Which additive in concrete is better at 10. Additives that give concrete special properties. How does the ambient temperature affect the consumption of chlorides

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

What is an antifreeze additive in the solution?

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

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

The problem of organizing brickwork in cold weather

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

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

Features of the preparation of the solution

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

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

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

Antifreeze additive: consumption

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

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

Air temperature	sodium formate	Potash	sodium nitrite

plasticizers

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

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

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

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

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

Eventually

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

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

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

Antifreeze additives in concrete: main varieties

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

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

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

Antifreeze;
sulfates;
Antifreeze additives-accelerators.

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

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

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

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

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

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

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

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

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

Advantages and disadvantages of antifreeze additives in concrete mortar

Advantages of antifreeze additives in concrete

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

Disadvantages of antifreeze additives in concrete

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

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

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

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

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

Dosage and consumption of antifreeze additive in concrete

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

The consumption of antifreeze additive depends on the following factors:

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

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

Do-it-yourself antifreeze additive in concrete

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

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

Benefits of an antifreeze additive based on chlorides

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

Disadvantages of antifreeze additive based on chlorides

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

How does ambient temperature affect chloride consumption?

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

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

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

30% after a week;

80% after a month;

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

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

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

Precautions when working with antifreeze additives

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

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

However, sometimes it becomes necessary to carry out construction work in winter at low temperatures. There may be several reasons:

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

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

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

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

Pouring concrete at low temperatures: general recommendations

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

At the turn of the seasons, the question of at what temperature it is possible to pour concrete under the foundation is of particular relevance so as not to endanger the structural elements of the new building. To get an answer, it is necessary to understand the ongoing processes inside the cement slurry.

Hydration of concrete - thickening and hardening of cement mortar

Hydration is the chemical process of hardening a mixture of cement and water into stone. It begins after mixing the mortar, however, the concrete setting occurs only after the foundation is poured. While the mixture is mixed with a mixer or concrete mixer, it is subjected to vibrations, due to which hardening is delayed, and the quality of the concrete does not suffer at all. After the mortar is removed from the concrete mixer, the material begins to harden and goes through two stages:

1. At the first stage, the mortar sets. This process, depending on the composition of the mixture and external conditions, takes from 1 to 20 hours.
2. At the second stage, the mortar hardens and gains up to 90% of its final strength. This process takes place within 28 days. After that, the concrete continues to harden throughout the entire service life.

The course of hydration directly depends on external factors, in particular, on the ambient temperature. At +5 degrees Celsius, the setting process begins after 2 hours and lasts up to 10 hours. At +20 degrees, 3 hours after pouring the concrete, its hardening begins, while the setting has not yet had time to complete. The hardening of cement is due to the components that make up its composition: tricalcium aluminate, tricalcium silicate, dicalcium silicate, tetracalcium aluminoferrite.

Answering the question at what temperature can the foundation be poured, we can say that ideal conditions for hydration are as follows:

1. The temperature of the mixture is +30 degrees Celsius in normal weather conditions, up to +70 degrees in the cold months due to the heating of the components (water, sand and gravel) with warm air or steam.
2. Ambient (air) temperature - from +5 to +30 degrees Celsius.

Due to the fact that the solidification (hardening) temperature of concrete has a framework, when pouring the foundation, it is necessary to take into account external conditions.

Rules for concreting the foundation in the summer months

It is believed that pouring the foundation in winter is the most difficult, because due to sub-zero temperatures, the solution may freeze before the completion of the hydration process. However, the heat is no less dangerous for a fresh foundation than winter frosts. Due to the high outside temperature during chemical reaction cement mixture will increase in volume. After the formation of the cement stone, it will inevitably cool and decrease, but this will not happen due to the formed crystalline structure.

As a result, freezing high temperature leads to strong internal stress in the foundation before construction begins structural elements a new house, and the owner will receive a foundation in operation, capable of cracking at any time. Usually, their first signs appear already a few hours after laying the solution inside the formwork.

High summer temperatures force builders to use special fast-hardening Portland cements if foundation pouring is planned to be carried out at temperatures above +25 degrees and at air humidity less than 50%.

The brand of cement used should be one and a half times the design parameters of concrete, in addition, to increase operational qualities foundation, plasticizers and all kinds of modifying additives will have to be added to the mixture, due to which hydration will slow down. For concreting, we recommend using the least hot hours of the day (early morning or evening). Another danger to the foundation of a house in the summer is the possible dehydration of the solution. To protect concrete from water evaporation, you must:

cover the surface with chips, sand or sawdust;
moisten the foundation from the watering can;
water wooden formwork from buckets.

Winter work – construction at low temperatures

At low temperatures hydration does not accelerate, but slows down, as a result of which the foundation does not have time to gain the strength it needs. At zero degrees, the process of solidification of the solution in the outer layer stops completely, and inside the structure it continues for several hours until all components have cooled down. In this case, water does not have time to react with cement, after which it freezes, increases in volume and literally breaks the structure of concrete.

Specialists are well aware at what temperature concrete can be poured for the foundation without fear of losing its performance. Frosts are a significant obstacle to concreting, therefore, in winter, specialists are forced to use special technologies and means:

heating of concrete elements before pouring and formwork heating;
laying a heated cable inside a slab or;
feed to reinforcing cage elements electric current for heating;
installation of heaters around the foundation for the first three days;
creating a greenhouse by covering the entire perimeter of the foundation with a film;
introduction to the mixture special reagents, which reduce the t of water crystallization or accelerate the hardening time of the foundation.

The use of any of the described technologies significantly increases the cost of building a foundation. Therefore, it is difficult for private owners to recommend these funds. There are other ways to pour concrete at sub-zero temperatures. One of them is to change the amount of water and cement in the produced solution. It requires the most accurate and competent dosage of the used components of the mixture. Calculate at home required amount water and cement to improve the hardening of the foundation in winter is almost impossible.

heating two-thirds of the water for the solution to t of the order of 70 degrees Celsius;
adding sand and gravel to the water;
adding the remaining third of the water and cement to the mixture.

Mixing the solution should be done twice as long as usual. The time of vibration compaction also increases by 1.5 times. Before pouring the solution, the formwork must be checked for ice, snow removed and the underlying layer warmed up. We cover the poured solution polymer film, which will keep the mixture warm for a while. If the above rules for concreting the foundation cannot be observed at home, it is recommended to wait for the air temperature to rise above +5 degrees. With a favorable forecast for the next three weeks, the owner of the house will be able to fill using standard technology.

The dependence of the cost of work on the weather - how to save on the foundation?

Almost all modern construction companies work on pouring concrete summer months, in late spring and early autumn. All this is explained very simply - at this time it is cheapest to carry out construction in general and build a foundation in particular.

Building a house in winter can lead to additional and extremely significant financial expenses:

with the most optimistic forecasts, the construction budget in the cold months increases by 25-30% ;
thaws in winter do not eliminate the need to use expensive reagents in the construction of the foundation;
in winter it is impossible to prepare the solution on the spot, therefore the owner will have to additionally order the delivery of concrete by mixers;
a transformer substation is required to heat the foundation, since the home electrical network cannot withstand such high loads.

The only advantage of building a foundation in winter months lies in the possibility in early spring to start erecting the structures of the facility and complete the construction, necessary finishing and other works by the end of autumn. In practice, the owner has to invest colossal funds in winter construction, which will definitely overshadow the joy of building a private house.

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. When it goes into a solid state, all processes stop.

But this is not the only problem. It is known that when freezing, the volume of water increases by about 9%. As a result, inside the mass of concrete is formed high blood pressure. 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 framework is not connected to 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. Optimum temperature the aging 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 entered into warm room for him to accept room temperature but 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 in industrial scale electrical heating is also used different kind electrodes. They can be located on the surface, fixed on the formwork or introduced into the concrete solution. 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. The frame is erected, it is covered with a film or other similar materials. Putting a stove inside heat gun etc., with their help maintain 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 heating concrete 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, you need a large number of lamps.

Additives and Additives

Another way to pour concrete at low temperatures is to use chemicals. Some of them accelerate curing by initial stage 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 temperatures is 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 whole tape into small areas, 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).

One more important condition- 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. Need helpers and careful preparation, but you can make a normal base at sub-zero temperatures. At what temperature can concrete be poured? Depends on its composition, but for private traders it’s real, albeit with at great expense, 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.

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