What is added to concrete at low temperatures. Varieties of antifreeze additives in concrete. Disadvantages of antifreeze additive based on chlorides

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

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

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

Pouring concrete

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

Direct exposure to sub-zero temperatures on a concrete structure is permissible only after it acquires required amount strength, frost resistance, etc. In construction terminology, this value is called the critical strength threshold - after overcoming it, frost does not adversely affect the structure of the concrete structure.

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

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

Among them are the following:

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

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

Mixture heating

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

Specialty Blends

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

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

thermal insulation

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

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

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

Internal and external heating

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

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

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

Outcome

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

Even at the beginning of the last century, work with concrete mixtures was seasonal. AT winter period concrete was not laid due to the loss of the strength characteristics of this building material. The builders tried different ways shift the schedule of concrete laying closer to the beginning of persistent frosts. To do this, the surface of the concrete monolith was insulated using various organic materials: sawdust, peat crumbs, reed mats woven for this purpose.

In parallel, scientists were trying to create concrete, the setting temperature of which would be below zero degrees. But since the builders were not satisfied with the gain in time, the search for alternative insulation (heating) of concrete at sub-zero temperatures continued.

Acceptable mixture temperature

During the course of the research, scientists determined what is the temperature of the concrete best for getting quality designs. Its values ​​are in the range between +5 and +15 degrees. The boundary indicators that were worked out by the researchers are minus 20 and plus 45 degrees. At outdoor air values ​​from +5 to -3 degrees. the temperature of the freshly prepared product is not allowed below +5 degrees. These indicators are suitable for a cement mass of 240 kg / cu. m (with brand M200 and more). If less cement is used, the temperature index of the mixture should correspond to +10 degrees. or higher.

Ways to increase the setting temperature of concrete

If it is necessary to pour concrete in winter, the temperature of the mixture can be increased in the following ways:

* through the use of heated water;

* by introducing frost-resistant additives into the mixture;

* with the help of electric heating;

* the method of steaming concrete structures in stationary conditions in special autoclaves up to a curing of 80-85%;

* using electric heating of a concrete monolith, which has reinforcement in its composition. In this case, the electrodes are switched over the entire area of ​​contact between the reinforcement and concrete when a low voltage current is connected;

* by using heat guns with concrete mix enclosure.

Dependence of concrete quality on outdoor air

Does the strength of concrete change with outside temperature? Certainly. When working with building materials winter season the chemical reaction that accompanies the curing decays. Therefore, at negative temperatures hardening will stop. "Save" the mixture of additives in the form of various salts that can stop the formation of ice.

There is a situation when the product began to set, but then froze. In this case, after thawing, it will harden only in the absence of internal damage by freezing water. Experts allow a one-time freeze-thaw cycle, subject to the condition: the temperature of the mixture for three days should not fall below +10 degrees.

If you know certain requirements, then in winter concreting can be done no worse than in the most favorable period. The first condition is the competent delivery of the material. The best option is to use . The second is to build an insulated formwork, it is even better to take care of heating the concreted area.

Speaking about at what temperature to pour concrete in the summer, it should be noted that the strength of the product decreases at +30 degrees. A practical way out is to moisten the concrete surface with water. In summer, due to evaporating moisture, concrete is made more liquid. And of course, it should be reported at what temperature to pour concrete in winter - it is recommended to perform all work up to -15C.

Reacting to the effects of temperature, concrete sets more evenly in wet and cool weather in summer. And if the work is carried out during the rainy period, then the resistance of the material to moisture is increased special cement. To prevent the solution from being washed away, the site is covered with polyethylene. However, in heavy rains lead concrete works outdoors is not recommended. If construction begins in a new climate zone, then experts advise testing concrete for strength in laboratory conditions or at a construction site.

Air temperature affecting concrete is not the only factor influencing given material. The quality of the product depends on the humidity of the environment, solar radiation, wind speed and how the mixture is handled.

And now, briefly:

At what temperature can concrete be poured? (on the street / in the foundation / in winter and summer)?
The optimum temperature is from 5 to 20 degrees C above zero. With the use of additives and heating of concrete in winter to minus 20 degrees C.

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

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

• Can also be used fixed formwork from extruded polystyrene foam, 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 the unnecessary internal stresses of the foundation structure.

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

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

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

Pouring the foundation with concrete

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

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

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

• According to all recommendations, concrete pouring should be carried out at a temperature of at least 5 degrees - this, in fact, is a critical indicator for normal maturation. However, the summer heat is also not 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.

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.

In order to provide the required minimum allowable temperature regime use several technologies:

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

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

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

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

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

However, this approach 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 everything financial risks and justification for such haste.

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

Are antifreeze supplements a "panacea"?

There is a very widespread opinion that the problem of winter filling concrete foundation it is quite possible to solve the use of 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 stated above, 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:

• First, the expansion of frozen, uncemented water causes internal pressure on the porous structure of the 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 of concrete in conditions of negative temperatures with the use of antifreeze additives:

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

A quite reasonable question arises: does it make sense for the owner of an individual plot to “get involved” with winter styling foundation (if this is not caused by some special circumstances), spend significant material resources, physical efforts 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 with a film until ripe. in the spring, at the end of stable cold weather.

Care behind the cast foundation

It would be a serious mistake to assume that even in ideal conditions you can only fill the formwork with concrete, and then maturation. 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 solidifying foundation as much as possible from temperature extremes, including daily ones.
• Do not allow the poured solution to dry out, the rapid evaporation of unbound water - this will most likely end in cracking the surface.
• 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 brand 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:

A few more important notes:

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

What can be the general conclusion?

Despite the fact that modern building technology, in principle, allow pouring the foundation at temperatures that are quite far from the optimal 15-25 degrees, the best option Nevertheless, there will be planning for 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

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

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

Application Benefits

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

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

The use of antifreeze additives allows:

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

Where is it used?

Antifreeze additives are used in the construction of structures:

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

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

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

Types of additives

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

plasticizers

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

Strengthening

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

The strength and durability of any building depends on the foundation that serves as its support. Currently, the most demanded in construction is concrete base capable of supporting the weight of a heavy structure. Since after the construction of the house the supporting structure will be difficult to repair, it is very important to properly fill the foundation in order to prevent it from sinking into the ground, as well as from the formation of cracks and other defects on it.

At what temperature can the foundation be poured

Planning the construction load-bearing structure, it is necessary to take into account weather conditions, brand and quality of cement. An important role in ensuring the strength of concrete is played by special additives that make it possible to reduce the crystallization temperature of water, as well as to maintain an optimal operating mode during the period of foundation hardening. After pouring, the base sets within a day and then gains strength in 28 days. The temperature range from + 3 to + 25 ° C is considered standard for creating a base. It is known that the warmer it is outside, the faster the mortar dries, but the heat can be dangerous for fresh concrete.

If at a temperature of + 5 to 15 ° C the composition seizes naturally, giving off heat to the environment, then in too hot weather it doesn't happen. Under such conditions, the concrete frame may begin to form when the volume of material is further increased. Cooling down, the surface begins to settle, and the already formed crystalline structure prevents this process. As a result, due to internal stress the foundation may become covered with shrinkage cracks 4–12 hours after pouring. So that the base does not crumble at temperatures above + 25 ° C, it is worth using quick-hardening Portland cement, which after 5–6 hours of pouring must be poured with water and shaded with old rags, cardboard or sawdust. To slow down hydration, it is permissible to introduce modifying additives and plasticizers. If cracks appear, re-tamping is required.

In hot weather, the foundation may crack

Is it possible to pour the foundation in winter

by the most favorable time for the construction of the supporting structure, the period from April to November is considered. However, the situation may develop in such a way that filling will need to be carried out in winter, because in some regions of Russia there is practically no summer. Modern building technologies make it possible to create solid foundations even in cold weather. The construction of the foundation in winter is especially important on shaky soils. After waiting for them to freeze, you can dig an excellent pit. In addition, for purchasing building materials off-season, you can save a certain amount. Most often, strip foundations are erected in winter using concrete blocks and concrete pile structures designed for lightweight wooden objects.

According to various estimates over the past five years, the share winter concreting in the total volume of construction varies from 10 to 17%. This is a solid jackpot for manufacturers and suppliers of construction chemicals, and, in particular, those additives that must ensure the efficiency of the process at low temperatures. On the other hand, it was manufacturers who influenced the growth of winter construction. The interest here is mutual.

How cement mortar behaves in frost

When planning winter work, it is worth remembering that ordinary concrete is not suitable for them. In frost, it is permissible to use only cement with special additives and modifying additives. The latter reduce water consumption by about 10-15%. At air humidity of 60% and above, the use of modifiers is not recommended, besides, it is worth remembering that they can react with some metals. To ensure the strength of the structure, concrete must be heated in the first two days after pouring. The desired temperature regime of the mixture can be maintained using:

• thermal guns;
• special heating wire laid when pouring concrete;
• electrodes (reinforcing bars) to which voltage is applied.

There is also a way to warm up the concrete mixture using welding machine, but it essentially boils down to the use of electrodes and is applicable only for small volumes of pouring.

Only water and fillers are allowed to be heated, but not cement, otherwise it will lose its qualities.

For winter work, concrete with special additives is required.

Typically, in the regions of the Russian Federation, a solution with a temperature above 21 ºC is not used, taking into account the fact that 4.5–5 ºC will go into the atmosphere. Therefore, for the working composition, the liquid is heated to 32 ºC. More hot water first stir with fillers, and then in portions - with cement.

Is it possible to pour concrete in frost without heating

About whether it is possible to pour the foundation in cold weather without heating should be discussed separately. Even temperature fluctuations from +5 to 0 ° C for concrete mortar are considered winter. In the cold season, when concreting, it is important to ensure smooth hardening of the mortar by at least 60%. This guarantees the preservation of the structure of the base and its ripening when the thaw comes.

However, the foundation will gain strength only at a positive temperature of the solution, therefore, without artificial heating for construction work, you need to choose a fine winter day. The composition of cement is also important: the so-called cold concrete contains antifreeze additives that lower the freezing point of water. For these purposes, potassium and sodium chlorides are used in concentrations from 2 to 15%. Using anti-frost modifiers, it is possible to dismantle formwork with M200 mortar already at 40% strength, M400 - at 20% and M300 - at 30%.

Video: heating concrete foundation in winter

When can you pour the foundation in the spring

Those who decide to start building the foundation in early spring (until April) should be careful. First you need to wait for the thawing of the soil and heat, when at night the temperature does not drop below 0 ° C. It is also necessary to take into account the "drying" of roads, which lasts one to two months, during which heavy vehicles (concrete pumps, scows, toners and other vehicles) are restricted from moving on regional roads. Without the listed transport, it is impossible to build a monolithic foundation. From April the cost Supplies starts to grow.

In the spring, the roads are washed away, so heavy equipment cannot pass through them.

Unexpected frosts can cause irreparable damage to the structure, so when the weather forecast is unstable and work is already planned, it is recommended to insure the purchase of antifreeze fillers. Even at an air temperature of +23 °C, concrete gains its normative strength only after three weeks. At lower temperatures, the terms increase markedly, as a result, it is impossible to hurry with laying the walls after pouring.

As practice shows, a house built on bare ground costs a few years. In the absence of a base, the lower blocks or wooden crowns collapse due to soil deformation.

Is it possible to pour the foundation in the rain

At present, rain is not a reason to stop concreting, as it was in the recent past. Using simple equipment and a suitable brand of cement, you can pour the foundation in wet weather. By itself, water does not have a negative effect on the solution, just before it hardens, erosion and imbalance can occur. Therefore, everything depends on the strength of the precipitation.

If the site is not flooded with rain, then a canopy will be enough to continue work. Ordinary will protect from light rain polyethylene film, which must be used with care, because concrete only cures for fresh air. Of course, in warm and sunny weather, the solution is better saturated with carbonic acid and hardens faster, forming a solid base. But there are also advantages to building foundations in the rain, since concrete mix becomes more durable at 80% humidity.

Polyethylene film cannot be kept on the surface for a long time, since the concrete does not harden without fresh air

How to work during the rain

The main requirements for the ongoing work on pouring the foundation in the rain:

1. The content in the solution of cements M400, M500 and M600, created for work in contact with moisture.
2. The right way to lay concrete. unusual shape foundation or its deepening involves the use of special equipment that does not allow the formation of voids and displaces excess liquid.
3. The use of waterproofing, which can be removed no earlier than two to three days.

The modern market offers a wide range building mixtures with different settings. Fast-hardening and long-hardening compositions are produced, as well as concrete with antifreeze additives. But pouring the foundation in extreme weather conditions is a risk that must always be taken into account. At low temperatures, cracks can form in the base, and erosion can occur during precipitation. All this can adversely affect the strength of structures.