Pouring concrete at minus 5. Additives that give concrete special properties. Antifreeze additive: consumption

Industrial construction does not stop during the cold season, but hardening of concrete at low temperatures is problematic. Crystallization of water leads to a decrease in strength, which negatively affects the quality of structures. The use of antifreeze additives in concrete will help to solve the problem, wide selection offered by the industry today.

The use of antifreeze additives allows pouring building mortars at temperatures up to -50ºС. They are liquid or powder formulations that are added to the mixture. It is important to know that concrete additives added during frost provide only 30% hardening. The final hardening occurs after the defrosting of the monolith.

There are several types of antifreeze additives that differ in the principle of action:

• Compositions that lower the freezing point of the liquid, as a result, the process of cement hydration continues, setting proceeds according to the standard mechanism;
• Additives based on sulfates accelerate the compaction of concrete, while generating excess heat, which increases the rate of hydration of the cement;
• Complex additives increase the solubility and activity of cement laitance, while the compounds that appear as a result of reaction with water reduce its crystallization temperature.

Varieties

There are various antifreeze additives, each of which has its own mechanism of action. A popular additive is sodium carbonate, otherwise known as potash. It is a powdery crystalline composition that accelerates hardening. concrete mix. The use of this type of additive reduces specifications material, including strength. To reduce this effect, sodium tetraborate is added to potash.

Attention! Potash belongs to dangerous substances, therefore, when working with it, safety requirements are observed.

Sodium tetraborate is a complex substance consisting of sodium and calcium salts, with the addition of ammonium. It is an additional antifreeze additive used with sodium carbonate. Without it, the structure can lose up to 30% of its strength after thawing and complete curing.

Sodium nitrite is an effective antifreeze additive that reduces the crystallization temperature of water, accelerates the hardening of the composition, and has an anticorrosive effect. Its use is dangerous, since sodium nitrite powder is a flammable, explosive, toxic substance. It is used in frosts down to -25ºС. It cannot be miscible with lignosulfonic acids, as it releases toxic gas when interacting with them. Calcium nitrite-nitrate has similar properties.

Sodium formate is an antifreeze additive for concrete that reduces the crystallization temperature of water and accelerates the hydration of cement. It is added in a proportion of not more than 6% of the total mass of concrete. To improve plasticization, naphthalene lignosulfonate is added to the additive.

Urea - PMD, prolongs the liquid phase of water, practically does not affect the setting speed.

Calcium and sodium chlorides, ammonia water reduce the freezing point, but have an increased corrosive effect. They strongly influence metal elements and therefore not recommended for use in reinforced concrete products.

How to use

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

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

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

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

Advantages and disadvantages of additives

The main advantage of concrete with antifreeze additives is the ability to perform work all year round. Picked up in correct proportion, they improve the adhesion of the components, improving the quality of the solution. They also have other advantages:

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

The use of antifreeze additives has its drawbacks. If used incorrectly, the strength characteristics of concrete are reduced, therefore, when working, it is necessary to strictly adhere to the instructions. Some additives are flammable and toxic, which must be taken into account when working with them. Even with additives, the hardening rate will be relatively slow in frost. To achieve the desired strength when laying in winter, it is required large quantity cement, which increases the cost of construction.

Do-it-yourself anti-frost additives

In private construction, if it was not possible to carry out all the work in the warm season, you have to continue in winter period. Therefore, it is allowed to prepare anti-frost additives for concrete with your own hands at home. To do this, you only need table salt or sodium chloride. Such an additive reduces the freezing point of water and reduces the time of critical solidification of the mixture.

To make a do-it-yourself antifreeze additive in concrete, salt is dissolved in water and added to the solution. The concentration up to -5 degrees is 2% by weight of the solution, up to -15 degrees, the mass fraction of chloride reaches 4%.

The disadvantage of this additive is its corrosive activity towards metal, so it is not suitable for reinforced concrete structures. It should be borne in mind that the rate of solidification of the solution at negative temperatures will be, on average, 3 times lower than under normal conditions.

Purpose and types

Hardening of concretes and mortars at low temperature occurs slowly, as the process of cement hydration slows down. Already at a temperature of - 3 ... - 6 ° C, water in concrete freezes, and the processes of hydration of the binder and hardening of concrete practically stop. When thawing, provided that the liquid phase is preserved, these processes are resumed, and the concrete continues to increase its strength. However, for concrete frozen in early age, after thawing and subsequent exposure, a loose structure, low strength and frost resistance are characteristic. This is due to the fact that freshly laid concrete contains a lot of water, which expands when frozen, loosens the cement stone and breaks the adhesion of the aggregate to the cement matrix.

You can buy antifreeze additives here: Petrovich , Stroyshopper , Stroylandiya

Therefore, to ensure the required set in winter time it is necessary to create such conditions under which the processes of hardening of the binder will actively proceed, i.e. it is necessary to ensure the presence of a liquid phase. This problem can be solved, for example, by keeping the concreted structure at a positive temperature. Such holding can be carried out when concrete is heated in a thermoactive formwork, using heated mixtures, followed by covering the surface of the structure. thermal insulation materials and in other ways.

In cases where such methods cannot be implemented at the construction site for technical or organizational reasons, it is advisable to introduce antifreeze additives- substances that lower the freezing point of water and contribute to the hardening of concrete at low temperatures.

Application of concrete with antifreeze additives carried out during the construction of monolithic concrete and reinforced concrete structures, monolithic parts of precast-monolithic structures, monolithic joints of prefabricated structures, in the manufacture of prefabricated concrete and reinforced concrete products and structures in a landfill at a steady average daily temperature of the outside air and soil of at least 5 ° C and a minimum daily temperature below 0 ° C.

Currently the most effective and field proven antifreeze additives are electrolyte additives: potash P, HH1, XK, NK, NNK, NNHK, their complexes NK + XN, NK + M, NNHK + M and others.

All of the above additives are both additives-accelerators of setting and hardening of concretes and mortars, however, their concentration in "cold" concrete is significantly (2...3 times) higher than that required to accelerate the hardening of concrete at temperatures above 0 °C.

In addition to those listed antifreeze additives also include:

Carbamide (urea) M. Colorless crystals of CO(NH 2) 2 , readily soluble in water.

Compound of calcium nitrate with urea NCM.

Sodium nitrite NN. Product in the form of NaNO 2 crystals white color with a yellowish tint, as well as in the form of aqueous solutions.

Accelerating antifreeze additive UPDM. Balanced by component composition a liquid mixture of waste products from the production of acetoacetic ester, acetylacetone and nitrochloractinide, taken in a ratio of 7:3:1 by volume. The solution is dark brown. The dosage is specified empirically within 0.1. ..0.42 l/kg of cement at ambient temperature from 0°C to -25°C.

Sodium formate alcohol FNS. Waste of petrochemical production, representing 30 ... 40% aqueous solution of sodium salts of formic and sulfuric acids. Straw to dark brown clear liquid. The recommended dosage is 2...6%, the admixture is introduced into the concrete mix with mixing water.

Asol-K. Product from organic and inorganic components: an aqueous solution of potash, corrosion inhibitors and modifiers. The additive provides hardening of concrete at temperatures up to -10 °C. At positive temperatures it causes rapid setting of mixtures (from 5 to 30 minutes).

Hydroconcrete - S-ZM-15. Antifreeze additive for concretes and mortars with plasticizing effect. Dark brown liquid 34...36% concentration. Provides hardening of concrete at temperatures up to -15 °C.

Hydrozyme. Liquid antifreeze for concretes and mortars in the form of a solution of 50% concentration. Provides hardening of concrete at temperatures up to -15 °C. Does not cause corrosion of reinforcement in concrete.

Lignopan-4. Antifreeze additive for concrete and reinforced concrete with plasticizing effect. Aqueous solution of 40% concentration. Provides hardening of concrete at temperatures up to -18 °C. Dosage: 2% at temperatures up to -5 °C, 3% up to -10 °C, 4% up to -15 °C.

WIN-Antimoroz. Antifreeze additive for dry mortars related to accelerators. The recommended dosage is 2...8% by weight of the components of the dry mixture, depending on the application temperature.

ammonia water. Product (NH 4 OH), which is ammonia gas NH 3 dissolved in ordinary water.

Additives of foreign manufacturers:

Betonsan. Dry salt-free antifreeze additive relating to accelerating modifiers for mortars. Provides hardening of concrete at temperatures up to -10 °C. Dosage: 1...2% of cement weight. Producer: CJSC "Company Convention Center".

Cementol B (Cementol B). Antifreeze additive-antifreeze for concrete and solutions. Provides hardening of concrete at temperatures up to + 5 °C. Recommended for concretes based on high-quality cement with increased exotherm. Dosage: 0.2...0.8% by weight of cement. Producer: Firm TKK (Slovenia).

economically rational antifreeze additive Ammonia water is the most important, since compared to aqueous solutions of potash and calcium chloride, it has a significantly lower percentage of volumetric expansion and therefore is the least dangerous in terms of possible deformations from the expansion of the liquid phase with the formation of ice.

Depending on the calculated minimum temperature outdoor air is assigned a certain concentration of the solution ammonia water mixing (Table 1). Unlike others antifreeze additives ammonia water not only does not cause corrosion of reinforcement, but can serve as an anodic steel corrosion inhibitor in reinforced concrete structures containing chloride salts. The additive does not impair the adhesion of reinforcement to concrete, does not reduce the frost resistance of concrete, does not cause efflorescence and the formation of spots on the surfaces of structures. Ammonia water somewhat slows down the setting time of cements, which makes it possible to maintain the workability of the concrete mix from 4 to 7 hours.

Antifreeze additives are allowed for use in heavy and light concrete (class B10 and above) in accordance with the "Guidelines for the use of concrete with antifreeze additives". indicative consumption of antifreeze additives depending on the design temperature of concrete hardening is presented in Table. 2.

The scope of antifreeze additives in concrete, presented in table. 3 is rather limited, which is explained by the following reasons.

Additives during curing of concrete can migrate and accumulate in separate zones structures (ribs, surface layers and other parts) with subsequent crystallization. These processes are intensified with multiple temperature drops, especially with a periodic transition to the region of positive temperatures, which is typical for the autumn-spring periods, as well as thaws in winter.

Table 2. Dosage of antifreeze additives

Notes.

1. *-ratio of components 1:1 by weight in terms of dry matter.

2. At a concrete temperature above - 5 ° C, instead of CN, it is possible to use HC (up to 3% of the mass fraction of cement).

3. The concentration of the mixing solution (taking into account the moisture content of aggregates) should not exceed,%:

They increase with decreasing relative humidity air, with an increase in the consumption of cement and antifreeze additives in concrete.

The process of salt crystallization occurs with an increase in volume, so their accumulation in individual zones of structures can lead to defects and destruction of these zones. Dangerous in this respect are additives containing potash and calcium nitrate. Due to the active participation of a number of additives in the processes of cement hydration, their optimal amount for a particular negative temperature, as well as freezing speed of concrete largely depend on the mineralogical and material composition of cement.

Most of the additives used form double salts, which are potentially dangerous components of cement stone during the operation of concretes with such additives in some aggressive aquatic environments. For example, sodium and calcium chlorides sharply intensify the corrosion process of steel in humid conditions with access to atmospheric oxygen.

Table 3. Scope of application of antifreeze additives

Note. "+" - allowed, "-" - not allowed for use, "+*" - allowed in combination with the addition of a setting retarder.

In some cases, the aggressiveness of chloride salts in relation to reinforcement and technological equipment can be reduced by using complex additives, including steel corrosion inhibitors. For example, with the simultaneous presence of nitrite ions in a solution at a mass ratio between HH and HK of at least 1:1, chloride ions become practically not dangerous for reinforcement. However, in order to exclude the possibility of a corrosion process, scope of antifreeze additives is significantly limited in prestressed structures, where such processes can cause catastrophic consequences associated with rupture or loss of the prestressed state of reinforcement in concrete.

Potash and calcium nitrate are neutral additives in relation to rebar. Sodium and calcium nitrites are inhibitors of reinforcement, but can cause stress corrosion cracking of thermally hardened steel, therefore their use is strictly limited in reinforced concrete products and structures with prestressed reinforcement.

Construction in modern world you can start not only in spring, summer and early autumn, but now late autumn and even in winter.

And this became possible with the invention of antifreeze additives. We will talk about this interesting additive later.

Application conditions

Such additives make it possible to use low-quality instead of expensive high-quality ones, and this makes it possible to reduce the cost of concrete products. Due to this, it is also possible to reduce the thickness of the product, for example, floor slabs, moreover, without compromising quality.

About the use of antifreeze additives

How to use

How to cook containing special additive?

An antifreeze additive is added to concrete along with other ingredients (sand, water, plasticizer). Better supplement add along with water, because the additive can replace water. Everything must be mixed well with a concrete mixer for an hour, until a homogeneous mass.

The additive is introduced into the mixture according to the instructions on the package. This amount is approximately 0.2% of the amount of cement at an air temperature not exceeding or decreasing the value indicated on the package.

In the event of a decrease in temperature, the dosage of the additive should be increased at the rate of 0.05% per degree. On the packaging, the dosage is indicated in grams.

In the event that the dosage of the additive is indicated in milliliters, then in order to determine the amount of the substance, its mass is divided by 1.45. The result obtained will be the volume in milliliters. Then we measure right amount and add to the mixture.

Antifreeze additives are used only at sub-zero temperatures. environment. They cannot be used under other conditions! After pouring concrete, structures made of this material are moistened for about two days.

Construction objects

The use of antifreeze additives makes it possible to build at any time of the year and under any weather conditions. Due to this, the construction time of facilities is reduced, as well as the cost is reduced due to rational operation. construction equipment and labor force.

Antifreeze additives are used:

• in the manufacture of heavy and light reinforced concrete structures,
• in the construction of monolithic reinforced concrete structures,
• it is added to
• when laying pavement and production of road elements,
• build bridges, oil and gas platforms, various buildings, dams, dams and much more.

Antifreeze additives are applicable at air temperatures from -15 to approximately -25 ° C, depending on the substance used.

Antifreeze additives are delivered to stores and retail chains in containers with a volume of 1 m3 or 5 liters each.

If you are thinking of building in the cold season, we recommend that you use antifreeze additives and be sure to carefully read the instructions on the packaging of additives.

We hope that this article was useful to you. We wish you good luck in your endeavors!

Features of concreting are that concrete base does not instantly become strong, but gains this indicator gradually. The process of curing is considered optimal if the concrete has reached the design indicator in 28 days. But this time indicator depends on some factors. And the most influential is the temperature and humidity indicators. Moreover, there is an opinion that it is impossible to pour concrete into a minus.

Features of concrete hardening

How does the strength of concrete take place? The simplest explanation is the loss of moisture from the concrete mixture. The moisture content must be distributed evenly, in accordance with regulatory requirements. And if the temperature is not optimal, but is approaching minus or negative?

In this case, the concrete will begin to harden within a few hours only due to recoil own heat and then there are two options:

• water in microcracks and pores will freeze and begin to expand, which will lead not to hardening of the monolith, but to its cracking;
• at very low temperatures the concrete itself will freeze and the process of curing will stop until it is completely thawed. Strength after thawing usually decreases, and the life of the entire structure becomes shorter.

Neither the first nor the second version of the builders are satisfied. Therefore, it is worth weighing the pros and cons of pouring concrete at sub-zero temperatures.

The organization of work depends on the grade of concrete being worked with. For different brands there is an indicator of critical strength, which sets the percentage of the design value at which freezing of concrete will not disrupt its structure so much as to affect the final strength value. For example, for the M300 concrete grade, this percentage is 40%, and for grades lower than M200 - 50%.

The task of the builders is to provide such conditions for concrete solidification so that it has time to reach critical strength before the moment of complete freezing.

There are several options for laying concrete at sub-zero temperatures, when the requirements for critical strength can be met:

• the use of electric heating;
• thermos method;
• the introduction of antifreeze additives;
• creation of shelters with the maintenance of a certain regime or a convective method.

Stage of production and transportation in winter

If you do not comply with all technological requirements at every stage of creation concrete structure in winter, you can lose quality even at the stage of mixture formation or its transportation.

The temperature of the transported mixture must be such that, at the time of its unloading at the construction site, it corresponds to the design temperature for a given brand and installation method. When using heating or additives, the concrete mixture can have a temperature of about 5 0 C, and if the thermos option is used, then it is necessary to provide a temperature of 25 0 C.

Note! High temperature reduces the mobility of concrete.

In order for the final product to have the required temperature, several technologies can be applied:

• use warmed up high temperature water;
• heat the aggregate - sand, crushed stone, gravel;
• steam heating of all components during mixing in a concrete mixer.

Note! In the manufacture of concrete on a construction site, the procedure is as follows: hot water is first combined with aggregate, and then only cement is introduced.

To maintain the temperature of the resulting concrete, the body is insulated in the machines or warm containers are used. But the most profitable way is to use truck mixers, when hot water right on the construction site.

In conditions when the mixture has cooled down during transportation, but has not begun to set, it is heated by electrodes to the required temperature.

Operation at sub-zero temperatures

It is impossible to avoid concreting at sub-zero temperatures, which means that it is necessary to reduce the time to reach the critical strength of the composition. In addition to the methods already listed, they often follow a simpler path and increase the grade of concrete, but this option requires careful calculations and selection of components.

With any method of concreting in winter, make sure that the temperature inside the entire structure is above 0 0 C during the entire time of gaining the required percentage of strength.

Creating an insulated protective structure or covering with a thermal film with a flooring of heat-insulating materials is considered the simplest. Sawdust, snow, peat serve as a material for flooring. They provide the necessary temperature, and only humidity control is required.

If necessary, bring the pouring of concrete at minus 5 0 C, insulation alone may not be enough. An effective option may become use electric current which will provide isothermal heating. In this case, the concrete mix itself becomes part of the electrical circuit like resistance. In her Electric Energy will turn into heat. Used as electrodes steel reinforcement. The electrodes themselves can be located inside the mixture and on its surface.

Electric heating is carried out not only with the help of electrodes. To do this, use several more methods and devices, such as:

• thermoactive formwork;
• electric reverberatory furnaces;
• infrared heaters;
• cylindrical resistance devices.

Any electrical appliance, steam generator, induction field can act as a heating device. The choice of instrument and heating method depends on the following factors:

• structure design, its geometrical parameters;
• index of critical strength of the composition;
• the presence of the required electric power.

Antifreeze additives

From the point of view of energy resources, the introduction of additives that increase the frost resistance of the concrete mixture is considered less expensive. Antifreeze additives can be up to 10% of the total volume of cement in the concrete mixture. They do not allow concrete to freeze and contribute to its strength development at temperatures below 0 0 С.

The most common chemical additives in concrete at sub-zero temperatures it is calcium or sodium chloride, sodium nitrate and sulfate, potash. AT reinforced concrete potash is used as an additive, which allows the mixture to harden at a temperature of -25 0 C. Sometimes you can use the so-called cold concrete. In it, the amount of additives reaches 15% by weight of cement. Such concrete is protected by a thermal cushion from all sides to ensure the same temperature throughout the structure.

It is impossible to use antifreeze additives if the structure itself will be operated at a temperature of more than 60 0 C or in an aggressive environment.

It is possible to carry out concreting work in the winter, but this is a rather costly and energy-intensive event. It may be worth waiting a bit to be able to comply with all technological requirements.

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

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

Application Benefits

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

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

The use of antifreeze additives allows:

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

Where is it used?

Antifreeze additives are used in the construction of structures:

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

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

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

Types of additives

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

plasticizers

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

Strengthening

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