Types of antifreeze additives in concrete. Pouring concrete at sub-zero temperatures: features and process of work. What you need to know about masonry work in the winter

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 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, 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 while negative 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 works 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. With more low 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 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.

Construction work is not always carried out under favorable weather conditions. Pouring a concrete floor or building a foundation - that is, all the processes associated with the preparation and placement of a concrete mixture are limited to a rather narrow temperature range environment. In particular, reduced values ​​to a large extent affect the processes of setting and hardening, as well as the time for concrete to gain grade strength. Is it possible to carry out such work at sub-zero temperatures and how justified is this? Let's try to answer this question.

Features of concrete mix

Physical and chemical properties of concrete determine optimal range temperatures when working with it, ranging from +17 to +25 degrees. Normal conditions provide the declared brand strength of the hardened solution after about 28 days.

The rate of the process of hydration of the cement mixture is greatly slowed down in the event of a decrease in temperature and practically stops at +5 degrees. Upon further reduction to negative values, the water contained in the solution freezes, and its volume increases significantly. The emerging forces of internal pressure lead to deconsolidation and loosening of the concrete structure, and its solidity is ensured only by frozen moisture.

With an increase temperature values to positive values, water thaws, cement hydration reaction resumes, and concrete gradually hardens. However, the consequences of structural damage during freezing significantly affect the strength of the monolith.

Experimentally and after carrying out various calculations, critical points were determined when different grades of concrete mortar could be subjected to freezing without tangible consequences. The critical strength of concrete, upon reaching which the negative process ceases to have a noticeable effect on the characteristics of the structure, was set at 50% of the branded strength index.

Thus, pouring concrete sub-zero temperatures is reduced to a set of measures to prevent freezing of water until it reaches critical strength. There are several methods for this:

• making a solution from preheated components;
• formwork insulation;
• heating the laid mixture;
• cold concreting with various chemical additives that lower the freezing point.

The rational use of one of the methods is determined by the volume of the structure being built, the performance of the declared strength characteristics, the availability and availability of energy resources. But meteorological conditions, nevertheless, are a decisive factor when choosing a filling option.

All of the above methods work well both singly and in combination.

Concreting using the mortar's own heat

This method is used for daily temperature fluctuations with its transition through the zero mark, as well as for slight frosts. The bottom line is that a heated concrete mixture is placed in the prepared insulated formwork, for the preparation of which it is important to choose the right brand of cement. The higher it is, the faster the setting and hardening of the solution will occur, and the more heat will be released during hydration.

Mixing is carried out on water having a temperature of at least 90 degrees, and fillers preheated by blowing hot air. This changes the order of laying the components of the mixture: first, water is poured into the concrete mixer, then - building sand and rubble. Adding cement, which must have room temperature, is produced last, after several revolutions of the tank.

Under no circumstances should the cement be heated or poured into hot water!

For concrete to gain critical strength, it is necessary to maintain optimal thermal conditions for as long as possible, preventing rapid cooling. For this purpose, any materials are used - plastic film, tarpaulin, straw mats. The most effective is the use of insulated polystyrene formwork. The material has a low coefficient of thermal conductivity, which allows to extend the cooling time interval, contributing to the high-quality maturation of concrete. Being non-removable, such formwork further provides reliable thermal insulation of structures.

Concreting with heat supply from external sources

Pouring concrete in winter period at sub-zero temperatures, it requires constant heating of the laid solution, preventing it from freezing. There are several ways to provide conditions for a monolith to gain critical strength.

The device of greenhouses

Most reliable way maintaining positive temperatures of the laid concrete implies the erection of a temporary structure above the poured structure. Teplyak is a frame upholstered with plywood or covered plastic wrap like a garden greenhouse. The dimensions of the temporary shelter should be minimal. The heating of the internal air is carried out with the help of heaters, infrared heaters or portable gas burners.

The most significant point here is the control and maintenance of the humidity regime, since the circulating heated air intensively takes moisture from the solution, which is necessary for a complete cement hydration reaction. To prevent moisture from evaporating, the laid concrete is covered with plastic wrap and moistened periodically.

During winter concreting, heating of the laid mortar with steam is sometimes used. low pressure. For this, a special formwork with a steam jacket is constructed, covering the entire structure with it. However, this method has recently been replaced by electric heating.

Electrical heating of concrete

The creation of conditions for the maturation of concrete at sub-zero temperatures can be carried out using an electric current supplied to the electrodes. Special metal rods or plates are placed on the surface of the formwork or immersed inside the solution by connecting to different poles of the mains. Wet concrete closes the circuit and, having a certain resistance, converts electricity into heat, heating the solution. This technology significantly reduces the aging of the mixture, which by 28 days of age can acquire up to 80% of critical strength.

This method is possible only for non-reinforced and low-reinforced structures, which is a significant disadvantage of its use for heating the solution. In addition, high electricity consumption makes it economically unprofitable.

In individual construction, it would be better to use the laying of special heating cables along the reinforcing cage or along inside formwork. At the same time, it must be reliably thermally insulated, preventing heat leakage through the walls. The heating of the concrete solution should be properly monitored around the clock, taking measurements every few hours and not allowing it to heat up more than 30 degrees.

A relatively new method of thermal exposure in winter construction is the use of thermomats. In fact, this is a large electric heating pad, consisting of a heating element and thermal insulation, hermetically mounted inside a waterproof shell. Heating mats provide a uniform distribution of the temperature field in the thickness of the concrete and along the perimeter at a distance of up to 20 cm from itself. Their use is possible at ambient temperatures up to -20 degrees.

Cold concreting

Antifreeze additives are widely used to enable concrete to gain critical strength under conditions of mortar pouring at low temperatures. They support the cement hydration reaction, prevent premature freezing of moisture in the mixture, normalize the concrete hardening process, and have the following positive qualities:

• accelerate the set of the required critical strength;
• lowering the crystallization point of the water contained in the solution;
• increase mobility concrete mass, making it easier to work with it;
• protect metal fittings from corrosion.

Antifreeze additives should only be used at low temperatures external environment and in strict accordance with the attached manufacturer's instructions, since their irregular use can change the properties of the concrete solution for the worse.

The most common antifreeze additives for concrete preparation are:

• potash and other substances, which are based on salts of monocarboxylic acids, accelerate the action during concrete hardening. They do not cause corrosion of reinforcement, do not form on the surface frozen solution efflorescence and allow working with it at temperatures up to -30 degrees, while maintaining its properties.
• sodium chloride - used in conjunction with Portland cements. It plasticizes the mixture, preventing its excessively rapid thickening. The main disadvantage is its corrosive effect on steel reinforcement.
• sodium nitrite - must not be used in conjunction with aluminous cements. The additive allows working with concrete solution at a temperature not lower than -15 degrees.
• sodium formate - used only in combination with plasticizing additives. Otherwise, it can cause defects in the concrete mixture in the form of voids due to the formation and accumulation of salts.

The cold concreting method has some disadvantages:

• its use is prohibited in prestressed structures;

• the laid mortar has increased shrinkage;
• concrete has a reduced rate of frost resistance and water permeability.

In addition, some additives impose their own additional restrictions on the use.

It is advisable to carry out work related to pouring concrete at the most favorable conditions. At the same time, it must be remembered that work should begin at a temperature of at least +10 degrees, and if it is not expected to decrease in the next 28 days. Modern technologies, of course, they allow concreting even at negative ambient temperatures, however, this leads to considerable additional financial costs and it is possible to start them only in case of emergency. If it is not possible to reschedule the work for a more favorable period, it is worth considering some expert advice to help achieve acceptable quality during pouring:

• fillers - sand and gravel used to prepare the solution, in without fail are warmed up to prevent inclusions of ice or snow from getting into the batch;
• the formwork must be cleared of ice and insulated in advance;
• the bottom of the pit and the fittings must be warmed up, achieving at least the minimum positive temperature values;
• pouring concrete should be done at one time with a continuous supply of the mixture;
• the maximum temperature of the solution used is allowed no more than 35-40 degrees;
• finished cast segments of the structure are covered with heat-insulating materials, preventing leakage own heat from concrete.

Throughout the entire period of concrete gaining critical strength, compliance with temperature regime. At the same time, one should not forget about the control of the uniformity of the distribution of the thermal field in the thickness of the structure, since the use of heating electric cables can lead to overdrying of its individual segments.

Pouring concrete at sub-zero temperatures is carried out mainly during large-scale capital construction, as it requires the use of special equipment, the availability of additional building materials and financial resources. The feasibility of carrying out such work on an individual basis largely depends on the availability of resources and is associated with certain risks.

Concrete is a versatile building material that is used for various purposes: from building a house to erecting decorative elements personal plot. It is practical, indispensable, economical, comfortable material. It has some disadvantages. Exposure to low temperatures is one of the main disadvantages. Concrete in frost can change shape, crack, crumble. The way out of the situation is additives that increase, allowing construction work to be carried out in the cold season.

Modern antifreeze additives reduce the freezing point of water from 0 to -15 degrees. Additives must be used according to the instructions. Uncontrolled use harms the structure, causes undesirable consequences. In frost, it is necessary to introduce the additive in the correct amount in order to avoid freezing, undesirable consequences. Frozen non-additive formulas are at greater risk.

Application Benefits

• the liquid present in the mixture freezes at lower temperatures than usual, allowing the solution to set;
• the solution becomes more plastic - it is easier to form individual parts of the structure;
• reinforcement does not oxidize due to corrosion inhibitors present in additives;
• increased water resistance of reinforced concrete;
• the mixture becomes strong in a shorter time.

After adding the additive to the solution, the mixture becomes more dense due to the saturation of the micropores in the concrete with carbonized calcium hydroxide, it becomes easier to pour it into the mold. The strength of the structure is doubled. 18 hours is enough for the concrete structure to fully harden. Extraction takes place without violating the integrity of the concrete. High-quality PMD do not allow the appearance of "salt" on the surface.

The use of antifreeze additives allows:

• mix the solution with low-grade concrete, reducing material costs;
• make concrete layers thinner without risking the quality of the structure (due to increased strength) - the solution is saved;
• concrete does not need to be treated with waterproofing agents.

Where is it used?

Antifreeze additives are used in the construction of structures:

• monolithic reinforced concrete;
• with off-design reinforcement, a solution layer of more than half a meter;
• prestressed reinforced concrete;
• mixture for plaster;
• tracks;
• oil and gas production platforms;
• dams, dams.

Before adding antifreeze, a test is carried out that determines:

• oxidizing effect on concrete;
• the formation of "salts";
• setting speed;
• strength.

Types of additives

High-quality additives for concrete mortar allow it to harden at severe frosts up to 35 degrees. Additives are divided (according to chemical action): superplasticizers, accelerators, regulators that increase frost resistance, modifiers, complex ones.

plasticizers

- naphthalene sulfate, melamine resin sulfate, organic polyacrylates. They have a plasticizing effect on the solution. Doesn't require a lot of water. Makes the solution more durable, moisture-proof, concentrated. The mixture is easier to fit - it can be poured in an even layer. Saves energy and water. The use of plasticizers allows you to qualitatively put the mixture into the mold, without the formation of voids. Concrete mortar microparticles retain moisture better.

Strengthening

Hardening accelerators - aluminum sulfate, iron sulfate, calcium nitrate, calcium chloride. They act by reducing. Seizing, concrete loses its plasticity, hardening - it acquires strength. Their action is calculated on the first three days of drying. During this period, the supplement has the most high level efficiency. The class strength of concrete also increases.

Pouring concrete is an integral part of most construction work. As is known, ideal period for repair and construction work - this is a warm season and pouring concrete is no exception to this rule. However, what should those who decide to continue construction despite the frosty weather do?

Pouring concrete at sub-zero temperatures in most cases is contraindicated by SNiP standards, since extreme cold does not allow the compositions that contain liquid to fully polymerize. But in some cases, the circumstances are such that the concrete must be poured, no matter what. And the question is quite natural, is it possible to pour concrete at sub-zero temperatures?

For areas where there is no warm season or situations in which winter construction is vital, there are several technological solutions that can be used to form concrete structures without compromising quality. In this article, you will be given detailed instructions how to pour concrete at sub-zero temperatures.

Pouring concrete

At sub-zero temperatures, the liquid in cement mortar freezes and the ice crystals break crystal lattice concrete, thereby weakening the strength future design. After thawing, the bond structure is not restored, and the structure loses a significant part of the strength potential, up to complete destruction.

The direct effect of sub-zero temperatures on concrete structure admissible only after she acquires required amount strength, frost resistance, etc. In construction terminology, this value is called the critical strength threshold - after overcoming it, frost does not negative impact on the concrete structure.

The threshold of critical strength is determined depending on the brand of concrete solution. The standard cement mix of the M400 brand must gain at least 30% of its maximum strength, and the lower the concrete grade, the higher the percentage of gained should be.

Before pouring concrete in sub-zero temperatures, it is necessary to create conditions that will prevent it from freezing. There are several technologies that help create or maintain the temperature necessary to overcome the critical strength threshold.

Among them are the following:

• Mixture heating. Before pouring concrete at sub-zero temperatures, the solution is heated to a certain state, which gives it the opportunity to overcome the critical strength limit as it cools;
• Internal heating. Maintain positive temperature in reinforced reinforced concrete structures it is possible through internal electric heating, which is carried out at the expense of electricity and metal components;
• External heating. It is possible to create the temperature necessary to achieve critical strength using external steam or;
• thermal insulation. Pouring concrete at minus 5 degrees can be carried out using high-quality insulated formwork, which does not release heat from the inside and allows cold to penetrate inside;
• The use of specialized additives that prevent water from freezing.

Each of these technologies has its own characteristics, which must be taken into account, giving them their preference. Consider the above options in more detail.

Mixture heating

The concrete solution is kneaded on heated water, the temperature of which can be from 60 to 90 degrees. This technology can only be used if the ambient temperature does not fall below -15 degrees. This circumstance should be taken into account if you are wondering, “At what sub-zero temperature can concrete be poured?”

Specialty Blends

AT cement mixture various antifreezes are added to prevent the formation of ice crystals. Most often, calcium chloride or sodium chloride (table salt) is used for this purpose, which can be no more than 2% of the total mass of the components. If the temperature does not fall below 15 degrees below zero, then modifying additives will save the structure from freezing.

Note!
Despite the fact that the price of modifying components is quite affordable, it is best to purchase factory mixtures that guarantee technical qualities product.
A homemade recipe mixed with your own hands can be a waste of resources.

thermal insulation

If you want to pour the foundation at sub-zero temperatures, then you can do without heating or third-party additives. It is enough to qualitatively insulate the formwork with sheet or loose insulation.

During the crystallization of the concrete solution, heat is released, which is quite enough to overcome the critical strength threshold if the formwork is assembled according to the thermos principle. However this technology undesirable to use at too low temperatures.

Note!
Heat-insulating formwork can be used in conjunction with the above technologies - thus, you will increase their effectiveness.

Internal and external heating

Internal heating is carried out by connecting to the reinforcing frame alternating current from a special transformer - the metal is heated and heats the cement mixture. External heating consists of a specialized mobile formwork, which contains heating elements that are powered by steam or electricity.

The disadvantages of this technology are the high cost of construction - the enormous consumption of resources for heating affects. Also, this technology cannot be used independently, since without the presence necessary knowledge and equipment, it is impossible to achieve the desired effect.

Among the advantages, it should be noted that you may not think about the question, “Up to minus how much concrete can be poured?” - concrete heating allows pouring at temperatures up to -25 degrees.

Outcome

The correct approach to the question of how to pour concrete in sub-zero temperatures makes it possible to obtain a high-quality result even in the most adverse conditions. In the future, eliminate small errors and establish additional elements concrete cutting will help you diamond circles and diamond drilling holes in concrete. More detailed information on this topic you can get by watching the video in this article.

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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 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 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 with 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 of structures subjected immediately after the end of curing to the design water pressure, and structures to which special requirements frost resistance and water resistance.

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 concrete components and prepare the concrete mixture. 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 the 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 small positive temperature is established in them.

Concrete in thin structures cools quickly, so they have to be heated electric shock, steam or hot 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 of winter concreting, based on concrete hardening at a positive temperature, there is a method of concrete hardening at a negative temperature. Wherein concrete mix 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. In case of impossibility of curing concrete in structures with the help of the indicated measures concrete works performed using heat sinks.

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

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