Concrete work at low temperatures. Pouring concrete at sub-zero temperatures: features and process of work. Pouring the foundation with concrete

General provisions. The concept of "winter conditions" in the production of concrete works differs from the calendar one. "Winter conditions" for a specific construction site begin when the average daily outdoor temperature drops to + 5 ° C, and during the day it falls below zero.

At temperatures below 0°C, hydration processes in concrete stop, i.e. interaction of cement minerals with water. The hardening of concrete is suspended, as the concrete freezes, turning into a monolith, the strength of which is determined by the forces of freezing. Internal stresses appear in concrete, caused by an increase in the volume of free water by about 9% during freezing. These stresses break the fragile adhesive bonds between the individual components of concrete, reducing its strength. Free water, freezing on the surface of the aggregate grains in the form of a thin film, prevents the cement paste from adhering to the aggregate. It also worsens the strength properties of concrete.

After thawing of concrete, hardening at a positive temperature resumes, but the strength is lower than the design one, i.e. the one that would be achieved by curing under normal conditions. Other properties of concrete also decrease: density, durability, adhesion to reinforcement, etc. The properties of concrete deteriorate the more significantly, the earlier it freezes after laying. If concrete gains a certain strength by the time of freezing, then the negative effect of freezing on its properties is small: after thawing, the strength of concrete can reach the design value. In this case, the adhesive bond between the cement paste and the aggregate is much greater than the internal stresses. Therefore, the probability of deformations in the contact zone is less.

The minimum strength of concrete at the time of its freezing, sufficient to achieve its design strength after thawing, is called critical. This strength for concrete in structures with non-stressed reinforcement should be at least 30 ... 50% of the design, depending on the class of concrete, and not less than 50 kg / cm2. In prestressed structures, it should be at least 70% of the design value. If structures are to be loaded into winter period, then by the time of freezing, the strength of concrete in them should reach 100% of the design value.

To receive in winter conditions For concrete of design quality, it is necessary to provide for it a temperature and humidity regime in which the physical and chemical processes of hardening are not disturbed and do not slow down. The duration of maintaining such a regime should ensure the achievement of critical or design strength.

The task of "winter" concreting: to obtain concrete of a given strength. For this, general activities and various technologies for ensuring the normal mode of concrete hardening.

General events:

a) Work is carried out on heated concrete mix. This mixture at the time of laying in the structure must have a positive temperature, the opposite of the ambient air temperature. This is achieved by heating water, crushed stone and sand (steam) during the preparation of the concrete mixture at the plant.

b) To prevent cooling on the way, the body of the dump truck is closed from above with shields, and from below it is heated by exhaust gases from the car engine through the arranged double bottom of the body.

c) Buckets and bunkers are covered with insulated wooden lids, and sheathed on the outside. In severe frosts, they are periodically heated with steam. Concrete pumps are installed in heated rooms. Before starting work, hot water is pumped through the concrete pipeline. Pipe links of the main concrete pipeline at a temperature below minus 10 ° C are enclosed in thermal insulation together with a heating rough pipeline.

d) Before laying the concrete mixture, the formwork and reinforcement are cleaned of debris, snow, ice. To do this, if necessary, hot air blowing from heaters or steam is used, as well as hot steam washing followed by hot air blowing.

e) In frosts below minus 15°C, reinforcement from rods with a diameter of more than 25 mm and rolled profiles is heated to plus 5°C to ensure good adhesion of concrete to reinforcement. For the same purpose, metal elements protruding beyond the insulated formwork after heating are insulated at a length of at least 1.5 m from the block.

f) The quality of concrete is strongly influenced by the condition of the base on which it is laid. It is important to exclude early freezing of concrete at the junction with the base and subsequent deformation of the heaving soils of the base.

Before concreting the foundations, heaving soils are heated by steam, fire or electricity. Non-heaving soils do not warm up. The temperature of the mixture to be laid must be at least 10°C higher than the temperature of the substrate. It is not allowed to lay the concrete mixture on frozen ground (“frozen” base).

If it is necessary to lay the concrete mixture on the previously laid and frozen concrete, it is heated to a depth of at least 400 mm and protected from freezing until fresh concrete acquires critical strength.

g) When concreting, to reduce heat losses, the concrete mixture is laid in small sections along the length and width, so that the previously laid layers overlap with new ones faster, and the concrete temperature does not have time to fall below the calculated one.

h) Concreting is carried out around the clock without interruptions, since the preparation of frozen working joints is very laborious and the required quality is not always ensured.

Technologies that ensure the normal mode of concrete hardening:

1. Application of chemical additives.

Chemical additives lower the freezing point of the liquid part of the concrete mixture, which ensures concrete hardening at temperatures below 0°C, which increases the curing time.

This method is relatively inexpensive (additional costs compared to normal conditions (price increase) of about 16%) and is widely used in construction. As additives are used: sodium chloride, calcium chloride, potassium carbonate (potash), sodium nitrite, etc.

Additives are introduced into the concrete mixture during its preparation. Depending on their number, a given effect is obtained:

At 1-2% by weight of cement - acceleration of concrete hardening;
- at 3–5% by weight of cement – ​​lowering the freezing point by 5–10°С;
- at 10–15% of the weight of cement - the complete elimination of freezing "cold concrete", but at the same time, curing continues for 40–90 days.

2. Concrete heating.

a) Thermos method. The heat released during the chemical reactions of concrete hardening is used. For this, the structure is additionally insulated.

The method is effective for massive structures of a simple shape, especially for buried structures and structures on the ground and in the ground (foundations, basement walls, foundations for equipment, floors on the ground, etc.). To enhance the effect in the preparation of the mixture, cements with increased heat release are used.

b) Steam heating. A "shirt" of roofing material, wooden or steel panels is arranged around the concreted structure, under which steam is supplied (Fig. 4.52). The “jacket” provides the necessary heating of the structure and humidity (does not dry out the concrete).

Used steam low pressure 0.5 -0.7 atm. with a temperature of 80–90°C. Approximate mode of steam heating: rate of temperature rise (gradient) no more than 5–10 deg/h; isothermal heating at a temperature of 80°C for concretes on ordinary Portland cement and 95°C on slag Portland cement and pozzolanic cement. The cooling rate (gradient) of concrete should be 10 deg/h. Steam heating of concrete can be carried out until it gains design strength, which is especially important for our eastern and northern regions, where the "winter period" is
8... 10 months.

The method is used to warm up various concrete structures, but only where there is steam in the required amount.

in) Electrical heating. Internal - with the help of electrodes. Heat is released when an electric current is passed through a wet concrete mix. Electrodes can be embedded in freshly laid concrete or heating wires are embedded in the structure prior to concreting. The number of electrodes, heating wires in each case is determined by calculation.

The advantage of the method is simplicity. Disadvantages - the complexity of control (round-the-clock surveillance) and high cost.

External - heat is released by "heating" formwork or heating flexible electrical cords.

3. Concreting in greenhouses. Above the concreted structure or part of it is arranged light frame fencing made of tarpaulin, film, etc. (tent) and warm air is supplied under it or heaters are placed inside the tent. Under the tent (temperature plus 5–10 °C), concreting is carried out under normal conditions.

Depending on the task, the greenhouse can “work” for 3–16 days, until concrete reaches 50% of the design (design) strength, or all of the design 28 days.

4. Concrete heating infrared rays(penetrating heating).

The peculiarity of the method is that the transfer of heat to concrete (warming up) occurs throughout the entire thickness of the structure simultaneously and with the same intensity (Fig. 4.53).

For heating monolithic concrete heating elements of the NVSZh type (heat-resistant air drying heater) or NVS (air drying heater) are used. The power of these heaters per 1 m of length ranges from 0.6 to 1.2 kW, the temperature of the radiating surfaces is from 300 to 600°C. Heating elements operate at a voltage of 127, 220 and 380 V.

Carborundum emitters have a power of up to 10 kW / h, and their working temperature reaches 1300–1500 °C.

The optimal distance between the infrared unit and the heated surface is 1–1.2 m.

It is possible to heat with infrared emitters both open surfaces of concrete and through the formwork. For better absorption of infrared radiation, the surface of the formwork is covered with black matte varnish. The temperature on the concrete surface should not exceed 80-90°C. To prevent intensive evaporation of moisture from concrete, open surfaces are closed plastic wrap, glassine or roofing material.

Infrared installations are placed at such a distance from each other to warm up all areas concrete surface. The heating of concrete by infrared rays is conventionally divided into three periods: holding of concrete and its heating; isothermal heating; cooling down.

The method is used for heat treatment of concrete in thin-walled structures with a large surface modulus (for example, walls concreted in sliding formwork, slabs, beams). This method is also used to thaw frozen concrete in working joints, when laying concrete in grooves, as well as to thaw reinforcement, embedded parts and the “active” surface of the formwork-cladding before placing concrete into it.

Source: Technology of building processes. Snarsky V.I.

In most of the territories of our country, cold or cool temperatures persist for more than half of the year. If we take into account that during concrete work, “winter” begins with a temperature drop to +5 o C, then the “window” for concrete work is very small. However, it can be extended, and significantly, through the use of various means. These are the so-called technologies of winter pouring of concrete.

During the normal course of the concrete curing process, moisture serves as a "gluing" element for cement particles. Upon her transition to solid state all processes are stopped.

But this is not the only problem. It is known that when freezing, the volume of water increases by about 9%. As a result, increased pressure is formed inside the mass of concrete. If the grains of cement up to this point have not yet gained a certain level of strength, they are destroyed under pressure. After freezing, they will no longer fully acquire their properties and the concrete will not be strong enough.

There is another unfavorable moment in the winter pouring of reinforced foundations. Steel is an excellent conductor of heat, and it facilitates the removal of heat from the thickness of the concrete. Possessing good heat-conducting properties, the rods quickly cool down. Around them, the water freezes first. Ice pushes concrete particles aside, and in their place comes water that has not yet frozen from the still warm layers. It also freezes, pushing the concrete further back. As a result, the array is no longer a monolith: the frame is not connected to the concrete stone. The strength of such a base after thawing and final hardening will be several times lower.

Of all these processes it follows that than less water in an incoherent state will be at the time of freezing, the less will be the loss of strength. Through various experiments and calculations, the boundary strength values ​​were determined at which concrete can be frozen. They are called the point of critical strength. Depending on the class of concrete and the purpose of the building, the type of use of the structure, it is required to wait for the maturation of some compositions by 20%, for others, all 100% is required.

For reinforced concrete with non-tensile reinforcement (the type used in private housing construction), it is 50%, for foundations that will be subjected to alternate defrosting / freezing (baths and country houses without heating) - 70%. After reaching this point, the foundation can be frozen. After thawing, all processes in it will resume. The loss of strength in this case is no more than 6%.

Concreting methods in winter conditions

The speed of the hardening process depends on the temperature of the solution. With its increase, the activity of water increases significantly, the rate of curing increases. Therefore, when carrying out concrete work in winter or at temperatures below +5 o C, it is important to create and maintain the required level of heating. The optimum aging temperature of the solution is from +20 o C to +30 o C. There are several ways to do this:

• make the solution warm;
• insulate the formwork;
• use additives and additives that accelerate hardening and/or lower the freezing point of water;
• preheat the already poured concrete mass.

All of these methods work well. They are used singly or in combination.

First of all, it is necessary to choose the right cement for winter concreting foundation. It is known that during the hardening of concrete, reactions occur in which heat is released. For winter, it's a great feature. At the same time, fast-hardening Portland cements and compositions of high grades emit a greater amount of heat. Therefore, for kneading at low or sub-zero temperatures, it makes sense to buy them.

Only this will allow you to fill the foundation with a strip or slab foundation at positive temperatures during the day, and slight frosts at night. But at the same time, it will be necessary to make the batch warm (read below), and after pouring the foundation, the formwork will need to be thermally insulated: covered with mats, straw, etc. If you have already purchased a heat insulator, you can use it, you just need to monitor its condition, cover it with a film or other moisture-proof materials.

Temperature increase during kneading

During the winter pouring of the foundation, the temperature of the solution is adjusted to 35-40 o C. To do this, heat the water and backfill. In no case should the cement be heated: it will “brew” and become practically useless.

It is good if it is possible to use an electrically heated concrete mixer: it is connected to the network and the drum is heated. In another case, it is advisable to preheat it by scrolling through the heated water.

When kneading, water is heated to 90 o C. Crushed stone and sand must be heated to 60 o C. This is done by blowing hot air, heating in special ovens. Furnaces are for a private builder from the realm of fantasy, but you can arrange hot air blowing. For example, from a stove or a fire, stretch several duct pipes into a pile of rubble or sand.

Once again, we pay attention: do not heat the cement. It can be brought into a warm room so that it takes room temperature, but it cannot be heated.

During the winter mixing of the solution, the order of laying the components changes: water is poured, crushed stone and sand are poured into it. After several revolutions cement is added.

In addition, it is necessary to increase the kneading time. It should be longer by 20-50%: due to better mixing, reactions are activated and the temperature rises during hardening.

Warming and heating solution

To extend the cooling time of concrete, it is required to retain heat to the maximum. Because using everything possible means and available materials, carry out the insulation of the walls of the formwork. You can use tarpaulins, mats, some old warm clothes, fill the gap between the walls of the formwork and the soil, straw. Anything, as long as the heat doesn't leak into the air.

One of the tasks is to keep the heat of the solution

During construction on an industrial scale, electric heating is also used using different kind electrodes. They can be located on the surface, fixed on the formwork or inserted inside. concrete mortar. The method is effective, but rarely implemented in private construction. This pleasure is very expensive: the consumption of electricity for heating a cubic meter of concrete is 60-80 kW / h. At the same time, it is necessary to strictly control the temperature: measure it every two hours (or more often) and turn it off when it reaches +30 o C. Then turn it on again after a while. Control must be around the clock.

When pouring the foundation with your own hands in winter, it is realistic to use only heating cables. They are attached with inside to the formwork, and after its removal, they are dismantled. There is a second option - to "drown" the wire in concrete. Both methods work well, but only if the walls are insulated from the cold.

There are also on sale special heating mats for heating concrete. They are laid out on the surface, included in the network. Its cost is 2.5 thousand rubles / m2.

To maintain the temperature, there are greenhouses above the object. These are structures very much reminiscent of greenhouses. And their task is similar: to keep warm. A frame is erected, it is covered with a film or other similar materials. Inside they put a stove, a heat gun, etc., with their help they maintain a positive temperature. But at the same time, it is also necessary not to forget about moistening so that the moisture from the solution does not evaporate.

Another method of concrete heating is using infrared emitters. This method is good because, under the influence of waves, the solution itself is heated directly. The emitters are covered with aluminum casings, creating a directed flow. However, for effective heating, a large number of lamps will be needed.

Additives and Additives

Another way to pour concrete negative temperatures- the use of chemicals. Some of them accelerate the hardening at the initial stage of the process. Mass fraction all additives - no more than 2% by weight of cement. Large quantities can adversely affect the quality of concrete, so stick to the recipes.

One of the methods of winter concreting is the addition of special antifreeze additives to the batch.

The most common additive that increases the “frost resistance” of concrete and accelerates its hardening is calcium chloride. Potash and sodium nitrate are also used. If you add them during normal mixing, the freezing point will drop to -3 o C.

One "BUT". Chlorides cannot be used for reinforced concrete - they provoke the rapid destruction of steel. So the most common concrete hardening accelerator - calcium chloride - is not suitable for pouring the foundation.

Pouring concrete at sub-zero temperature possible if the solution is heated with the same additives. In this case, you can work at -15 o C. But for the normal quality of the foundation, you will need to insulate the fill and follow simple but mandatory rules.

Rules for winter pouring concrete

The solution is poured into the prepared formwork. Preparation consists in removing ice and snow, heating the reinforcement and the bottom of the foundation. This is the most difficult stage. Scraping off ice is half the trouble, but warming up the reinforcement and the entire perimeter of the foundation is a problem. The temperature should not be high, but it is necessary to achieve its positive values.

As an option, you can consider the device of portable braziers, which are lowered into the pit and kindled there. It is possible to use heat guns powered by gas cylinders. The use of other means is difficult due to their high cost.

For this reason, concrete in winter slab foundations problematic: such areas cannot be heated. For this type of bases, "winter" will be limited to light frosts at night and positive daytime temperatures. Filling can be started after the reinforcement and the bottom have a positive temperature.

The strip foundation can also be poured during frosts: it is realistic to heat such a base and reinforcement in a limited volume. Not easy, but possible.

Everything can be done step by step. Break the entire tape into small sections, start heating at the same time or with a certain time interval on several of them (two or three, depending on the time required for kneading and heating the pit). Start pouring one area by moving the braziers further. While the first heated area is being poured, the next one will reach the required temperature. The flooded area is immediately covered with heat-insulating materials and proceed to the next, and moving along the entire perimeter.

It is imperative to knock down the ice and heat the reinforcement - this is the only way the foundation will be strong

The mechanism is clear. So it is possible to pour the foundation with concrete at -15 o C (but with appropriate additives, "hot" mixing and measures to preserve heat).

Another important condition is that the work must be carried out continuously. In winter, it is impossible to fill the foundation in parts. This is 100% correct. The gap between fillings should be such that a film does not have time to form on the surface of the previous part, and even more so that moisture does not freeze. Work must be carried out continuously until the end of the pour. The flooded parts must immediately be covered with heat-insulating mats. As you can see, several people are needed for this work. One cannot cope with all tasks.

note that Maximum temperature solution should be 35-40 o C. Its excess leads to a slowdown in the curing process. The situation will, of course, be better than when freezing, but not by much.

Results

Pouring the foundation in winter is not an easy task, but it is possible even with your own hands. You will need helpers and careful preparation, but you can make a normal base even at sub-zero temperatures. At what temperature can concrete be poured? It depends on its composition, but for private traders it is realistic, albeit at high cost, to achieve normal quality at temperatures not lower than -10-5 o C. Filling at positive temperatures during the day and frost at night will turn out to be less expensive.

The reliability and durability of the entire structure directly depends on the strength of the foundation. When planning such a "zero" construction cycle, many factors must be taken into account. Of particular importance is the information at what temperature the foundation can be poured.

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

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

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

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

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

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

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

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

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

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

Pouring the foundation with concrete

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

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

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

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

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

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

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

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

hardening time of concrete, days	-3°C	0°C	+5° С	+10° С	+20° С	+30° С
1	3%	5%	9%	12%	23%	35%
2	6%	12%	19%	25%	40%	55%٭
3	8%	18%	27%	37%	50%٭	65%
5	12%	28%	38%	50%٭	65%	80%٭٭
7	15%	35%	48%٭	58%	75%٭٭	90%
14	20%	50%٭	62%	72%٭٭	90%	100%
28	25%	65%	77%٭٭	85%	100%	-

Notes:

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

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

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

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

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

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

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

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

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

However, this approach only reduces Negative influence negative temperatures during the maturation of concrete, but will not completely eliminate the problem.

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

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

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

Are antifreeze supplements a "panacea"?

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

Video: one of the options for antifreeze additives in concrete

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

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

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

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

The danger of negative temperatures lies in several reasons:

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

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

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

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

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

Type of antifreeze additive	average temperature during ripening	1 Week	2 weeks	4 weeks	3 months
sodium nitrite	-5°C	30%	50%	70%	90%
	-10°C	20%	35%	55%	70%
	-15°C	10%	25%	35%	50%
Potash	-5°C	50%	65%	85%	100%
	-10°C	30%	50%	70%	90%
	-15°C	25%	40%	60%	80%
	-20°C	23%	35%	55%	70%
	-25°C	20%	30%	50%	60%

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

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

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

Care behind the cast foundation

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

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

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

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

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

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

Actions taken to ensure normal maturation of concrete	less - 3 ° С	from - 3° to + 5° С	from + 5° to + 10° С	from + 10° to + 15° С	from + 15° to + 25° С	over + 25° С
Covering with a film, constant moistening of the poured surface and formwork, covering concrete with moisture-saving material	No	No	No	No	in severe windy weather	always
Covering with a film, moistening the concrete surface	No	No	Yes	Yes	Yes	not enough
Covering with film and thermal insulation material	No	Yes	No	No	No	No
Covering with a film and thermal insulation material, creating a greenhouse with maintaining a temperature of +10 ° C for at least 3 days	Yes	No	No	No	No	No
Permanent maintenance of a thin layer of water on the concrete surface	No	No	Yes	Yes	Yes	Yes

A few more important notes:

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

What can be the general conclusion?

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

Video: the complexity of the foundation pouring processes in winter

To Category:

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

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

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

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

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

For concrete without antifreeze additives of monolithic structures and the monolithic part of prefabricated-monolithic structures, the strength at the time of freezing should be at least 50% of the design one at a concrete grade of 150, 40% for concrete of grade 200-300, 30% for concrete of grades 400-500, 70% - regardless of the brand of concrete for structures subjected to freezing and thawing at the end of curing, 80% - for concrete in prestressed structures, 100% - for concrete structures exposed immediately after the end of curing to the design water pressure, and structures to which presented 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 additives-accelerators, cements with increased heat release and quick-hardening cements, and also combine the thermos method with various methods heating of concrete, for example with peripheral electric heating or heating of structures.

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

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

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

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

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

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

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

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

To Category: - Concrete works in winter conditions

The 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 hardening process, it is undesirable to pour concrete and reinforced concrete foundations 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. It hardens by the gradual loss of water molecules 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, will decrease operational terms or even have to do the work again from scratch.

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 foundation devices. For example, use the bored method or carry out factory production.

For those who are not satisfied with alternative methods, 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, selected the best option. 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 their characteristic features, familiarize yourself with the minuses and pluses.

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 filled very quickly concrete mix, heated above standard indicators, are 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 in a monolithic slab for freezing 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 participation professional electrician. Truth, craftsmen in search of an answer to the question of whether ordinary concrete can be poured into formwork at sub-zero temperatures, they found a very ingenious way out with the supply of energy by a welding machine. But even this requires at least initial skills and knowledge in difficult building disciplines.

In the technical documentation, the 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 lightly 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.

The most rational way of heating concrete is curing with the help of an 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 indoor or outdoor 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 a thinner thickness, 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 early spring, if concrete stone must be cured by a certain deadline, and alternative options 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.

Preparation of mixtures with antifreeze additives is carried out special order. First, the aggregate is mixed with the main part of the water. Then, after light mixing, cement and water are added with diluted in it chemical compounds. 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 of binder to aggregate is 1:3, nitrite nitrate in the amount of 5-10%. Both antifreeze agents are not recommended for use in pouring structures operated in a watered 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 factory conditions. 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 interruptions cannot be avoided, the intervals between grouting should be kept to a minimum. If the technological subtleties are observed, the concrete monolith will gain the necessary margin of safety, will be mothballed for the winter and 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.