Liquid antifreeze additive in solution. Pouring concrete at sub-zero temperatures - possible options for concreting. External conditions "for ripening"

Minimum temperature for pouring concrete - this is approximately 5 ° C. That is, this indicator is considered critical - up to this figure, any work with concrete can be carried out as usual. However, it must be remembered that optimum temperature for pouring concrete - 17-25 ° C, since such conditions make it possible to obtain the maximum strength of the solution. If the temperature approaches 5°C, the grout will likely be less solid and less durable and will not reach the brand specifications. Even when carrying out work, it should be remembered that the hardening time can increase significantly.

However, sometimes it becomes necessary to construction works in winter period at negative temperatures Oh. There may be several reasons:

• limited construction time during the summer period due to unfavorable climatic conditions;
• the need to pour concrete on loose soils;
• seasonal decline in prices for materials, including cement;
• reduction in the cost of work by specialized firms due to low demand for their services.

There are two main technologies with which you can carry out concreting in the cold season.

The first is that concrete is poured at low temperatures on heated fittings, which can be ordinary electrodes. A standard 12-volt cable is connected to the armature, through which current flows. This is quite enough to metal rods heated up and heated the solution, preventing it from freezing. The disadvantages of this method are obvious - in addition to the use of special materials, you will have to spend a hefty amount on electricity.

In addition, pouring concrete at low temperatures can be carried out using warm formwork. The essence of this technology is to insulate the solution with special heat-insulating materials, such as foam or mineral wool. But there are also disadvantages here - it is necessary to cover concrete from all sides, which leads to high consumption. auxiliary materials and increase the time of work.

Pouring concrete at low temperatures: general recommendations

Thus, we can conclude that pouring concrete at negative temperatures should be carried out only if it is not possible to postpone this stage of construction work until more favorable conditions occur.

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Concrete work in winter conditions

Features of concreting at negative temperatures

In the production of concrete and reinforced concrete works in winter conditions, when the expected average daily outdoor temperature is below 5 °C and the minimum daily temperature is below 0 °C, as well as when concreting structures located in permafrost soils, concreting methods are used that make it possible to obtain concrete of the required quality.

If not applied special ways concreting, then when the concrete freezes, the free water contained in it turns into grandfather and the hardening of the concrete stops. If hardening did not begin before freezing, then it will not begin after it, but if it did, then it practically stops until the free water in the concrete is in a frozen state. Water frozen in concrete increases in volume by approximately 9%. The resulting internal ice pressure breaks the weak bonds in the unhardened concrete.

Water accumulating on the surface of grains of coarse aggregate, when frozen, forms a thin ice film that breaks the adhesion between aggregate and mortar and reduces the strength of concrete. An ice film forms on the reinforcement, which breaks the adhesion of the reinforcement to the concrete.

When concrete thaws, the ice in it melts and the hardening of concrete resumes, but the final strength of concrete, its density and adhesion to reinforcement are reduced. These losses are greater the more early age frozen concrete.

The most dangerous freezing of concrete during the setting of cement. Also harmful is repeated freezing and thawing of concrete at the beginning of hardening, which happens when thaws are replaced by frosts. The strength of concrete at the time of freezing or cooling below design temperatures, the so-called critical strength, at which the final strength does not decrease or decreases slightly, should be indicated in the work design or in the technological map.

For concrete without antifreeze additives of monolithic structures and the monolithic part of prefabricated-monolithic structures, the strength at the time of freezing should be at least 50% of the design one at a concrete grade of 150, 40% for concrete of grade 200-300, 30% for concrete of grades 400-500, 70% - regardless of the brand of concrete for structures subjected to freezing and thawing at the end of curing, 80% - for concrete in prestressed structures, 100% - for concrete structures exposed immediately after the end of curing to the design water pressure, and structures to which there are special requirements for frost resistance and water tightness.

For concrete with antifreeze additives, the strength at the time of its cooling to the temperature for which the amount of additives is calculated must be at least 30% of the design value for grades up to 200, 25% for grade 300 concrete and 20% for grade 400 concrete.

The conditions and period by which the freezing of concrete blocks of massive hydraulic structures is allowed are indicated in the project.

Concrete that has reached critical strength by the time of freezing acquires design strength only after thawing and keeping at a positive temperature for at least 28 days. In cases where structures concreted in winter (including concrete of prefabricated elements with conventional and prestressed reinforcement, which are part of prefabricated monolithic structures) are subject to full loading at a negative outside temperature, it is required to withstand the concrete at a positive temperature until until design strength is reached.

The value of the strength of concrete in the structure at the time of its freezing is determined by the minimum strength of the sample from the control series.

To obtain the necessary strength of concrete, special measures are taken to prepare the components of concrete and prepare concrete mix. Particular attention is paid to the protection of concrete structures from direct exposure to negative temperatures and wind.

It is necessary that the concrete mixture placed in the formwork has a certain temperature set by the calculation.

Various methods are used to protect concreted structures from exposure to negative temperatures, to create an artificial heat and moisture environment for concrete prepared on heated materials, and to keep it under such conditions until the required (critical) strength is acquired.

Concrete laid in massive structures in winter is most often cured using the thermos method, based on the use of insulated formwork, the heat of the heated components of the concrete mixture and the heat released during setting and hardening of cement. Well-covered concrete cools so slowly that it has time to gain critical strength by the time it freezes.

To expand the scope of the thermos method, they use preliminary electrical heating of the concrete mixture before laying it in the formwork, chemical accelerator additives, cements with increased heat release and quick-hardening cements, and also combine the thermos method with various methods heating of concrete, for example with peripheral electric heating or heating of structures.

When using preliminary electrical heating of the concrete mixture, the heating temperature for concretes based on Portland cements with a content of tricalcium aluminate up to 6% should not exceed 80 ° C; on Portland cements with a tricalcium aluminate content of more than 6%, it is established by a construction laboratory after experimental verification; for concretes based on Portland slag cements - should not exceed 90°G.

The concrete mixture is heated in specially equipped bunkers and tubs, which ensure its uniform heating, as well as in car bodies equipped for this purpose.

Often, when concreting foundations located in separate pits, the thermos method is combined with the use of heat transfer from thawed soil. In this case, the pits are well insulated from above, due to which a slight positive temperature is established in them.

Concrete in thin structures cools quickly, so they have to be heated electric shock, ferry or warm air. Sometimes, in order to save electricity, they combine the method of a thermos with heating.

Lightweight concrete on porous aggregates in winter conditions is kept according to the thermos method with preliminary electrical heating of the concrete mixture.

In addition to the above methods winter concreting based on the hardening of concrete at a positive temperature, there is a method of hardening of concrete at a negative temperature. In this case, the concrete mixture is prepared with the introduction of antifreeze additives. Antifreeze additives lower the freezing point of water to such an extent that they provide hardening of concrete at negative temperatures down to -25°C. When choosing a concrete curing method, first of all, consider the possibility of using the thermos method, the thermos method with additives - hardening accelerators.

If, using this method, it is impossible to obtain the required strength of concrete within the specified time, then the possibility of using concrete with antifreeze additives, methods of electrical heat treatment, heating with steam, warm air is consistently considered. If it is impossible to keep concrete in structures with the help of these measures, concrete work is carried out using greenhouses.

One or another method of producing concrete and reinforced concrete works in winter conditions is adopted on the basis of comparative technical and economic calculations.

To Category: - Concrete works in winter conditions

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, should be considered weather, 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 to the 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 technologies make it possible 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, you can save a certain amount on the purchase of building materials out of season. 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 of winter concreting in the total volume of construction ranges 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 method of heating the concrete mixture using a 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

About 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 decide to start building the foundation in early spring (until April) should be careful. 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. An ordinary plastic film will protect from light rain, which must be used with caution, because concrete freezes only on fresh air. Of course, in warm and sunny weather, the solution is better saturated with carbon dioxide and hardens faster, forming solid foundation. But building foundations in the rain also has its advantages, since the concrete mixture becomes stronger 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:

1. The content in the solution of cements M400, M500 and M600, created for work in contact with moisture.
2. 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.
3. The use of waterproofing, which can be removed no earlier than two to three days.

The modern market offers a wide range of building mixtures with various parameters. Fast-hardening and long-hardening compositions are produced, as well as concrete with antifreeze additives. But pouring a foundation in extreme weather is a risk that must always be considered. At low temperatures, cracks can form in the base, and erosion can occur during precipitation. All this can adversely affect the strength of 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 winter time, in connection with which, they face the question: “How to prolong the liquid phase of concrete, and, consequently, its vital activity. 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 the liquid state of the concrete solution and the subsequent acceleration of its hydration, which significantly slows down at low temperatures.

Important! When using antifreeze additives in concrete, it is important to remember that the strength of concrete with antifreeze additives under conditions of negative temperatures does not exceed 30% of the maximum possible design strength, the remaining 70% of strength is gained by concrete during 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 additives based on sulfates 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 primary setting, affecting 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 the strength of the concrete structure, and in order to minimize this negative impact on the building, 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 temperature environment 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 can be used as antifreeze additives under conditions of negative temperatures.

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 work at 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 large quantity 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 concrete shrinkage. monolithic construction;
• 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. The calculation of the required amount of antifreeze additive is made taking into account 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?

• The calculation of the proportion of chlorides in the finished solution is carried out 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 hitting open areas 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 reliability and durability of the entire structure directly depends on the strength of the foundation. When planning such a "zero" construction cycle, many factors must be taken into account. Of particular importance is the information at what temperature the foundation can be poured.

If you do not take into account the weather conditions during the process, the quality and grade of the solution, the use of additives that can reduce the temperature crystallization of water, measures to maintain the necessary conditions for the maturation of concrete, then the work can be done in vain, and the erected foundation of the building will begin to crumble immediately after hardening.

Some owners of suburban areas are in a hurry to build capital structures on their newfound territory, not paying attention to the season. In some, rather rare cases, this is justified, however, there are many difficulties with this approach, and they begin already at the stage of preparatory work.

Regardless of the season, preparatory activities will include a whole list of mandatory work:

• The place where the foundation for the construction of the structure will be arranged must be cleared of the topsoil and marked accordingly. Removing the top layers of soil in frosty weather is a rather time-consuming task.
• When a common place is determined, the internal boundaries of the trench are marked, which must be dug under the foundation. Its depth should be from 500 to 800 mm - this value will depend on the type of soil of the area where construction is being carried out, the depth of their freezing, the features of the building being erected (its number of storeys, wall and roof material, etc.) Earth-moving equipment for extracting narrow and deep enough trenches with even walls can not always be used. Manual digging of frozen soil is another difficulty during winter work.
• A waterproofing and reinforcing pillow is laid at the bottom of the trench pit. Sand is laid first and compacted well, the layer thickness can be from 100 to 150 mm. Gravel is poured on it and it is also well compacted. Very often in winter, both sand and gravel are in a state “stuck” by frost. There is a good chance that as the temperature rises, the pad may lose the required density, even with the highest quality compaction.

• In addition, there is no complete certainty that during the general thawing of the soil in the spring and its possible movements, the entire structure of the foundation under construction will not “lead”, and this can lead to the formation of internal stresses and cracks.
• The next step is to install or wooden shields, which waterproofed dense plastic wrap. On the severe frost polyethylene often loses elasticity, becomes brittle, and waterproofing can be damaged.

• Fixed formwork made of extruded polystyrene foam can also be used, which, in addition to its direct function, also performs the role of a heater.

• Further, it is necessary to install a reinforcing structure in the formwork, which is welded or twisted with steel wire. Reinforcement for this design is taken from 10 to 15 mm thick. We must not forget that reinforcing steel has a fairly significant coefficient of linear thermal expansion. A reinforcing cage welded in severe frost will certainly tend to change dimensions with increasing temperatures. This is another significant "additive" to unnecessary internal stresses foundation structures.

Nevertheless, as already mentioned, there are situations when, for one reason or another, the construction of a foundation in winter season is justified:

• This may be due to the nature of the soil. If sandy loose soils predominate in the area where the construction is being carried out, then it is better to build the foundation in frozen solid soil, which retains the shape necessary for the foundation pit.
• Should not be dropped from accounts the impossibility of construction in the summer due to special climatic conditions of the region.
• In a number of areas, due to the poor development of road networks, delivery large volumes building materials or the movement of heavy special equipment is possible only on frozen ground.
• Sometimes to winter construction are resorted to in order to save money, since during this period prices for necessary materials. This will be beneficial if the work is carried out independently.
• Often there is an opportunity to save money by reducing the cost of services by construction companies, due to a sharp decrease in demand for their activities in the cold season.

When all the preparatory processes are completed, it is possible to calculate the density and composition of the solution, the parameters of which will depend on the temperature at which it will be poured into the formwork.

Pouring the foundation with concrete

• Whenever pouring is carried out, the foundation mortar should not be too thin, so it is most often made from cement and medium-sized gravel.
• Often, plasticizers are added to the mortar, which improve the condition and strength, increase its adhesion to reinforcing structures, and increase the moisture resistance of the foundation. In addition, according to manufacturers, when pouring, plasticizers reduce the consumption of cement mortar by 20%.

Due to the fact that plasticizers have a positive effect on the frost resistance of the solution, they are often added in cases where it is necessary to fill the foundation at and below freezing air temperatures.

Optimal conditions for pouring concrete - temperature from 15 to 25 degrees

• According to all recommendations, concrete pouring should be carried out at a temperature of at least 5 degrees - this, in fact, is a critical indicator for normal maturation. However, the summer heat is also not very suitable for these construction processes. The optimal temperature regime for pouring the solution into the pit is +15 ÷ 25 degrees. Such conditions will allow you to get extra costs and technological methods as much as possible solid foundation for the construction of walls and in the shortest possible time.

• In the case when the solution is made independently right at the construction site, all materials used for it should not be in a frozen state and should not contain snow or ice crystals. Therefore, it is better to purchase them in companies that are guaranteed to provide them with proper storage.
• The solution must be poured and distributed over the formwork quickly so that the frost does not have time to grab the moisture in the solution. Therefore, the filling of the entire volume is carried out in such conditions only at a time. If the foundation has a large volume and area, then it is better to use offers of specialized companies, which engaged in the manufacture, delivery and unloading required solution into the prepared formwork.

• It is not recommended to pour concrete in layers, because between them, due to low temperatures, gaps may form, which will make the foundation less durable.

If circumstances have developed in such a way that do work under conditions of critical temperatures, you need to know that the processes of setting and hardening will be increased several times. Therefore, pouring the foundation in the winter is carried out only when absolutely necessary.

Below is a table that clearly shows how the ambient temperature affects the maturation time and the full set of the required strength of a conventional concrete mortar grade M200 - M300, made on the basis of Portland cement M-400 or M-500.

Notes:

- percentages are calculated in relation to the reference strength of mature concrete of a given grade.

- under the icons (٭) the so-called conditional normative-safe terms for the stripping of the poured concrete structure are indicated.

- badges (٭٭) - these are the maturation dates for the start of completely safe further work.

To ensure the required minimum allowable temperature regime, several technologies are used:

• The process is carried out with heating of the reinforcing structure or with the installation of special heating cables. In this case, the appropriate electrical voltage must be supplied to the foundation. There are several technologies, both with the use of currents high voltage(before 380 volts) and low-current (12 volts). Having warmed up, the reinforcing structure or the heating cable will not let the wet, not seized mortar freeze.

However, such methods are justified only for large-scale industrial construction - such technologies are very dangerous and require the highest qualifications of specialists. In addition, the cost will be significant. a large number electricity, which means you have to pay a hefty amount. As a result, the total budget for such an arrangement of the foundation is hardly acceptable for average Russian private developer.

• You can use another technology - this is the use of fixed insulated formwork for the foundation.

For this method, hollow blocks of extruded polystyrene foam are used, which are convenient to install on top of each other, thanks to the existing teeth on the side and upper surfaces. They are ideally combined with each other, leaving no gaps (a kind of analogue children's constructor Lego). In inner space install reinforcing structures that give the foundation the required overall rigidity.

They do not remove it from the foundation, and after the concrete has hardened, the surface is covered with a reinforcing sickle mesh, plastered and waterproofed.

However, this approach will only reduce the negative impact of negative temperatures during the maturation of concrete, but will not completely eliminate the problem.

• In any case, for a reliable setting of the poured foundation at sub-zero temperatures, it must be closed from above with a dense polyethylene film. To do this, erect a temporary structure made of wood or reinforcing bars over it, which is also tightened with polyethylene. In the resulting closed room, outwardly resembling a greenhouse, the temperature necessary for high-quality solidification is maintained with the help of heat guns. It is clear that this will require very significant material costs.

As can be seen, even with the economic from the point of view of carrying out work on pouring the foundation in winter is a big concern. Therefore, before starting such work during the cold weather, you need to carefully weigh everything financial risks and justification for such haste.

Video: work on the "winter" laying of concrete in the foundation

Are antifreeze supplements a "panacea"?

There is a very widespread opinion that the problem of pouring a concrete foundation in winter can be completely solved by using special salt additives in the prepared solution. Judging by the numerous advertisements, it is worth adding this component when mixing, and then everything will go on as usual. This should be dealt with in more detail.

Video: one of the options for antifreeze additives in concrete

First of all, it is necessary to understand how, in fact, the process of hardening and maturation occurs. concrete stone.

When the mortar is poured into the formwork, it goes through two stages until it is ready - this is setting and hardening.

• The poured concrete sets within 24 ÷ 30 hours. During this time, the liquid consistency turns into a solid state, however, it still does not have sufficient strength. It is during this period that crystalline bonds begin to form, the binding of free water and the cement components of the solution occurs.
• Then the second stage begins - this is the final hardening, maturation and hardening of the concrete structure - it passes within much longer period. This period depends on several factors, such as the brand of the prepared solution, the level of humidity and temperature, as well as the presence of special hardening additives.

As mentioned above, the optimum temperature for chemical reactions both processes varies from 15 to 25 degrees. The higher it is in this range, the faster the final crystallization will take place, the transition of water to a gel-like state. But even in optimal conditions you can talk about the readiness of the foundation no earlier than after 4 weeks - the base is completely ready for the construction of walls.

The danger of negative temperatures lies in several reasons:

• Firstly, the expansion of frozen water not bound by cement causes internal pressure on the porous structure of concrete, which leads to its destruction. This becomes especially noticeable after the temperature rises to positive levels - such concrete is neither strong nor goes nothing compared to "normal".
• Secondly, the complex chemical process of cement hydration itself requires a certain temperature regime. Already at temperatures below +5° With the activity of these processes decreases to critical levels, and the colder it is, the more sluggish the maturation of concrete will be. And even in this case, such an "intermittent" process s ssignificantly degrades the quality finished concrete structure.

Potash is a very common additive for increasing the frost resistance of freshly poured concrete.

In order to minimize the negative impact of frost to some extent, special additives have been developed. Technologists are trying to solve both problems in this way. The addition of saline solutions increases the density of water, sharply reducing the temperature of its crystallization. Special additives, in addition, are intended for a kind of catalyzation and additional involvement of air in the processes of chemical aging of concrete stone under conditions of negative temperatures. Typically, such compounds are made on the basis of potash, lignosulfonate, calcium hydrochloride, nitrite or sodium formate.

However, if with the freezing of water the issue is more or less resolved positively, then it is much more difficult to “deceive” the laws of chemistry. The ripening process is still not fast, and takes much longer than under optimal conditions.

For example, the table below shows the approximate maturation time of concrete in conditions of negative temperatures with the use of antifreeze additives:

It can be seen that even at -5 °, the complete readiness of the concrete structure can only be discussed after 3 months. In a colder atmosphere, the period increases even more.

A quite reasonable question arises: does it make sense for the owner of an individual site to “tie up” with the winter laying of the foundation (if this is not caused by some special circumstances), to spend significant material resources, physical effort on this, if the real gain in time is practically unattainable. Moreover, with antifreeze additives, too, everything is not so simple:

• Some types of additives cause active corrosion processes on the metal reinforcing cage. Not all steel grades are suitable for these purposes.
• Mixing "winter" concrete mortar is much more difficult than usual. It is simply impossible to carry out such work manually, since particularly thorough mixing of the components to an absolutely homogeneous consistency is required. The mixing time increases significantly, the components must undergo certain preparation (warming up to the desired temperature), a strictly verified order of supplying materials to the mixer is necessary, etc. a very precise dosage of additional additives is needed, depending on both the brand of concrete and the air temperature - here it is required professional approach. As an option - the delivery of a ready-made modified solution made in the factory - but this again rests on the question of the profitability of such construction.
• Even with the use of additives the temperature is below -20° With everything early is critical, and such a sharp fall in winter, for example, at night, is by no means uncommon.
• It is impossible to fill in such solutions even if a thaw suddenly begins, it rains or relative humidity air jumped above the 60% mark.
• The use of such additives does not exempt from necessary activities on the device of the "greenhouse" after pouring, and maintaining the desired temperature with the help of heat guns. If this is not possible, then the foundation etc it is necessary to cover with heaters (for example, with a layer of dry sawdust, grass or turf, about 300 mm thick, and then cover with a film until ripe. in the spring, at the end of stable cold weather.

Care behind the cast foundation

It would be a serious mistake to believe that even under ideal conditions one can only pour the formwork with concrete and then curing. No matter how strange it may sound, but a freshly poured foundation always, under any circumstances, needs some care. The main objectives of such technological events are:

• Minimizing shrinkage of the poured concrete structure.
• Provide the most optimal modes for the aging process.
• Protect the hardening foundation as much as possible from temperature extremes, including daily ones.
• Prevent the poured solution from drying out, the rapid evaporation of unbound water - this will most likely end in cracking the surface.
• To create protection for a structure that has not hardened and has not gained strength against mechanical damage.

Measures for such care should begin literally from the moment the foundation is poured, and can be considered fully completed only when the concrete has gained at least 70% of brand strength, that is, with the optimal time for formwork removal (as indicated in the first table).

• Immediately after pouring, you should make sure that you have not lost the specified geometric shapes - before the initial setting (the first 1 ÷ 2 hours), there is still an opportunity to make adjustments.

• No one is immune from sudden rains. In order to prevent erosion of a fragile surface or its mechanical damage, immediately after pouring, cover the surface with plastic wrap, burlap or tarpaulin.
• Do not forget that too high temperatures are also quite detrimental to the normal course of maturation processes. First of all, this is due to the active evaporation of water, the drying of the surface layer and the appearance of cracks. Necessarily steps are being taken surface wetting and moisture retention. In addition to covering with a vapor barrier film, it is sometimes necessary to resort to more drastic measures, for example, after the initial setting, cover the surface with a layer of material that absorbs moisture well. It can be wet sawdust or a rough cloth - it creates a semblance of a constant wet compress under a plastic cover.

In a word, each temperature regime requires its own concrete care measures. For ease of selection of the necessary, you can give the following table:

A few more important notes:

• Even if shallow strip foundation poured in ideal conditions for this, you should not leave it “naked” and unloaded for the winter. This will inevitably lead to the onset of surface erosion processes, and the structure will lose its strength, begin to crack and crumble. Thus, it is necessary to plan the construction work in such a way that during the season we can move on to the construction of walls on created basis.
• Immediately after dialing concrete structure the required 100% strength, it is recommended to carry out and without delay. More about these technological processes described in the relevant articles of our portal.

What can be the general conclusion?

Despite the fact that modern building technologies, in principle, allow pouring the foundation at temperatures that are quite far from the optimal 15-25 degrees, the best option would still be to plan such work in the most favorable conditions. So the foundation will turn out to be guaranteed reliable and of high quality. If, nevertheless, circumstances force a “zero cycle” to be carried out in other conditions, all technological recommendations on pouring and care of concrete, in relation to the real temperature regime.

Video: the complexity of the foundation pouring processes in winter