Overview of antifreeze additives in concrete - description and properties. Additives that give concrete special properties At what temperature to add additives to concrete

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

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

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

Pouring concrete

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

The direct effect of sub-zero temperatures on concrete structure admissible only after she acquires required amount strength, frost resistance, etc. In construction terminology, this value is called the critical strength threshold - after overcoming it, frost does not negative impact on the concrete structure.

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

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

Among them are the following:

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

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

Mixture heating

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

Specialty Blends

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

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

thermal insulation

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

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

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

Internal and external heating

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

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

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

Outcome

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

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

At what temperature can the foundation be poured

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

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

In hot weather, the foundation may crack

Is it possible to pour the foundation in winter

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

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

How cement mortar behaves in frost

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

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

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

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

For winter work requires concrete with special additives

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

Is it possible to pour concrete in frost without heating

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

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

Video: heating concrete foundation in winter

When can you pour the foundation in the spring

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

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

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

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

Is it possible to pour the foundation in the rain

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

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

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

How to work during the rain

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

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

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

Let's try to answer this question, taking into account the characteristics of concrete and its behavior at sub-zero temperatures.

To begin with, water in concrete is needed not only for its fluidity, it also plays a very important role in the hardening process.

At sub-zero ambient temperatures, water begins to turn into ice, as a result of which it not only stops the hardening process, but also contributes to the destruction of the bonds that formed before it freezes.

You should be aware that concrete can freeze at a temperature of about -4 0 C. At temperatures below +5 0 C, the process of its hardening slows down several times, and strength gain is delayed until it becomes warmer. So, the longer the stagnation during the hardening process, the less strength it will gain in the end.

This means only one thing - at sub-zero temperatures, we need to create conditions under which concrete will not only not freeze, but will continue to gain its strength.

Let's try to figure out how to do it.

Technology of pouring concrete at sub-zero temperatures

There are several technologies for pouring concrete when the ambient temperature is below zero:

By adding antifreeze additives to concrete
With the help of electrical heating of concrete from the inside
With the help of insulation of the pouring object

The use of additives in pouring concrete

The use of antifreeze additives in prepared concrete is very common. This is due, first of all, to low costs and their availability. And if you use purchased concrete, then all the necessary antifreeze additives will already have to be in it, in accordance with the values of sub-zero temperatures.

These additives contain various chemical impurities, like salts of monocarboxylic acids, sodium nitrite and formate, etc., which significantly accelerate the hardening process, increase the final strength of concrete, and most importantly, prevent the water contained in concrete from freezing.

The main disadvantages of using various kinds additives in concrete is that they do their job well only at low sub-zero temperatures - about -5 0 C.

In severe frosts, some of the additives will work, but all the same, hardening will slow down significantly and eventually there will be a shortage of concrete strength up to 30%. Also, some additives are aggressive to metal reinforcement, and act destructively on it.

The technology of heating concrete during its pouring

Heating of concrete with electricity is carried out in two ways:

Passing current through concrete using electrodes
By passing current through a pre-laid wire inside the concrete

If someone is interested in the technology of electric heating of concrete in winter, I described it in detail in one of my articles. Therefore, I will not focus on this technology much attention here.

The first method is much cheaper, since fittings can act as electrodes.

If you follow the rules, then additional special equipment is needed for these purposes, but some craftsmen, having inserted reinforcing electrodes into concrete, connect a welding machine to them, thereby passing current through the concrete and heating it.

It is worth noting that reinforced concrete they are heated with voltage up to 127 V, and concrete without metal reinforcement can be heated with voltage up to 380 V.

The second method implies additional costs for a special heating cable, which, as a rule, must be laid along the reinforcing cage and connected to the current through special substations.

This method is much more expensive, but at the same time - much more efficient than heating concrete with electrodes.

The main disadvantage of using this method is significant financial costs, and at the same time, when heating concrete, it is necessary to constantly monitor its temperature. Heat will cause the concrete to dry out and can cause significant damage to the future structure.

In severe frosts additional insulation formwork or concrete.

Insulation of concrete during curing

In addition to creating artificial heating of concrete, at a slight sub-zero temperature, standard methods of insulation can be applied.

As a rule, the formwork itself is insulated, if any, as well as all visible parts of the concrete. Warming is carried out various materials, from conventional sawdust to the use of Styrofoam.

One of the most popular methods of insulation is the creation of a so-called tent around the concreting object. Additionally, heating guns can be installed inside such a tent.

The disadvantage of this method is that the concrete must be supplied already heated, and conventional insulation, without additional heating, will be ineffective in severe frosts.

So we examined the main methods of pouring concrete at sub-zero temperatures, to all this I would like to add that often for this purpose they use not one specific method, but a set of measures is planned in advance, ranging from the addition of antifreeze additives to heating with subsequent insulation .

But despite this, the process of pouring concrete in sub-zero temperatures is not cheap, despite the fact that manufacturers make huge "winter discounts" on building materials.

In addition to this, it is very difficult with the help of artificial heating to maintain a constant comfortable temperature, and what is not unimportant - the temperature should be evenly distributed throughout the entire volume of the fill.

Attention! Pouring concrete at sub-zero temperatures is only possible if you have no other choice, because minimum temperature environment in the process of hardening, without additional interventions, in spring should be +5 0 С, and in autumn - +10 0 С.

For autumn, the requirements are stricter, because the main hardening period is 28 days, and during this time the autumn air temperature can drop significantly.

The foundation is the fundamental structure, the quality of which determines the geometric, technical and operational characteristics of the structure under construction. Due to the specifics of the curing process by pouring concrete and reinforced concrete foundations it is undesirable to engage in winter in order to avoid their deformation and premature destruction. Minus thermometer readings significantly limit construction in our latitudes. However, if necessary, pouring concrete at low temperatures can still be successfully carried out if the right 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" of the concrete mass into 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 concrete mass the water will crystallize and increase in volume.

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

Minus temperature and foundation

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

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

For those who are not satisfied with alternative methods, there are several proven successful practices. Their purpose is to bring concrete to a state of critical strength before freezing.

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

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.
The introduction of modifiers into the concrete solution, lowering the freezing point of water or activating processes.

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

How to pour a concrete foundation in winter

To know which method is better to use for curing concrete to critical strength indicators, you need to know their characteristic features, familiarize yourself with the minuses and pluses.

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

External conditions "for ripening"

Favorable 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 filled very quickly concrete mix, heated above standard indicators, are 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 monolithic slab frozen 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 the fate of a 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 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 what concrete warms up electric currents, which supply electrodes laid inside the formwork, which can be rod or string. 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 appliances 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 simplest and cheapest way of concreting at sub-zero temperatures. According to it, concrete pouring in winter can be carried out without the use of heating. However, the method may well complement heat treatment indoor or outdoor type. Even when used in conjunction with heating the hardening foundation with steam, air, electricity, there is a reduction in costs.

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

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

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

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

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

Common antifreeze additives for pouring concrete:

Potash or otherwise potassium carbonate (K 2 CO 3). The most popular and easy-to-use modifier of "winter" concrete. Its use is a priority due to the absence of reinforcement corrosion. For potash, the appearance of salt stains on the surface of concrete is not typical. It is potash that guarantees the hardening of concrete at thermometer readings down to -25°C. The disadvantage of its introduction is to accelerate the setting rate, which is why it will be necessary to cope with pouring the mixture in a maximum of 50 minutes. In order to maintain plasticity for the convenience of pouring into a 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 with chemical compounds diluted in it are added. 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 flooded or very humid environment, because. they contribute to the formation of alkalis in concrete.

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

Cold mixtures are prepared in hot water, the proportion of additives is introduced in strict accordance with weather conditions and the type of structure being built.

Concrete pouring methods winter period:

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 irregularities 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. Subject to technological subtleties the concrete monolith will gain the necessary margin of safety, will be mothballed for the winter and will 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.

The maturation of concrete slows down significantly at temperatures below +5°C, and completely stops at minus. This is due to the freezing and crystallization of water entering the solution. But builders are often forced to continue work in the cold season. The problem with freezing under adverse conditions is solved by introducing special antifreeze additives. When using this method, it must be taken into account that the strength of a material with such impurities at low temperature is no more than 30% of the design one, it will gain full strength after thawing.

Benefits offered by the use of antifreeze components:

the ability to perform work related to mixing concrete at any time of the year;
many important characteristics material - density, moisture and frost resistance;
the plasticity, mobility and stability of the solution increase, cracks do not appear after it hardens;
mixture separation is prevented;
lower cost compared to alternative ways combating the delay in maturation;
the risk of shrinkage is reduced.

Disadvantages of using antifreeze additives:

more consumption of the binder component (cement) - due to this, and also because of the need to spend on the additives themselves, concrete is more expensive;
some substances that accelerate hardening at low temperatures are poisonous;
maturation is accelerated, but strength development may be slowed down.

Types of antifreeze

According to the effect on concrete, antifreeze additives are distinguished:

antifreezes and accelerators - help to lower the freezing point of water in solution;
sulfates - warm the mixture due to the release of heat during the reaction;
complex - are at the same time antifreeze components, hardening accelerators, plasticizers for concrete, as well as masonry and plaster compositions.

PMDs are classified according to the lowest temperature level at which they are effective: down to -10, -15, -20 or -30°C.

List of substances that accelerate the maturation of concrete at low temperatures

In pure form or as part of ready-made complex mixtures, as antifreeze additives, the following are used:

1. Sodium nitrite. At temperatures from 0 to -25°C, the inscription Poison should be on the container. It is flammable, the use of this component in combination with lignosulfonic acids is prohibited, since as a result of their reaction poisonous gaseous nitrogen compounds are formed. Sodium nitrite is sold in powder form or solution. Consumption: 4-10% of the weight of the cement in the mixture.

2. Sodium tetraborate (borax, sulfate-yeast mash) and calcium carbonate (potash). These substances are recommended to be used together, since calcium carbonate without borax reduces the strength of the finished concrete (up to 30%), provokes its cracking. Potash is harmful, be sure to take precautions. Requires a plasticizer, consumption: 5-10% by weight of cement.

3. Sodium formate. It goes on sale in the form of a white crystalline powder, it dissolves well in water. When using it, a plasticizer is required. Sodium formate is usually added together with powdered or liquid naphthalene lignosulfonate, which is the thinner of the mixture. Due to the content of phenol and formaldehyde, it is classified as dangerous substances. Consumption of sodium formate: 2-3% by weight of cement.

4. Ammonia water. It is sold as an aqueous solution at 25% concentration, suitable for use at the lowest temperatures (theoretically ammonia water can be used even at -100°C). Positive properties - not only does not provoke corrosion, but, on the contrary, creates an effect on the reinforcement protective film, significantly increases frost resistance finished construction. In the warm season, ammonia in the form of a gas evaporates from concrete and it becomes the same as mixed with ordinary water.

Complex means

Complex additives suitable for use at temperatures down to -20°C:

calcium nitrite and nitrate (NNK);
calcium nitrite with urea (NKM);
nitrite and calcium nitrate with urea (NNKM).

Complex frost-resistant additives for concrete, suitable up to -30°C:

nitrite, nitrate and calcium chloride (NNHK);
nitrite, nitrate and calcium chloride with urea (NNHKM).

Subject to the ratio between salts and urea in a mixture of 3:1, the listed antifreeze additives do not contribute to the oxidation of reinforcement, do not reduce frost resistance. They are not used in the manufacture of:

span structures made of reinforced concrete, if their length is more than 6000 mm;
products on the surface of which the appearance of efflorescence is not allowed;
structures exposed to sulfate type corrosion;
structures located at a distance of less than 100 m from sources direct current high voltage.

Complex PMD can be made from individual components with your own hands or purchased ready-made in liquid form with already selected proportions. It is more profitable to use professional complex solutions due to lower consumption. Several options for such additives:

Ivitek - up to -10°C.
Frieze De Lux - up to -15°C, when carrying out masonry, plastering work, as well as pouring screeds.
Hermes - up to -30°C, optional positive properties- reduces cement consumption by 10%, increases strength characteristics by 14%.
Will establish Safescreen SN1 - when erecting monolithic and prefabricated monolithic structures and products made of concrete or reinforced concrete, it is also suitable for adding to masonry, insulating and assembly mortars.

For efficient and safe use antifreeze liquids, you must follow the rules:

1. Added to concrete with the last third portion of water, which must be heated.

2. It is undesirable to make a dry mix.

3. To obtain the effect, you should wait for some time (up to 15 minutes). This is necessary for uniform distribution of the substance.

4. The temperature of the mixture at the outlet of the mixer should be in the range from +15 to +25C.

5. During snowfall, it is imperative to install a canopy over the tank. Otherwise, the snow, getting into the mixture, will worsen its properties, as it will change the ratio of the components. Laying during precipitation is not possible. If the snowfall begins during pouring, then the already laid concrete is covered with a layer of waterproofing.

6. When working with the addition of anti-frost ingredients, as well as when mixing, be sure to use protective equipment: gloves, goggles. In case of contact with skin - wash with soapy water, in eyes - rinse abundantly with clean water and seek medical advice.

7. Never pour PMD residues onto the ground, into sewers or waterways.

Despite the introduction of anti-frost components into the composition of the mixture, it is recommended to cover and heat the concrete in winter.

Do-it-yourself antifreeze additive

If for some reason it is not possible to purchase PMD professional quality, then it is permissible to use the usual technical salt - sodium chloride. An additional advantage of this tool is that it reduces the consumption of cement. The disadvantage is that it increases the corrosion of the metal, therefore it is impossible to use salt for concrete used for the manufacture of reinforced products and structures, as this leads to peeling of the frame, deterioration of performance. Salt consumption depending on the air temperature at the construction site:

not lower than -5°C - no more than 2% by weight of the solution;
from -5 to -15°C - up to 4%.

When using technical salt instead of ready-made PMD, concrete strength development is worse - 100% of the design will be only three months after pouring a solution with a 2% salt concentration. If sodium chloride is poured up to 4%, then during the same time the concrete will gain only 50% strength. It is acceptable to use it as an independent additive, but best effect can be achieved in combination with calcium chloride. It is administered in an amount of 0.5% by weight of the mixture at temperatures up to -5 ° C and up to 2% if it is from -5 to -15 ° C outside.

Price

The price depends on the composition and volume of the party. They can be bought as powders, packaged in 25 and 50 kg bags, or liquids in 10 or 20 liter cans.

Minimum prices for large batches of antifreeze additives in concrete:

Via various formulations you can solve the problem of slowing down and completely stopping the maturation of concrete at low air temperatures (below + 5 ° C) on your own. The need for their application arises if for some reason it is necessary to continue construction in the winter period.

This measure is forced and may lead to a deterioration in technical characteristics. Many of the components of PMD are themselves toxic or are capable of releasing them over time. Therefore, it is recommended, if possible, to avoid introducing these agents into the solution, to supplement them with plasticizers.

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