Do-it-yourself plasticizers and additives for concrete. Overview of additives for concrete: types, features, application Concrete additives

Despite the fact that modern concrete, in its quality production, is quite ready for use, however, there are certain special mixtures that make it even better by increasing:
strength;
moisture resistance;
mobility;
crack and frost resistance:
protection from salts and other useful qualities.

Additives for concrete

The main chemical additives in concrete that are successfully used in production can be divided into the following groups:

1. Additives for concrete, the influence of which is carried out on its main properties (pore formation, water retention, plasticity, and others).
2. Additives that affect the speed of hardening, the process of hydration, hardening and strength.
3. Antifreeze additives, thanks to which it is possible to work with mixtures in sub-zero temperatures.
4. Additives that improve corrosion resistance, frost resistance and strength.
5. Special additives in concrete, giving polymeric, biocidal properties and others.
6. Expanding, which reduce the shrinkage of structures, increase the resistance to cracking and create self-stressing reinforced concrete products.
7. Waterproofing additives in concrete.
8. Dyes-pigments.
9. Gas-, foam-forming and other additives that create pores in concrete (used for lightweight types of concrete).
10. Corrosion inhibitors, which are more suitable for steel reinforcement and prevent its destruction.

The main types of additives in concrete

Additives in concrete, the composition of which is significantly improved due to their presence, are very diverse. Based on the groups described above, there are even more species. We will dwell on the main ones in more detail.

Plasticizers and Superplasticizers- this is perhaps one of the most used among the rest of the additive. The main purpose of such substances is to absorb water in the mixture, or rather, to reduce the ratio of cement and water in it. In practice, if the amount of water is reduced, the mixture becomes stiff and difficult to lay. Therefore, for the mobility of concrete, more water is added, and in order for the structure to be durable, plasticizers are used, or rather, superplasticizers, their improved counterparts. As a result, concrete becomes:
more plastic;
denser;
more frost-resistant;
waterproof;
economical to use.

At the same time, concrete products are stronger on average by 25%, and freshly laid mixtures do not need to be vibrated. They are easy to pour and adhere better to the reinforcement. However, there is one minor drawback - concrete structures set and harden a little longer than usual. Although, to neutralize this effect (if it is really important that the mixture hardens faster), concrete hardening accelerators are used.

Accelerators as additives in concrete, its composition does not change, but it helps to reduce the hardening time. They are used mainly along with plasticizers or when pouring this type, when it is necessary for the structures to set faster to continue work. As an example, concrete hardening accelerators are used in the construction of pool bowls. This property of concrete is also useful in cool weather.

Retarders concrete hardening is another type of additive, the effect of which is the opposite of the previous one. Their use is necessary to increase survivability, for example, during long-distance transportation or when quick filling is not possible. These additives include water reducers, which also help slow down hardening.

Antifreeze additives provide the possibility of placing concrete in winter period. Thanks to them, even in sub-zero temperatures, finished structures do not require warming up. Due to the fact that there are such additives for concrete, even at -25, work can continue. Of course, such weather conditions in themselves are uncomfortable for work, but in extremely extreme and urgent cases, antifreeze additives will be useful. Concrete for the foundation especially needs to be reinforced with special additives and plasticizers.

Air-entraining additives when mixing the mixture, they contribute to the formation of small small air bubbles, which is why the structure of the concrete is microporous. From this, the structures become more frost-resistant. However, while protecting the cement stone from destruction in the compositions, these concrete additives do not protect the aggregates. In addition, structures with pores are less durable, so these additives are not used as often.

As a rule, they use complex additives in concrete and. From this, its composition immediately acquires several additional properties, and the mixture is the most optimal in terms of characteristics for pouring. There are even special two-component additives, for example, with a superplasticizer in the base and a hardening accelerator or an air-entraining additive in the appendage. This results in excellent high-strength mixtures. The main thing is to introduce additives in the correct ratio and concentration and use them correctly for different types concrete structures.

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 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. To date, 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.

Nowadays, more and more often complex views concrete additives. 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 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. Probably remember that salty water - classic example freezing temperature drop. 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 some lag in the rate of strength gain, but upon reaching the classical adolescence For 28 days, the leading role of the laboratory concrete sample without additives (hardening at +20 degrees) disappears, and then a greater increase in brand strength is often observed for 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 process of cement hydration 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.

For completely free-of-charge concretes, accidentally frozen at sharp decline 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. It is one thing for Cherkizovsky Gucci and Karden, and quite another when an ersatz product concerns health and construction. If you think about possible consequences, becomes a little uneasy.

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.

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

Each time when designing objects, the calculation of structures is carried out, taking into account all the conditions not only for their construction, but also for their further operation. And since the operating conditions are different, then concrete mortar should also be different.

Therefore, to give concrete the desired properties, various additives are used that 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, and therefore they are classified in different ways. The following is one of the most commonly used classifications:

Concrete modifiers - are able to increase the strength of the concrete mixture and its frost resistance, reduce its permeability, extend the service 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 work.
Mobility regulators - they are used in hot weather or in cases of long-term transport of concrete in order to maintain the necessary plasticity.
plasticizing additives. Their use allows to reduce the consumption of concrete without reducing its strength. They also make it possible to improve the mobility of the solution, increase its density, and in some cases its water resistance.
Antifreeze additives - are used when laying concrete in winter at temperatures up to -15 and even up to -25 degrees.
Additives for self-compacting concrete - used when it is necessary to pour thin-walled concrete structures.
Additives to accelerate the curing of strength - improve this indicator in the first day after laying the mixture, and also increase the strength of already hardened concrete.

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

The use of several additives in such a situation can lead to unpredictable results, and a properly dosed complex preparation guarantees the required quality of concrete.

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

(powders, emulsions and aqueous solutions) - are introduced into concrete in small quantities.
Finely ground substances (mineral substances of fine grinding) - are used if it is necessary to save cement and obtain resistant dense concrete.

Chemical additives subdivided according to the effect that they have on the concrete mix:

hydrophobic;
increasing the plasticity and mobility of the mixture;
antifreeze;
reducing the separation of liquid from the solution;
stabilizers that do not liquid concrete exfoliate;
curing accelerators;
regulators of deformation processes;
setting retarders;
gas and foaming additives that increase the porosity of concrete;
increasing resistance to aggressive environments, corrosion.

concrete modifiers

These substances are intended for the manufacture of special-purpose concretes 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, stressing and compensating for shrinkage of concretes and mortars.

These additives are mainly used for the manufacture of conventional and prestressed products by vibrocompression and molding.

Concrete flow regulators

They are used in situations where it is impossible to organize the production of concrete mix the right quality right next to the construction site and you 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 made from:

inorganic substances;
organic materials;
organomineral combinations.

Natural additives are produced mainly from waste products of the agrochemical, petrochemical and timber industries.

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

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, have a positive effect on the adhesive properties of reinforcement (improve the adhesion of reinforcement to concrete).

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

Antifreeze additives

In the cold season, the process of concrete hardening slows down significantly, which has an extremely negative effect on its strength indicators - concrete becomes loose, and its frost resistance index decreases.

If it is not possible to use concrete heating at the construction site, then they are used, which reduce the freezing point of water and, thus, normalize the concrete hardening process.

Antifreeze additives are a liquid with a density of approximately 1.4 l/kg with a mass fraction of calcium nitrate from 42 to 45% and an 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 effects on concrete:

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

The use of antifreeze additives prevents the appearance of efflorescence on the surface of the concrete structure, increases its strength, allows the use of cement of lower grades for the mixture, 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 platforms.

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

Such concretes are used in densely reinforced structures, when the usual compaction of the mixture is impossible, therefore, concrete is needed, which can only be compacted by its own weight.

Hyperplasticizers are added to these concretes, which make it possible to obtain concretes with ultra-high performance properties.

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

Additives to accelerate curing

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;
densely reinforced and thin-walled structures;
products of non-standard forms;
pools.

All these substances are mainly used in the industrial production of concrete and concrete products. In private housing construction, the most used are antifreeze additives and concrete mix hardening accelerators.

What to Consider When Using Concrete Admixtures

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

When mixing concrete with additives on your own, you need to strictly observe the proportions, otherwise you can get poor quality concrete.

Also learn exactly how to add the supplement - some are administered with water, while others require pre-mixing with one of the dry components of the mixture.

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Sika (Switzerland), one of the world's leading manufacturers of construction chemicals, produces various concrete additives: plasticizers, modifiers, waterproofing materials, hardening accelerators and other materials. These substances improve concrete mixtures in many respects - strength, mobility, water resistance, frost resistance, chemical resistance and others. Chemical additives for Sika concrete allow the construction of reinforced concrete and monolithic buildings and structures at temperatures up to -25 ° C, which is very important for our country.

Main Types of Sika® Concrete Admixtures

Waterproofing additives in concrete - Sika® 1 Plus. This material is widely used in cement floor screeds and plaster mortars. Chemical water-repellent additives for concrete contain water repellents that block the capillaries in the cement stone and at the same time maintain its vapor permeability.
Plasticizers for concrete - Sikament® BV 3M, Sika® Antifreeze N9, Sika® Latex. These materials are added to concretes and mortars, adhesives and plasters, cement-sand floor screeds. Chemical plasticizing additives for concrete improve the workability and plasticity of mixtures and increase the strength and water resistance of concrete. Sika® Antifreeze N9 Mortar and Concrete Plasticizer is a complex additive that provides rapid curing of concrete.
Hardening accelerators - Sika® Antifreeze N9, Sika® Antifreeze FS-1, Sika®-4A. These chemical admixtures for concrete ensure rapid hardening of concrete and mortar at temperatures down to -25 °C. Distinctive feature– the absence of chlorides and other substances that cause corrosion of steel reinforcement. The chemical additive Sika®-4A is used in cement slurries designed to quickly seal active water leaks and fix various parts.

Benefits of Sika® Concrete Admixtures

Concrete admixtures can be purchased from Sika at a bargain price. Sika plasticizers have many competitive advantage. They:

reduce cement consumption;
increase the mobility and workability of concrete and mortar;
improve the plastic, waterproofing and frost-resistant properties of concrete;
can be used in solutions for thin-walled and densely reinforced structures.

Where to buy plasticizers for Sika concrete?

Today in Russia there are 4 factories for the production of concrete additives and 5 branches of the Swiss concern Sika, whose products are sold through a developed dealer network. To buy plasticizers for concrete, use the services of our regional offices.

Are you planning to perform concrete work, but do not know how to make a high-quality mortar yourself? I will talk about various additives in concrete for frost resistance and improving its performance. And as a bonus, I will offer a detailed concrete preparation technology.

What is concrete made from?

Concrete is an artificial stone material that is formed as a result of compaction and solidification of a liquid solution. Concrete mortar consists of coarse aggregate, fine aggregate, binder and water. It includes the following components:

Cement- a binder that hardens when interacting with water, forming an artificial cement stone.

Cement in the solution binds and fastens the particles of the aggregate together, therefore, the grade strength of concrete depends on its quantity and quality;
For the manufacture of building ready-mixed concrete, cement grades M200-M500 are used.

rubble- a large aggregate and the basis of any concrete product. During operation, it takes on the main compression load.

The most durable and high-quality crushed granite crushed stone is considered to be from 10 to 150 mm in size;
The maximum particle size of crushed stone in the solution should be three times less than the minimum thickness of the concrete product;
For example, to fill concrete screed 80 mm thick, crushed stone should have particles 15-25 mm in size.

Sand- fine aggregate, which is enveloped by cement particles, and together with it fills the voids between the crushed stone particles.

Sand can be fine or coarse, the main thing is that it does not contain clay, since it significantly degrades the quality of concrete;
For this reason, washed river sand is best suited for preparing a solution.

Water- necessary for the formation of cement stone. In the process of chemical reaction of water with cement, its particles are firmly bonded to each other:

This reaction is called hydration;
Water must be clean, without acid salts and impurities, with a temperature of 15-25 °C.

Modifiers- a complex of special additives that give the concrete solution certain properties.

Preparation of concrete mortar with additives

You can buy ready-made concrete mix, or you can make it yourself. To prepare concrete of various grades, all components are mixed with each other in a strictly defined proportion until a thick homogeneous mass is obtained:

Turn on the concrete mixer and pour half of the required volume of water into it;
Pour half of the total volume of rubble and mix for 2-3 minutes;
Pour cement, and after a couple of minutes add sand, and mix for another 2-3 minutes;
After that, add all the remaining rubble.

Illustration	Instructions for the preparation of concrete
	Application of concrete grades M100-M400: Solution brand M100-M150 is suitable for the manufacture garden paths or blind areas around the house; Concrete grades M200-M250 can be used for foundations one-story houses or pouring floor screed; Grades M300-M400 are able to withstand heavy loads, therefore they are used for foundations and floors of high-rise buildings, as well as for the manufacture of monolithic concrete products (septic tanks, cellars, caissons, etc.)

	Introduction of additives: In a bucket of water, dilute the modifier for concrete, in accordance with the factory instructions for use; In the process of mixing the solution, add water with additives and bring its density to the desired consistency. After adding all the components, mix the solution for no more than 5 minutes. Otherwise, it delaminates, and its quality deteriorates.
	Use of concrete: Freshly prepared concrete mortar must be used up within 2-3 hours; If you are concreting in several stages, you need to have time to fill in the entire volume of the solution until it is completely set; This period is 6-12 hours, so the work must be completed in one day.

The branded strength of concrete is indicated by the index "M" and a numerical value, for example, M100, M200, etc. The numerical value characterizes the maximum allowable static load in kilograms per 1 cm². For example, for concrete grade M150, the maximum allowable compressive load is 150 kg / cm².

What affects the quality of concrete

In some cases, the actual strength of concrete products, even after the maturation of the cement stone, may be lower than the declared grade hardness of concrete. There may be several reasons for this:

Cement brand:

The higher the brand of cement used, the better and more durable the concrete solution will be;
Another advantage of high grades is cement savings. For example, for the preparation of the same brand of concrete, cement M400 requires two times less than M200.

The table shows the proportions of the components and the water-cement ratio for various grades of concrete.

Water cement ratio (W/C):

This indicator is characterized by the ratio of the amount of water to the amount of cement in the concrete solution. For example, if 2 parts of cement and 1 part of water are used for preparation, then the W / C of such a solution is 0.5;
For the hydration process, a ratio of 0.2 is sufficient, however, such a solution will turn out to be very thick;
To increase the plasticity and fluidity of the solution, W / C is usually increased to 0.3-0.5;
At the same time, excess water significantly reduces the strength of concrete, so I do not advise increasing the W / C ratio more than 0.8. That is, no more than 0.8 buckets of water can be poured into 1 bucket of cement.

Solution viscosity:

In order for the concrete solution to fill the entire formwork without the formation of voids and air pockets, it must be fluid and plastic;
To increase the plasticity of the concrete mixture, excess water cannot be added to the solution;
To make it more fluid without the addition of water, plasticizers are used.

Water penetration:

Even the heaviest grades of concrete have an open-cell structure;
Through the pores, water gradually seeps through the thickness of the concrete;
This leads to corrosion of the reinforcement, leakage of the walls of the pools and destruction by the forces of frost heaving.

Air cavities:

The presence of voids, shells and air pockets reduces the density and grade strength of concrete products;
When water freezes in voids, it expands and forms microcracks in the concrete body;
Under the influence of repeated freeze / thaw cycles, the strength of the concrete structure is gradually reduced.

Ambient temperature:

For normal work with concrete mortar, the ambient temperature must not be lower than 0 ° C, however, even when the temperature drops to + 5 ° C, its setting deteriorates noticeably;
At sub-zero temperatures, freezing water increases in volume and breaks bonds between cement particles;
Ice cannot react with cement, so hydration and formation of cement stone stops in the frozen solution.

Varieties of additives for concrete

plasticizing additives

Plasticizers are considered the most common additive used in residential construction throughout the year. They are made on the basis of liquid surface-active substances (surfactants) with the addition of auxiliary components.

Action of plasticizers:

Surfactants reduce the surface tension of water, and improve the wettability of dry solids;
Water with the addition of surfactants becomes slippery and slightly soapy to the touch, and due to this, friction between the particles of coarse and fine aggregates is reduced;
The solid components of the solution are enveloped in a soapy liquid, and easily slide down relative to each other under their own weight, and air bubbles between them freely go up;
Thus, when pouring concrete, a dense homogeneous mass is obtained without voids, shells and air bubbles.

Features of the use of plasticizing additives:

The addition of plasticizers makes it possible to obtain a thick and dense concrete solution with good indicators of mobility, fluidity and workability;
It flows well into narrow and deep places, penetrates heavily reinforced structures, does not stick to the walls of molds and formwork, and after solidification it has increased resistance to frost and temperature changes;
To achieve a normal mortar consistency, less water is required, resulting in an increase in the density and strength of concrete;
According to their action, plasticizing additives are divided into two types:

Superplasticizers- allow to reduce the amount of water by 10% without compromising the quality and mobility of the concrete mix;
Hyperplasticizers- have the same properties, but allow to reduce the amount of water in the solution by 20% of the required volume;

Due to the smaller amount of water, a smaller amount of binder can be added to the mortar, which allows more economical use of expensive cement.

If you do not have a plasticizer, then any liquid soap or dishwashing detergent can be used to improve the flow of concrete. It must be added to the water to mix the solution, at the rate of 1 cap per 2 buckets of finished concrete.

Curing accelerators

Under normal conditions, the setting time of the concrete mortar can last from 6 to 12 hours, and the final maturation period can last from 7 to 28 days. In some cases, the setting time must be increased or decreased.

To do this, retarders or accelerators of concrete hardening are used. Such an additive is sold in the form of powdered sodium chloride or calcium chloride with various additives. The chloride salts included in its composition have a double effect on hardening concrete:

Quick grip. An aqueous solution of sodium chloride enters into a chemical reaction with cement, and accelerates the setting of the cement stone;
Low freezing point. Salt solution has a freezing point well below 0°C, so concrete with such additives does not turn into a block of ice at low temperatures.

Scope of application:

It makes sense to use accelerators in cases where it is possible to pour a new portion of concrete only after the previous layer of mortar has completely solidified;
In housing construction, such an additive to concrete may be needed when pouring the pool bowl, when installing a monolithic ceiling, in the manufacture of artistic stucco or other details of architectural decoration;
When concreting in severe frost, it is important that the concrete gain at least 50% of its strength before the water in the solution completely freezes, otherwise its quality will be very low and it will quickly collapse;
In this case, the addition of chloride salts reduces the freezing point of water, and accelerates the hardening time of concrete, so it has time to gain the necessary strength.

Chloride salts in contact with ferrous metals cause active corrosion. Therefore, such substances are not recommended for use in reinforced concrete products with a reinforcing bar diameter of less than 5 mm.

hardening retarders

This concrete admixture inhibits the hydration reaction and slows down the setting of the cement stone, prolonging the pot life of the concrete mixture. In residential construction, retarding additives are used infrequently, but in some cases they cannot be dispensed with, for example:

Long transport:

If the concrete solution needs to be transported over long distances, then during the delivery time it can begin to set right in the mixer, even if it is constantly mixed;
To prevent this from happening, a moderator is added to the solution.

Continuous Fill:

If you are concreting a long strip foundation or monolithic slab large area, then each new portion of the solution must be poured before the setting of the previous layer begins;
Otherwise, the product will turn out to be non-monolithic, and shrinkage cracks may appear at the joints;
With the addition of a retarder, the work will take longer, however, the entire volume of poured concrete will solidify at the same time.

The setting time of concrete directly depends on the ambient temperature, therefore, in cold weather, less retarder should be added, and on the contrary, more in summer heat.

Winter supplements

Above, I described the main disadvantages of performing concrete work in the cold season, however, with the proper use of antifreeze additives, concrete can be poured even at negative temperatures down to -25 ° C.

There are several types of frost-resistant additives for concrete. Each of them is applied depending on specific conditions:

plasticizing additives- improve the mobility and workability of cold concrete, but do not by themselves protect concrete from freezing:

Plasticizers can be effective at temperatures from +1° to +35°C;
At temperatures below +1 °C, they must be used in combination with antifreeze.

Antifreeze additives - organic matter and soluble alkali metal salts, which significantly lower the freezing point of water:

Sodium chloride and calcium chloride have a good antifreeze effect, but cause severe corrosion of steel reinforcement. Such antifreeze additives are suitable for very low temperatures (below -20 °C);
Sodium nitrite and calcium nitrite they cost a little more, but they do not react so strongly with metals, therefore they are suitable for pouring railway products with thin steel reinforcement. Can be used at temperatures down to -15 °C;
Urea and potash practically do not react with metals, but they have more high temperature freezing, therefore, they are used at not very low temperatures (from +5 to -10 ° C).

Hydrating additives- the same as hardening accelerators, which I wrote about above.

The purpose of winter hydrating additives is to ensure concrete strength gain of at least 50-70% before all the water turns into ice;
For this, complex additives are most often used, consisting of sodium and calcium chloride salts, sodium nitrite and organic components;
The recommended temperature for the use of hydrating additives is from -25 to +10 °C;

Salt additives must be used with caution. If during the preparation of the solution you exceed the recommended dosage, then the concrete mixture may already set within 10-20 minutes.

Air-entraining and gas-forming additives

From the name it is clear that these types of additives help to saturate the concrete solution with air and gas bubbles. They apply in the following cases:

Gas-forming additives- mineral substances that react with the components of the solution and release carbon dioxide bubbles:

They are used in the production of light grades of cellular concrete, foam concrete and aerated concrete;
Due to their low density and porous structure, such materials have a small specific gravity and have good heat and sound insulating properties;
The foamed mortar increases in volume due to gas bubbles, which allows more economical use of expensive components for the production of concrete.

Air-entraining additives- chemicals that help capture and hold air bubbles while mixing the solution in a concrete mixer:

Many air bubbles penetrate between coarse and fine aggregate particles and thus provide natural lubrication;
Due to the air cushion, the friction force between solid particles is reduced, so the solution is more mobile and plastic;
Air bubbles do not come to the surface and remain in the hardened concrete, forming damper cavities;
When the freezing moisture in the pores begins to increase in volume, it does not break the concrete, but expands in the damper pockets;
The entrainment of air thus protects the concrete from cracking and allows for more freeze/thaw cycles.

Auxiliary additives

Below I will talk about chemicals, which in themselves do not affect the formation of cement stone, but at the same time improve the performance properties of concrete:

Hydrophobic compounds allow to reduce the permeability of concrete for water molecules. They are made on the basis of polymer, bitumen or silicate resins.

Water repellents are used when pouring foundations, building swimming pools, cellars, septic tanks, caissons and other buried concrete structures;
Liquid glass- the most common and inexpensive option. As the concrete hardens, the liquid glass particles crystallize and fill the pores in the concrete;
Penetron- a penetrating polymer-based water repellent. It can be used even after the concrete has hardened. Synthetic resins, when interacting with cement, polymerize and tightly clog all voids, pores and cracks.
As a result of the reaction, an oxide film remains on the metal, protecting it from oxidation;
Such preparations are used in the manufacture of concrete solutions with the addition of salt plasticizers and antifreezes.

modifiers and hardeners- a generic name for complex additives, which may include several components. For example, the preparation "Polyplast" contains plasticizing, antifreeze components and a cement setting accelerator;
Biocidal additives contain antimicrobial and antiseptic preparations. They prevent the growth and development of putrefactive bacteria, mold fungus, moss, lichen and other harmful organisms.
Pigment dyes allow you to paint concrete products in any suitable color. Used in the manufacture paving slabs, wall blocks, bulk concrete floors and small architectural forms.

When using pigment paints, it must be borne in mind that the concrete itself has grey colour. Therefore, even with the addition of a large amount of dyes, you will not be able to achieve bright and saturated shades.

The cost of additives for concrete

All described chemicals are sold in a wide range in any building hypermarket. Dry preparations are usually packaged in paper bags of 2.5 or 25 kg. Liquid reagents are poured into plastic bottles or canisters from 1 to 10 liters.

Estimated prices:

The cost of super- and hyperplasticizers, as well as retarders and concrete setting accelerators, is approximately the same, and ranges from 110 to 250 rubles per kilogram;
Antifreeze salt additives are cheaper - from 80 to 150 rubles/kg;
The average price of complex modifying additives can be from 200 to 400 rubles/kg;
Hydrophobic compounds will cost more - from 280 to 500 rubles / kg;
Air-entraining components are considered the most expensive - from 300 to 650 rubles / kg;
Coloring pigments, depending on their color, can cost from 160 to 350 rubles / kg.

Conclusion

Now you know how to properly prepare a concrete solution, and in what cases it is necessary to use plasticizers, accelerators, retarders and other waterproofing additives in concrete. I recommend watching the video in this article, and leave all your wishes and questions to me in the comments.