Foreign additives for the destruction of concrete. Additives in concrete and mortar

Concrete is a multifunctional building compound of cement, water and aggregates. It is used to create artificial stone surfaces, the properties of which it acquires when completely solidified.

By itself, it is extremely stable, strong and durable, but to enhance individual qualities, there are now a huge number of TYPES OF ADDITIVES FOR CONCRETE on the market.

If the use of these components is often neglected during the internal repair of an apartment, then they are simply necessary when repairing airfields, swimming pools, roads and piers.

Such an additive should be used if the simultaneous use of several additional components is required, but their self-mixing can give an unpredictable result.

Still to be remembered

Also, do not mix additives from different countries of origin, because. no one can guarantee a positive result. Until the end of the work, it is advisable to keep all receipts or photos of the concrete additive, as well as other components, in case you need to buy some material.

Plasticizers for concrete

This is the most common component mixed into the concrete composition. They are divided according to the degree of manifestation of properties. They have been used in our country for about 60 years, but in recent years their quality in the competitive market has developed greatly.

The main advantages of such mixtures include savings in the base material, increased strength by about 20%, and ease of use.

With the use of such an additive, it becomes possible to fill thin and reinforced structures, increase resistance to temperature extremes, and also save energy for cooking in specialized equipment.

The disadvantages include the extension of the hardening of the composition. In case of limited time, it is better not to mix this additive with a hardening accelerator, but to purchase a complex one at once.

Curing accelerators and retarders

Accelerators are used for pouring reinforced concrete and non-standard structures when a rapid increase in the number of layers is required. It is also often used when pouring pools, so as not to waste extra time waiting for several layers to harden first on the bottom, and then also on the walls.

This additive is very popular for outdoor work in winter, because. the composition contains salt that prevents the freezing of water, and in the future - the formation of cracks.

It is also advisable to use it for large thicknesses, when concreting takes place continuously, in order to avoid delamination of the concrete.

Air-entraining components

Required to increase the porosity of the finished layer, mainly in the northern regions, so that additional voids do not form during freezing and thawing. Basically, this additive is used only for the top layer or exterior finish.

Frost-resistant additives

Antifreeze additives are not designed to enhance the resistance of the finished coating, but specifically for construction work in cold weather, when water solidifies faster than concrete hardens.

The most powerful additives allow construction at temperatures up to -25 degrees.

Modifiers

Such a component is classified into many subspecies, depending on the purpose.

It is used to give a mixture of certain properties necessary for a particular structure, so both the well and the facade of the building are built on the same concrete composition with different modifiers.

Of course, there is an even larger list of various admixtures for concrete on the market, which allows you to choose the necessary components for any specific case.

Photo of additives for concrete

Any modern construction is not complete without the use of special additives for concrete mixtures and cement masonry mortars. Additives are needed to modify concrete and mortars in order to give them certain properties that simplify work and improve the quality of construction. In this case, a number of errors are made that can lead to negative results. In particular, the use of an excess amount of water, in order to increase the workability of the mixture, and the use of household detergents as additives.

In this part of the training course, we will talk about how the use of special plasticizing additives allows you to get a plastic mixture and at the same time avoid a drop in the strength of concrete.

• Why can't concrete be modified with excess water.
• What are plasticizers for?
• How additives change the properties of concrete and masonry mortars.
• What additives should be used when carrying out monolithic and masonry work.
• As additives, it is possible to avoid the appearance of efflorescence on facing bricks.

Why Excess Water Reduces Concrete Strength

Concrete is a composite material consisting of cement, crushed stone, sand and water. Cement is the main component of concrete, because. when the mixture is mixed with water, a hydration reaction occurs. Those. the so-called. cement adhesive that binds all other fillers to each other. After hardening, a durable artificial material is obtained - cement stone.

Water is the cheapest component in the concrete mixture and at the same time a plasticizing element. This is often used by negligent or inexperienced builders, adding excess water to the mixture, because. the more water, the more mobile, which means that the concrete is more workable.

Such an approach leads to negative results. Important: the more water in the concrete, the less durable it becomes, i.e. its value drops. Its durability, frost resistance and water resistance also decrease. The addition of excess water leads to stratification of the concrete mix, strong shrinkage and increased cracking of the structure.

Concrete parameters are characterized by class and grades: B (concrete class for compression),F (mark for frost resistance),W (mark for water resistance and P (mixture mobility P1-P5). The higher the mobility grade, the more mobile (liquid) concrete mixture. It is convenient for builders to work with a mobile mixture, for example, laying concrete in a densely reinforced structure. But for concrete hardening it is necessary a certain amount of water, and the more "extra" water there is, the more pores will remain, therefore, the strength of concrete will decrease. Therefore, each composition of the concrete mix must be correctly calculated. Moreover, in different designs, depending on their purpose, a certain strength of concrete is required.

Why use plasticizers

In pursuit of plasticity, as mentioned above, builders often pour additional water into concrete, which further leads to a decrease in the strength of, for example, a foundation. At first glance, it seems that in order to avoid this, it is necessary to reduce the amount of water, because. it does not require much for the hydration reaction to proceed.

But, insufficient plasticity, the so-called. "hard mix", in turn, can also lead to voids, since the concrete mixture simply cannot penetrate through the thick reinforcement in the structure. Therefore, it is necessary to use an additive for water reduction, i.e. reducing the amount of mixing water while increasing the mobility of the concrete mixture.

Kirill Lebedev

Depending on destinationadditives , as plasticizing components, manufacturers use various chemical compounds. Additives are classified into: plasticizing, slowing down and accelerating setting (hardening), antifreeze, allowing work to be done in winter, etc.

The required amount of additive must be calculated from the mass of cement, and not from the mass of the finished mixture. Plasticizers also help reduce cement consumption.

In addition, the concrete mixture with a plasticizer does not stick to the walls of concrete mixers, it is easier to be supplied by a concrete pump, and the time for delivery of the solution using a mixer from a concrete unit to a construction site is also extended.

Features of the use of additives in masonry work

When carrying out construction work, it is important to separate additives, depending on the structures where they are to be used. For example, in monolithic works, pouring foundations, ceilings, load-bearing columns, it is important to achieve design structural strength. While masonry mortar does not need excessive strength.

Kirill Lebedev

There are a large number of different plasticizers. You can not thoughtlessly use the same additives for masonry and for concrete work, because. they differ from each other in chemical composition. Also additives differ in "power" of action, influence on the viability of the solution and mixture. The similarity of all plasticizers is that they reduce the amount of mixing water, but completely different requirements are imposed on concrete for the foundation and on the masonry mixture. If you neglect this rule, you can get a negative result, which will lead to big problems.

During masonry work, the bricklayer needs to make it convenient to work with the mortar. The solution should be light, airy, as they say, "reach for a trowel."

For this, additives are used that provide not only plasticity, but also increased air entrainment. This leads to a decrease in the strength of the solution, which is not needed by builders when laying facing bricks.

The usual strength limit for mortar when laying facing bricks is up to M150.

Special additives for masonry increase the output of the volume of the finished mortar. For example, without an additive, it is possible, from an equal volume of components, to obtain 200 liters of a solution, and with an additive, already 230-240 liters.

Important: If you use an additive for masonry mortar when concreting a foundation, where the density of concrete is important, this can lead to a significant decrease in the strength of the structure. Those. instead of the planned M350, you can get concrete M100-M50. As a result: the foundation will not be able to withstand and redistribute the load on the ground, the weight from the overlying structures, and it will have to be dismantled.

Conversely, concreting additives should not be used during masonry work, as they will not provide lightness, airiness of the mixture and a long mortar life, which is important for masons.

Kirill Lebedev

Efflorescence appears due to the fact that moisture begins to migrate through the masonry mortar, taking with it salt and other easily soluble compounds to the front side of the brick. Because the additive blocks the capillaries (the permeability of the solution decreases), then through them moisture can no longer easily carry soluble compounds. In addition, the amount of water for preparing the solution is reduced, and this also reduces the likelihood of efflorescence.

Most bricklayers usually, always, when doing masonry work, use a means to modify the mortar. Often household detergents are used for these purposes - liquid soap, powder, etc. This is motivated by the fact that both professional additives and "folk" products contain surfactants (surfactants) that affect the entrainment of air into the mixture.

Important: household detergents that modify the mixture provide only a similar visual effect as when using special plasticizers. But there are various surfactants in additives for masonry mortars, which, for example, involve air into the mixture for large air pores. Other surfactants do not just entrain air, but break it up into micropores. It turns out a system of closed micropores, which provides an increase in the frost resistance of the mixture, etc.

The use of professional additives from a well-established manufacturer guarantees the quality of concrete mixtures and masonry mortars.

In the cost of the entire stone facade, the price of professional additives is low, so it makes no sense to risk expensive face bricks and use household detergents for masonry. Because this can lead to unpredictable end results in the long run.

Although it is said that the best is the enemy of the good, the technologists of our Company do not think so. Virtually no modern enterprise engaged in the production of reinforced concrete, cement or concrete mixtures can do without the use of special additives for concrete, which significantly improve the quality and characteristics of the mixture and regulate the processes of cement setting and hardening.

It would seem, why these additives for concrete, if the concrete mixture is 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, high-quality fillers were used: cement, sand, crushed stone, water ? A good concrete mixture is good in itself, but if there is an opportunity to make it better: increase its strength, make it more mobile, increase its moisture resistance, frost resistance, crack resistance, protection from salts, oil products, and so on, then why not do it ?

The modern production of concrete, reinforced concrete products and cement is modern for that, which takes into account all the possibilities and nuances that make it possible to make products "faster, higher, stronger." This is where special additives for concrete come to the aid of factories producing reinforced concrete products and various concrete plants, affecting the behavior of cement at various stages of setting and hardening, and affecting the quality characteristics of the manufactured reinforced concrete products, or monolithic reinforced concrete structures, throughout the entire period of operation.

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

• additives in concrete that regulate the main properties of the mixture, such as mobility, plasticity, water retention, pore formation, etc.
• types of additives that regulate the preservation and are responsible for the rate of hardening of concrete, the rate of setting of cement, mainly affecting the hydration process in the initial stage of setting, hardening and curing of concrete.
• additive for giving reinforced concrete or reinforced concrete special properties: polymeric, biocidal, etc.
• antifreeze additives for concrete, allowing concreting at sub-zero temperatures.
• additive in concrete that increases its strength, frost resistance, corrosion resistance.
• steel corrosion inhibitors, because steel reinforcement, 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-stressing reinforced concrete products and monolithic reinforced concrete structures.
• coloring additives - pigments for concrete.
• additives in concrete for waterproofing, which include various colmatizing additives, water repellents and other agents that reduce the permeability of a concrete structure.
• various types of porous additives for lightweight concrete: gas-forming, air-entraining, foaming, etc.

If we have so many groups, how many supplements will there be? Let me tell you - a lot! To list them all is hardly enough time and effort. We highlight only the main ones that can be useful to a wide range of builders. I’m probably not lying if I say that, or rather, its more advanced successor is the most used concrete additive used today in the production of concrete mixtures. In any case, BESTO Company uses s-3 plasticizer almost always. In general, chemical additives that help reduce the water content in the composition of concrete mixtures are the 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, cement is saved, density, water resistance, frost resistance, etc. increase.

This is where special additives for concrete come to the rescue - plasticizers, which began to be used since the forties of the last century. Today, we mainly deal with their new version, the so-called superplasticizers. They appeared in the USSR in the early eighties. The undisputed leader here - plasticizer s-3. One of the main manufacturers of superplasticizer s-3 is the company "Polyplast". Why plasticizers are so good, let's see:

• Saving cement. To obtain equal-strength concrete of the same mobility with the use of plasticizer s-3 and without it, 15% less cement is consumed per cubic meter of concrete mix. This magnificence is achieved by reducing the amount of mixing water. But in order to maintain the necessary mobility of the mixture, manufacturers must introduce superplasticizers or plasticizers into concrete. Thus, the water-cement ratio is simultaneously reduced without reducing the mobility.
• Without prejudice to the strength of future concrete products and reinforced concrete structures, the mobility of the mixture increases. Which is especially important for monolithic construction, where concrete pumps and concrete pumps are used with might and main, requiring concrete p4-p5 for normal operation (cone draft from 16 cm).
• Increase in final strength characteristics up to 25%.
• Thanks to the improved workability, there is no need to vibrate the fresh mix!
• The ability to pour heavily reinforced structures without any problems: columns, narrow wall formwork, and so on.
• Obtaining compositions of increased density (high impermeability), which has a positive effect on the water resistance of reinforced concrete products and reinforced concrete structures in general.
• Increased frost resistance up to F350 and crack resistance.
• Shrinkage of hardening concrete or reinforced concrete products is reduced.
• The ability to obtain high-strength reinforced concrete products and concrete, with compressive strengths over 100 MPa! For example: a concrete sample of grade m-350 (B25) 28 days old has a compressive strength of only 25 MPa. That is - four times smaller. Using special modifiers, it is possible to obtain a mixture with a grade strength exceeding the grade of cement used for mixing.
• Precast concrete plants benefit from the use of plasticizers by reducing the steaming time or lowering the temperature in the chambers. And this is a significant saving of energy resources, acceleration of mold equipment turnover and, as a result, an increase in production volumes.
• The adhesion of reinforcement to concrete increases by as much as 1.5 times (if physicists-chemists do not lie, of course)

It seems to me that the listed advantages are quite enough to understand that producing concrete mixes or reinforced concrete products without plasticizers is not the most profitable measure. However, in our barrel of honey there is also a fly in the ointment. It's small, but it's there. And this tar is a slight delay in the setting and hardening of the concrete structure. You can consider this a negative effect, maybe it will seem positive to someone, but the essence is the same. To compensate for the retarding effect of plasticizers, a special additive for concrete is sometimes introduced - a hardening accelerator. It compensates for everything that the plasticizer spoiled, namely, the schedule of normal hardening of the cast structure.

Today, complex types of additives in concrete are increasingly used. As a rule, they are two-component. For example: based on the plasticizer s-3, and in the appendage a hardening accelerator, or an air-entraining additive, or microsilica, etc. Thanks to such combinations, concrete plants obtain high-strength mixtures with unique characteristics.

Other types of additives for concretes and mortars

Concrete hardening accelerators To compensate for the action of the plasticizer, which slightly slows down the hardening process, special additives are sometimes introduced - hardening accelerators. Also, hardening accelerators can be used for non-standard pours, when a quick setting of the lower layer of the concrete mass is required, so that you can continue to pour further without any problems. A classic example is a monolithic pool bowl, when it is necessary to lay a concrete mixture in the combined formwork of the bottom and walls of the pool so that when it is poured into the walls, it does not squeeze out the newly cast bottom with its mass. Usually this process is stretched in time, but it can be significantly reduced if concrete hardening accelerators are used. Another area of ​​application for accelerators is concreting in cold weather. After all, the lower the ambient temperature, the slower the process of cement hydration, the beginning and end of setting and curing occur at a slower pace. Accelerators also help here.

Concrete hardening retarders By the name it is clear what these types of additives do. They are used to increase the pot life of the concrete mixture. Basically, this may be necessary for transportation over long distances, when it is impossible to quickly fill, and so on. That is, with the use of hardening retarders, we take a time out to have time to do something: eat donuts, drink beer, sleep while the concrete rests in a tub or trough. Moreover, this pleasure stretches for several hours. Something like this. Water reducers can be included in the group of retarders. They also have a retarding effect.

Air-entraining additives As you already understood from the name, they "involve" the air. When mixing the mixture, millions of tiny micro-bubbles of air are created. What is it for. The main task is to create a microporous structure in concrete or reinforced concrete products. Remember aerated chocolate? Here is the same thing, only the pores are microscopic. Due to the presence of these same pores, the frost resistance of a concrete structure or reinforced concrete products increases. Why? Yes, because the water that has soaked the concrete structure, when it freezes, has room to expand. In those very times. Cheap and angry.

However, here is not without tar. They protect cement stone from destruction, but aggregates do not. Rubble 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, you cannot make high-strength concrete with such additives. And frost resistance can be increased in other ways, for example: reduce the water-cement ratio, or introduce fly ash into the mixture, with the same amount of cement. This significantly increases the water resistance (W factor 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 poured structure. Certain types of additives allow concreting at temperatures up to -25 degrees. This is "tin" of course, but if there is such a need, then there is no need to choose. So how do antifreeze additives work. For those who are familiar with the "subject" and so it is clear, I will try to explain to everyone else in a few phrases.

The main essence of the solidification of a mortar or concrete mixture is the so-called cement hydration. Simply - the process of crystallization of minerals (silicates, aluminates) present in cement, when it interacts with water. The rate of this process depends significantly on the ambient temperature. At low positive temperatures, the cement setting process stretches in time (several times), at negative temperatures, it stops altogether, due to the banal reason for the freezing of that very water. It is with these two nasty things that the antifreeze additive for concrete fights, by virtue of its capabilities.

The main tasks of modern antifreeze additives are to reduce the setting time of cement and speed up the hardening time of concrete (at low temperatures), to lower the freezing point of water. In Russian, to put it - to make the water freeze not at 0 degrees, but at -10 or -20. You probably remember that salt water is a classic example of lowering the freezing point. There is one more task for modern antifreeze additives - do no harm. Just like in Hippocrates: "... in accordance with my strength and my understanding, refraining from causing any harm ..." But they can do harm. Not all, but they can.

There are quite a few myths about the harmfulness and usefulness of certain antifreeze additives for concrete. All terrible sins are attributed to them: corrosion of reinforcement, and a decrease in strength, and a decrease in frost resistance, and the dog knows what else comes into his head. Unfortunately, I am not a chemist or a naturalist, but I will try to summarize what I once read, heard and tried myself.

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

Myth two: reduced strength. With a normal % introduction of additives into concrete, there is a slight lag in the rate of strength gain, but upon reaching the classical teenage age of 28 days, the leading laboratory without additive concrete sample (hardening at +20 degrees) disappears, and then a greater increase in grade strength is often observed in concretes. with antifreeze additives. Here's a grandmother and a decrease in strength.

However, do not forget about the abnormal% introduction of additives into concrete. This is where potential troubles lie. Here the conversation can drag on if you start to remember all sorts of early freezing techniques, etc. Therefore, we will manage with two replicas. With insufficient introduction of PMD, the mixture freezes, the cement hydration process 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, this is not a bridge and not a load-bearing crossbar, which they managed to load with something heavy during the winter.

In completely free-of-charge concretes, accidentally frozen during a sharp drop in temperature, the situation is somewhat worse, but also quite tolerable, provided that the cast structures are not loaded. However, much depends on the size (volume) of the cast concrete products. Again, it is important - when exactly the concrete froze: at what stage was the cement, whether critical strength was gained; whether water (rain, melting snow) affected the weak concrete surface, etc. Here, perhaps, a loss of strength is possible on average up to 20% and in some cases a decrease in frost resistance up to 50 percent, peeling of the upper layer, erosion, etc. is also observed.

If we consider the results of laboratory and field tests, we can conclude that the antifreeze additive for concrete (especially complex) has a positive effect on the resulting characteristics of a concrete structure, or reinforced concrete. The density (water impermeability) increases, a positive inhibitory effect on the reinforcement is promised, the design strength increases in comparison with concrete without additives.

Again, all this is possible under one condition that the additive is not left. If there is no certainty, then the risk is akin to Russian roulette. There is a time-tested Poliplast, but where is the guarantee that this is Poliplast, and not Ravshanplast spilled in a nearby hangar on the construction market. Counterfeiting is our common misfortune. One thing is Cherkizovsky Gucci and Karden, and quite another - when an ersatz product concerns health and construction. If you think about the possible consequences, it becomes a little uncomfortable.

Of course there are many additions. Listing them and describing them is not an easy task. I have mentioned only the most used ones. To the best of my ability and strength, I will try to supplement this page with a description of the compositions that have now been ignored. In the meantime, what is - is. With superplasticized non-freezing greetings, Eduard Minaev.

A durable monolith is obtained after solidification of a mixture of cement, water and various fillers (sand, lime, crushed stone, slag). Such compositions are widely used in the construction of foundations, cast walls, pools, piers, airfields, roads. With the help of special additives for concrete, you can prepare the perfect mortar for any object, increase the pace of construction and reduce the overall cost of it. Additional components give the finished composite the required properties, allow you to work regardless of the season.

Types of additives, overview of characteristics and properties

The need to change the structure of concrete is determined by various factors:

• technological - accelerated concreting, increased plasticity for better laying, the need for a reserve of time for transportation;
• operational - increased strength, density, water resistance, resistance to extreme temperatures, thermal insulation properties (for cellular concrete);
• climatic - frost resistance and rapid hardening of the composition in winter, and if work is carried out in the heat - delayed setting;
• economic - reducing the volume of cement in the solution;
• aggressive environment - salty sea water, mineralized ground water, fungal microorganisms.

Classification

Based on each factor, you can choose the appropriate compositions. Classifiers usually distinguish several groups of additives in concrete mixtures, each of which has its own purpose:

• plasticizers;
• gas and foam-forming;
• mobility regulators;
• anti-frost;
• accelerators (retarders) of hardening and setting (more on);
• seals;
• increasing the water resistance of concrete structures.

Brief description of the main types of additives

1. Plasticizers.

Builders observe a strict proportion, called the water-cement ratio - it is determined by the purpose of the concrete structure. To obtain a solid wall, no more than 7 liters of water are poured into 10 kg of cement, paving slabs - no more than 4 liters (to resist high loads). Plasticizing additives make it possible to make the solution fluid without pouring water into it and thereby not reducing the strength characteristics of the finished product. The adhesion between the particles of the mixture decreases, but it does not delaminate, there are no voids in it.

The composition becomes more mobile, concreting is facilitated. Without the help of a vibrator, a tile mold or thin-walled formwork is filled to make a foundation. By reducing the weight of cement due to the introduction of additives and without violating its share in relation to water, it is possible to save significant funds. They are divided into super- and hyperplasticizers, the former allow to reduce the amount of cement by 10%, and the latter by 20%.

2. Waterproofing.

Concrete is used for the manufacture of monolithic and block foundations. Gradually, through micropores, it absorbs subsoil or atmospheric moisture. The waterproofing of the structure is provided with the help of rolled materials, bituminous coating, and today additives for waterproofing are used for this purpose. They give the artificial stone hydrophobic properties: its particles begin to repel water molecules.

More recently, waterproofing was achieved by introducing liquid glass (silicate glue). Its price is affordable, but the consumption is too high: 1 liter of material is required for 10 liters of concrete. The purpose is not only waterproofing, but also corrosion protection of reinforcing metal parts. Additives are usually produced on the basis of polymers, the properties of which are to increase their volume in solution and plug microcracks when the mass hardens.

The waterproofing of structures is ensured by Penetron penetrating waterproofing and its analogues. Reacting with cement, they form crystals that fill the air pores.

3. Hardening accelerators and setting retarders.

It is necessary to increase the rate of hydration of cement stone in cold weather, especially if work is carried out in winter. At low temperatures, the setting and hardening of the mixture is inhibited, and at frost, these processes stop. In order to work normally in winter, compounds are introduced for quick setting.

How to perform concreting if transportation takes a long time? Special retardants help to slow down maturation. They are used when pouring large and massive objects so that the concrete remains in a fluid state all this time.

4. Frost-resistant additives.

In winter, concrete hardens at a very low rate - as a result, the product turns out to be loose, and its frost resistance decreases. To avoid this, the solution is heated at the construction site, and in the absence of such an opportunity, special components are used. Their purpose is to ensure filling at sub-zero temperatures (below -5°C). In winter, antifreeze compounds are needed to reduce the freezing point of water in the mixture and stimulate setting in the range from -5 to -25°C.

The following chemical compounds are widely used as winter additives:

• potash or potassium carbonate - with its help, concrete sets and hardens even at -30 °;
• calcium nitrate - stimulates hardening in winter;
• sodium nitrate and nitrite, calcium nitrate - in combination with urea, at low temperatures, they not only contribute to hardening, but also protect the reinforcement from corrosion (sodium nitrite is poisonous and flammable);
• calcium chloride;
• sodium formate and other salts of organic acids are frost-resistant components that do not have a harmful effect on health (they do not have plasticizing properties).

When these compounds are introduced into the solution, salt deposits do not appear on the structures, they become more durable even with the use of cement of low grades. Additives to improve frost resistance are used when concreting monolithic, as well as prestressed structures - dams, dams, bridges.

Antifreeze mixtures are not recommended to be introduced if it is raining or the air humidity exceeds 60%. The presence of more than 50 mg / mol of reactive silica in the aggregate is also a contraindication - because of this, additional pores appear in the concrete. There is a side effect of calcium chloride: it corrodes the reinforcement.

5. Sealing.

Their purpose is to reduce the percentage of pore content by filling microvoids between molecules. Simultaneously with the compaction of the material, its strength and frost resistance increase, and water absorption decreases. The cost, taking into account the low consumption (approximately 0.5 kg per 100 kg of cement), is low, and the economic effect is significant.

6. Air-entraining.

When water freezes in micropores, it expands, and the concrete is torn like paper. Its strength and frost resistance can be increased by a normalized increase in porosity. For this purpose, concreting is carried out with a minimum amount of air-entraining preparations.

Gas-forming additives also produce the effect of pore formation, but the purpose of the technology is different - to reduce the volumetric weight of the solution, to give it heat-insulating qualities. Blowers are introduced into the mixture in the manufacture of foam and aerated concrete.

7. Complex.

They combine the effect of two or more ingredients. The option is optimal for obtaining the predicted result if the characteristics of the concrete mix should be changed in several directions. Separate components may react incorrectly with each other, so experts advise buying a complex prepared at the factory and balanced in composition. Complex additives simultaneously improve its pore structure and other characteristics - water resistance, frost resistance.

The combined action is performed by the following types:

• Modifiers - their purpose in obtaining special concrete with improved technical characteristics. With the help of additives, waterproofing (water permeability grade from W12), corrosion resistance, durability, strength not lower than B125 are provided. Concrete only with modifier additives is prepared if it should be expanding, straining, compensating for shrinkage, used for vibrocompression.
• Fiber additives. These are fibrous materials based on polymers, glass, steel. They reinforce concrete (increase its resistance to loads and deformations), increase heat resistance, reduce shrinkage, and increase plasticity.

The cost of additives

It is worth paying attention not only to foreign brands, but also to the products of reliable domestic companies. In order to really increase frost resistance, intensify or slow down setting, the proportions of the solutions indicated in the instructions should be strictly observed.

Concrete is a building mixture of cement, sand and gravel with or without any additives. Concrete is one of the most widely used building materials. It goes to the foundation, walls, window and door openings, rough flooring, floor slabs, pools - and this is only a small part of the spectrum of its application. Characterized by strength, durability and environmental friendliness.

What else to add, and why? It turns out that you can add a lot of various improvements and modifications, and they will be discussed in the article.

Classification of types of additives for concrete by purpose

What are additives used for? Their use allows, with minimal material and energy costs, to significantly improve any specific quality of the solution.

The most popular and common types are listed below, and there are many photos of concrete additives on the Internet.

Modifiers

With their help, you can change the hardening time of concrete, its frost resistance, increase its mobility, extend its service life, and impart water-repellent properties.

They are classified depending on the purpose of their application - for wells, screeds, foundations, pools. Thus, the range of their properties is the widest.

plasticizers

They increase the strength of concrete with a lower consumption of cement, make it more plastic and mobile, denser. They are divided depending on the effectiveness of the action into weak, medium, strong, as well as super-plasticizers.

The technology is not new, the first additives of this type appeared in the middle of the twentieth century. They allow to reduce the cost of cement by 10%, with the same quality of the solution, and also make it easier and more convenient to work with it.

Mobility regulators

They are used when transporting a concrete mixture over long distances so that its setting does not begin during the delivery. They allow to slow down the hardening process at high air temperatures, which is important when pouring the screed in the summer.

Frost-resistant additives

Allow to work with mixtures at temperatures up to -15..-25 degrees Celsius. The principle of their operation is to change the freezing point of the water contained in the mixture. The most popular component of this series is sodium nitrate.

Set Accelerators

They are used when it is necessary to quickly harden concrete immediately after pouring. They also increase the final mechanical strength of the composition. They are used in the construction of structures with an aggressive external environment, high humidity.

Additives for self-compacting compounds

Used for pouring structural elements of small thickness. These include super-plasticizers, which give a tangible gain in material savings without loss of quality.

Anti-corrosion

The principle of operation is based on the binding of free calcium hydroxide, preventing it from reacting with the environment.

Thus, a gain in the service life of concrete is achieved. In addition, it becomes denser, and its water-repellent properties are enhanced.

There are also complex additives that give the solution useful properties from two or more classes at once. It is better to use just such additives, because the effect of mixing two or more separate additives is unpredictable - the ingredients may be incompatible.

Composition classification

Additives by composition are divided into finely ground and chemical. The radical difference between them is in their amount added to the mixture. The spectrum of action of chemical additives is listed above.

Whereas solutions, powders and emulsions added in small quantities are chemical, finely ground are mineral additives from industrial waste, intended for the most part to save cement. They are added in much larger quantities than chemical ones, that is, they function as fillers.

Supplement Manufacturers

Like any industry, there are leaders in the production of concrete admixtures. Among domestic manufacturers, the following companies can be distinguished: Master, Superplast, MetaPro; among foreign manufacturers, BASF has proven itself well.

There are plenty of products of different quality and price on the market, thanks to which everyone can choose something that suits him according to both criteria.

Photos of the best additives in concrete