produced with an error of 2%.

Do-it-yourself antifreeze additive in concrete

If the warm days have already passed, but you are suddenly faced with the need to pour a monolithic structure, you can not do without the use of an antifreeze additive in concrete. The most preferable option, in this case, would be to purchase an antifreeze additive in a specialized store, which is explained by their relative cheapness, low consumption and the ability to significantly improve the properties of the concrete solution, subject to minimal negative consequences. If the proposed scope of work is small, and you plan to carry out installation activities at a temperature of at least -10 degrees, this option is the most optimal.

However, if you do not have the opportunity to purchase a ready-made antifreeze additive in concrete, you can easily make it yourself, since the only material that you need in the process of work is chlorides (salts). Chloride salts reduce the freezing point of the solution, reduce the time of its initial setting and reduce the consumption of cement. However, experts are sure that a self-made chloride-based antifreeze additive can only be used for non-reinforced structures, which is due to corrosion processes developing under the action of chlorides.

Benefits of an antifreeze additive based on chlorides

Low cost;
No effect on the rate of hardening of concrete, due to which, the preparation of the solution can be carried out in advance;
No effect on the structure of the cement mortar;
Increased particle mobility, thanks to which you can give the cement mortar the desired shape.

Disadvantages of antifreeze additive based on chlorides

A high level of corrosive activity, as a result of which, an antifreeze additive based on chlorides cannot be used for the manufacture of structures in the structure of which metal and reinforcement are present. The latter will oxidize under the influence of chlorides and exfoliate from the concrete structure, violating its integrity.

How does ambient temperature affect chloride consumption?

Calculation of the proportion of chlorides in ready solution produced according to the following scheme:
If installation activities are carried out at an average daily temperature of at least -5 degrees, the optimal proportion of chlorides in the finished solution should not exceed 2%;
If work is carried out at lower temperatures (-6 to -15 degrees), the optimal proportion of chlorides should be 4% of the total mass of the solution.

Important! In this case, the scheme for gaining the expected strength of the structure during drying under conditions of negative temperatures will look like this:

For the first option, where the salt concentration is 2%:

30% after a week;

80% after a month;

The construction will reach 100% strength only after 3 months.

For the second option (salt concentration is 4%), these figures will be 15%, 35%, 50%, respectively.

Important! Despite the fact that salt is an independent antifreeze additive, experts recommend using it in conjunction with calcium chloride, mass fraction which, when used at temperatures up to - 5 degrees, is 0.5% by weight of the solution, and 2% - when used at temperatures from -6 to -15 degrees.

Precautions when working with antifreeze additives

In the process of working with antifreeze additives, it is necessary to use protective gloves;
In case of contact with exposed skin, wash with soap and water. Avoid contact of the antifreeze additive with the eyes, if this cannot be avoided, rinse the eyes with plenty of water and consult a doctor immediately.
Disposal of the additive is carried out in accordance with local regulations, which is explained by the presence of harmful components in the composition of antifreeze additives. As a result, it is forbidden to pour the mixture into the soil, waterways or sewers.

The strength and durability of any building depends on the foundation that serves as its support. Currently, the most demanded in construction is concrete base capable of supporting the weight of a heavy structure. Since after the construction of the house the supporting structure will be difficult to repair, it is very important to properly fill the foundation in order to prevent it from sinking into the ground, as well as from the formation of cracks and other defects on it.

At what temperature can the foundation be poured

Planning the construction load-bearing structure, it is necessary to take into account weather conditions, brand and quality of cement. An important role in ensuring the strength of concrete is played by special additives, allowing to reduce the crystallization temperature of water, as well as maintaining the optimal operating mode during the period of solidification of the foundation. After pouring, the base sets within a day and then gains strength in 28 days. The temperature range from + 3 to + 25 ° C is considered standard for creating a base. It is known that the warmer it is outside, the faster the mortar dries, but the heat can be dangerous for fresh concrete.

If at a temperature of + 5 to 15 ° C the composition seizes naturally, giving off heat environment then in too hot weather it doesn't happen. Under such conditions, the concrete frame may begin to form when the volume of material is further increased. Cooling down, the surface begins to settle, and the already formed crystalline structure prevents this process. As a result, due to internal stress the foundation may become covered with shrinkage cracks 4–12 hours after pouring. So that the base does not crumble at temperatures above + 25 ° C, it is worth using quick-hardening Portland cement, which after 5–6 hours of pouring must be poured with water and shaded with old rags, cardboard or sawdust. To slow down hydration, it is permissible to introduce modifying additives and plasticizers. If cracks appear, re-tamping is required.

In hot weather, the foundation may crack

Is it possible to pour the foundation in winter

by the most favorable time for the construction of the supporting structure, the period from April to November is considered. However, the situation may turn out so that the filling will need to be carried out in the winter, because in some regions of Russia there is practically no summer. Modern building technology allow you to create solid foundations even in cold weather. The construction of the foundation in winter is especially important on shaky soils. After waiting for them to freeze, you can dig an excellent pit. In addition, for purchasing building materials off-season, you can save a certain amount. Most often, strip foundations are erected in winter using concrete blocks and concrete pile structures designed for lightweight wooden objects.

According to various estimates over the past five years, the share winter concreting in the total volume of construction varies from 10 to 17%. This is a solid jackpot for manufacturers and suppliers of construction chemicals, and, in particular, those additives that must ensure the efficiency of the process at low temperatures. On the other hand, it was manufacturers who influenced the growth of winter construction. The interest here is mutual.

How cement mortar behaves in frost

When planning winter work, it is worth remembering that ordinary concrete is not suitable for them. In frost, it is permissible to use only cement with special additives and modifying additives. The latter reduce water consumption by about 10-15%. At air humidity of 60% and above, the use of modifiers is not recommended, besides, it is worth remembering that they can react with some metals. To ensure the strength of the structure, concrete must be heated in the first two days after pouring. The desired temperature regime of the mixture can be maintained using:

thermal guns;
special heating wire laid when pouring concrete;
electrodes (reinforcing bars) to which voltage is applied.

There is also a way to warm up the concrete mixture using welding machine, but it essentially boils down to the use of electrodes and is applicable only for small volumes of pouring.

Only water and fillers are allowed to be heated, but not cement, otherwise it will lose its qualities.

For winter work requires concrete with special additives

Typically, in the regions of the Russian Federation, a solution with a temperature above 21 ºC is not used, taking into account the fact that 4.5–5 ºC will go into the atmosphere. Therefore, for the working composition, the liquid is heated to 32 ºC. More hot water first stir with fillers, and then in portions - with cement.

Is it possible to pour concrete in frost without heating

Whether it is possible to pour the foundation in cold weather without heating should be discussed separately. Even temperature fluctuations from +5 to 0 ° C for concrete mortar are considered winter. In the cold season, when concreting, it is important to ensure smooth hardening of the mortar by at least 60%. This guarantees the preservation of the structure of the base and its ripening when the thaw comes.

However, the foundation will gain strength only at a positive temperature of the solution, therefore, without artificial heating for construction work, you need to choose a fine winter day. The composition of cement is also important: in the so-called cold concrete includes antifreeze additives that lower the freezing point of water. For these purposes, potassium and sodium chlorides are used in concentrations from 2 to 15%. Using anti-frost modifiers, it is possible to dismantle formwork with M200 mortar already at 40% strength, M400 - at 20% and M300 - at 30%.

Video: heating concrete foundation in winter

When can you pour the foundation in the spring

Those who decided to start building the foundation in early spring(until April), care should be taken. First you need to wait for the thawing of the soil and heat, when at night the temperature does not drop below 0 ° C. It is also necessary to take into account the "drying" of roads, which lasts one to two months, during which heavy vehicles (concrete pumps, scows, toners and other vehicles) are restricted from moving on regional roads. Without the listed transport, it is impossible to build a monolithic foundation. From April the cost Supplies starts to grow.

In the spring, the roads are washed away, so heavy equipment cannot pass through them.

Unexpected frosts can cause irreparable damage to the structure, so when the weather forecast is unstable and work is already planned, it is recommended to insure the purchase of antifreeze fillers. Even at an air temperature of +23 °C, concrete gains its normative strength only after three weeks. At lower temperatures, the terms increase markedly, as a result, it is impossible to hurry with laying the walls after pouring.

As practice shows, a house built on bare ground costs a few years. In the absence of a base, the lower blocks or wooden crowns collapse due to soil deformation.

Is it possible to pour the foundation in the rain

At present, rain is not a reason to stop concreting, as it was in the recent past. Using simple equipment and a suitable brand of cement, you can pour the foundation in wet weather. By itself, water does not have a negative effect on the solution, just before it hardens, erosion and imbalance can occur. Therefore, everything depends on the strength of the precipitation.

If the site is not flooded with rain, then a canopy will be enough to continue work. Ordinary will protect from light rain polyethylene film, which must be used with care, because concrete only cures for fresh air. Of course, in warm and sunny weather, the solution is better saturated with carbon dioxide and hardens faster, forming solid foundation. But there are also advantages to building foundations in the rain, since concrete mix becomes more durable at 80% humidity.

Polyethylene film cannot be kept on the surface for a long time, since the concrete does not harden without fresh air

How to work during the rain

The main requirements for the ongoing work on pouring the foundation in the rain:

The content in the solution of cements M400, M500 and M600, created for work in contact with moisture.
The right way to lay concrete. unusual shape foundation or its deepening involves the use special equipment, which does not allow the formation of voids and displaces excess liquid.
The use of waterproofing, which can be removed no earlier than two to three days.

The modern market offers a wide range building mixtures with different settings. Fast-hardening and long-hardening compositions are produced, as well as concrete with antifreeze additives. But pouring the foundation in extreme weather conditions is a risk that must always be taken into account. At low temperatures, cracks can form in the base, and erosion can occur during precipitation. All this can adversely affect the strength of structures.

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