Features of winter concreting. Technology of concrete work in winter conditions

"Winter conditions" are created at a facility under construction, where a significant proportion of the work is associated with monolithic reinforced concrete, much earlier than winter comes according to the calendar. Construction becomes "winter" as soon as the average daily temperatures drop to +5 o C and at night the temperature drops below 0 o C.

At sub-zero temperatures, the water in the composition of completely uncured concrete stops reacting with cement and freezes, becoming ice. The intensity of hydration processes decreases sharply, the concrete stops hardening. At the same time, internal pressure builds up in the thickness of the concrete due to a 9% increase in the volume of water that has turned into ice. If freezing of concrete casting occurs at an early stage of work (immediately after concrete is laid), then the structure of reinforced concrete is completely broken, since it lacks the ability to withstand the processes of freezing of the internal volume of the liquid. In the case of concrete thawing, the ice becomes water again and the hydration process is activated, but the complete restoration of the concrete structure will not occur.

When freshly laid concrete freezes, an ice crust is formed around its internal reinforcing “skeleton” and filler grains, which grows due to the incoming water from the internal zones of concrete with a higher temperature. Each ice crust gradually increases the wall thickness and moves the cement paste away from the concrete filler and reinforcement, which reduces the strength characteristics of concrete and negatively affects its durability.

If the concrete has time to gain the minimum sufficient strength before freezing, then negative processes will not develop in its structure. The degree of strength of concrete, at which low temperatures do not pose a danger to it, is called "critical".

The standards for the critical strength of concrete are associated with its class, type and conditions in which this structure will operate. In the case of structures made of concrete and reinforced concrete (non-stressed reinforcement), the critical strength should be at least 50% of the design strength for B7.5-B10, at least 40% for B12.5-B25, and 30% for more than B30. For concrete structures containing prestressed reinforcement, the critical strength must be at least 80% of the design strength. For concrete structures subject to alternating cycles of freeze and thaw, 70% strength must be achieved. Loaded structures are required to gain full, 100% strength from the design before being exposed to sub-zero temperatures.

The duration of the concrete curing period, during which a set of necessary strength characteristics is achieved, largely depends on the temperature conditions at the construction site. The higher the air temperature, the higher the activity of the water component concrete mix- the reaction processes with cement clinker are faster, which accelerates the internal coagulation and the formation of a crystalline structure. Accordingly, a decrease in temperature leads to a slowdown in these processes.

Concrete work in winter must be carried out under artificially created conditions in terms of temperature and humidity, achieving concrete hardening to critical or design strength in less time and at lower cost. In order to achieve the desired results, special mixing technologies, delivery to the location on site, as well as the subsequent curing of the concrete are used.

Preheating of the concrete mix

During the preparation of the concrete mixture at low temperatures, it is heated to 35-40 ° C, provided by the preliminary heating of the components. Water is heated in boilers to a temperature of 90 ° C, and the filler is heated to 60 ° C in drums using steam, flue gases and hot water. It is absolutely impossible to heat cement.
Artificially heated concrete mix for a "winter" construction site is made differently than in the warm season. If in summer the dry components of the mixture are simultaneously loaded into the mixer hopper, where water was previously poured, then in winter the order is as follows - water is first poured and large aggregate fractions are poured. When the mixing drum makes several revolutions, cement and sand are loaded into it. Ignoring this sequence of actions will lead to the "brewing" of cement.

The duration of mixing the concrete mixture at negative temperatures must be increased by 1.2-1.5 times compared to the "summer" period of its mixing. Transportation of ready-made concrete is carried out in a heated, insulated and closed container, whether it is a tub or a car body. The vehicle body is heated in this way - it is made double, exhaust gases from the engine are directed into the cavity created in this way, which will reduce heat loss. Delivery of the concrete mixture should take place as quickly as possible and without any intermediate overloads. The areas where the concrete mixture is loaded and unloaded must be fenced off from the wind, and the means through which the concrete enters (trunks) must be insulated.

Preparing concrete work in winter

Concrete should be laid on a base, the state of which completely excludes the freezing of the mixture along the junction line with it, as well as the possibility of deformation due to the heaving of the soil. For these purposes, the base of the concreting area is heated until it reaches a positive temperature, and after laying the mixture, it is preserved from freezing until the concrete gains critical strength.

Immediately before the start of concreting, the formwork and reinforcement are cleaned of ice and snow masses. If the diameter of the reinforcement exceeds 25 mm, or it is made of rigid profiled rolled products or contains metal embedded elements of a significant size, then in conditions of negative temperatures less than -10 ° C, the reinforcement should be heated.

Concreting processes in winter conditions are carried out quickly and continuously - each underlying layer of concrete must be covered with a new one before its temperature drops below the calculated one.

Modern execution technologies concrete work in winter, they allow to achieve high quality building structures with optimal level costs. Conventionally, they are divided into three groups:

• "thermos" technology, based on the preservation of the initial heat of the mixture, heated during the preparation process or before laying on site, as well as on the use of heat emissions resulting from the reaction of cement with water during concrete curing;
• technology of artificial heating of the concrete mixture after it has been laid into the structure;
• technology for chemically lowering the freezing point of water in the concrete mixture and increasing the reaction rate of cement.

Depending on the situation at the construction site, the given methods of curing concrete during low temperatures can be used in combination. The final choice in favor of one of the technologies is based on the type of structure and its dimensions, on the type of concrete, its composition and design strength that it must gain, local climatic conditions at the time of work, energy capabilities at the construction site, etc.

Concrete work in winter and "thermos" technology

Its essence is in laying a mixture of concrete, having a temperature in the range from 15 to 30 ° C, in a formwork with insulation. This will ensure that the concrete builds up sufficient strength due to its initial thermal energy and the exothermic reaction of the cement, which will not allow the concrete structure to freeze prematurely. The amount of heat generated as a result of exothermic reactions depends on the holding temperature and the type of cement used in the preparation of the mixture.

The best heat dissipation data show Portland cements of high grades and with fast curing. The preservation of heat in concrete significantly depends on exotherm, therefore, concrete work using the "thermos" technology should be carried out on mixtures with fast-hardening and highly exothermic Portland cements, placed with an artificially raised initial temperature in a well-insulated structure.

Application of special chemical additives. Some chemicals - potash K 2 CO 3, calcium chloride CaCL, sodium nitrate NaNO 3, etc. - being introduced into the concrete in a small volume, usually not more than 2% of the amount of cement, increase the rate of concrete hardening by initial stage keeping. For example, with the introduction of calcium chloride in an amount of 2% by weight of cement, it provides 1.6 times the strength of concrete after 2.5 days from the moment of laying in the structure, compared with concrete of an identical composition, but not containing a special additive. Chemical additives also provide a shift in the freezing point of water to -3 ° C, which allows you to increase the cooling time of concrete and thereby provide it with a greater set of strength. More detailed information on the methods of chemical improvement of the characteristics of concrete for winter construction is disclosed.

The preparation of concrete mixtures, including chemical additives, is carried out using hot water and heated filler grains. When removed from the mixer, such concrete usually has a temperature of from 25 to 35 ° C, immediately before laying its temperature drops to about 20 ° C. Laying in the structure of chemically modified concrete is carried out at an external air temperature of -15 to -20 ° C, after placement in the insulated formwork, one or two layers of thermal insulation are laid on top. The curing of the concrete structure occurs due to the effect of "thermos" with the simultaneous action of dosed chemical components. The technology of "thermos" concreting, along with the use of chemicals, is simple and relatively inexpensive, it can be used to create a structure with a surface modulus (Mn) of less than five.

Concreting according to the "hot thermos" method. It is based on the rapid heating of concrete to 60-80 ° C and the compaction of the mixture in the structure before it cools down. Further, the concrete mixture is aged according to the “thermos” technology, or it is additionally heated during the period of critical strength gain.

At the construction site, the concrete mixture is most often heated using electric current - electrodes are placed in it and alternating current is supplied, heating occurs due to the resistance of concrete. The power and amount of thermal energy generated per unit of time is directly proportional to the voltage on the electrodes and inversely proportional to the ohmic resistance of the mixture. In this case, the intensity of ohmic resistance depends on the planar dimensions of the electrodes, the distance between them and the specific ohmic resistance of the concrete mixture.

Electric heating of the concrete mixture is carried out under a current of 380V, in more rare cases - under 220V. To ensure this operation, the construction site is equipped with a transformer post, switchboard and control panel. The mixture is heated in a bucket or in the body of a dump truck directly. The first method is carried out in the following sequence - the mixture compiled at the concrete plant is transported by road to the construction site, special buckets equipped with electrodes are reloaded, heated until its temperature is 70-80 ° C, and then placed in the formwork on the spot works. As a rule, tub shoes are used, equipped with three 5 mm steel electrodes, powered to the mains through cable connectors. In order for the concrete to be evenly distributed in the electric tub, as well as to simplify further unloading, a vibrator is mounted on the tub body.

Following the second method, a dump truck, which contains a concrete mixture in its body, arrives at the construction site and follows to the heating post - its body is located exactly under the electrode frame. The operation of the vibration unit is activated, then electrodes are inserted into the concrete contained in the body, and an electric current is supplied to them. The heating of the mixture is carried out for 10-15 minutes when it is heated to 60 ° C (true for fast-hardening Portland cements), up to 70 ° C for Portland cements and up to 80 ° C for Portland slag cements.

To quickly and extremely short term to heat the concrete to the required temperature, it is important to provide the site with high electrical power. For example, a 15-minute warm-up of a cubic meter of concrete mix to 60 ° C will take 240 kW, and a faster 10-minute warm-up to the same temperature - 360 kW.

The next part of the article, devoted to heating the mixture laid in the structure, is located.

The foundation is the fundamental structure, the quality of which determines the geometric, technical and operational characteristics of the structure under construction. Due to the specifics of the curing process by pouring concrete and reinforced concrete foundations it is undesirable to engage in winter in order to avoid their deformation and premature destruction. Minus thermometer readings significantly limit construction in our latitudes. However, if necessary, pouring concrete at low temperatures can still be successfully carried out if the right method is chosen and the technology is followed with accuracy.

Features of winter "national" filling

The vagaries of nature often make adjustments to development plans in the domestic territory. Either heavy rain interferes with digging a ditch, then a heavy wind interrupts, or it hampers the onset of the summer season.

The first frosts generally radically change the course of work, especially if it was planned to pour a concrete monolithic base.

The concrete foundation structure is obtained as a result of hardening of the mixture poured into the formwork. It consists of three almost equal components: aggregate and cement with water. Each of them makes a significant contribution to the formation of a durable reinforced concrete structure.

In terms of volume and mass, aggregates prevail in the body of the created artificial stone: sand, gravel, gruss, crushed stone, broken brick etc. According to the functional criteria, the leader is the binder - cement, the share of which in the composition is less than the share of the filler by 4-7 times. However, it is he who binds the bulk components together, but acts only in tandem with water. In fact, water is just as important a component of the concrete mix as cement powder.

Water in the concrete mixture envelops the fine particles of cement, involving it in the hydration process, followed by the crystallization stage. The concrete mass does not harden, as they say. She hardens by gradual loss water molecules flowing from the periphery to the center. True, not only the components of the solution are involved in the "transition" of the concrete mass into an artificial stone.

The environment has a significant influence on the correct course of processes:

• At average daily temperatures from +15 to +25ºС, the hardening of the concrete mass and curing takes place at a normal pace. In the specified mode, concrete turns into stone after 28 days specified in the regulations.
• With average daily thermometer readings of +5ºС, hardening slows down. The concrete will reach the required strength in about 56 days, if no noticeable temperature fluctuations are foreseen.
• Upon reaching 0ºС, the hardening process stops.
• At negative temperatures, the mixture poured into the formwork freezes. If the monolith has already managed to gain critical strength, then after thawing in the spring it will concrete again enter the hardening phase and continue it until a full set of strength.

Critical strength is closely related to the brand of cement. The higher it is, the less days the concrete mixture is needed before it is set.

In case of insufficient strength development before freezing, the quality of the concrete monolith will be very doubtful. Freezing in the concrete mass, water will crystallize and increase in volume.

As a result, internal pressure will arise, destroying the bonds inside the concrete body. The porosity will increase, due to which the monolith will pass more moisture into itself and resist frost more weakly. As a result, operational periods will be reduced or you will have to do work from scratch again.

Minus temperature and foundation

It is pointless to argue with weather phenomena, you need to competently adapt to them. Therefore, the idea arose of developing methods for constructing reinforced concrete foundations in our difficult climatic conditions, possible for implementation in the cold period.

Note that their use will increase the construction budget, therefore, in most situations, it is recommended to resort to more rational options for constructing foundations. For example, use the bored method or carry out factory production.

At the disposal of those who are not satisfied alternative ways, there are several proven successful practices. Their purpose is to bring concrete to a state of critical strength before freezing.

According to the type of impact, they can be conditionally divided into three groups:

• Providing external care for the concrete mass poured into the formwork up to the stage of gaining critical strength.
• Increasing the temperature inside the concrete mass until the moment of sufficient curing. It is carried out by means of electrical heating.
• The introduction of modifiers into the concrete solution, lowering the freezing point of water or activating processes.

The choice of the winter concreting method is influenced by an impressive number of factors, such as the power sources available on the site, the weather forecast for the hardening period, the ability to bring a heated solution. Based on local specifics, the best option is selected. The most economical of the listed positions is considered the third, i.e. pouring concrete at sub-zero temperatures without heating, which predetermines the introduction of modifiers into the composition.

How to pour a concrete foundation in winter

To know which method is better to use for curing concrete to critical strength indicators, you need to know them. characteristics to get acquainted with the pros and cons.

Note that a number of methods are used in combination with any analogue, most often with preliminary mechanical or electric heating concrete mix components.

External conditions "for ripening"

Favorable external conditions for hardening are created outside the object. They consist in maintaining the temperature of the environment surrounding the concrete at a standard level.

Concrete poured "in minus" is cared for in the following ways:

• Thermos method. The most common and not too expensive option, which consists in protecting the future foundation from external influences and heat loss. The formwork is extremely quickly filled with a concrete mixture heated above standard values, quickly covered with vapor barrier and heat-insulating materials. The insulation prevents the concrete mass from cooling down. In addition, during the hardening process, concrete itself releases about 80 kcal of thermal energy.
• Keeping a flooded object in greenhouses - artificial shelters that protect against external environment and allowing to carry out activities for additional heating of the air. Tubular frames are erected around the formwork, covered with a tarpaulin or sheathed with plywood. If braziers or heat guns for the supply of heated air, then the method goes into the next category.
• Air heating. It involves the construction around the object of a closed space. At a minimum, the formwork is covered with tarpaulin curtains or similar material. It is desirable that the curtains be thermally insulated to increase the effect and reduce costs. In the case of curtains, steam or air flow from the heat gun is supplied to the gap between them and the formwork.

It is impossible not to notice that the implementation of these methods will increase the construction budget. The most rational "thermos" is to force you to buy covering material. The construction of a greenhouse is even more expensive, and if you also rent a heating system for it, then you should think about the cost figure. Their use is advisable if there is no alternative type and it is necessary to fill monolithic slab frozen and spring defrosting.

It should be remembered that repeated defrosting is destructive for concrete, therefore, external heating must be brought to the required hardening parameter.

Methods for heating concrete mass

The second group of methods is used mainly in industrial construction, because. needs a source of energy, accurate calculations and the fate of a professional electrician. True, craftsmen, in search of an answer to the question of whether it is possible to pour ordinary concrete into formwork at sub-zero temperatures, found a very ingenious way out with the supply of energy welding machine. But even this requires at least initial skills and knowledge in difficult building disciplines.

AT technical documentation methods of electric heating of concrete are divided into:

• Through. According to this, the concrete is heated by electric currents, which are supplied by electrodes laid inside the formwork, which can be rod or string electrodes. Concrete in this case plays the role of resistance. The distance between the electrodes and the applied load must be accurately calculated, and the feasibility of their use has been unequivocally proven.
• Peripheral. The principle is to heat the surface zones of the future foundation. Thermal energy is supplied by heating devices through tape electrodes attached to the formwork. It can be strip or sheet steel. Heat is distributed inside the array due to the thermal conductivity of the mixture. Effectively, the concrete thickness warms up to a depth of 20 cm. Further, it is less, but at the same time, stresses are formed that significantly improve the strength criteria.

The methods of through and peripheral electrical heating are used in non-reinforced and small reinforced structures, because fittings affect the heating effect. With a dense installation of reinforcing bars, the currents will be closed to the electrodes, and the generated field will be uneven.

The electrodes at the end of the warm-up remain forever in the structure. In the list of peripheral methods, the most famous is the use of heating formwork and infrared mats laid on top of the base being constructed.

Most in a rational way warming up of concrete, curing with the help of electric cable. The heating wire can be laid in structures of any complexity and volume, regardless of the frequency of reinforcement.

The disadvantage of heating technologies is the ability to dry out concrete, therefore, calculations and regular monitoring of the temperature state of the structure are required for carrying out.

Introduction of additives into concrete solution

The introduction of additives is the simplest and cheapest way of concreting at sub-zero temperatures. According to it, concrete pouring in winter can be carried out without the use of heating. However, the method may well complement heat treatment of the internal or external type. Even when used in conjunction with heating the hardening foundation with steam, air, electricity, there is a reduction in costs.

Ideally, the enrichment of the solution with additives is best combined with the construction of the simplest "thermos" with a thickening of the heat-insulating shell in areas with thinner, at corners and other protruding parts.

Additives used in "winter" concrete solutions are divided into two classes:

• Substances and chemical compounds that lower the freezing point of a liquid in solution. Provide normal hardening at sub-zero temperatures. These include potash, calcium chloride, sodium chloride, sodium nitrite, combinations thereof, and the like. The type of additive is determined based on the requirements for the temperature of the solution hardening.
• Substances and chemical compounds that accelerate the hardening process. These include potash, modifiers with a base of a mixture of calcium chloride with urea or calcium nitrite-nitrate, with sodium chloride, one calcium nitrite-nitrate, etc.

Chemical compounds are introduced in a volume of 2 to 10% by weight of the cement powder. The amount of additives is selected based on the expected hardening temperature of the artificial stone.

In principle, the use of antifreeze additives allows concreting even at -25ºС. But such experiments are not recommended for builders of private sector facilities. In fact, they run late autumn with single first frosts or in early spring, if concrete stone must be cured by a certain deadline, and alternatives not available.

Common antifreeze additives for pouring concrete:

• Potash or otherwise potassium carbonate (K 2 CO 3). The most popular and easy-to-use modifier of "winter" concrete. Its use is a priority due to the absence of reinforcement corrosion. For potash, the appearance of salt stains on the surface of concrete is not typical. It is potash that guarantees the hardening of concrete at thermometer readings down to -25°C. The disadvantage of its introduction is to accelerate the setting rate, which is why it will be necessary to cope with pouring the mixture in a maximum of 50 minutes. In order to maintain plasticity for the convenience of pouring into the solution with potash, soap naphth or sulphite-alcohol bard is added in a volume of 3% by weight of the cement powder.
• Sodium nitrite, otherwise a salt of nitrous acid (NaNO 2). Provides concrete with a stable set of strength at temperatures up to -18.5 ° C. The compound has anti-corrosion properties, increases the intensity of hardening. The downside is the appearance of efflorescence on the surface of the concrete structure.
• Calcium chloride (CaCl 2), which allows concreting at temperatures down to -20 ° C and accelerates the setting of concrete. If it is necessary to introduce a substance into concrete in an amount of more than 3%, it is necessary to increase the grade of cement powder. The disadvantage of the application is the appearance of efflorescence on the surface of the concrete structure.

The preparation of mixtures with antifreeze additives is carried out in a special order. First, the aggregate is mixed with the main part of the water. Then, after light mixing, cement and water with chemical compounds diluted in it are added. The mixing time is increased by 1.5 times compared to the standard period.

Potash in the amount of 3-4% by weight of the dry composition is added to concrete mortars, if the ratio binder to aggregate 1:3, nitrite nitrate in the amount of 5-10%. Both antifreeze agents are not recommended for use in pouring structures operated in a flooded or very humid environment, because. they contribute to the formation of alkalis in concrete.

In pouring critical structures, it is better to use cold concrete, prepared mechanically in the factory. Their proportions are calculated with accuracy based on the specific temperature and humidity of the air during the pouring period.

Cold mixtures are prepared in hot water, the proportion of additives is introduced in strict accordance with weather conditions and the type of structure being built.

Methods for pouring concrete in winter:

Winter concreting with a greenhouse device:

Antifreeze agent for winter concreting:

Before pouring solutions with antifreeze additives, it is not necessary to warm up the bottom of the pit or trench dug under the foundation. Before pouring heated compositions, warming up the bottom is mandatory in order to avoid unevenness that may result from ice melting in the ground. Filling should be carried out in one day, ideally in one step.

If breaks cannot be avoided, the intervals between fillings concrete mortar needs to be minimized. Subject to technological subtleties the concrete monolith will gain the necessary margin of safety, will be mothballed for the winter and will continue to harden with the advent of warm weather. In the spring, it will be possible to start building walls on a ready-made reliable foundation.

Comments:

With the widespread use of concrete, people are faced with one significant problem - winter concreting. Today the main building material it is concrete that is used in the construction of any structure.

The temperature of the concrete mortar must not be lower than 5 ° C when pouring monolithic structures, and not lower than 20 ° C - for thin concrete.

In the southern regions, you can suspend work in the cold, but what about in places where sub-zero temperatures last for a long period? Winter concreting is a very real construction process, which has been repeatedly tested in practice and is standardized by a number of documents.

Features of construction in the winter

The main feature of the winter period is the low temperature, which has a significant impact on the properties of concrete. The main process of concrete structure formation is cement hydration. An increase in temperature plays the role of a catalyst in this process and accelerates the formation of the final structure (set of strength).

Strength calculations are based on an optimum temperature of around 18-20°C at which the concrete will reach its intended strength 28 days after pouring.

Lowering the temperature slows down the cement hydration process, and at a mortar temperature of 5°C, the concrete reaches only 70% of the required strength after 4 weeks. At temperatures below 0 ° C, hydration stops due to the freezing of water, without which this process is impossible. Thus, you need to do following output: at concrete temperatures less than 10 ° C, the period of material strength development is noticeably lengthened, which must be taken into account when building at sub-zero temperatures (water freezing), the hardening process stops.

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Requirements for winter concreting

It has been established that the temperature of the concrete solution at the time of pouring should not be below 5 ° C for monolithic structures, below 20 ° C - for thin layers concrete. In the process of cement hydration, heat is released inside the mixture, but it is enough to reduce the freezing point of water by only 2-3 ° C (compared to ambient air).

In addition, the solution itself after mixing must have a temperature of at least 20 ° C (preferably 30 ° C), otherwise its plasticity will be lost, laying will become a big problem. Compaction of the cold mass will not achieve the desired effect - zones of insufficient compaction of the mixture will appear.

The above conditions necessary for the formation of a high-quality structure necessitate the use of special measures when laying concrete in the winter. The technology should provide either warming up the solution and maintaining the desired temperature, or introducing additives that can lower the freezing point of water, accelerate the process of concrete hardening at low temperatures and increase the plasticity of the solution in cold weather.

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Winter concreting methods

In winter, the mortar is concreted in 4 main ways that can meet the requirements, or (most often) a combination of these methods. These include:

1. Warming up the concrete solution during mixing and laying.
2. Introduction of special antifreeze additives.
3. Providing a thermos effect.
4. Long lasting during curing.

Heating the solution can be done in different ways. The most common are heating with steam, heating with air flow (converter method), induction heating, heating with infrared radiation, direct electric heating.

Long-term heating is carried out in special formwork, where heating elements, provides forced heating of concrete during its hardening to a temperature not lower than 5-10 ° C. The thermos effect is achieved by preserving the heat released during cement hydration or another reaction when an additive is introduced, by providing good thermal insulation of the concrete structure after pouring.

For winter concreting, the following tools will be required:

• construction mixer;
• shovel;
• scales;
• Master OK;
• putty knife;
• thermometer;
• Bulgarian;
• electric drill;
• a hammer;
• pliers;
• screwdriver;
• plumb;
• level;
• roulette;
• a hammer;
• grater;
• trowel.

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Special admixtures for concrete

Winter concreting expands its capabilities with the introduction of antifreeze additives. Such concrete mixtures without heating can be used at a temperature of 0-5 ° C. Potash and sodium nitrate are the most common antifreeze additives. The amount of added additive depends on the conditions of concrete hardening:

• at air temperatures down to -5 ° C, 5-6% of these additives will be required;
• at temperatures up to -10 ° C - 6-8%;
• at -15 ° C - 8-10%.

If the hardening of the mass takes place at a greater frost, then sodium nitrate is not used, and the amount of potash increases to 12-15%. In addition to these substances, urea or a mixture of calcium nitrate and urea can be used.

The effect of increasing frost resistance is enhanced by the simultaneous addition of mass hardening accelerators. The most common include sodium formate, asol-K, a mixture based on acetylacetone, and some others. The following can be recommended as standard antifreeze additives with additional plasticizing and accelerating properties:

• hydroconcrete S-3M-15;
• hydrozyme;
• lignopan;
• win-antifrost;
• betonsan;
• cementol.

The most economical additive for homemade mixtures is ammonia water.

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Using the thermos effect

Concreting in winter conditions using the thermos effect is to increase the cooling time of the concrete structure for a period sufficient to gain the desired strength. The main task is to keep the heat of the solution provided during its preparation, and the heat released during the hydration of the cement.

The thermos method is usually used in conjunction with the introduction of additives that accelerate the solidification of the mass and reduce the freezing point of water. As such additives, calcium chloride and sodium or sodium nitrite are used in an amount of up to 5% by weight of the cement.

The "thermos" itself is mounted in the form of an insulated formwork, the walls of which are covered with heat-insulating materials in several layers. Good thermal insulators are expanded polystyrene and mineral wool. Thermos walls are made in the following order: a layer of waterproofing is attached to the formwork ( polyethylene film), on top - thermal insulation, on top - another layer of waterproofing. Above concrete structure also securely covered with similar layers of insulation. The thermos effect is most noticeable in monolithic structures with a significant volume of concrete and can be used up to a temperature of -5 ° C.

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Electric heating

Concrete work in winter can be carried out with preliminary electrical heating of the solution. The technology of the method is based on heating using electrodes immersed in concrete composition. Typically, plate-type electrodes are used for a voltage of 380 V, while the container must be grounded.

As a result of heating the mass, the solution may lose its elastic properties, therefore it is recommended to introduce plasticizing additives. Warming up the mixture can also be carried out in the drum of a concrete mixer using electrodes in the form of rods. Warming up is carried out in such a way that the mortar to be laid has a temperature of 30-40 ° C.

The electrical method can be used to heat up the mortar while pouring the formwork. Two methods are used: peripheral heating (flat electrodes are placed on the surface of a concrete element) and through heating (rod electrodes are passed through the thickness of concrete and formwork). In the latter case, contact of the electrodes with the reinforcement of the concrete structure should be excluded.

The concept of "winter conditions" in technology monolithic concrete and reinforced concrete is somewhat different from the generally accepted - calendar. Winter conditions begin when average daily temperature outside air is reduced to +5°C, and during the day there is a drop in temperature below 0°C.

At negative temperatures, water that has not reacted with cement turns into ice and does not enter into a chemical combination with cement. As a result, the hydration reaction stops and, consequently, the concrete does not harden. At the same time, significant internal pressure forces develop in concrete, caused by an increase (by about 9%) in the volume of water when it passes into ice. With early freezing of concrete, its fragile structure cannot withstand these forces and is broken. Upon subsequent thawing, the frozen water again turns into a liquid and the cement hydration process resumes, however, the destroyed structural bonds in concrete are not completely restored.

Freezing of freshly laid concrete is also accompanied by the formation of ice films around the reinforcement and filler grains, which, due to the influx of water from less cooled concrete zones, increase in volume and squeeze the cement paste from the reinforcement and filler.

All these processes significantly reduce the strength of concrete and its adhesion to reinforcement, and also reduce its density, durability and durability.

If concrete acquires a certain initial strength before freezing, then all the processes mentioned above do not adversely affect it. The minimum strength at which freezing is not dangerous for concrete is called critical.

The value of the normalized critical strength depends on the class of concrete, type and operating conditions of the structure and is: for concrete and reinforced concrete structures with non-stressed reinforcement - 50% of the design strength for B7.5 ... B10, 40% for B12.5 ... B25 and 30% for V 30 and above, for structures with prestressed reinforcement - 80% of the design strength, for structures subjected to alternate freezing and thawing or located in the zone of seasonal thawing of permafrost soils - 70% of the design strength, for structures loaded with design load - 100% design strength.

The duration of hardening of concrete and its final properties largely depend on the temperature conditions in which the concrete is kept. As the temperature rises, the activity of water contained in the concrete mixture increases, the process of its interaction with cement clinker minerals accelerates, and the processes of formation of the coagulation and crystalline structure of concrete intensify. When the temperature drops, on the contrary, all these processes are inhibited and the hardening of concrete slows down.

Therefore, when concreting in winter conditions, it is necessary to create and maintain such temperature and humidity conditions under which concrete hardens to acquire either critical or specified strength in the shortest possible time with the lowest labor costs. For this, special methods of preparation, supply, laying and curing of concrete are used.

When preparing a concrete mixture in winter conditions, its temperature is increased to 35 ... 40C by heating aggregates and water. Fillers are heated up to 60C by steam registers, in rotating drums, in installations with flue gases blowing through the filler layer, with hot water. Water is heated in boilers or hot water boilers up to 90C. Heating of cement is prohibited.

When preparing a heated concrete mix, a different order of loading the components into the concrete mixer is used. In summer conditions, all dry components are loaded into the mixer drum, pre-filled with water, at the same time. In winter, in order to avoid “brewing” of cement, water is first poured into the mixer drum and coarse aggregate is loaded, and then, after several turns of the drum, sand and cement are loaded. The total duration of mixing in winter conditions is increased by 1.2 ... 1.5 times. The concrete mixture is transported in a closed container (buckets, car bodies), insulated and warmed up before starting work. Cars have a double bottom, into the cavity of which the exhaust gases of the engine enter, which prevents heat loss. The concrete mixture should be transported from the place of preparation to the place of laying as quickly as possible and without overloading. The places of loading and unloading must be protected from the wind, and the means of supplying the concrete mixture to the structure (trunks, vibrating hobs, etc.) are insulated.

The condition of the base on which the concrete mixture is laid, as well as the laying method, should exclude the possibility of its freezing at the junction with the base and deformation of the base when laying concrete on heaving pounds. To do this, the base is heated to positive temperatures and protected from freezing until the newly laid concrete acquires the required strength.

Formwork and reinforcement before concreting are cleaned of snow and ice, reinforcement with a diameter of more than 25 mm, as well as reinforcement from rigid rolled profiles and large metal embedded parts at temperatures below -10 ° C are heated to a positive temperature.

Concreting should be carried out continuously and at a high rate, while the previously laid concrete layer should be covered before the temperature in it falls below the intended one.

The construction industry has an extensive arsenal of efficient and economical methods of curing concrete in winter conditions, allowing to ensure high quality structures. These methods can be divided into three groups: a method that involves the use of the initial heat content introduced into the concrete mixture during its preparation or before laying in the structure, and the heat release of cement that accompanies concrete hardening - the so-called "thermos" method, methods based on artificial heating of concrete laid in the structure - electrical heating, contact, induction and infrared heating, convective heating, methods that use the effect of lowering the eutectic point of water in concrete with the help of special antifreeze chemical additives.

These methods can be combined. The choice of this or that method depends on the type and massiveness of the structure, the type, composition and required strength of concrete, the meteorological conditions of the work, the energy equipment of the construction site, etc.

Thermos method

The technological essence of the "thermos" method lies in the fact that having a positive temperature (usually in the range of 15 ... 30 ° C), the concrete mixture is placed in an insulated formwork. As a result, the concrete of the structure gains the desired strength due to the initial heat content and exothermic heat release of the cement during cooling down to 0°C.

In the process of concrete hardening, exothermic heat is released, which quantitatively depends on the type of cement used and the curing temperature.

High-quality and fast-hardening Portland cements have the highest exothermic heat release. The exotherm of concrete provides a significant contribution to the heat content of the structure, maintained by the "thermos" method.

Concreting by the method "Thermos with additives-accelerators"

Some chemical substances(calcium chloride CaCl, potassium carbonate - potash K2CO3, sodium nitrate NaNO3, etc.), introduced into concrete in small quantities (up to 2% by weight of cement), have the following effect on the hardening process: these additives accelerate the hardening process in the initial period of curing concrete. So, concrete with the addition of 2% calcium chloride by weight of cement already on the third day reaches a strength 1.6 times greater than concrete of the same composition, but without the additive. The introduction of accelerator additives into concrete, which are also antifreeze additives, in the indicated quantities lowers the freezing point to -3 ° C, thereby increasing the duration of concrete cooling, which also contributes to the acquisition of greater concrete strength.

Concrete with accelerator additives is prepared on heated aggregates and hot water. At the same time, the temperature of the concrete mixture at the outlet of the mixer varies between 25...35°C, decreasing by the time of laying to 20°C. Such concretes are used at an outdoor temperature of -15 ... -20 ° C. They are laid in insulated formwork and covered with a layer of thermal insulation. Concrete hardening occurs as a result of thermos curing in combination with the positive effect of chemical additives. This method is simple and quite economical, allows you to use the "thermos" method for structures with Mn

Concreting "Hot thermos"

It consists in short-term heating of the concrete mixture to a temperature of 60 ... 80 ° C, compacting it in a hot state and thermos keeping or with additional heating.

In the conditions of a construction site, the heating of the concrete mixture is carried out, as a rule, by electric current. To do this, a portion of the concrete mix is ​​connected by means of electrodes to an alternating current electric circuit as a resistance.

Thus, both the released power and the amount of heat released over a period of time depend on the voltage supplied to the electrodes (direct proportionality) and the ohmic resistance of the concrete mixture being pierced (inverse proportionality).

In turn, the ohmic resistance is a function of the geometric parameters of flat electrodes, the distance between the electrodes and the specific ohmic resistance of the concrete mixture.

The electric heating of the concrete mixture is carried out at a voltage of 380 and less often 220 V. To organize electric heating, a post with a transformer (voltage on the low side 380 or 220 V), a control panel and a switchboard is equipped at the construction site.

The electrical heating of the concrete mixture is carried out mainly in tubs or in the bodies of dump trucks.

In the first case, the prepared mixture (at a concrete plant) having a temperature of 5...15°C is delivered by dump trucks to the construction site, unloaded into electric tubs, heated to 70...80°C and placed in the structure. Most often, ordinary tubs (shoes) are used with three electrodes made of steel 5 mm thick, to which wires (or cable cores) of the mains are connected using cable connectors. For uniform distribution of the concrete mixture between the electrodes when loading the bucket and better unloading of the heated mixture into the structure, a vibrator is installed on the body of the bucket.

In the second case, the mixture prepared at the concrete plant is delivered to the construction site in the back of a dump truck. The dump truck enters the heating post and stops under the frame with electrodes. When the vibrator is running, the electrodes are lowered into the concrete mixture and voltage is applied. Heating is carried out for 10 ... 15 minutes to the temperature of the mixture on quick-hardening Portland cements 60°C, on Portland cements 70°C, on slag Portland cements 80°C.

To heat the mixture to such high temperatures for short span time, large electrical power is required. So, for heating 1 m of the mixture to 60°C in 15 minutes, 240 kW is required, and in 10 minutes - 360 kW of installed power.

Artificial heating and heating of concrete

The essence of the method of artificial heating and heating is to increase the temperature of the laid concrete to the maximum allowable and maintain it for the time during which the concrete gains critical or specified strength.

Artificial warming up and heating of concrete is used when concreting structures with Mn> 10, as well as more massive ones, if in the latter it is impossible to obtain a given strength in a timely manner when cured only by the thermos method.

The physical essence of electrical heating(electrode heating) is identical to the method of electric heating of the concrete mixture discussed above, i.e., the heat released in the laid concrete when an electric current is passed through it is used.

The resulting heat is spent on heating the concrete and formwork to a predetermined temperature and compensating for heat losses to the environment that occur during the curing process. The temperature of concrete during electrical heating is determined by the amount of electric power released in concrete, which should be assigned depending on the selected heat treatment mode and the amount of heat loss that occurs during electrical heating in the cold.

For summing up electrical energy various electrodes are used for concrete: plate, strip, rod and string.

The following basic requirements are imposed on the designs of electrodes and their layouts: the power released in concrete during electrical heating must correspond to the power required by the thermal calculation, the electric and, therefore, temperature fields must be as uniform as possible, the electrodes should be located as far as possible outside the heated structure to provide minimum flow metal, the installation of electrodes and the connection of wires to them must be carried out before laying the concrete mixture (when using external electrodes).

Plate electrodes satisfy the stated requirements to the greatest extent.

Plate electrodes belong to the category of surface electrodes and are plates made of roofing iron or steel, sewn onto the inner surface of the formwork adjacent to concrete and connected to opposite phases of the power supply network. As a result of the current exchange between the opposite electrodes, the entire volume of the structure is heated. With the help of plastic electrodes, weakly reinforced structures of the correct shape of small sizes (columns, beams, walls, etc.) are heated.

Strip electrodes are made from steel strips with a width of 20 ... 50 mm and, like plate electrodes, are sewn onto the inner surface of the formwork.

The current exchange depends on the connection scheme of the strip electrodes to the phases of the supply network. When opposite electrodes are connected to opposite phases of the supply network, current exchange occurs between opposite faces of the structure, and the entire mass of concrete is involved in heat release. When adjacent electrodes are connected to opposite phases, current exchange occurs between them. In this case, 90% of all input energy is dissipated in peripheral layers with a thickness equal to half the distance between the electrodes. As a result, the peripheral layers are heated due to the Joule heat. The central layers (the so-called “core” of concrete) harden due to the initial heat content, exotherm of cement, and partly due to the influx of heat from the heated peripheral layers. The first scheme is used for heating weakly reinforced structures with a thickness of not more than 50 cm. Peripheral electrical heating is used for structures of any massiveness.

Strip electrodes are installed on one side of the structure. In this case, adjacent electrodes are connected to opposite phases of the supply network. As a result, peripheral electrical heating is realized.

One-sided placement of strip electrodes is used for electrical heating of plates, walls, floors and other structures with a thickness of not more than 20 cm.

With a complex configuration of concreted structures, rod electrodes are used - reinforcing bars with a diameter of 6 ... 12 mm, installed in the body of concrete.

It is most expedient to use rod electrodes in the form of flat electrode groups. In this case, a more uniform temperature field in the concrete is provided.

With electrical heating concrete elements small cross-section and considerable length (for example, concrete joints up to 3 ... 4 cm wide) use single rod electrodes.

When concreting horizontally located concrete or having a large protective layer reinforced concrete structures use floating electrodes - reinforcing bars 6 ... 12 mm, sunk into the surface.

String electrodes are used for heating structures whose length is many times greater than their cross-sectional dimensions (columns, beams, girders, etc.). String electrodes are installed in the center of the structure and connected to one phase, and the metal formwork (or wooden formwork with roofing steel decking) to the other. In some cases, a working fitting can be used as another electrode.

The amount of energy released in concrete per unit time, and hence temperature regime electrical heating depends on the type and size of the electrodes, the scheme of their placement in the structure, the distances between them and the scheme of connection to the mains. In this case, the parameter that allows arbitrary variation is most often the input voltage. The generated electric power, depending on the parameters listed above, is calculated by the formulas.

The current to the electrodes from the power source is supplied through transformers and switchgears.

Used as trunk and switching wires insulated wires with a copper or aluminum core, the cross section of which is selected from the condition of passing the calculated current through them.

Before turning on the voltage, the correct installation of the electrodes, the quality of the contacts on the electrodes and the absence of their short circuit to the armature are checked.

Electrical heating is carried out at low voltages within 50 ... 127 V. Average specific consumption electricity is 60 ... 80 kW / h per 1 m3 of reinforced concrete.

Contact (conductive) heating. At this method The heat released in the conductor when an electric current passes through it is used. Then this heat is transferred by contact to the surfaces of the structure. The transfer of heat in the concrete of the structure itself occurs by thermal conduction. For contact heating of concrete, thermoactive (heating) formworks and thermoactive flexible coatings (TAGP) are mainly used.

Heating formwork has a deck of sheet metal or waterproof plywood, on the back of which there are electric heating elements. In modern formwork, heating wires and cables, mesh heaters, carbon tape heaters, conductive coatings, etc. are used as heaters. The most effective use of cables, which consist of constantan wire with a diameter of 0.7 ... 0.8 mm, placed in heat-resistant insulation . The surface of the insulation is protected from mechanical damage by a metal protective stocking. To ensure uniform heat flow the cable is placed at a distance of 10 ... 15 cm branch from the branch.

Mesh heaters (metal mesh strip) are isolated from the deck with an asbestos sheet gasket, and on the back side of the formwork shield - also with asbestos sheet and covered with thermal insulation. For creating electrical circuit individual strips of the grid heater are interconnected by distributing tires.

Carbon tape heaters are glued with special adhesives to the deck of the shield. To ensure strong contact with the switching wires, the ends of the tapes are copper-plated.

Any inventory with a steel or plywood deck can be converted into a heating formwork. Depending on the specific conditions (heating rate, temperature environment, thermal protection power of the rear part of the formwork), the required specific power can vary from 0.5 to 2 kV A/m2. Heating formwork is used in the construction of thin-walled and medium-massive structures, as well as in monolithic units of prefabricated reinforced concrete elements.

Thermoactive Coating (TRAC) is a lightweight, flexible device with carbon tape heaters or heating wires that provide heating up to 50°C. The basis of the coating is fiberglass, to which the heaters are attached. For thermal insulation, staple glass fiber is used with a shielding layer of foil. Rubberized fabric is used as waterproofing.

Flexible coating can be produced in various sizes. For fastening individual coatings to each other, holes are provided for the passage of braid or clips. The coating can be placed on vertical, horizontal and inclined surfaces of structures. At the end of work with the coating in one place, it is removed, cleaned and rolled into a roll for ease of transportation. It is most effective to use TRAPS in the construction of floor slabs and coatings, floor preparation, etc. TRAPS are manufactured with a specific electrical power of 0.25 ... 1 kV-A/m2.

Infrared heating uses the ability of infrared rays to be absorbed by the body and transformed into thermal energy, which increases the heat content of this body.

Infrared radiation is generated by heating solids. In industry, infrared rays with a wavelength of 0.76 ... 6 microns are used for these purposes, while bodies with a radiating surface temperature of 300 ... 2200 ° C have the maximum flux of waves of this spectrum.

Heat from the source of infrared rays to the heated body is transferred instantly, without the participation of any heat carrier. Absorbed by irradiation surfaces, infrared rays are converted into thermal energy. From the surface layers heated in this way, the body warms up due to its own thermal conductivity.

For concrete work, tubular metal and quartz emitters are used as generators of infrared radiation. To create a directed radiant flux, the emitters are enclosed in flat or parabolic reflectors (usually made of aluminum).

Infrared heating is used in the following technological processes: heating of reinforcement, frozen bases and concrete surfaces, thermal protection of laid concrete, acceleration of concrete hardening during the installation of interfloor ceilings, erection of walls and other elements in wooden, metal or structural formwork, high-rise structures in sliding formwork (elevators , silos, etc.).

Electricity for infrared installations usually comes from a transformer substation, from which a low-voltage cable feeder is laid to the work site, supplying distribution board. From the latter, electricity is supplied through cable lines to separate infrared installations. Concrete is treated with infrared rays in the presence of automatic devices that provide the specified temperature and time parameters by periodically switching infrared installations on and off.

At induction heating concrete use the heat released in the reinforcement or steel formwork, located in the electromagnetic field of the coil-inductor, through which the alternating electricity. To do this, an insulated wire-inductor is laid in successive turns on the outer surface of the formwork. An alternating electric current passing through an inductor creates an alternating electromagnetic field. Electromagnetic induction causes eddy currents in the metal (reinforcement, steel formwork) located in this field, as a result of which the reinforcement (steel formwork) heats up and the concrete heats up from it (conductively).

Concrete work should preferably be carried out at a round-the-clock outdoor temperature above +5°C. But then all construction projects in the climatic conditions of most regions of our country would be mothballed for more than half a year. To make concreting in winter conditions possible, we developed and introduced into production various methods, This:

• The use of special additives that lower the freezing point of water. The most famous additive is table salt.
• The use of formwork with heating.
• Preparing concrete mix with hot water.
• Use of high-quality fast-hardening cements;
• Warming up the concrete mass after molding.

All these methods can be used when pouring concrete in winter, as independent options or in combination.

What happens to concrete at sub-zero temperatures

During hardening of the concrete mix under normal temperature and humidity conditions, water, interacting with cement, sand and gravel, contributes to their strong adhesion to each other. The result is a monolith endowed with high strength characteristics. If water is allowed to freeze in the composition of the concrete mixture, then the opposite, destructive effect will occur.

The water component at low temperatures, expanding, increases in volume, making the mass loose. BUT main element concrete - cement - loses its properties. In addition, frozen water will create cavities around parts. reinforcing cage, thereby violating the integrity of the structure. After defrosting, the concrete mass will no longer be able to restore the necessary qualities. This is bad for any structure, but with regard to foundations, this state of affairs is catastrophic. So is it possible to pour concrete in winter? Undesirable, but acceptable subject to certain rules and requirements of SNiP for implementation construction works at low outside temperatures.

Practical studies have established the boundary strength limit for various grades of concrete, after which freezing will not be critical for it. The loss of strength in the finished form will be, in this case, no more than 6%.

Additives that increase the frost resistance of concrete

Concrete work in winter should be carried out with the addition of special antifreeze additives to the concrete mixture. They help lower the freezing point of the composition and accelerate the setting and hardening of concrete. These substances include:

• calcium chloride (table salt);
• sodium chloride;
• sodium nitrite and nitrate;
• sodium formate;
• potash;
• lignosulfanate.

Any of these additives is introduced into the concrete mixture in small doses. 1-2% by weight of cement is enough for winter concrete to acquire the desired qualities.

In addition to their main purpose, antifreeze additives improve the strength characteristics of the material, increase its density, and positively affect the durability of the structure.

Preparation of concrete mix in winter

In addition to the use of anti-frost additives, winter concreting is performed with a warm composition. The temperature of the concrete mixture must be brought to 35-40 degrees. To do this, water and aggregates, small and large, are heated. Cement cannot be heated categorically, but it must be stored in a warm room.

It is great if there is an electrically heated concrete mixer on the construction site, since in winter it is only necessary to pour concrete when it is warm. A conventional stirrer is heated by scrolling very hot water in it. In the cold season, the procedure for preparing the concrete mix differs from the usual one:

• first poured into a concrete mixer hot water with additives dissolved in it;
• fall asleep heated aggregates;
• sand and gravel can be heated with hot air using a compressor or in special furnaces;
• after mixing, cement is added;
• the process of mixing the concrete mixture in time increases by about half, against the usual terms.

The finished mixture is poured into a pre-prepared formwork. Before this, it is necessary to remove possible frost and warm up the reinforcing cage with any convenient way: portable braziers with fuel, heat guns, electricity.

Concreting in winter must be carried out continuously so that the structure is strong and uniform. The time interval between pouring individual portions of the concrete mix should be such that the sub-zero temperature does not have time to affect the previous part. The molded part of the structure must be immediately covered with heat-insulating materials, PVC film.

Winter concrete care

The use of a hot solution and the use of anti-freeze additives are very important when working in winter. But it is no less essential to competently organize the conditions for hardening and the appropriate care of concrete in the winter. To extend the cooling time of the finished structure, use any suitable materials: film, hay, straw, heat-insulating mats.

Excellent effect gives the use fixed formwork from polystyrene foam. It will help the concrete mass to mature evenly, without freezing, and after the concrete has gained design strength, it will serve as high-quality thermal insulation and protect it from the harmful effects of the environment.

In industrial conditions and on large-scale construction sites, another method such as electric heating is used. Pleasure is not cheap, but very effective. There are two ways to carry out electrical heating: by connecting the electrodes to the reinforcing cage or by placing them in a concrete mass.

To control the process, special automatic devices with sensors. If there are none, then the work is performed manually by periodically measuring the temperature and turning on/off the electrodes when the temperature reaches +30°C.

To implement the heating of the concrete mass with the help of electricity, the following means are used:

• PNSV wire, consisting of a steel rod and PVC insulation. The cross section can be from 1 to 6 mm. Let's apply for electric networks with alternating current up to 380 V or with direct current - up to 1000 V. As a heating element for concrete hardening in winter conditions, it is used through a step-down transformer.
• VET cables Finnish manufacturer and KDBS from a Russian manufacturer are designed specifically with the intention of using them in the construction industry to accelerate the hardening of concrete. It is noteworthy that the use of these wires does not require transformers, they operate from a conventional household electrical network of 220V.

The heating cable of the selected brand, calculated power is wrapped around the reinforcing cage with an approximate step of 250-300 mm. Inside the structure, the wires should not overlap, sag strongly, and they should not be laid deeper than 200 mm either. If it is not a free-standing element that is to be poured with a concrete mixture, but one that is joined to an existing part, then the laying of the wire must begin from the junction.

About 4 m of wire is usually consumed per square meter. This amount was determined empirically, based on such a calculation that 0.4-1.5 kW of power is needed to warm up 1 m3 of concrete. The thickness of the product, the type of formwork, the properties and composition of the concrete mix itself affect the establishment of the exact figure. For fastening cables, knitting reinforcing wire is used.

Connection to the network or transformer is carried out at the end of the entire complex of molding works. In this case, the possibility of damage to the heating cables must be completely excluded.