Protection of concrete against corrosion. Concrete protection

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Currently, concrete is one of the most popular building materials that are used for both internal assembly and finishing works, and for the construction of external walls of buildings and other load-bearing structures.

Due to the wide operating conditions, concrete is exposed to various natural factors which can lead to corrosion over time.

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The widespread use of new high-quality materials and increasing the durability of structures through anticorrosive protection of concrete and reinforced concrete is one of the important national economic tasks. The most intense corrosion is observed in buildings and structures chemical industries, which is explained by the action of various gases, liquids and fine particles directly on building structures, equipment and structures, as well as the penetration of these agents into soils and their effect on foundations. The main task facing anti-corrosion equipment is to increase the reliability of protected equipment, building structures and facilities. This should be done through the widespread use of high-quality paints and varnishes, and primarily epoxy resins, fiberglass, polymeric underlayer materials and new sealants.

Corrosion- the process of destruction of materials due to chemical or electrochemical processes. Erosion is the mechanical destruction of a surface. By appearance corrosion is distinguished: spots, ulcers, dots, intracrystalline, subsurface.

By the nature of the corrosive environment There are the following main types of corrosion: gas, atmospheric, liquid and soil. Gas corrosion occurs in the absence of moisture condensation on the surface. In practice, this type of corrosion occurs during the operation of metals and concrete at elevated temperatures. Atmospheric corrosion refers to the most common type of electrochemical corrosion, since most metal and reinforced concrete (concrete) structures are operated in atmospheric conditions. Corrosion occurring in any wet gas can also be referred to as atmospheric corrosion. Liquid corrosion depending on the liquid medium, there are acidic, alkaline, saline, sea and river. According to the conditions of liquid exposure to the surface of concrete and reinforced concrete, these types of corrosion receive additional characteristics: with full and variable immersion, drip, jet. In addition, according to the nature of the destruction, uniform and uneven corrosion is distinguished.

Concrete and reinforced concrete are widely used as a structural material in the construction of buildings and structures of chemical industries. But they do not have sufficient chemical resistance against the action of acidic environments. The properties of concrete and its durability primarily depend on the chemical composition of the cement from which it is made. Concretes based on Portland cement are most widely used in structures and equipment. The reason for the reduced chemical resistance of concrete to the action of mineral and organic acids is the presence of free calcium hydroxide (up to 20%), tricalcium aluminate and other hydrated calcium compounds. With the direct action of acidic environments on concrete, alkalis are neutralized with the formation of salts that are readily soluble in water, and then acidic solutions interact with free calcium hydroxide to form salts in concrete that have different solubility in water. Corrosion of concrete and reinforced concrete is the more intense, the higher the concentration of aqueous solutions of acids. At elevated temperatures of an aggressive environment, the corrosion of concrete accelerates. Concrete made on aluminous cement has a somewhat higher acid resistance due to the lower content of calcium oxide. The acid resistance of concretes based on cements with a high content of calcium oxide depends to some extent on the density of the concrete. With a higher density of concrete, acids have a slightly lesser effect on it due to the difficulty of penetrating an aggressive environment into the material. The alkali resistance of concrete is determined mainly by the chemical composition of the binders on which they are made, as well as the alkali resistance of small and large aggregates.

An increase in the service life of building structures and equipment is achieved by right choice material, taking into account its resistance to aggressive environments operating in production conditions. In addition, preventive measures must be taken. Such measures include sealing of production equipment and pipelines, good ventilation of the premises, trapping of gaseous and dusty products released during the production process; correct operation of various drain devices, excluding the possibility of penetration into the soil of aggressive substances; the use of waterproofing devices, etc.

The most common way corrosion protection of reinforced concrete (concrete), various building structures and facilities and equipment is the use of non-metallic chemically resistant materials: acid-resistant ceramics, liquid rubber compounds, sheet and film polymer materials(vinyplast, polyvinyl chloride, polyethylene, rubber), paintwork materials, synthetic resins, etc.

Paint coatings due to cost-effectiveness, convenience and ease of application, good resistance to industrial aggressive gases have found wide application for protecting metal and reinforced concrete (concrete) structures from corrosion. Protective properties paintwork largely due to mechanical and chemical properties adhesion of the film to the surface to be protected. Perchlorovinyl and copolymer paintwork materials are widely used for anticorrosive protection of concrete and reinforced concrete.

For anti-corrosion protection of concrete chemically resistant perchlorovinyl materials are used: enamel XB-785 and chlorine copolymer primers, XC-068, as well as coatings based on coal tar lacquer XC-724 with epoxy putty. Protective coatings are obtained by sequentially applying primer, enamel and varnish to the surface. The number of layers depends on the operating conditions of the coating, but must be at least 6. The thickness of one coating layer when applied with a spray gun is 15-20 microns. Intermediate drying is 2-3 hours at a temperature of 18-20°C. Final drying lasts 5 days for open surfaces and up to 15 days indoors. Painting with a chemically resistant complex (XC-059 primer, XC-759 enamel, XC-724 varnish) is designed to protect external metal and concrete surfaces of equipment exposed to aggressive alkaline and acidic environments from corrosion. This complex is characterized by increased adhesion due to the addition epoxy resin. A chemically resistant coating based on a composition of EP-0010 epoxy putty and XC-724 lacquer combines high adhesive properties characteristic of epoxy materials and good chemical resistance characteristic of perchlorovinyls. Crack-resistant chemically resistant coatings are used on the basis of chlorosulfonated polyethylene KhSPE. To protect reinforced concrete and concrete load-bearing and enclosing building structures with a crack opening width of up to 0.3 mm, enamel based on chlorosulfonated polyethylene and HP-734 varnish are used to protect against corrosion. Protective coatings are applied to the surface of concrete after the end of the main shrinkage processes in it. At the same time, structures should not be exposed to liquid (water) under pressure on the side opposite to the coating, or this effect should be prevented by special waterproofing. Materials based on chlorosulfonated polyethylene are suitable for operation at a temperature of -60 to +130°C (above 100°C - for short-term operation, depending on the heat resistance of the pigments included in the coating). ChSPE-based coatings resistant to ozone, gas-vapor environment containing acid gases Cl2, HCl, SO2, SO3, NO2 and acid solutions can be applied with a paint sprayer, brush, airless application unit. When working with a paint sprayer and brush, paints and varnishes should be diluted to working viscosity with xylene or toluene, and when applied with an airless spraying machine, with a mixture of xylene (30%) and solvent (70%).

Call! The company's specialists will help you choose anticorrosive paints and varnishes for concrete and reinforced concrete.

Aggressive environment negatively affects the condition building materials. Salt, carbon dioxide, water, and temperature fluctuations (freeze-thaw cycles) often lead to corrosion. Therefore, the protection of concrete from corrosion is the most important task in the construction or operation of any objects.

Causes of corrosion

Concrete produced on a mineral basis has a capillary-porous structure and is subject to the greatest impact in comparison with other materials. As a result of atmospheric action, crystals are formed in its porous structure, the increase of which leads to the appearance of cracks. Carbonates, sulfates and chlorides, dissolved in large quantities in the air, also have a devastating effect on building structures.

Types of corrosion

Corrosion of concrete is divided into three types. The main criterion for such a classification is the degree of deterioration of its characteristics and properties.

First degree - washout constituent parts concrete;

The second degree is the formation of corrosion products without binding properties;

The third degree is the accumulation of poorly soluble crystallizing salts, which increase the volume.

Protection methods

To protect concrete and increase its durability, you should apply primary and secondary protection.

Primary protection methods include the introduction of various modifying additives. They can be plasticizing (increasing), stabilizing (preventing delamination), water-retaining, and also regulating the setting of concrete mixes, their density, porosity, etc.

Secondary protection methods include the application of various protective coatings:

Biocidal materials - destroy and suppress fungal formations on concrete structures. The principle of operation is the penetration of chemically active elements into the structure of concrete, and their filling of microcracks and pores.

Pasting coatings - are used when exposed to liquid media (for example, if a concrete pile is heated groundwater), in soils, and also as an impervious sublayer in facing coatings. These can be oil bitumen rolls, polyethylene film, polyisobutylene sheets, etc.

Sealing impregnations - give concrete high hydrophobic properties, dramatically increase water resistance and reduce water absorption of the material. Due to these properties, they are used in conditions high humidity and in places where there is a need to ensure special sanitary and hygienic requirements.

Lacquer and acrylic coatings - form a weather-resistant, strong and durable protection. So, for example, acrylic prevents destruction by creating a polymer film. Another advantage of this method of combating corrosion is the protection of the surface from fungi and microorganisms.

Paint and varnish mastic coatings - are used when exposed to liquid media, as well as in direct contact of concrete with a solid aggressive environment.

Anti-corrosion coatings can be applied wherever there is a similar need for concrete. Structures made of this material are found in the floors and walls of residential premises, foundations, garage complexes, greenhouses, greenhouses, treatment facilities, collectors. Also, when choosing protective equipment, you should take into account the characteristics of the environment, possible physical and chemical effects.

Concrete, thanks to its technical specifications and design capabilities, won a leading position in the building materials market. However, it, being exposed to aggressive external influences, is gradually destroyed with a deterioration in consumer qualities. This process is called concrete corrosion. According to modern concepts, corrosion is a whole series of chemical, physico-chemical reactions and biological processes provoked by exposure to external environment and leading to the destruction of the material.

Types of concrete corrosion

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There are three main types of corrosion of this building material:

• The first type of corrosion includes all processes that occur in concrete under the influence of soft water. In this case, the components of the cement stone dissolve in water and are carried away by it. This process can proceed at different speeds. In dense concretes of massive hydraulic structures, the corrosion process proceeds slowly and can last for several decades. In thin-walled concrete structures, the components of the cement stone decompose quickly, and after several years of operation, it may be necessary to repair work. If the water filtration process begins through the concrete, then the decomposition of the concrete components is accelerated, a large number of calcium hydroxide and concrete becomes highly porous, which means fragile.

The leaching of calcium hydroxide is slowed down if the concrete element is exposed to air. Under the influence of carbon dioxide in the air, calcium hydroxide is converted into calcium carbonate. That's why concrete blocks, intended for the construction of hydraulic engineering facilities, are kept in the air for several months before lowering to the installation site. This measure allows time for the calcium hydroxide to carbonate on the surface of the concrete.

• Corrosion of the second type - chemical corrosion - includes those processes that occur in concrete during the interaction chemical substances contained in water or the environment, with the constituents of cement stone. As a result of these reactions, easily soluble products and amorphous masses are formed in the body of concrete, which do not have an astringent ability. Because of this, concrete can gradually turn into a spongy mass with extremely low strength. For example, this type includes sulfate corrosion, which occurs due to the interaction of concrete with water containing a large amount of sulfates.

From corrosion processes of the second type highest value have magnesia and carbon dioxide corrosion.

• Corrosion of the third type includes processes in which sparingly soluble salts accumulate in the capillaries and pores of concrete. The crystallization of these salts causes stresses in the capillaries and pores, which leads to the destruction of the concrete structure. Sulfate corrosion has the greatest practical significance in the processes of this category.

In addition to the listed types of corrosion damage caused by exposure of concrete to a liquid, biological corrosion is distinguished. It affects mainly buildings. Food Industry. The cause of its occurrence are fungi, bacteria, algae. The destruction of concrete is caused by the products of their metabolism. Especially this process is activated in conditions of high humidity.

Protection of concrete against corrosion by increasing the resistance of the material itself

One of the ways to prevent corrosion is. Read our article on how to properly increase the density of concrete.

Preparation of cinder concrete - all about how to choose the right slag and manually prepare cinder concrete.

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Many corrosion control measures are difficult or not very effective. In practice, they try to use the most simple and inexpensive ways and, above all, increase the stability of the concrete itself by using corrosion-resistant cement or by making the material of high density and water resistance.

• Use of corrosion resistant cements. In some cases, the occurrence of sulfate corrosion of concrete can be avoided by using sulfate-resistant cements instead of Portland cement or Portland slag cement. These special cements contain active ingredients that make it possible to increase the resistance of concrete not only to sulphate, but also to fresh water.
• Increasing the density of concrete. This kind of corrosion control is an effective way to protect the material from all kinds of corrosive processes. Increasing the density of concrete reduces its water resistance. This makes it difficult for aggressive media to penetrate into the pores of the material. For the manufacture of high-density concrete, cements with low water demand are used, the water-cement ratio is reduced, and the mixture is compacted with special care in the manufacture of a concrete element.

If these measures did not give a result, then they resort to the optimal method of waterproofing in a particular case.

Types of waterproofing

One of the most common waterproofing methods for concrete and reinforced concrete products - piles, pipes, columns, slabs - is impregnating waterproofing.

For effective protection material from the destructive effect of corrosion, it is sufficient to impregnate it to a depth of 10-15 mm. The surface waterproof layer creates protection against water penetration for the rest of the volume of the structural element.

Impregnation methods are distinguished by temperature and pressure. According to the impregnation temperature, there are hot and cold.

• For hot impregnation petroleum bitumens, paraffins, petrolatum, synthetic compounds are used. The impregnation operation is carried out, as a rule, in baths at temperatures of 80-180°C. When heated, the impregnating composition transforms into liquid state, its viscosity decreases, it easily penetrates into the pores of concrete, clogging them tightly when solidified.
• As cold impregnations, compositions are used, which are based on mineral binders - cement, sodium silicate, or organic low- and high-molecular substances - styrene, methyl methacrylate, polyurethane.

Impregnation waterproofing can be carried out at different pressures:

• The simplest operation is impregnation under atmospheric pressure. In this process, the penetration of the composition into the pores occurs only due to the capillary effect.
• Impregnation in autoclaves is carried out at a pressure of 0.6-1.2 MPa, but despite high pressure, the rate of the process increases by no more than two times. This is due to the presence of air in the pores, which occupies a part of the volume and counteracts the impregnating composition.
• Vacuuming increases the efficiency of concrete processing by 3-4 times. Impregnating compositions easily penetrate into the pores, from which the air is pumped out, without encountering opposition.

Surface impregnation is carried out directly on the object with highly penetrating compounds. Processing is usually carried out twice.

Other types of waterproofing: injection, hydrophobization, mastic and roll pasting waterproofing.

Corrosion destruction of reinforcement in concrete

The service life of building structures is reduced not only by corrosion of concrete, but also by corrosion of metal reinforcement. The process of destruction of the metal is carried out for some time, but to determine the exact service life metal elements theoretically impossible. Corrosion of reinforcement in heavily loaded structures is especially dangerous.

Impregnating waterproofing with application is a very effective way to protect against corrosion if the impregnation is chosen correctly.

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To prevent corrosion, care must be taken that the concrete does not contain substances that are aggressive to the metal. But in practice, this task is impossible, since it is impossible to check chemical composition all concrete aggregates.

Corrosion of reinforcement is initiated by elements contained in the air and moisture penetrating through the pores of the concrete. Due to the unevenness of this process, different potentials arise in different parts of the reinforcement, which causes electrochemical corrosion. The rate of this corrosion process increases with an increase in the porosity and moisture permeability of the material, and also due to an increase in the electrolyte concentration, which is increased by substances dissolved in water.

Electrical corrosion, which occurs due to leakage currents and stray currents that appear at the locations of electrical poles, causes great damage to metal fittings.

Reinforced concrete supports of contact networks are the most vulnerable components on electrified sections of railways.

Ways to combat corrosion of reinforcement

IN modern construction water-repellent lubricants and protective coatings for fittings are used. One of the ways to protect metal elements is to provide a concrete cushion of the required size with the help of clamps.

One of the main difficulties in combating corrosion of reinforcement is the impossibility of metal re-treatment, which can be carried out for open metal structures.

Most promising direction the use of polymer mixtures in the composition of concrete is considered. Polymers introduced into concrete in combination with cement create additional protection for reinforcement. In some cases, cement is completely replaced by polymers, obtaining polymer concrete.

For thin-walled structures, it is possible to use fundamentally new materials:

• steel-fiber-reinforced concrete is a concrete mixture to which steel wire trimmings are added, occupying up to 6% of the total volume of the material;
• In addition to traditional components, alkali-resistant fiberglass is added to fiberglass concrete.

So far no universal and effective ways to combat metal corrosion in reinforced concrete, builders are forced to lay reinforcement in more than it should be in accordance with the technical calculations.

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The durability and strength of concrete structures largely depends on the degree and quality of waterproofing performed before construction begins. Only well-chosen waterproofing systems can prevent the ingress of substances that destroy it into concrete, which can extend the life of a concrete structure and also significantly reduce the cost of its maintenance and restoration.

Concrete is a very durable material in its structure, which can only grow stronger over the years, but only if the conditions for its preparation and operation were correctly observed. The durability of concrete directly depends on the conditions of its environment. Periodic exposure of concrete to an aggressive environment, frost, water, moisture leads to the fact that concrete structures collapse over the years, and the once strongest material turns into dust.

Corrosion protection is essential:

• for bridges and facades, periodically getting wet from precipitation;
• so that aggressive reagents and industrial gases do not destroy concrete;
• to waterproof concrete structures of various tanks that are constantly in contact with water. In this case, materials are used that guarantee not only high waterproofing, but also resistance to chemicals and abrasive loads. By the way, in such tanks, the depth of corrosion damage can reach 50 cm.

Materials for concrete protection

Water-repellent substances will help protect the concrete structure from corrosion, moisture and destruction, as well as increase the strength of the material.

There are two ways to improve the quality of concrete products from cement:

1. Impregnation of concrete. As a result, the contact angle decreases due to the impregnation of concrete with an organosilicon composition. Advantage this method in that the silicon-containing substance is quite durable, has waterproof properties and strength. Such substances in the form of enamel can be purchased at any hardware store. The disadvantage of this method is the fragility of the coating. Under the influence of alkalis, it becomes soluble and loses its hydrophobic properties.

1. Creation of a waterproof film when a concrete structure is formed on the surface protective layer from various resins - polyurethane, polyvinyl chloride and so on. The disadvantage of this method is low vapor permeability. With prolonged exposure to steam on the coating, it collapses and delaminates.

To get rid of these shortcomings, it is necessary to combine both the impregnation and the protective layer, but on the basis of one protective composition. In this case, the film must be resistant to alkalis, and the protective layer must have increased vapor permeability.

Material Requirements

Requirements for materials to protect concrete from corrosion:

1. The material to protect concrete from corrosion must have technical certificate and comply with the requirements of GOST.
2. Apply protective equipment necessary, taking into account the impact on the concrete of the external environment.
3. Corrosion protection materials are selected based on their fire resistance.
4. To protect the concrete surface of an underground structure, an anti-corrosion material is selected taking into account the type of reinforced concrete product, its arrays, construction technology.
5. Underground structures in contact with groundwater or soil should be protected from corrosion, taking into account the possibility of rising groundwater.

Protection of concrete from destruction

Protecting concrete from further destruction under the action of an aggressive environment is the primary task of builders both during its construction and before finishing work.

1. Moisture, and as a result, the fungus on the surface, are the first destroyers of concrete, which is in a humid environment. The means of protection against destruction by fungus include antiseptics, paints and varnishes, antifungal impregnations.
2. During the manufacture of concrete structure elements and their further construction, it is necessary to carefully observe the technology and use the composition of materials that can withstand environment where the structure will be installed.
3. It is possible to protect concrete from destruction by applying an anti-corrosion coating, impregnation and insulation on it.

Corrosion protection of concrete

The first sign of corrosion on concrete is the appearance of small cracks. Concrete made on a mineral basis is porous in its structure. And it is precisely when chemical precipitation and moisture that destroy it get into the pores of concrete, corrosion occurs that destroys concrete.

There are three types of concrete corrosion:

• chemical corrosion;
• chemical-physical corrosion;
• biological corrosion of concrete.

Chemical corrosion occurs under the influence of precipitation, especially with the presence of sulfates. Acid rain has a detrimental effect on the concrete facade, which leaches it. A clear sign of leaching is white stains on the concrete structure. In the future, the concrete cracks, under the influence of internal stress.

Getting into the pores of concrete in winter, moisture freezes, and thaws in spring. This action on concrete is called chemical-physical corrosion. The ice inside the concrete breaks it down over time.

In case of improper use of concrete building structure biological corrosion occurs, the cause of which are microorganisms that form chemical compounds and thus destroy the concrete.

Methods for protecting concrete from corrosion:

1. Corrosion successfully develops due to the porosity of concrete. Therefore, it is very important to limit concrete structures from contact with moisture, as well as to eliminate the possible impact of precipitation. If this cannot be avoided, then it is necessary to produce concrete with increased density, without pores. Or, apply to the design protective covering with hydrophobic properties.
2. Water repellent - the best option concrete protection. It differs from water-repellent coatings in that it preserves the porosity of the material, providing guaranteed protection for the structure at an ambient temperature of minus 40 to plus 50 degrees.
   Among other things, the water repellent prevents the concrete from cracking.

It is most reliable to carry out anticorrosion protection of concrete in several stages:

• the introduction of various additives into cement, which increase its density and regulate porosity;
• the use of antifungal materials. Impregnations that seal the structure of concrete. Paints and varnishes are used to protect against moisture;
• the use of carbon fiber belts that are not subject to corrosion. They are especially necessary in the case when the carrier has rusted metal structure structures.

Protection of concrete from moisture

With the onset of bad weather outside the window, the issue of protecting concrete from moisture becomes relevant. A concrete basement, a garage, dams on a dam, a foundation - all these structures require protection from the water that destroys them. raw walls concrete structures are easily saturated with moisture and mold. These influences further lead to their destruction.

Previously, in the fight against moisture, only dry cement mixtures, roofing felt, synthetic gaskets and sheets. This, of course, is not enough to fully protect the concrete from water. The first in the fight against excess liquid is the treatment of concrete surfaces with materials with water-repellent abilities. The water-repellent coating will fill the cracks and pores of concrete, providing it with reliable protection and durability.

By its structure, the concrete foundation has the ability to absorb moisture in unlimited quantities. Naturally than worse quality solution and the lower its price, the worse its ability to repel water. Therefore, when you come to a specialized store, choose only high-quality and preferably certified materials.

Of course, the foundation does not need to be treated with coating water repellents in cases where favorable conditions its operation. I.e dry room with minimal moisture.

You can protect the finished foundation from moisture in several stages:

• a sheet of roofing material or waterproof building material is laid on the finished dry layer of the foundation;
• the seams of the sheets are smeared with bituminous emulsion;
• top sheets are covered with a water-repellent coating, varnish or paint.

Outdoor Concrete Protection Methods

On the street, concrete can be protected in the following ways:

1. Application of UV resistant coatings.
2. Wear-resistant coatings for outdoor areas.
3. The use of fluating impregnation, which improves the strength of street concrete and resistance to chemical attack.
4. Application of polyurethane and epoxy coatings.

Any object, like the environment that surrounds it, is unique in its properties. Therefore, it is necessary to choose wisely waterproofing materials and accurately determine their compatibility with the concrete structure being designed.

Protecting concrete from destruction by corrosion, moisture and temperatures is a top priority in the planning and construction of reinforced concrete and concrete structures. Compliance elementary rules protection of the foundation with the help of high-quality materials, will provide it with strength and long term operation.