Additives in concretes and solutions: types, characteristics.

Concrete is a building mixture that provides durability, reliability, and durability of the finished structure to impacts of any nature. Growing demands for building materials have caused the need to improve their properties. Special additives for concrete improve the characteristics of the mortar and, accelerate the pace of construction, reduce the cost of materials and energy. The question of which categories of additives exist is detailed below.

The use of chemical additives is a simple, affordable and effective way to improve the quality of concrete solutions. Their application today is important, as are the main components. Additives for concrete are designed for:

• achieve high performance of cement stone;
• acceleration or deceleration of hardening;
• improving water resistance;
• increase resistance to temperature changes and frost;
• elimination of the need for a metered solution supply;
• obtaining concrete with specified characteristics.

Their amounts for this or that mixture are selected under experimental conditions using SkyTrade technology.

Types of additives for concrete

There are two types of additives to concrete: liquid, powder. Mostly they affect the specific properties of fresh mortar - workability, the beginning of solidification. Additives in concrete must be added to the mixing water, or to the ready mix.

There is a separate type of specific additives - air-entraining, foam-forming. For example, an addition to the concrete of the squamotron, etc. This type of modifier is characterized by a complex action. It is added to improve several parameters at the same time. Additive for concrete significantly reduces costs, avoids the incompatibility of several individual additives.

Accelerators and retardants of hardening are also important. Popular additives for concrete of this category are such as calcium chloride, sodium sulfate, calcium and sodium nitrates. Multicomponent compositions include: calcium nitrite-nitrate, calcium nitrite-nitrate-chloride. Below is a species classification of additives.

Modifiers

  Complex protein modifier "Biotech".

Modifying compounds - a category of substances that improves strength, durability, resistance to low temperatures. They reduce the permeability of concrete. Working with a modified product is more convenient, as its mobility improves. The solution falls evenly, filling all the cracks and depressions.

Modifiers are classified according to the purpose of the concrete. For example, there are additives in concrete, designed for the construction of wells, swimming pools. Another type of additive is used in the construction of facades or the formation of floor screeds. Such a regulator, improving the performance of the building mass, reduces its moisture permeability.

Plasticizers

This group is the most in demand. There are four:

1. Strong.
2. Weak.
3. Medium.
4. The newest superplasticizers.

Additives of the latter category include substances for the integrated solution of the tasks that have been set, increasing several characteristics of the cement mass. Depending on the scheme of exposure to concretes and process chemistry, plasticizers are:

1. Increasing mobility with an unchanged amount of water.
2. Reducing the consumption of cement to 10% without changing the mobility.
3. Increasing strength with constant mobility.

Additives are characterized by such advantages as:

• saving consumables;
• improving mobility of sand-cement;
• increase in reliability by 20-25%;
• production of workable mass;
• possibility of pouring thin-walled or densely reinforced structures;
• compaction of cement composition;
• improvement of frost resistance and crack resistance;
• saving energy by reducing the time to obtain a cement mass.

Lack of plasticizers - speeding up the curing speed. Therefore, additional chemistry for concrete is recommended, which accelerates this process. The resulting concrete is widely used in structures where perfectly flat floors and walls are needed.

Antifreeze

Additives for concrete and mortar are necessary to reduce the freezing point of water, which is included in their composition. Chemistry, which increases the antifreeze characteristics of these products, facilitates the process of laying the solution, accelerates the process in the cold season. These indicators allow you to save consumables, extend the life of the finished product. Cement is frost-resistant. Sodium nitrite is the most popular filler material. Other air entraining components are also available.

Mobility regulators

These specific additives, added in order to maintain the plasticity of the solution under adverse conditions, are actively used in hot summer. Concrete regulators are also suitable for transportation of mortar for a long time. Regulators improve the convenience of solutions when laying floor screeds.

Additives in concrete for strength

One of the types of complex action additives are fortress accelerators or concrete hardeners. They are endowed with the qualities of both superplasticizers and hardening accelerators. They include organic and inorganic compounds without alkalis. Accelerators have a wide field of use in construction, industry, road and transport when they receive a commodity product or area where they are needed.

Chemical additives

There are several target categories of chemical additives blended into the concreting solution. Classification is based on the effect they have.

1. Concrete modifiers of mobility and plasticity of the mixture.
2. Substances to reduce moisture evaporation from solution.
3. Waterproofing additives.
4. Concrete stabilizers of the process of delamination of sand-cement mass.
5. Hardeners.
6. Retardation retention.
7. Antifreeze additives.
8. Pen- and gas generators.
9. Protective connections.
10. Air-entraining compounds.
11. Concrete additives that improve the resistance to corrosion, the effects of living organics (mold, fungi).

Chemical substances can affect several properties, but there will be only one. The principle of the action of additives is similar to that of surfactants and can form a material with a spatial structure. This category includes additives based on nitrite compounds. Such chemistry is very dangerous, therefore it is necessary to work with it cautiously, being guided by instructions скайтрейд.

Anticorrosive

Modifying products give durability to concrete under the influence of fresh water-filter, aggressive liquid, which causes corrosion of the material. These additives to concrete solve several problems:

• prevent the dissolution of the constituents of the finished stone;
• prevent washing out of reaction products of concrete and water;
• protect the surface from crystalline, hardly soluble formations, leading to the destruction of the stone.

During the action of anticorrosive chemicals, complete or partial binding of free calcium hydroxide in concrete is carried out. The additive is admixed in order to increase the density and moisture resistance of the stone, reducing the pore volume in its structure. Due to this, cements are endowed with hydrophobicity.

NitCaL is a specially developed nitrate for speeding up a set of strength, crack resistance, production of high-quality monolith and reinforced concrete, preventing corrosion processes of reinforcement in concrete.

Additives for self-compacting mixtures

A specific type of additive is used when pouring thin-walled structures. This category includes some new superplasticizers that improve both reliability and density from the finished product. Concrete regulators allow to reduce the consumption of cement without loss of quality of the received design. Chemical modifiers of this type raise the grade of the mixture and the speed of the set of the fortress at the initial stage of hardening.

Complex additives for thin-walled and thick-reinforced products greatly simplify the process of selecting the necessary components and determining their compatibility. Stabilizing superplasticizers are designed to solve several problems by adding only one substance. Their goal is to obtain the maximum effect from interaction with the components of the mixture.

Examples of manufacturers

The domestic market offers a wide range of products of Russian brands such as Polyplast, Superplast, Technotest, MetaPro, Coral, Master. Chemistry from foreign manufacturers is not endowed with the required ability to increase the strength of concrete used in the domestic construction industry. The BASF concern produces products that are interesting for the domestic market.

Conclusion

A wide range of modifying chemicals allows you to choose the product that will best meet the requirements of each specific case, increase the efficiency of sand and cement, and extend the operation of the finished product. However, when working with cement additives, it is important to follow the recommendations and instructions for the proportions used by the specialists of the Skytrayd. The desired effect will not be achieved if a disproportion or disruption of the cooking sequence is tolerated.

In any case, the amount of all additives used for a single volume should not exceed 1.5-3% of the cement mass. Despite its positive effect, the use of modifiers does not exclude the importance of observing the exact technology of preparation, mixing to homogeneity, masonry and aging of the building mass.

Concrete, prepared on the basis of high-quality cement and high-quality fillers, has sufficient strength without adding additives. Nevertheless, there are a number of factors when, in terms of operation, concrete hardening is required by adding special additives.

Why additives?

To increase the strength of highly loaded and special concrete structures, special additives are used, which are added directly to the prepared cement-sand or concrete mortar.

After setting and hardening, the mixtures in which the reinforcing additives were added acquire additional operational properties: water resistance, corrosion resistance, frost resistance and significantly higher compressive strength and bending strength.

Given the relatively high cost of concrete and cement mortar with additives, their use is economically feasible in the following cases:

• Increased requirements for frost resistance and water resistance of concrete structures;
• Use as a filler of non-standard materials. For example, very fine sand;
• Manufacturing of high-loaded reinforced concrete products. For example, the production of paving slabs, foundation blocks, etc .;
• Preparation of fine-grained concrete;
• Building of monolithic buildings and structures, in which expansion additives are used.

Types of reinforcing additives for cement

Plasticizer. At this point in time, the best additive in cement for strength, increasing the strength of the construction is on average 125-140%. The main task of the plasticizer is to increase the mobility of the solution.

Also, the use of an additive of this kind allows to increase the frost resistance of concrete by 1,5 marks, water resistance to 4 marks and to reduce the consumption of the binder by 25%. A popular "folk" plasticizer is a usual liquid soap or detergent powder.

Strength accelerator. The additive task of this type is an increase in the speed of setting and hardening of concrete and a corresponding increase in its vintage strength for bending and contraction.

The most popular and most inexpensive accelerator for durability is conventional calcium chloride. Used in the production of: paving slabs, foam concrete blocks, wall and foundation blocks, polystyrene concrete, etc. Thanks to the use of accelerators, hardening significantly reduces the time of its exposure in the mold. Accordingly, the productivity is increased, the yield is improved, and the strength of reinforced concrete is increased by several percent.

Antifreeze additives. In accordance with the name, the purpose of the antifreeze additive is to allow the concrete works to be carried out in conditions of low temperatures (up to minus 25 degrees Celsius).

In parallel with this, there is an increase in the strength of concrete, increasing water resistance, reducing the delamination of finished concrete during transportation, and improving workability. The most popular antifreeze additive is a neutralized resin in a mixture with Sofisil-gel or Tiprom-S hydrophobizer.

Complex additives. Accelerate hardening, increase strength, significantly reduce dust separation, increase frost resistance. In particular, due to the use of a complex additive, it is possible to achieve: increasing the strength of concrete by 70-110%, with the same mobility, reducing shrinkage by 60-70%, and two-threefold increase in water permeability. One of the most popular types of domestic complex additive for concrete is the additive "Elastobeton": A, B or C (depending on the purpose of the concrete or building).

Subtlety of application

All types of additives in concrete should be diluted or dissolved in warm water. If the additive is mixed with the cement-sand mortar in the liquid aggregate state, it starts to work immediately after addition.

Dry additive will start to "work" only after complete dissolution and thorough mixing. Dosage of additives depends on the specific material, specific tasks and requirements of the manufacturer's instructions. In general, the amount of additives should not exceed 1% by weight of the binder (cement).

Often, construction companies and private developers are forced to go for additional costs - add special reinforcing additives to concrete or concrete mortar. Due to this, building structures acquire additional strength, durability and other useful qualities.

In connection with the fact that the introduction of additives leads to a significant increase in the cost of the final material, it is worth mentioning the main cases in which it is required to introduce reinforcing and other additives into concrete:

• Increased requirements for strength, waterproofness and frost resistance of building structures;
• Use as a filler of fine sand;
• In the manufacture of products experiencing increased mechanical and abrasive loads: paving stones, curb stone, paving slabs;
• The erection of buildings and structures using monolithic technology.

Additives in concrete for strength improvement  are special chemicals added to concrete at the time of mixing with the main fillers. Depending on the purpose of the additive for concrete and reinforced concrete solutions are divided into the following types:

•   . The main purpose of the plasticizer is to increase the mobility of the material. At the same time, concrete with a plasticizer has a higher final strength than a structure filled with concrete without a plasticizer. Increase strength up to 25%. In passing, the consumption of cement is removed, on average by 15%, water resistance, frost resistance and crack resistance also increase. The most common plasticizer - "S-3" from the company "Polyplast";
• Strength accelerator. It is a complex chemical additive based on aqueous solutions of chloride salts (sodium, calcium and others). The salt solution acts on the concrete mixture, activating the clinker hydration processes. This results in a significant reduction in setting and hardening time. The use of a strength accelerator allows: to increase the vintage strength of concrete by several percent, to reduce the amount of water for mixing and to significantly speed up the process technologically. The additive is used in the manufacture of paving slabs, commercial concrete and various types of concrete products. The most widely dispersed hardening accelerators are the line of additives "Relaxix" and "Economix" from the company "Polipast";
• Antifreeze additives. This kind of additives not only increases the frost resistance and waterproofness of the concrete structure, but also significantly increases its strength due to the so-called formation of the primary structural framework of solidified concrete, which is surrounded by calcium hydrosilicates. Thanks to the latest factor, the use of antifreeze additives makes it possible to reduce the "material consumption" of the filling by 5-10% due to the reduction in design dimensions of the structure. The most common antifreeze additives: potash, carbamide, calcium nitrate compounds with urea,

Although it is said that the best is the enemy of the good, but the technology of our Company is not considered so. Practically no modern enterprise that carries out the production of concrete products, cement or concrete mixtures can not do without the use of special additives for concrete, which significantly improve the quality and characteristics of the mixture and regulate the processes of setting the cement and hardening it.

It would seem, why these additives for concrete, if made on modern equipment, and during its production, all the norms and requirements for the time and thoroughness of mixing were not violated, the composition of the mixture was observed, quality fillers were used: cement, sand, gravel, water? A good concrete mixture is good in itself, but if it is possible to make it better: to increase strength, to make it more mobile, to increase its moisture resistance, frost resistance, crack resistance, protection from salts, oil products, etc., why not do it ?

Modern, reinforced concrete and cement for this and modern, which takes into account all the opportunities and nuances that make the product "faster, higher, stronger." Here, special concrete additives affect the behavior of cement in various stages of setting and hardening, and affect the quality characteristics of the made, or monolithic reinforced concrete structure, during the whole period of operation to help the plants producing concrete products and various concrete plants.

Let's look at the main types of chemical additives that are used in modern concrete and concrete products. They can be divided into groups:

• additives to concrete that regulate the basic properties of the mixture, such as mobility, ductility, water retention, pore formation, etc.
• types of additives regulating the retention and responsible for the rate of hardening of concrete, the speed of setting the cement, mainly affecting the process of hydration in the initial stage of setting, hardening and strength strength of concrete.
• additive for reinforced concrete or reinforced concrete special properties: polymer, biocidal, etc.
• antifreeze additives for concrete, allowing to produce concreting at sub-zero temperatures.
• additive to concrete, increasing its strength, frost resistance, corrosion resistance.
• corrosion inhibitors of steel, because steel, which is part of any reinforced concrete or monolithic reinforced concrete, is subject to the destructive effect of aggressive environments in which many reinforced concrete structures have to work.
• expanding additives in cement, reducing shrinkage, increasing crack resistance, creating self-stress of reinforced concrete and monolithic reinforced concrete structures.
• coloring additives.
• additives in concrete for waterproofing, to which can be attributed various colmatizing additives, water repellents and other means of reducing the permeability of the concrete structure.
• various porous types of additives for lightweight concretes: gas-forming, air-foaming, foaming, etc.

If we have so many groups, how many supplements will there be? Immediately I will say - a lot! Enumerate them all - hardly enough time and effort. We will single out only the basic ones, which can be useful to a wide range of builders. Probably not to the point, if I say that, or rather, its more advanced heir - is the most used additive for concrete used today for the production of concrete mixtures. In any case, the company Besto plasticizer c-3 is used almost always. In general, chemical additives that contribute to reducing water content in concrete mixes are most in demand. There are a lot of advantages from their use, namely: the fluidity of the concrete mix increases without adding excess water, it becomes more plastic, it saves cement, increases density, water resistance, frost resistance, etc.

Here, special additives for concrete come to the rescue - plasticizers, which began to be used since the forties of the last century. To date, we are basically dealing with their new version, the so-called superplasticizers. They appeared in the USSR in the early eighties. Unconditional leader here - plasticizer c-3. One of the main producers of superplasticizer c-3 is Polyplast. What is so good for plasticizers, let's have a look:

• Saving of cement. To obtain an equally strong concrete of the same mobility with the use of the plasticiser c-3 and without it, one cubic meter of concrete mix consumes 15% less cement. This magnificence is achieved by reducing the amount of mixing water. But in order to maintain the necessary mobility of the mixture, producers necessarily introduce superplasticizers or plasticizers in concrete. Thus, the water-cement ratio is simultaneously reduced and the mobility is not reduced.
• Without compromising the strength of future reinforced concrete products and reinforced concrete structures, the mobility of the mixture increases. That is especially important for monolithic construction, where concrete pumps are used in full and requiring concrete p4-p5 (sediment of 16 cm) for normal operation.
• Increase of final strength characteristics up to 25%.
• Due to the improved workability, there is no need to vibrate the freshly mixed mixture!
• The possibility without any problems to fill the thick-reinforced structures: columns, narrow formwork walls and so on.
• The preparation of compositions of increased density (high impermeability), which positively affects the waterproofness of reinforced concrete and reinforced concrete structures in general.
• Increased frost resistance up to F350 and crack resistance.
• Reduces the shrinkage of hardening concrete or reinforced concrete.
• Possibility to receive high-strength reinforced concrete and concrete, with compressive strengths over 100MPa! For example: a concrete sample of brand m-350 (B25) 28 days old has a compressive strength of only 25 MPa. That is - four times less. Applying special modifiers it is possible to obtain a mixture with a branded strength exceeding the brand of cement used for sealing.
• Plants that produce concrete products benefit from the use of plasticizers due to a reduction in the time of steaming or a decrease in the temperature in the chambers. And this is a significant saving of energy resources, acceleration of the turnover of the molds and, as a consequence, an increase in the volume of production.
• Increases the adhesion of reinforcement with concrete as much as 1.5 times (if not physicists-chemists lie, of course)

It seems to me that the above pluses are enough to understand that producing concrete mixtures or reinforced concrete without plasticizers is not the most profitable measure. However, there is a fly in our barrel of honey. A little one, but there is. And this tar is an insignificant slowing of the timing of setting and hardening of the concrete structure. It can be considered a negative effect, it may seem to someone and positive, but the essence is one. To compensate for the retarding effect of plasticizers, a special additive for concrete is sometimes added-a hardening accelerator. It also compensates for everything that has spoiled the plasticizer, namely the graph of the normal hardening of the cast design.

At present, complex types of additives to concrete are increasingly being used. As a rule, they are two-component. For example: at the base plasticizer c-3, and in the appendage accelerator hardening, or air-entraining additive, or microsilica, etc. Thanks to such combinations, concrete plants receive high-strength mixtures with unique characteristics.

Other types of additives for concretes and mortars

Accelerator hardening concrete   To compensate for the action of the plasticizer, which slows down the hardening process a little, special additives are sometimes introduced-hardening accelerators. In the same way, hardening accelerators can be used for non-standard fillings, when quick setting of the lower layer of the concrete massif is required so that it is possible to continue casting without problems. A classic example is a monolithic basin bowl, when in the combined bottom and pool formwork it is necessary to lay the concrete mix so that when pouring into the walls it does not squeeze out its freshly cast bottom with its mass. Usually, this process is stretched in time, but it can be significantly reduced if using concrete hardening accelerators. Another area of ​​application of accelerators is concreting in cold weather. After all, the lower the ambient temperature, the slower the process of hydration of cement, the beginning and the end of setting and the strength set take place at a slowed pace. Accelerators also help here.

Modifiers of hardening concrete   By name it is clear - what do these kinds of additives do. They are used to increase the lifetime of the concrete mix. Basically, this may be necessary for transportation to long distances, when it is not possible to fill quickly and so on. That is, with the use of hardening retarders, we take a time out to do something: eat donuts, drink beer, sleep until the concrete rest in a tub or trough. Moreover, this pleasure stretches for several hours. Something like this. In the group of retarders can be attributed douche. They also have a slowing effect.

Air-entraining additives   As you already understood from the title, they "involve" the air. When mixing the mixture, millions of minute microbubbles of air are created. What is it for. The main task is the creation of a microporous structure in concrete or reinforced concrete. Do you remember porous chocolate? That's the same thing, only the pores are microscopic. Due to the presence of these very pores, the frost resistance of a concrete structure or reinforced concrete is increased. Why? Yes, because the water soaked in concrete construction, when freezing, there is much to expand. In those same pores. Cheap and angry.

However, and here not without tar. Cement stone is protected from destruction, but there are no fillers. Crushed stone also gets from frost and water, as well as without magic bubbles. But this is a completely different song. Of the minuses of such additives is a decrease in the strength of the concrete structure. Slightly, but there is. In any case, high-strength with such additives you will not do. And frost resistance can be increased by other methods, for example: to lower the water-cement ratio, or to introduce fly-ash in the mixture, with the same amount of cement. This significantly increases water resistance (W coefficient in the labeling of mixtures) and density. Water simply does not enter the concrete structure.

Antifreeze additives for concrete The main purpose of antifreeze additives (PMD) is to provide the possibility of winter concreting at sub-zero temperatures and the absence of additional heating of the filled structure. Some types of additives allow concreting at temperatures up to -25 degrees. This "tin" of course, but if there is such a need, then there is no choice. So how do antifreeze additives work? Those who are familiar with the "subject" and so it is understandable, I will try to explain to the rest in several phrases.

The main essence of the solidification of mortar or concrete mixture is the so-called. Simply - the process of crystallization of minerals (silicates, aluminates) present in cement, when it interacts with water. The speed of this process depends significantly on the temperature of the surrounding air. At low positive temperatures, the process of setting cement expands in time (several times), at negative temperatures it stops at all, for the simple reason that the same water freezes. Here with two of these mucks and struggles, by virtue of their capabilities, a frost-free additive for concrete.

The main tasks of modern antifreeze additives are to shorten the setting time of cement and accelerate the hardening time of concrete (at low temperatures), lower the freezing point of water. In Russian, to put it so that the water freezes not at 0 degrees, but at -10 or -20. Perhaps remember that salted water is a classic example of lowering the freezing point. There is another task for modern antifreeze additives - do no harm. Just like Hippocrates: "... in accordance with my strength and my understanding, refraining from causing any harm ..." And they can do harm. Not all, but they can.

There are quite a few myths about the harmfulness and usefulness of these or those antifreeze admixtures for concrete. They are credited with all the terrible sins: and you are corroding the reinforcement, and reducing strength, and reducing frost resistance, and even the dog knows what's coming to mind. Unfortunately, I'm not a chemist or a natural scientist, but I'll try to summarize what I once read, heard and myself tried.

Myth one: when using antifreeze additives, in monolithic reinforced concrete or self-made concrete products, corrosion of the reinforcement occurs. This myth came to us from distant times - "when the trees were big." Take the most common sodium nitrite in Russia, so on the contrary it is a corrosion inhibitor. Many antifreeze additives have a positive effect on the adhesiveness of reinforcement to concrete. I'm not talking about modern complex supplements.

Myth number two: reduction in strength. At normal% introduction of additives to concrete, some lag in the rate of the set of strength is observed, but after reaching the classical adolescent age of 28 days, the lead of the laboratory no-additive concrete sample (hardening at +20 degrees) comes to naught, and further a greater increase in brand strength is observed in concretes with antifreeze additives. Here is your grandmother and a decrease in strength.

However, do not forget about the abnormal% introduction of additives in concrete. That's where the possible troubles lie. Here, the conversation can take a long time, if you start remembering all the techniques of early freezing, etc. Therefore, we will manage with two cues. With insufficient introduction of PMD, the mixture is frozen, the process of hydration of cement stops and resumes only with the arrival of a temperature sufficient to thaw the frozen liquid. In most cases, this is painless. Unless of course it's a bridge and not carrying a bolt, which managed to load something heavy over the winter.

At absolutely no-additions of concrete, accidentally frozen with a sharp drop in temperature, things are somewhat worse, but also quite tolerable, provided that the cast structures are not loaded. However, much depends on the size (volume) of the cast iron ore. Again, it is important - when concrete was frozen: at what stage it was, whether the critical strength had accumulated; whether the water (rain, snow melting) worked on the uneven concrete surface, etc. Here, perhaps, loss of strength on average to 20% and in some cases a decrease in frost resistance of up to 50%, as well as exfoliation of the upper layer, erosion, etc. is possible.

If we consider the results of laboratory and full-scale tests, it can be concluded that the antifreeze additive for concrete (especially complex) positively affects the resulting characteristics of the concrete structure, or reinforced concrete. The density increases (water resistance), a positive inhibitory effect on the reinforcement is promised, the design strength is increased in comparison with no-additive concrete.

Again, all this is possible under one condition, that the additive is not left. If there is no certainty, then the risk is similar to "Russian Roulette". There is a time-tested Polyplast, but where is the guarantee that it's Polyplast, not Ravshanplast bottled in a nearby hangar on the construction market. Counterfeit is our common misfortune. One thing Cherkizovsky Gocha and Cardin, and quite another - when the ersatz product concerns health and construction. If you think about the possible consequences, it becomes a bit uncomfortable.

Supplements of course a lot. List them and describe - the task is not easy. I mentioned only the most used ones. As far as possible and effort, I will try to supplement this page in due course with a description of the currently ignored compositions. In the meantime, that is - that is. With superplasticized non-freezing greetings, Eduard Minaev.

Concrete is the most famous and often used building mix consisting of cement, aggregate and water. But since it is used not only for the construction of walls and ceilings of residential and public buildings, but also for hydraulic structures, foundations, special purpose structures (bridge supports, viaducts, etc.), in each individual case a substance that has a common name "concrete" can not be the same.

Each time when designing objects, the design is calculated taking into account all the conditions not only for their construction, but also for further operation. And since the operating conditions are different, then the concrete solution must also be different.

Therefore, to give concrete the right properties, various additives are used, which change not only the properties of the liquid concrete mixture, but also the hardened concrete itself.

Additives for concrete - classification

There are a lot of additives, that's why they classify them in different ways. The following is one of the most commonly used classifications:

1. Modifiers of concrete - able to increase the strength of the concrete mixture and its frost resistance, reduce its permeability, extend the operational life of the finished concrete mixture. At the same time, they do not reduce the mobility of the mixture, which increases the efficiency of its use and facilitates the production of work.
2. Mobility regulators - they are used in hot weather or in cases of prolonged transport of concrete in order to maintain the necessary ductility.
3. Plasticizing additives. Their use makes it possible to reduce the consumption of concrete, without reducing its strength. They also provide an opportunity to improve the mobility of the solution, increase its density, and in some cases, waterproofness.
4. Antifreeze additives - used in the laying of concrete in the winter at temperatures up to -15 and even to -25 degrees.
5. Additives for self-compacting concrete - use, if necessary, pouring thin-walled concrete structures.
6. Additives to accelerate the recruitment of strength - improve this figure in the first day after laying the mixture, as well as increase the strength of the already hardened concrete.

There are situations when it is necessary to improve several parameters of a concrete mix. Then, complex additives are used that can affect several indicators at once.

The use of several additives in this situation can lead to unpredictable results, and correctly dosed complex preparation guarantees the necessary quality of concrete.

All substances added to the concrete mixture can also be divided into 2 large groups:

1.   (powders, emulsions and aqueous solutions) - are introduced into concrete in small quantities.
2. Thin-hulled substances (fine-grained minerals) are used when it is necessary to save cement and obtain stable dense concrete.

Chemical additives  subdivided by the effect they have on the concrete mixture:

• hydrophobizing;
• increasing plasticity and mobility of the mixture;
• antifreeze;
• reducing the separation of liquid from solution;
• stabilizers, not allowing liquid concrete to separate;
• curing accelerators;
• regulators of deformation processes;
• retarders of setting;
• gas and foam forming additives, increasing the porosity of concrete;
• increasing resistance to corrosive environments, corrosion.

Modifiers of concrete

These substances are intended for the production of concretes of special purpose with high technological properties: low water permeability (grade not lower than W12), high strength (up to B125), corrosion resistance and durability.

Some modifiers are designed to produce expanding, tensile and shrinkage-compensating concretes and solutions.

These additives are mainly used for the manufacture of normally and prestressed products by vibration pressing and molding methods.

Mobility regulators for concrete mixes

They are used in those situations where it is impossible to organize the production of concrete mix of the right quality directly next to the construction site and have to transport concrete from afar. These substances are also necessary when the production technology provides for a long process of laying the mixture.

Usually, these substances are part of complex additives.

They are produced from:

• inorganic substances;
• organic materials;
• organomineral combinations.

Natural additives are produced mainly from agrochemical, petrochemical and timber processing waste.

Additives of inorganic origin are made on the basis of concentrates of formaldehyde and naphthalenesulfonic acid.

They give the mixture the following qualities:

• high fluidity;
• increased strength;
• resistance to temperature changes.

These substances reduce the cost of concrete work, reduce the consumption of cement in the manufacture of concrete, positively affect the adhesive properties of the reinforcement (improve the adhesion of reinforcement with concrete).

In such works as filling columns or thickly reinforced structures, the use of these substances is mandatory.

Antifreeze additives

In the cold season, the hardening process of concrete is significantly slowed down, which has a very negative effect on its strength indexes - concrete becomes loose, and its frost resistance index decreases.

If there is no possibility to use concrete heating on the construction site, then they use that reduce the freezing point of water and, thus, normalize the hardening process of concrete.

Antifreeze additives are a liquid with a density of about 1.4 l / kg with a mass fraction of calcium nitrate from 42 to 45% and activity of hydrogen ions from 5 to 8 pH. The color of the additive depends on the manufacturer and can be light gray, yellowish and even dark brown.

These additives have the following effect on concrete:

• accelerate the set of strength;
• increase the waterproofness of concrete;
• increase its mobility;
• the corrosion inhibitor contained in the additive protects against oxidation.

The use of antifreeze additives prevents the appearance of highs on the surface of the concrete structure, increases its strength, allows the use of lower grades for the mixture of cement, which reduces the cost of concrete products.

These substances are introduced into the concrete mixture when pouring monolithic and prestressed products - bridges, dams, dams, oil and gas production platforms.

The main requirement for these concretes is their stability to water separation and delamination.

Such concretes are used in densely reinforced structures, where conventional compaction of the mixture is not possible, so concrete is necessary, which can be compacted only by posing by its own weight.

In these concretes, hyperplasticizers are added, which make it possible to produce concretes with ultra-high performance properties.

They are used for the construction of monolithic seamless high-strength, shotcrete, reinforcement and restoration of structures.

Additives to accelerate the recruitment of strength

Most often, aqueous solutions of calcium chloride, sodium chloride and other chloride salts are used here. They accelerate the hardening of concrete and are used in the construction of the following structures:

• prefabricated reinforced concrete structures;
• thick-walled and thin-walled structures;
• products of non-standard forms;
• swimming pools.

All these substances are used mainly in the industrial production of concrete and products from it. In private house-building, the most used are the anti-freeze additives and hardening accelerators of the concrete mix.

What to consider when using additives for concrete

When buying an additive, pay attention to the manufacturer. Many import additives are designed only for concrete, made from high quality components, which are rarely used. It is better to buy a domestic supplement of a reliable manufacturer.

When mixing concrete with additives yourself, you need to carefully observe the proportions, otherwise you can get poor quality concrete.

Also study, in what way it is necessary to drive the additive - some are introduced with water, and others require preliminary mixing with one of the dry components of the mixture.