How to protect freshly poured concrete from night frosts

• November 29, 2020

The basis of any building is the foundation; the reliability and durability of the entire structure depends on it.
When laying it, special knowledge and compliance with all building codes and requirements are required, and it is imperative to take into account the climatic conditions in a particular location. Not so long ago, foundation pouring was carried out only in the warm season, at subzero temperatures; the concrete froze before hardening. Subsequently, the entire mass was deformed, cracks and failures appeared. If the process took place in cold weather, the base was covered with reed mats, mineral wool, and various methods were used to prevent premature freezing of the mass.

The scientific world has also tried to find a way in which work with concrete mixture can be carried out at subzero temperatures. In the course of scientific research, the optimal temperature was established - from +5 to +15C. It is these conditions that contribute to obtaining a solid foundation that will last for many years without damage.

How to make your own anti-frost additive to concrete?

To prevent the water from freezing and the mixture to set quickly, use an anti-frost additive in concrete, which you can make with your own hands. These are mainly salt substances that allow concrete to harden in frosty weather. They affect the temperature of the mixture, which results in faster setting and reduced financial costs due to a reduction in the amount of cement. However, experienced builders warn: additives should not be used if the concrete structure is operated at high humidity, since salts can negatively affect the reinforcement.

1. Types of additives
2. Pros and cons of antifreeze impurities
3. How to do it yourself?
4. Rules for adding to the solution

Types of antifreeze substances

All antifreeze additives that are added to the concrete mixture can be divided into the following groups:

1. Retarders or weak accelerators of hardening. They serve as a barrier to the crystallization of water in the concrete solution and work by reducing its freezing temperature. Most often, weak and strong electrolytes play this role.
2. Additives to accelerate the curing of concrete. They have strong antifreeze properties and cause faster hardening of the solution.
3. Sulfates. They increase the density of the mixture and increase the release of heat.

Purpose and scope

The operating principle of PMD is based on the properties of a complex of additives, which, when combined with water, change the freezing point, lowering it below zero. Concrete or mortar with an additive accelerates the process of setting and gaining brand strength.

The properties of antifreeze compounds are regulated by GOST 21411-2008, GOST 31384-2008.

Cement mortars with PMD are used in the following cases:

• construction in cold weather at sub-zero ambient temperatures;
• transportation in winter;
• the need to increase the strength of concrete;
• reducing solution consumption.

Additives are actively used in the northern regions, in winter throughout Russia. Used when there is a need for urgent repairs of reinforced concrete structures. At a temperature of +1...+5 °C, PMD is used to improve strength, uniformity, and ease of concrete laying.

High quality for perfect results

Sika products are manufactured by one of the leaders in the construction chemicals market, a Swiss concern that has its factories in Russia. Thanks to international quality standards and strict controls at all stages of production, Sika winter concrete strength additives ensure continuity of construction during the winter period and improve the properties of the concrete mortar.

Benefits of Sika anti-freeze additives:

1. They allow concreting to be carried out at almost any sub-zero temperatures. Operating range – up to -25C.
2. Their use significantly accelerates the rate of concrete hardening. The process of gaining strength does not drag on even in severe frosts. From a structure made with the use of Sika additives, the formwork can be removed without defects or chips within a short period of time after pouring.
3. Additives improve the structure of concrete, increase its strength, moisture resistance, and protect metal structural elements from corrosion.
4. Sika additives are economical to use and reduce cement consumption. This allows you to reduce the cost of construction without losing the quality and strength of the structure.

The high European quality of Sika additives will ensure the continuity of your construction process at any external temperature and guarantee a long service life of the constructed facility.

Operating principle and types of frost-resistant compounds

Loading into a concrete mixer.

What to add to concrete at sub-zero temperatures is far from an idle question. There is no completely, 100% universal composition.

The choice depends on many factors, primarily on the temperature itself.

• The size of the monolith also has a big influence. Plus, you should take into account the purpose of the product, the fact is that different additives can change some of the physical properties of concrete and what is suitable for a strip foundation in a private house may not be suitable for the construction of a bridge or a large self-leveling plinth.

Warming up using the Thermos method.

How it works

As you know, the main task of water in a solution is to create conditions for the crystallization of the components of the solution, silicates, aluminates, and so on. In the language of professionals, this is called cement hydration.

Most comfortably, without additives, the solution hardens at a temperature of 15 - 20 ºС; everything higher and especially lower requires the creation of special conditions.

• The main task of this type of additive is to reduce the setting period of the solution and reduce the maturation time of concrete at low temperatures. That is, to reduce the level of freezing of water and at the same time not harm other processes occurring in the solution.

Dependence of strength gain on temperature.

Common compositions and methods of operation

• The most common materials for the manufacture of frost-resistant additives can safely be considered salts of monocarboxylic acids; among professionals this composition is known as “Potash”. The price for these compounds on the domestic market is quite reasonable.
• When pouring concrete at sub-zero temperatures, monocarboxylic acid additives must be strictly dosed. For each temperature, the number of additives is different. With such additives, you can prepare the solution for temperatures down to minus 30ºС. The lower the temperature, the more composition will be required.

Monocarboxylic acid salt.

Important: as mentioned earlier, the additive, if used incorrectly, can reduce other characteristics of the solution. Therefore, the principle, the more the better, can do harm here.

• The next leader in our market is sodium nitrite. The price for it is also not very high, but this substance has a strong, pungent, unpleasant odor. In addition, this composition can easily ignite. Upon contact with some types of modern plasticizers, poisonous and toxic gases may be released.

• The maximum temperature that sodium nitrate can hold is not lower than -15ºС. Experts recommend its use when preparing solutions using Portland cement or Portland slag cement. Adding this additive to aluminous cements is strictly prohibited.
• Sodium formate and calcium nitrate have a wide range of uses. In addition to the production of reinforced concrete products, these additives can be used in plaster mortars and mortars intended for bricklaying. But these compositions are used only in combination with a plasticizer, since due to the accumulation of salts, voids and efflorescence can form in the monolith.

Concreting techniques in winter conditions

The main condition for the correct pouring of concrete at subzero temperatures is the preservation of heat sufficient to ensure strength gain. Popular methods of laying mortars in winter:

• Preheating of the mixture being prepared;
• Installation of reliable thermal insulation and maintenance of the solution;
• Electric heating of concrete poured into formwork;
• Addition of special additives that reduce the freezing point of water and accelerate hardening.

Thus, it is possible to concrete outdoors in winter without loss of strength indicators, but for this you need to adhere to the chosen methods. In terms of costs, the use of heat guns is the most unprofitable option; the cheapest method is the addition of additives. Electric heating and thermal insulation are intermediate options.

Temperature increase during kneading

To pour concrete at sub-zero temperatures, the components are heated. The fillers are heated to 55-60⁰С, and water is supplied to the solution at 90⁰С. Cement is heated to room temperature before adding, otherwise it loses its bonding properties. Before laying, the temperature of the solution should not be lower than 35⁰C.

When mixing, you need to use a concrete mixer, into which heated water is supplied first, then fillers, and only then cement. When pouring such a mixture, the thermal energy of the monolith is enough to gain critical strength, taking into account the fact that additional heat is released during cement hydration.

Heating and insulating the solution

At very low temperatures, the heated mixture requires additional insulation or heating. It is more economically feasible to insulate using inexpensive heat-insulating materials that do not require additional energy sources. The concrete surface is covered with hay or straw, old rags, peat, film or heat-insulating blankets are used. Sometimes so-called “warmhouses” are set up, similar to greenhouses.

If you concrete at temperatures below -5⁰С, additional heating will be required. The following technologies are used for this:

• Heating with heat guns or stoves under greenhouses. This is a costly method that requires constant additional moisture. Suitable for areas without electricity.
• The use of thermomats powered by electricity. They are laid out on the surface of the poured concrete and connected to a power source. Requires a large amount of electricity. Infrared emitters are installed above the poured surface or around the formwork; the intensity and direction of heating is regulated by reflectors. Suitable for vertical and inaccessible structures.
• To warm up a concrete area, special cables or electrodes are used through which electric current is passed. The technique is convenient to use, but requires large amounts of electricity. Installing an electrode system is more expensive because the resistance of the solution, which itself is a conductor, increases as it dries.

Introduction of additives

Improving the characteristics of the solution with special additives is the most convenient and economical method of filling the solution in winter. By using it in conjunction with heating, you can speed up work and improve the quality of concrete. There are two main types of additives for pouring concrete mortar in winter:

1. Compositions that reduce the freezing point of water. The solution hardens for quite a long time, but the water does not crystallize, so the quality of the concrete does not suffer. To speed up the reaction, thermal insulation is required. For this purpose, calcium or sodium salts and potash are used, which prevent water crystallization.
2. Additives that increase the rate of hardening of the solution. They reduce the time necessary for concrete to gain critical strength, so the water in the heated mixture does not have time to crystallize. Calcium nitrite-nitrate, the same potash, calcium salts mixed with urea are used.

The amount of additives depends on the temperature range in which the concrete structure will be poured. From -5 to -10⁰С, up to 5-8% by weight of cement is added. With a decrease in temperature to -15⁰C, the concentration is increased to 10% by weight of the added cement, and at -25⁰C, at least 15% of additives must be added.

How to use

The choice of additive and the method of its application depends on the condition and material where it will be introduced. Any additives to concrete used at sub-zero temperatures are added to the solution with water, according to the instructions from the manufacturer. After thorough mixing, it is recommended to wait a while for this component to diffuse through the composition.

According to SP 70.13330.2012, in order for the composition to achieve the required strength, it is important that before the temperature of the composition reaches the level for which the additive is designed, it gains no more than 20% of the planned strength.

The consumption of antifreeze additive per 1 cubic meter of material depends on the average daily ambient temperature. Up to -5 degrees it is recommended to add up to 2% of the additive by weight of the solution, up to -10 degrees this figure increases to 3%, up to -15 degrees no more than 4%. In severe frosts, calculations are made individually for each type. The rate of hardening of the solution decreases, and maximum strength is achieved after the end of frost.

When adding plasticizers and PMD, certain operating rules must be followed. The recommended range for the solution to be poured is from +15 to +25ºС. To dissolve additives, a certain amount of water is required, which must be heated, this ensures complete dissolution of the substances. Sand and crushed stone used in the solution are also heated immediately before adding. Cement cannot be heated, as it will lose its astringent properties. The poured solution must be covered, this is especially true during snowfall.

At what temperature can a foundation be poured in winter: pros and cons

A stable and reliable house is the result of carefully done work, the basis of which is a high-quality foundation. Its placement plays an important role, so it is worth considering a large number of factors that accompany a successful process. This work process requires compliance with many conditions. The strength of the mixture is determined by the composition, laying technology, and weather conditions under which the laying was carried out. It is these conditions that allow you to achieve excellent results and at the same time save money.

Features of concrete under different weather conditions

Modern building materials contain many additives that allow work to be carried out both in summer and winter. However, concrete has chemical and physical properties that dictate certain conditions for working with it.

The process of concrete hardening. It is divided into two stages - setting and hardening. The time required for setting does not exceed one day, but the time for final hardening is much longer and is determined by the brand of concrete, the presence of chemical additives, temperature and humidity conditions. The optimal temperature is considered to be from 3 to 25 degrees above zero. This mode allows the concrete to go through the setting and hardening stage with the best performance. The speed of the process depends on the temperature; the higher it is, the faster the process of strength gain occurs.

The grade of concrete and humidity conditions play an important role in this process.

The higher the air humidity, the faster the concrete gains its strength. This indicator characterizes its compressive strength. After 28 days of curing, any concrete should acquire its design strength, after which its hardening slows down and continues for several more years. There is another indicator - critical strength. It means the degree of concrete hardening at which low temperatures do not cause irreversible changes. Thus, the foundation, or rather concrete, must set (transition from a liquid to a solid state) and harden within a time sufficient for it to achieve its design strength.

Temperature and other weather conditions have a significant impact on the rate of hardening of concrete, as well as on its strength. This is due to the presence of moisture in concrete. At a temperature of 3 degrees below zero, water begins to turn into ice. In this case, the structure of concrete may be damaged, and microcracks will appear, which over the years will turn into ordinary cracks, and the process of destruction of the foundation will begin. A decrease in temperature below zero leads to a stop in the process of concrete hydration. That is, the hardening process stops. When the temperature rises, thawing will occur, but the damaged connections will not be restored. However, construction has its deadlines and you have to work even in frost. In order for the foundation to reach its maximum strength even at sub-zero temperatures, you can resort to the following techniques:

1. Heat the solution to be poured or ensure the heating of the already poured foundation.
2. Choose a high grade of concrete.
3. Add special additives and plasticizers to the solution.

The temperature of concrete can be increased by adding hot water to it or heating its components to a temperature of 30 degrees. At sub-zero temperatures, warm concrete poured into the formwork is insulated with film and thermal insulation materials (sawdust, peat, snow, straw). If the process of laying the foundation occurred in the off-season, then there are dangers. In autumn and spring, temperatures often cross freezing at night, so the strength of concrete can be compromised due to this. In order to avoid unpleasant consequences, you should play it safe by adding anti-freeze compounds to the solution or think about how to protect the foundation from exposure to low temperatures. Based on this, it is best to make the foundation in the warm season. This will allow not only to pour a strong and reliable foundation, but also to achieve its design strength in the shortest possible time.

The question of when it is best to pour concrete into the formwork is decided in advance, so it is difficult to foresee weather conditions. Rain is not an obstacle to this work. The main thing is to provide waterproofing. This is necessary so that the concrete does not gain excess moisture. To do this, freshly poured concrete must be covered with film. After the concrete has set and become hard, the film can be removed. But on hot summer days, the film allows you to avoid premature drying of the mixture and achieve standard strength within a specified time frame. Thus, it is best to fill the foundation in the summer, when the air temperature is stable. This approach will allow you to avoid significant financial costs for heating and other additional techniques. Watch our video selection on the topic:

At what time of year is it economically feasible to fill the foundation?

Today it is possible to carry out any type of work at any time of the year, but the cost of such work will vary. This also applies to pouring the foundation. This type of work is best carried out in the summer, when the temperature is stable. However, modern additives make it possible to fill the foundation even in winter.

Concreting the foundation in winter will cost more, and this process will also be more labor-intensive. In winter, pouring concrete into formwork requires strict adherence to temperature conditions.

Therefore, you will need to warm up the foundation, insulate it, and these are all additional costs. The answer to the question at what temperature the foundation can be poured will sound like this. In the warm season, you can prepare the mixture at the construction site; in the cold season, you need to order concrete from the factory and deliver it to the installation site. The cost of the concrete itself will be higher due to the fact that antifreeze additives are added to it.

Among other things, it is necessary to use electric heating of concrete laid in the formwork. And this also entails additional costs and increases the working estimate by 30-40%. If you had to build a foundation in winter, then you need to consult a specialist in the preparation of electric heating of concrete and prepare in advance hydro- and thermal insulation. When answering the question whether it is possible to fill the foundation in winter, it is necessary to take into account the fact when further construction work is planned to begin. If you plan to lay walls immediately after pouring the foundation, then this must be done as early as possible so that the foundation hardens and reaches maximum strength.

You can also lay the foundation in the fall and take a break until spring.

Thus, in order for the foundation of the house to be strong and reliable, it is necessary to begin its construction in the warm season. This will significantly reduce the cost of work and avoid the appearance of microcracks in its structure. Therefore, it is economically profitable to carry out work in summer, spring and autumn.

Is it possible to fill in rainy or frosty weather?

Until recently, frost or rainy weather led to construction delays. With the advent of modern technologies, it has become possible to continue construction and installation work even in winter. In order to obtain a strong and durable foundation for a country house, the following actions must be taken:

• Dig a pit, build formwork and install a frame of reinforcement and wire.
• Provide artificial heating of the area using heaters where the concrete will be poured. It is especially important to warm up the formwork and concrete in the first two days when it sets.
• Prepare waterproofing materials to cover the poured concrete.
• After this, you can reduce the heating. After the concrete has hardened, the formwork can be removed and left to gain strength.

If concrete is poured in the rain, then it is worth taking care of waterproofing. Excess moisture dilutes the concrete and makes it less durable. This is a significant disadvantage in the process of laying the foundation of a building.

Every process has its downsides. Pouring concrete was no exception. First of all, there is a risk of getting a fragile structure that will have to be redone.

Therefore, in order to avoid troubles, the hydration process should be brought closer to established standards by covering the foundation. The hydration process is accompanied by the release of heat.

Therefore, the larger the concrete layer, the more heat is released and the slower it cools. In winter, it is better to lay a strip foundation or a monolithic one. The disadvantages of laying a foundation, both on a hot day and on a frosty one, lie in the crystallization or evaporation of moisture at high speed. This can lead to the appearance of voids, which will have a destructive effect in the future. Nevertheless, the advantages of pouring concrete into formwork outweigh the disadvantages of this work at any time. So, when and what kind of foundation to pour is up to the designer, but it is still worth taking into account the physical and chemical properties of concrete, weather conditions and other factors.

Recommendations for working in frosty weather

The construction of the base of a building is a responsible process that requires strict adherence to technological norms and rules.

Therefore, when starting to build a foundation, you need to know some of the features of the process.

If you plan to lay concrete at sub-zero temperatures, then you should make sure that there are all conditions for the foundation to harden and reach its standard strength without damage or microcracks.

Mixing concrete entails a chemical reaction with the release of heat, so the mixture can warm itself. In order to increase the temperature, it is necessary to use concrete with a fine fraction, it reacts faster with water. It is important to remember that only water and other impurities need to be heated , cement cannot be heated. In this case, it will lose its binding properties. Thus, from all of the above it is clear that today the foundation can be laid at any time of the year, the main thing is to know the technology and sequence of work, and it is also important to meet the deadlines for the final hardening of the cement. However, it is best to choose a warm time of year to start building your own home. Watch our video selection on working in winter:

Tips for choosing

When choosing antifreeze additives, they take into account the method, circumstances of operation of the concrete structure, ambient temperature, brand, composition of cement, and quality of the additive. The PMDs used by specialists the most are considered optimal:

• potash (7% concentration) is suitable for Portland cement;
• sodium nitrite;
• sodium chloride is used for rapid hardening modifications.

When choosing PMD, you need to pay attention to the experience, image of the manufacturer, reviews in order to avoid purchasing a low-quality product.

Where is it used?

Any additive to concrete for frost resistance is a real godsend for modern construction. Additives are used in a variety of situations where work needs to be done at low temperatures without compromising quality.

Where are anti-frost additives for concrete used:

• When pouring monolithic reinforced concrete structures and parts of buildings.
• In prestressed reinforced concrete.
• With off-design reinforcement, where the mortar layer should be more than 50 centimeters.
• In light types of concrete.
• For mixing plaster mixtures.
• When pouring paths and various surfaces of private housing construction.
• When performing important structures and structures - bridges, dams, dams, gas and oil production platforms, etc.

Regardless of the scope of application, before starting work with concrete, tests must be carried out to determine the level of strength, setting speed, characteristics of the oxidizing effect on the concrete mixture, the presence of “salts,” etc.

A variety of additives are added to concrete - it all depends on the material, work conditions and future use. All types of additives are added to the solution with water in accordance with the instructions. Then the mixture is thoroughly mixed, wait a certain time and use.

SP 70.13330.2012 indicates that in order for the composition to acquire the required level of strength, it is necessary that before the temperature of the composition reaches the mark indicated on the additive, the mixture must gain at least 20% of the planned strength.

Typically, the consumption of additives per cubic meter of solution depends not so much on the substance as on the average daily ambient temperature. So, at temperatures down to -5, it is recommended to add no more than 2% of the additive by weight of the solution, at -10 degrees 3% is possible, at -15 - a maximum of 4%. If the frosts are very severe, they are calculated individually.

To improve the results, it is recommended to adhere to the following rules: the temperature of the poured solution should be from +15 to +25 degrees, additives are dissolved in heated water, crushed stone and sand are also preheated, but not cement.

The influence of temperature on concrete hardening

Concrete is a mixture of fillers - sand and crushed stone, bonded together with hardened cement laitance. When it reacts with water, it hydrates, then it hardens with the simultaneous evaporation of water. Critical strength at normal temperatures is achieved within one or one and a half days, depending on the humidity of the surrounding air.

The optimal temperature for the reaction to occur is about 20⁰C; the solution gains design strength within 28 days. To prevent water from evaporating too quickly in the first days, the concrete is covered with waterproofing.

What happens in concrete when it freezes?

During the normal course of the concrete hardening process, moisture serves as a “gluing” element for cement particles. When it transforms into a solid state, all processes stop.

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

In order for winter concrete to be strong, it is necessary to create conditions or additives for its ripening

There is another unfavorable point in winter pouring of reinforced foundations. Steel is an excellent conductor of heat, and it helps remove heat from the thickness of the concrete. Possessing good thermal conductivity properties, the rods cool quickly. The water around them freezes first. Ice pushes aside concrete particles, and they are replaced by not yet frozen water from still warm layers. It also freezes, pushing the concrete even further. As a result, the massif 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.

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

Critical strength of concrete depending on its grade

For reinforced concrete with non-stressed reinforcement (the type used in private house construction) it is 50%, for foundations that will be subject to alternate defrosting/freezing (baths and country houses without heating) - 70%. Once this point is reached, 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%.

Dosage of antifreeze additive required for concrete to gain the required strength

We must not forget that in the cold season, while negative temperatures persist, the strength of concrete with antifreeze additives does not exceed 30% of the possible design strength.

According to GOST 24211, the strength gain of “cold” concrete must be at least 30% of its brand strength 28 days after laying. Concrete will reach the remaining grade flowability at above-zero temperatures. Concrete can be loaded when it reaches 70% brand strength. Under “normal” conditions, this occurs 7 days after laying the concrete. Accordingly, at a temperature of +5 C, concrete will not reach 70% strength without additional heating. The use of high-quality plasticizing additives allows you to speed up this process

Rules for winter concrete pouring

The solution is poured into the prepared formwork. Preparation consists of removing ice and snow, heating the reinforcement and the bottom of the foundation. This is the most difficult stage. Scraping off the ice is not so bad, 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 positive values.

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

Before pouring warm mortar, it is necessary to heat the base and reinforcement to positive temperatures

For this reason, concreting slab foundations in winter is problematic: such areas cannot be heated. For this type of base, “winter” will be limited to light frosts at night and positive daytime temperatures. Pouring can begin after the reinforcement and bottom have a positive temperature.

A strip foundation can also be poured in frosty conditions: it is possible to heat such a foundation and reinforcement to a limited extent. Not easy, but possible.

Everything can be organized in stages. Break the entire tape into small sections, start heating simultaneously 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, moving the fryers further. While the first heated section is being poured, the next one will reach the required temperature. The flooded area is immediately covered with heat-insulating materials and moved on to the next one, moving along the entire perimeter.

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

The mechanism is clear. So you can pour the foundation with concrete at -15oC (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% true. The interval between fills should be such that a film does not have time to form on the surface of the previous part, and even more so that the moisture does not freeze. Work must be carried out continuously until the filling is completed. Filled parts must be immediately covered with heat-insulating mats. As you can see, this job requires several people. One person cannot cope with all tasks.

Work must be carried out continuously

Please note that the maximum solution temperature should be 35-40oC. Its excess leads to a slowdown in the rejection processes. The situation will, of course, be better than when it freezes, but not by much.

Types of additives

High-quality additives for working at low temperatures allow you to work with concrete in temperatures down to -35 degrees. There are many types of additives - these can be accelerators, plasticizers, mobility regulators, modifiers, complex substances. They can be purchased ready-made or made yourself. The second option is more risky, since the exact recipes and properties of various substances with an antifreeze effect are not precisely known.

Many craftsmen use ordinary salt (sodium chloride) - it lowers the freezing point of the liquid and reduces the critical hardening time of the solution. To prepare such an additive, salt is dissolved in water and added to the mixture. For -5 degrees the concentration is 2% by weight of the solution, -15 - 4%. The disadvantage of this solution is its corrosion activity towards metal, so reinforced concrete structures cannot be filled with such a mixture.

Plasticizers

Organic polyacrylates, melamine resin or naphthalene sulfate are used as plasticizers. These additives have a plasticizing effect on the mixture and do not require large water consumption. The monolith becomes more waterproof, durable, concentrated (dense).

The mixture with the additive is much easier to place and is poured evenly, significantly saving water and energy costs. Thanks to the introduction of plasticizers into the composition, it is possible to accurately place the mixture in molds and eliminate the possibility of voids forming. Microparticles of the mixture retain moisture more effectively.

Strengthening

Such additives for concrete are also called hardening accelerators - the group includes calcium nitrate and chloride, iron and aluminum sulfate. Additives work by reducing the curing time of the mixture. At the moment of setting, concrete loses its plasticity, and during the hardening process it becomes strong.

Mobility regulators

These are special substances that make it possible to extend the period of work with a ready-made solution. They are divided into 2 types: additives that are introduced in minimal volumes and regulate characteristics (0.1-2%) and finely ground alloys (5-20%) to reduce cement consumption and without changing properties.

• The most effective are chemical plasticizers and superplasticizers.
• Additives increase the mobility of solutions and reduce water demand.
• Ligatures of the same class can have different effects on the solution.
• Superplasticizers are considered the best, which: increase the construction and technological properties of the mixture, increase the mobility of the solution, and reduce cement consumption.

Frost-resistant

These additives make it possible to carry out work at subzero temperatures without changing the technology or deteriorating the characteristics of the concrete solution.

Corrosion resistant

These modifiers are used where it is necessary to protect reinforced concrete structures from oxidation, which significantly extends their service life and prevents destruction and the negative effects of external factors.

Complex

There are additives that have several effects on the concrete mixture at once - they can simultaneously have a positive effect on the reinforcement and protect it, improve the performance properties of concrete, and increase the strength characteristics of a reinforced concrete structure.

DIY plasticizers

History knows many recipes and techniques for improving the characteristics of concrete. For example, already in the 19th century, to increase plasticity and adhesion, protein from a chicken egg was added to the solution; in the 20th century, after the advent of slaked lime (fluff), they switched to it. Nowadays, at home, washing powder or other detergents are sometimes added.

Making your own plasticizer for concrete and cement mortar at home

Recipe 1: add liquid soap or shampoo

It is introduced when mixing the mixture. Requires 200-250 ml per 50 kg of cement (hereinafter referred to as a bag).

• Mix water with 200-250 ml. liquid soap and pour into a bucket/trough to prepare the solution.
• We begin to add cement (1 bag) and filler.
• Mix the solution thoroughly and fill our forms or formwork with it.

Keep in mind that if you do not reduce the amount of water by 200-250 ml. (i.e. by the amount of liquid soap we added) - the concrete hardening time will increase by 3 hours.

Recipe 2: add washing powder

Pre-dissolves in water. It is introduced when mixing the mixture. 100-150 g per bag of cement is required.

• Dissolve 100-150 g of washing powder in warm water
• Mix water with the powder solution and pour it into a bucket/trough to prepare the solution.
• We begin to add cement (1 bag).
• Mix the solution thoroughly and fill our forms or formwork with it.

Commentary on Recipes 1 and 2:

It is worth considering that the soap solution is poured first and must be mixed very carefully - this will avoid the appearance of foam, which, when interacting with small particles of cement, neutralizes its properties - i.e. will spoil the cement-containing mortar.

What disadvantages and problems can be obtained from using such a soap plasticizer:

• Soap solutions wash salts onto the surface, which leads to the appearance of efflorescence (salt stains).
• The surface of the finished concrete is not covered with a special water-repellent film
• Liquid soap does not allow microbubbles to form inside the concrete solution, which makes it difficult for water to migrate through the solution. As a result, the concrete structure quickly becomes wet and, in poorly ventilated areas or without antiseptic treatment, can become covered with mold and mildew.

Recipe 2: add slaked lime fluff

This technology, perhaps with minor deviations, was widely used in the construction of brick houses in Soviet times. Slaked lime gives the solution increased adhesiveness and elasticity, adds adhesive capabilities, and also gives the concrete bactericidal properties and prevents the appearance of mold and mildew on the surface.

Like a soap solution, slaked lime is added first in an amount of no more than 15-20% by weight of cement.

Recipe 2: add PVA glue

The technology is widely used in country construction and renovation work in garages and apartments. PVA glue added to cement mortar improves its mobility, increases the final strength and water resistance of concrete.

It is introduced when mixing the mixture. Requires 200 g per bucket of solution.

Economic feasibility of application

The use of antifreeze additives in mortar or concrete, of course, increases the cost of these building materials.

It is economically feasible to use antifreeze additives in winter

However, this requires a cold-blooded calculation about what is more profitable:

• or save on additives, but mothball the construction site for six months, and in warmer months, re-deliver the equipment to the construction site and correct defects that formed during the winter, associated, for example, with the divergence of seams between rows of bricks and the general loss of strength of already erected structures;
• or spend money on antifreeze additives.

In accordance with the standard (specified in SNiP), the cost of a day of construction downtime in a mothballed state in relation to downtime in operating mode is 1:2. Yes, it’s cheaper, but the duration of conservation extends to 180 days.

Even the naked eye can see that it is more economically profitable not to stop construction, but to spend money on anti-frost additives. These financial losses are much less than those that will have to be incurred as a result of the conservation of the facility.

Micro-reinforcing additives - fiber

It is used as an alternative to reinforcing mesh or as a complementary element, helping to combat the formation of microcracks in concrete. The factories produce metal, polypropylene, basalt, polyester fiber and glass fiber. Modern technologies make it possible to produce micro-reinforcing additives that can completely squeeze out traditional reinforcement methods from a number of construction and manufacturing industries. For example, you rarely see reinforced curbs, well rings, etc. anywhere.

At home, making high-quality fiber fiber from polypropylene or basalt is extremely difficult, or rather even impossible, but making metal fiber is quite possible.

The principle of operation of the antifreeze additive

Most developers try to start building the foundation in the warm season, because the optimal temperature for hydration, the chemical reaction between cement and water, as a result of which setting occurs, is +15 - +20 degrees.

But often circumstances force us to start construction in the cold season, and besides, winter construction has its own benefits and advantages. When the average daily temperature drops to +5 degrees, building codes regulate the transition to winter work, and here the use of anti-frost additives is necessary.

Vasily Shramko regional technical specialist in construction chemicals for concrete at TECHNONICOL Corporation

The use of the additive is advisable when the ambient temperature drops below +5 degrees, because At low temperatures, the chemical reaction of cement with water practically stops.

In addition to the fact that the reaction between cement and water stops and, accordingly, worsens, and in some cases the setting of the solution stops, water, freezing, expands in volume and destroys the structure of concrete. If the concrete mixture freezes after being placed in the formwork, then it is pointless to wait for the required strength to gain after thawing. Its structure will be loose, and its strength will be significantly lower than the strength of concrete of the same composition, but not subjected to freezing.

Therefore, when constructing reinforced concrete structures and monolithic structures at temperatures below 0 degrees, antifreeze additives are used. They have an antifreeze effect and accelerate the setting and hardening of solutions at subzero temperatures.

The action of the anti-frost additive is aimed at ensuring that the water included in the concrete mixture does not freeze, and the concrete structure gains its strength after laying.

The use of anti-frost additives allows the construction of foundations at temperatures from +5 to -25 degrees.

According to the principle of action, all antifreeze additives can be divided into two groups:

• Additives that lower the freezing point of the liquid phase of concrete; water does not turn into a solid state at -10 degrees and below.
• Additives that speed up the setting process.

When using additives in each of these categories, you must carefully read the manufacturer's instructions and also pay attention to the price tag. A cheap, low-quality antifreeze additive can worsen the performance of concrete.

High-quality antifreeze additives include special components - corrosion inhibitors, which do not contain aggressive salts that corrode reinforcement. They can be used in reinforced concrete, incl. densely reinforced. Unfortunately, this cannot be said about all PMDs presented on the construction chemicals market. It all depends on the composition.

A set of concrete care measures

The finished mixture begins to harden after pouring into a mold or trench, and lasts approximately 28 days. During this time, it gains strength and requires careful treatment. The process of maintenance and protection includes a number of measures, we list them:

• protection against rapid drying;
• ensuring the required temperature;
• exclude physical impact;
• prevent the influence of the external environment - sun, frost, rain, snow;
• protect the water in it from freezing;
• provide hydration in sub-zero temperatures.

The optimal temperature for gaining strength is 20 degrees, air humidity 80%.

Warmhouses to protect concrete - you can build even in cold weather

Over most of Russia, winter reigns for 6 months a year, significantly shortening the period suitable for construction. The main problem that prevents the construction of high-rise buildings in the cold season is the inability to provide concrete (foundations, screeds) with optimal conditions for setting and gaining strength. In accordance with established practice and building regulations, after pouring the cement-sand mixture, the ambient temperature should not fall below +20 0 C. But no one will stop work because of cold weather, the onset of autumn or winter. What should those who are forced to lay the foundation in January or December do? At the first stage, let's find out why pouring concrete at sub-zero temperatures is undesirable? The main reason is a large amount of water, without which the mixture will not be fluid and will not fill existing voids. If the ambient temperature drops below 0C, the familiar liquid transforms into a different state of aggregation, becomes ice and expands. The process of gaining strength is suspended or stops completely. If it's -4C outside, the concrete begins to freeze. When warming or a thaw occurs, the ice melts, returns to its original state, and the process of hardening of the screed resumes. It will not be possible to achieve the required strength.

Warming up concrete in winter To prevent negative temperatures from affecting hardening, it is necessary to create certain conditions using one of the methods listed below:

• modifiers are added to the solution to change the physical and chemical properties of concrete;
• electric heating;
• using hot water to prepare concrete;
• installation of greenhouses around the formwork and on top of the screed.

Next, let's look at the advantages and disadvantages of each option.

Use of additives and modifiers

Frost-resistant additives are designed to reduce the time it takes for concrete to gain strength. Manufacturers and sellers report that the foundation will not differ in strength from what is poured in the summer, that the water simply will not have time to freeze. Practice often differs from theory. If we talk about the disadvantages, it is important to highlight the following:

• limited temperature range of action. Additives will help if the air outside has not yet cooled below -50C. In severe frosts there is no need to talk about the effectiveness of the method.
• The reinforcement corrodes, quickly oxidizes and collapses. Adhesion to concrete deteriorates, the foundation becomes less reliable.

Electric heating as a way to fill screeds in winter

The most common options for winter heating of concrete are:

• current is passed through electrodes used as reinforcement;
• Before pouring the mixture, a special heating cable is laid.

The first option assumes that current from a welding machine or special equipment is connected to the laid reinforcement mesh. Voltage - 127 V (no more). If the foundation or screed is laid unreinforced, or fiberglass is used, special electrodes are introduced into the solution, and the current strength is increased to 380 V.

Electric heating as a way to protect concrete in winter. The second method leads to a significant increase in the cost of the project, since a special heating cable is laid along the entire reinforcing mesh, connected to a source of electricity. But it is important to recognize that the efficiency is higher in comparison with the first option. The main disadvantage of heating with electricity is that you will not be able to plug the equipment into an outlet once and calmly wait 30 days until the base gains strength. You will have to constantly monitor the temperature, which is difficult with a large foundation area. The likelihood of the surface layer drying out increases.

Using hot water to make concrete

Another way to pour concrete in winter conditions is to preheat the water to 60-70C. The advantages include the opportunity to obtain a high-quality base without additional costs. But there are much more problems:

• it is difficult to calculate the correct temperature taking into account the climatic characteristics of the region;
• The method only works in mild frost. If the thermometer shows -10C or lower, the effect will quickly disappear;
• It is difficult to prepare large volumes of concrete. The heated mixture is good for building a small private house, but not an industrial workshop.

The installation of heat guns or special greenhouses - awnings or canopies - will help solve all the problems described earlier. Supplying heat is a very expensive proposition. You will have to pay the same amount for electricity, gas or diesel fuel per month as the foundation itself costs.

Warmhouses made from canopies and awnings

A temporary tent made of special insulated fabric (PVC, Oxford, tarpaulin) is erected over the construction site. If the foundation is of significant size, the awning is installed sequentially over the areas under work. For small construction sites, the greenhouse is mounted above the entire facility. This allows you not to worry about uneven setting of concrete or subsidence of individual sections. The advantages of greenhouses made from awnings and canopies include:

• reusable. As soon as the concrete gains strength, the awning or canopy is removed and transported to another facility. For example, it will not be possible to remove the heating cable. The installation/dismantling operation of the structure requires 5-6 hours depending on the volume;
• maintaining uniform temperature and humidity throughout the entire perimeter.

Tarpaulin with a density of 180 g/m2 for the installation of shelters for pouring concrete Let's consider the main types of greenhouses used on construction sites.

Warehouses from Tarpaulin: advantages and disadvantages

Tarpaulin thermomats are most in demand in the construction of greenhouses. The base is isolon, protected from external influences by layers of laminated polyethylene. To counteract ultraviolet radiation, a light-stabilizing film is applied to the outer surfaces. The advantages of tarpaulin greenhouses include:

• the ability to maintain a single microclimate in a closed space with thermometer readings in the range from -40C to +80C. You can save on installing additional heat guns or roasters;
• moisture and vapor tightness. Tarpaulin, manufactured in accordance with GOST, can withstand up to 1000 mm of water column. Water, snow, and fog from the street do not penetrate inside the greenhouse;
• resistance to rot and mold for a long time;
• light weight (lighter than tarpaulin). No heavy frame is required; light guides are sufficient;
• elasticity. You can create structures of any shape without any problems. There are no stretch marks or deformed areas;
• minimum price among analogues;
• Easy to clean from dirt and dust. Small stains are removed with a sponge; for “general” cleaning, a hose connected to the water supply is used.

In fairness, it is necessary to note the relative disadvantages of tarpaulin greenhouses:

• An additional problem is that with regular use, the edges of thermomats fray. They have to be additionally glued or sheathed.

The assortment includes tarpaulin in blue, blue-green, yellow, black and white colors. It is possible to choose the best option based on size and type of connection of individual panels.

Warmhouses made of tarpaulin

For production, a special three-layer material is used. The top and bottom layers are tarpaulin made of linen or cotton fibers. Medium - isolon (sintepon). The advantages of tarpaulin greenhouses include:

• maintaining the temperature inside the “room” even with a sharp drop in temperature down to -60C;
• wear resistance and increased strength. Tarpaulin curtains do not lose their performance even after 5 years. Cuts can be easily repaired with patches that do not create cold bridges;
• the use of special impregnations avoids the formation of mold, rot, fungus, and protects against fire;
• water- and dirt-repellent properties. A water column thickness of up to 1000 mm will not harm the material and the structure as a whole.

Among the disadvantages of canvas greenhouses, we highlight:

• high density (up to 650 g/m2). The awning or canopy turns out to be quite heavy. In practice, this means special requirements for fastenings.
• this “point” is significant for aesthetes. The color range of the material is inexpressive and is limited to black and khaki variations.

In the assortment you can buy tarpaulin canopies with additional anti-rot impregnation, manufactured in accordance with the standards.

Oxford fabric warmers

Oxford awnings are made from particularly durable synthetic fabric (polyester or nylon).
A hydrophilic membrane is applied to protect against water. The middle layer is padding polyester with a thickness of 5 to 25-30 mm (thermal mats). Warm houses made from Oxford fabric The advantages of warm houses made from Oxford include:

• ability to withstand temperatures down to -60C;
• water- and dirt-repellent properties. No special effort is required for care. Dust, clay, dirt can be washed off with water from a hose.

But Oxford has many more shortcomings. And you need to know about them:

• to protect against external influences, the fabric is treated with either polyvinyl chloride (PVC) or polyurethane (PU). In the first case, the material becomes more rigid and more difficult to roll and store. The second treatment option gives Oxford greater flexibility and water-repellent properties;
• The greenhouses do not allow air and steam to pass through. Water evaporating from the concrete screed remains inside; a kind of greenhouse is created;
• nylon fabric accumulates static electricity, but at the same time burns out even from the smallest spark. Polyester does not burn, but is less durable than nylon;
• To create awnings and canopies, modifications of fabric with a density of 600 denier are intended.

PVC greenhouses

PVC greenhouses are based on fabric made of polyester or polyester impregnated with PVC. In construction modifications, polyethylene foam up to 10 mm thick is added. It is “thanks to” him that PVC greenhouses have the maximum weight among analogues - up to 1100 g/m2. Among the advantages of PVC awnings and canopies, it is necessary to highlight:

• resistance to water, mechanical shock, cuts, tears;
• maintaining the microclimate inside the greenhouse at outside temperatures down to -45C;
• wind and direct sunlight do not lead to deformation of the internal structure;
• long service life (up to 10 years);
• elasticity, flexibility, the ability to give almost any shape.

If we talk about the disadvantages of PVC, they are associated not with the physical properties of the fabric, but with the production method and raw materials, as well as the excessive weight of the finished products, which increases the cost of their delivery.

Finally

The trade and production company "Stroy Vybor" offers to buy at competitive prices the optimal means for protecting concrete from frost and winter cold snaps - awnings made of tarpaulin, PVC, tarpaulin and Oxford. All materials fully comply with building regulations, GOSTs, and are safe for humans and the environment. For use in Russia, no special permits or approvals are required.

Warmhouses for protecting concrete - can be built even in cold weather. Components from the world's leading suppliers (Russia, Europe, Asia) are used as raw materials. We have our own production, the best technologies and equipment have been selected. Tents for pouring concrete in cold weather can be purchased with delivery both in Moscow and Moscow Region, as well as in the regions of the country by transport companies of the buyer’s choice. To place an order, you can send an application by email or call the phone numbers listed on the website. A manager contacts each client. His task is to clarify the volume of delivery, delivery time, and type of payment. Don’t stop construction in winter, contact Stroy Vybor.

In this case, the structure of the concrete may be damaged, and microcracks will appear, which over the years will turn into ordinary cracks, and the process of destruction of the foundation will begin.

Application benefits

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

Concrete hardens faster in cold weather - one of the advantages.

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

The use of antifreeze additives allows you to:

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

Return to contents

Advantages and disadvantages of additives

The main advantage of concrete with anti-frost additives is the ability to perform work all year round. Selected in the correct proportion, they improve the adhesion of the components, increasing the quality of the solution. They have other advantages:

• increasing service life due to concrete compaction;
• increase the plasticity of mixtures, making them easier to work with;
• the frost resistance of ready-made concrete increases, which is important for elements of load-bearing structures;
• the use of PMD is the cheapest method of filling at subzero temperatures;
• the use of additives reduces shrinkage during solidification, maintaining the integrity of the structure;
• anti-frost additives fill the pores of concrete, thereby significantly increasing its water resistance;
• some compositions significantly increase the corrosion resistance of the monolith, extending the service life of structures, buildings and structures significantly.

The use of antifreeze additives also has its disadvantages. If used incorrectly, the strength characteristics of concrete are reduced, so when working, you must strictly adhere to the instructions. Some additives are flammable and toxic, which must be taken into account when working with them. Even with additives, in frosty conditions the hardening rate will be relatively low. To achieve the required strength when laying in winter, a larger amount of cement is required, which increases the cost of construction.

Possible consequences

In special frosty conditions, you must remember to follow all the rules for winter filling, otherwise irreversible consequences may occur, after which there can be no talk of any further operation of your facility. Therefore, you must strictly take into account all the standards and calculation data of this matter.

If you pour liquid into concrete during frost and do not do it correctly or with some, even minor, violations, then the thermal processes of hydration in the formwork, which proceed and are completed after about three to five days, may stop completely.

This leads to sad consequences; as a rule, the surface layer of your fill will be loose and crumbly. In this case, the work needs to be completely redone.