Pouring concrete at low temperatures. Pouring concrete at negative temperatures: the secrets of winter concreting technology. Formwork insulation after pouring

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

What is an antifreeze additive in the solution?

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

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

The problem of organizing brickwork in cold weather

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

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

Features of the preparation of the solution

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

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

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

Antifreeze additive: consumption

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

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

plasticizers

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

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

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

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

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

Eventually

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

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

The foundation is the fundamental structure, the quality of which determines the geometric, technical and performance characteristics erected structure. Due to the specifics of the hardening process, it is undesirable to pour concrete and reinforced concrete foundations in winter in order to avoid their deformation and premature destruction. Minus thermometer readings significantly limit construction in our latitudes. However, if necessary, concrete pouring at negative temperatures can still be successfully carried out if selected the right way and with precision observed technology.

Features of winter "national" filling

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

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

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

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

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

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

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

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

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

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

Minus temperature and foundation

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

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

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

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

• Security external care behind the concrete mass poured into the formwork up to the stage of gaining critical strength.
• Increasing the temperature inside the concrete mass until the moment of sufficient curing. It is carried out by means of electrical heating.
• Introduction to concrete mortar modifiers that lower the freezing point of water or activate processes.

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

How to pour a concrete foundation in winter

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

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

External conditions "for ripening"

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

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

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

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

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

Methods for heating concrete mass

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

In the technical documentation, the methods of electric heating of concrete are divided into:

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

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

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

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

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

Introduction of additives into concrete solution

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

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

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

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

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

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

Common antifreeze additives for pouring concrete:

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

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

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

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

Prepare cold mixes hot water, the proportion of additives is introduced in strict accordance with the weather conditions and the type of structure being constructed.

Methods for pouring concrete in winter:

Winter concreting with a greenhouse device:

Antifreeze agent for winter concreting:

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

If interruptions cannot be avoided, the intervals between grouting should be kept to a minimum. If the technological subtleties are observed, the concrete monolith will gain the necessary margin of safety, will be mothballed for the winter and continue to harden with the advent of warm weather. In the spring, it will be possible to start building walls on a ready-made reliable foundation.

At temperatures below zero, the hardening of the concrete solution becomes problematic. This is often encountered when building foundations in autumn and winter. Experts assure that pouring concrete at sub-zero temperatures is possible without heating, but certain requirements are met for this to ensure proper hardening of the concrete mixture.

Concrete is a mixture of aggregates - sand and gravel, fastened together by a hardened cement milk. When it reacts with water, it hydrates, then it hardens with the simultaneous evaporation of water. Critical strength at normal temperature is gained within one or one and a half days, depending on the humidity of the surrounding air.

The optimal temperature for the reaction is about 20⁰С, the solution gains its design strength within 28 days. So that in the early days the water does not evaporate too quickly, the concrete is covered with waterproofing.

At 5⁰С, the solidification of the composition slows down by 2 times, and at zero temperature, hydration stops. If before that the critical strength of concrete is gained, nothing will happen to it, it will gain strength after warming. If, before freezing, a set of critical strength did not occur, the material will not gain the required indicators, and will crumble after defrosting. In this case, it is impossible to pour any brand of concrete at sub-zero temperatures.

Methods of concreting in winter conditions

The main condition for the correct pouring of concrete at low temperatures is the preservation of heat sufficient to ensure curing. Popular styling methods mortars in winter:

• Pre-heating of the produced mixture;
• The device of reliable thermal insulation and care of the solution;
• Electric heating of concrete poured into the formwork;
• The addition of special additives that reduce the freezing point of water and accelerate hardening.

Thus, it is possible to concrete on the street in winter without loss of strength indicators, but for this you need to adhere to the selected 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 device are intermediate options.

Temperature increase during kneading

To pour concrete in sub-zero temperatures, the components are heated. Fillers are heated to 55-60⁰С, and water is fed into the solution at 90⁰С. Cement before adding is warmed up to room temperatures, otherwise it loses its binding properties. Before laying, the temperature of the solution should not be lower than 35⁰С.

When mixing, it is required to use a concrete mixer, into which heated water is first supplied, 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 insulation of the solution

At very low temperatures heated mixture requires additional insulation or heating. It is more economically feasible to insulate with the help of inexpensive heat-insulating materials that do not require additional sources energy. Hay or straw is lined on a concrete surface, old rags, peat, film or heat-insulating blankets are used. Sometimes the so-called "greenhouses" are arranged, similar to greenhouses.

If concreting at temperatures below -5⁰С, additional heating will be required. For this, the following technologies are used:

• Heating with heat guns or stoves under greenhouses. This is a costly method that requires constant additional moisture. Suitable for sites that do not have electricity.
• The use of thermomats powered by electricity. They are laid out on the surface of poured concrete and connected to a power source. Requires a large amount of electricity.
  Infra-red radiators are installed above the flooded surface or around the formwork, the intensity and direction of heating is regulated by reflectors. Suitable for vertical and inaccessible structures.
• Used to heat concreted area special cables or electrodes through which an electric current is passed. The technique is convenient to use, but requires large volumes electricity. Installation of the electrode system requires more costs, because when drying, the resistance of the solution, which itself is a conductor, increases.

Introduction of additives

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

1. Compounds 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. In this capacity, calcium or sodium salts and potash are used, which prevent the crystallization of water.
2. Additives that increase the rate of hardening of the solution. They reduce the time required 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 add up to 5-8% by weight of cement. With a decrease in temperature to -15⁰С, the concentration is increased to 10% by weight of the added cement, and up to -25⁰С, at least 15% of additives must be added.

To achieve maximum strength, you need to know at what temperature to pour concrete, and the best methods for ensuring curing. In addition, it is required proper preparation formwork. Before pouring the solution, it is necessary to thoroughly clean it from frost. The soil and reinforcement must be warmed up, for which braziers, heat guns, infrared emitters and other devices are used. That's why to do slab foundations in the low temperature range is not recommended, since it is difficult to fully heat all the elements over a large area.

Working with a strip foundation in such weather is quite possible. To do this, you need to warm up the trench gradually, pouring concrete into it. After pouring, a mandatory step is high-quality thermal insulation. The process continues until the perimeter is closed. With the use of additives in concrete mortar and high-quality insulation strip foundation can be poured at temperatures up to -15⁰С.

When working on laying concrete, regardless of the type of structure, continuity of work is needed until the monolith is completely poured. For the successful completion of the work, it is necessary to calculate the supply of the required amount of solution and the optimal number of workers.

Filling in parts can lead to uneven properties of the structure and reduce its quality.

Before pouring the solution into the formwork, you need to make sure that its temperature is optimal - in the region of 38 ° C. If it exceeds 40 degrees, then the hardening rate will decrease due to a decrease in the quality of the cement. As a result, it will take too long to reach critical strength, the liquid in the solution risks freezing, and the concrete will lose its properties.

Answering the question whether it is possible to pour concrete in winter, one can say - definitely yes. With the right technological approach, these works can be carried out at the lowest temperatures. Laying without additional heating can be carried out in slight frosts, this will require good thermal insulation and pre-heating of the concrete solution.

At low temperatures, additional It is carried out various methods, which you need to choose directly at the construction site. The cost of heating and thermal insulation pays off, since substandard concrete will reduce the quality of the entire structure.

In winter, when the temperature outside drops below zero, the construction of reinforced concrete, monolithic and concrete structures becomes more difficult. The liquid, which is part of the cement mortar, begins to crystallize, as a result, the process of concrete hardening almost completely stops.

As soon as the warm season sets in, the hydration of the cement resumes, and the mortar that has frozen during the construction phases has a high thermal conductivity and low strength. This is due to the fact that the frozen water expands, making the concrete loose. In order to eliminate such consequences, it is customary to use antifreeze additives. They resist liquid crystallization at sub-zero temperatures.

Additives in concrete

Having visited hardware store, you can find concrete additives in large assortment. For example, sodium nitrite is in the form of a liquid or white crystals. Carbamide is known by its second name - urea - and is produced in the form of colorless crystals. You can find compounds of calcium nitrate and urea. The kind of white powder is sodium formate.

The dark brown liquid is a compound that suggests the presence of:

• acetylacetone;
• nitrochloractinide;
• acetoacetic ether.

It is noteworthy that this composition is used at temperatures up to -25 ° C. Asol-K is made from special modifiers and potash solution. It is able to withstand temperatures down to -10 °C, while when the temperature changes above 0 °C, concrete hardening is accelerated. High-quality antifreeze for mixtures is Hydrozim, which provides hydration at temperatures below -15 ° C. From NH3 gas and ordinary water, a composition is made that can withstand frosts down to -30 ° C. Hydroconcrete has plasticizing properties, which can be used at temperatures not lower than -15 °C.

Additives for cement slurries

Antifreeze additive into the solution allows you to use the latter in the construction monolithic structures, buildings and the manufacture of reinforced concrete elements. Today, such additives are presented in a wide range, but the most popular are electrolyte compositions and their compounds. They provide antifreeze effect and accelerate the hardening of the solution. Among the most common are:

• HK, HH1.
• NNHC.

sodium formate

Formate is an antifreeze additive that has the appearance of a crystallized white powder that dissolves well in water. An additive is made from sodium salts of formic acid. The main actions are aimed at reducing the temperature of the water in the solution and prolonging the hydration of the concrete.

The additive does not have plasticizing properties and is capable of creating tension in the structure due to salt crystallization. In order to avoid this, you should additionally use the C-3 plasticizer, which is available in liquid and powder form.

Consumption

The consumption of an antifreeze additive must be known in order to purchase right amount funds. In the manufacture of a solution with an antifreeze additive FN + S-3, warm water, into which sodium formate and a plasticizer should be poured. The amount of additive is determined depending on weather conditions. If the temperature varies from 0 to -5 ° C, then the consumption will be 3% of the total mass of cement.

When the temperature changes in the range from 0 to -10 ° C, an additive in the amount of 4% by weight of cement should be used. The amount of additive increases to 6% if the ambient temperature drops to -15 °C. The volume of C-3 plasticizer always remains at the level of 0.8-1% by weight of cement, which does not depend on air temperature. For an antifreeze substance, the consumption will be different. This parameter will be influenced by the properties of the additive and the air temperature.

Application of additives

Antifreeze additives must be added to the solution along with the liquid. It is desirable to do this with the last third of the water. Additives should not be added to the dry mix. As soon as the additive is added, you should wait a certain time, which is necessary for the distribution of the components. Antifreeze additives are used at sub-zero temperatures according to certain rules.

If you have to work in snowy conditions, then it is important to take care of shelter. When the solution leaves the mixer, it is important to keep its temperature in the range from +15 to +25 °C. The working mixture should be prepared using heated water. Aggregates are heated before direct use.

Application restrictions

Antifreeze additives of some types can be used subject to restrictions. They apply to prestressed structures and products that will be subjected to dynamic loads. Use when sealing joints reinforced concrete structures solutions of chloride salts are not allowed. This applies to products that have embedded parts and fittings. The rule is relevant if chemical protection has not been carried out.

Mixtures of antifreeze additives should be used after preliminary testing of samples for corrosive attack. The described means can cause efflorescence on the concrete surface, as well as reduce the strength characteristics of structures. Concrete with additives must have a positive temperature by the beginning of curing.

This parameter should be higher than the outside air temperature by 5 °C or more with a plus sign. For example, if the air temperature is -13 °C, then the concrete temperature should be +18 °C. Unburied surfaces of structures should be thermally insulated to prevent freezing of water from these areas.

The use of antifreeze additives requires compliance with the outside temperature limits. If chloride salts (sodium nitrate) are used, the temperature should be -15°C or higher. As for potash, this limit will be -25 °C. The technology of using the described additives has one important virtues, which consists in the minimum material and physical costs for implementation. The downside of the technology is the long period of critical strength acquisition by the structure. If the rules for using additives are violated, some problems may arise, such as efflorescence on the surface and corrosion of the reinforcement.

When an antifreeze additive is used in concrete, complex methods of maintaining structures are often used. Thermos technology is used to reduce the hardening time. To do this, the mixture is prepared on the heated components of the liquid with the thermal insulation of concrete.

Why You Should Use a Chloride-Based Supplement and When You Should Avoid It

Antifreeze additives made on the basis of chlorides have many advantages, among them should be highlighted:

• low cost;
• no effect on the structure of the solution;
• no effect on the rate of solidification, so that the solution can be prepared in advance;
• an increase in the mobility of the particles, due to which it is possible to give the solution the desired shape.

The above additive has a minus, which is expressed in a high level of corrosive activity. As a result, such a tool can be used only for those structures that do not have reinforcement and metal in the structure. The latter begins to oxidize, exfoliate from the structure, thereby violating the integrity.

Precautions for use

Wear protective gloves when handling additives. If the product got on open areas skin, they should be washed with soap and water. The additive should not get into the eyes, but if this could not be avoided, then they should be rinsed large quantity water and see a doctor. Additives must be disposed of in accordance with local regulations, as these formulations contain harmful components. This indicates that the mixture must not be poured onto the soil, discharged into sewers or waterways.

Conclusion

Using antifreeze additives, it is possible to increase the structural strength by almost 2 times. These ingredients allow you to save on cement, because it can be of a lower class, which means it will cost less. Structures can be made of less impressive thickness, while strength and other properties will not be lost.

The specificity, and often the problem of construction, is seasonality - it is impossible to carry out many types of work in winter. Concreting is considered the most critical process for low temperatures. Given the responsibility of such work, especially when pouring foundations, the developer must have a good idea of ​​how to pour concrete, how low temperatures affect the hardening process of the concrete mixture and what problems may arise in connection with this. We will tell you at what temperature concrete can be poured, how to pour concrete correctly in frost, whether it is possible to pour concrete at sub-zero temperatures, and what needs to be done for normal concrete hardening in such conditions.

Of the components of the concrete mix in the process of hardening with the formation concrete stone involved cement and water. Aggregates (sand, gravel, crushed stone) are bound into a single complex due to the hardening of the cement milk between them - a mixture of water and cement. Crystallization occurs when cement particles are hydrated with water. Water molecules bind with cement to form a crystalline mass, i.e. gradual hardening occurs due to the loss of water.

The direction of the process is from the periphery to the center of the stone, and the process itself takes place under conditions with certain restrictions. Some characteristics of the process under different conditions:

• If the hardening temperature of the laid concrete is +15 - +25ºС, then the concrete poured into the formwork will gain maximum design strength in 28 days. For the first week in normal conditions the concrete mixture gains up to 70% of the design strength. are most important for the normal curing of concrete during the first few days after pouring. At this time, for normal hydration, you need to retain moisture. To do this, the concrete surface is covered with a PVC film or wet burlap.

• If the temperature of the medium drops to +5ºС, the process of stone formation slows down by half, i.e. it will be possible to count on the normative strength of concrete in about two months.

• Hardening stops completely at 0ºС - the freezing point of water. At lower temperatures, the water in the concrete mixture freezes. If by this moment the critical strength of concrete has already been gained, then hardening continues until the end after defrosting. The critical strength of concrete characterizes the moment when the hardening of the mixture is achieved to such an extent that a favorable result of the process is already provided. At normal temperature, critical strength occurs one day after concrete is poured. Such a threshold also depends on the brand of cement - mixtures on cements of high grades have a critical strength that is only a quarter of the full standard.

• If the strength of concrete before freezing is less than critical, then the freezing water inside the monolith expands and breaks the bonds, increasing the porosity of the stone. Such a monolith loses strength, passes water - its service life decreases, and often the concreting has to be done again.

Pouring concrete in winter conditions

The necessary conditions for concreting in winter are described above - the main thing is to ensure a sufficient temperature of the mixture during hardening. The choice of a specific method depends on the specifics of the work and the nature of the object. For example, if it is not possible to provide concrete heating, and the foundation is small, instead of belt type foundation to arrange bored.

All measures to ensure reliable concreting in winter conditions can be divided into:

• Preheating of the concrete mix before laying.

• External care of the concrete mixture poured into the formwork.
• Increasing the temperature of the poured concrete mass by electrical heating.
• Adding to concrete mix modifiers that accelerate hardening or shift the crystallization temperature of water.

The final choice of winter concreting method depends on many factors. For example, if it is not possible to deliver a heated mix to an object due to the large concrete delivery arm, then it makes no sense to consider this option. In addition, often the building site is not electrified or the supplied power is limited. Great importance has a reliable weather forecast for the period of hardening of the mixture. If we compare the cost of each of the proposed methods, then the most budgetary is last option– adding to concrete mix special additives. Let's briefly review each of the methods.

Heating the mixture during cooking

The method consists in preheating the components of the mixture (except cement) so that at the time of laying the mixture its temperature is 35-40 o C. Sand and gravel are heated to about 60 o C, water - up to 90 o C. The cement is first placed in a heated room and heated to room temperature. It is impossible to warm up the cement - it quickly irretrievably loses its activity and becomes simply unusable!

For kneading, mixers with or without heating can be used. At large construction sites, aggregates can be heated in special drying ovens. A private developer can use the hot air of a heat gun or heat from a stove transferred through an air duct.

Winter concrete mixing has technological features. Water is poured into the mixer, crushed stone and sand are added to it, and only then cement. The mixture is kneaded especially carefully, in time a third longer than usual.

Formwork insulation after pouring

The method is especially relevant for maintaining heat after laying the heated mixture. Various methods can be used:

• At large construction sites, electric heating mats are used, which are laid on poured concrete and connected to the network. The method is expensive - the cost of such a mat is 2500 rubles per square meter.

• Pouring concrete at negative temperatures in an individual construction can be accompanied by insulation with everything that is at hand: old clothes, straw bales, etc. Often satisfied with the so-called. "greenhouses" - a kind of greenhouses over poured concrete, where warm air from oven, heater, etc. At the same time, the concrete surface must be moistened. The surface of concrete can also be covered with film, sawdust, peat and even snow.

• Laid concrete at sub-zero temperatures can be heated infrared emitters for directional heating of concrete. The flow is regulated by aluminum guides. The method is expensive due to the large need for lamps and power consumption.

Electric heating of laid concrete

Such methods are usually used in industrial construction. For their implementation, sufficient electrical power and an electrician with a serious vocational training. Electric heating can be:

• Through - when the mass of concrete is heated from the inside by currents going inside the formwork along rod or string electrodes. The layout of the electrodes and the load must be accurately calculated. The mass of concrete acts in this case as a source of resistance.

• Peripheral - when heat is transferred from sources to strip electrodes fixed to the formwork (steel strip or sheet). Warming up to a depth of about 0.2 m is intensively provided, but even deeper incoming heat affects the strength criteria.

Methods are used with a small reinforcing cage or without it at all. With a thick reinforcing mesh, the currents close to it and the system does not work or works unevenly. After the mixture hardens, the electrodes remain inside the monolith forever.

Additives in concrete mix

The most cost-effective method. Often used in conjunction with different methods heating, increasing their efficiency and reducing costs. At certain conditions can be used without warming up. Additives in laid concrete at sub-zero temperatures can be divided into:

• Lowering the freezing point of water in solution.

Promote crystallization at low temperatures. Salts of calcium, sodium or potassium are used. The most common reagent is potash.

• Increasing the speed of curing.

Such reagents include potash, mixtures of calcium salts with urea, calcium nitrite-nitrate, etc.

Additives in liquid concrete at sub-zero temperatures, they are introduced at a dosage of 2 - 15% of the mass of cement in the mixture. Yes, at design temperature concrete - 10 o C - 15 o C requires potash in the amount of 10% by weight of cement, and at a temperature of - 21 o C - 25 o C - in the amount of 15% by weight of cement.

Benefits of winter concreting

Concrete laying and curing at low temperatures for Russian conditions often a necessity. Residents in many regions can count on just a few months of the year when concrete can be laid without creating special conditions for hardening. Postponing work for 7-8 months is unreasonable, therefore, it is natural to know how to properly pour concrete in frost and achieve standard hardening for our conditions. There are clear advantages in winter concreting:

• Frozen soil in winter can be used as the most durable formwork, since it is rigid, does not crumble and does not require strengthening.

• In winter, the price usually drops sharply. building materials, therefore, it is possible to significantly reduce the cost of construction.

• Most of the construction crews are out of work waiting for the season, so it is possible to agree on work on pasture conditions.

The negative factor is low speed process, but nothing can be changed here - the technology of laying concrete at low temperatures has its own laws: the acceptance of concrete on the foundation (or floor) must be continuous, i.e. "cold seams" are excluded. Otherwise, it is important to choose the right best method concreting and exactly fulfill the requirements of the technology for the care of the laid mixture.

Pouring concrete at low temperatures updated: December 13, 2016 by: Artyom