Waterproof concrete: description, types, characteristics, photos, videos.

Speaking about concrete, I would like to note that its water resistance depends on density, and density depends on the presence of pores and voids, which are formed as a result of improper selection of source materials and granulometric (grain) composition of aggregates, insufficient compaction of the concrete mixture and especially from excess water in solution (as water evaporates, it leaves pores).

The water-cement ratio, that is, the ratio of the mass of water to the mass of cement, is very important for the waterproofness of concrete.

If the amount of gravel in the concrete mixture does not exceed more than twice the amount of sand, then the concrete is quite dense and easily compacted. In this case, the lowest porosity is achieved when using sand, in which the proportion of grains with a size of 0.25; 1 and 3 mm is 25; 25 and 50% respectively.

To make waterproof concrete, you can use cement grade 300 or 400 (must be freshly prepared). Before using cement, it is recommended to sift it through a sieve (mesh size - 1 x 1 mm) to remove lumps formed during storage.

The size of gravel (crushed stone) should not exceed 1/3–1/4 of the thickness of the concrete walls.

In this case, the size of small crushed stones should be 2–3 times smaller than large particles. The total volume of fine-grained gravel should be at least 20% of the volume of coarse-grained gravel. It is recommended to select aggregates not from porous, but from dense rocks. For example, crushed stone of granite rocks is more preferable than crushed stone of limestone rocks.

When ensuring the waterproofness of concrete, the conditions of cement hardening, or hydration, are of no small importance. In order to create normal conditions, it is necessary to select the minimum amount of water that would simultaneously ensure normal hardening of concrete and good plasticity during laying.

So, to obtain waterproof concrete, you need to take cement, sand and gravel (crushed stone) in a ratio of 1: 1: 4 or 1: 2: 3 with a water-cement ratio of 0.5–0.7. You can increase the amount of sand and gravel by taking the components in a ratio of 1: 2.5: 5.5.

It is advisable to carry out the laying of waterproof concrete without interruption, for which all the necessary material and formwork should be prepared in advance. With careful and proper preparation of concrete, you can obtain fairly dense and waterproof concrete with a masonry thickness of 10 to 40 cm.

To speed up the hardening of concrete, it should be tightly covered with plastic film. If the strength of concrete still turns out to be low, the following measures must be taken: reduce the amount of water, leaving the volume of cement unchanged, reduce the amount of sand and increase the amount of crushed stone.

Does concrete allow water to pass through?

Once the cause of dampness has been established, waterproofing of concrete structures can begin.
There are so many ways to waterproof concrete structures that it’s easy to get confused. Here are brief practical recommendations for choosing waterproofing materials that change the properties of concrete, i.e. making the concrete itself a waterproofing and protective layer.

There are two main directions (classes) of how to make concrete a waterproofing and protective layer:

1. Make concrete waterproof
2. Make concrete waterproof

Waterproof concrete

1.1. Features of waterproof concrete

The job of waterproof concrete is to:

• or “repel” water (not get wet), which is ensured by the use of water repellents:

Photo 1. Operation of water repellent

• or do not let water inside, but if there is no high water pressure, which is ensured by partial closure of capillaries by using clogging materials in minimal dosages, or better yet, specially developed materials for partial clogging (such as Kontacid grade 3):

Photo 2. Work of Contacida brand 3

Hence the main use of waterproof (and especially hydrophobized) concrete is above the water level (i.e. protection from dampness and corrosion):

• walls in the above-ground part of the structure on the windward side;
• concrete floor in workshops, warehouses, not in contact with groundwater.

1.2. Obtaining waterproof concrete

You can get waterproof concrete:

• from a concrete mixture , for example, by introducing into it a water repellent or a bridging additive (optimized in quantity and formulation - such as Kontacid grade 3 (for highly porous concrete) or Betonoprav luxury grade 2 (for ordinary low-porous concrete));
• or by treating the existing concrete with a water repellent or bridging impregnation (optimized in quantity and formulation - such as Contacid grade 3 solution).

However, when using a water repellent, you should remember its features. Any water repellent, due to its water-repellent properties (i.e. the target effect - see photo 1), is a material that prevents:

• penetration of aqueous solutions into the substrate, incl. clogging pores;
• wetting the substrate and adhesion of water-containing solutions to it, incl. solutions based on cement, lime, gypsum, as well as water-based paints and varnishes.

Taking into account these features of water repellents, the creation of water-resistant concrete using a system of compatible materials Dehydrol, Betonoprav, Kontatsid is based on partial clogging (see photo 2). For the production of homogeneous, highly water-resistant concrete, incl. on porous aggregates, you can use the optimized additive Betonoprav lux grade 2 in an amount of 3-4 liters per cubic meter of concrete mixture. This additive also gives concrete corrosion resistance (frost resistance) and further increases its water resistance.

Example of a waterproof concrete recipe:

In the case of cellular concrete (foam concrete, aerated concrete), Contacid grade 3 should be used.

Waterproof concretes are not able to effectively withstand water pressure; they are resistant to splashes of water or to slight moisture, i.e., mainly dampness. If you need concrete to withstand water pressure, such as in underground structures or tanks, then you need waterproof concrete.

Waterproof concrete

The term “waterproof concrete” itself characterizes the way such concrete works and typical areas of its application - where it is necessary that water does not pass through the concrete even in the presence of water pressure:

• water intake and water treatment blocks, drinking water collectors and reservoirs, concrete filter structures, settling tanks and process water collectors, aeration tanks, cesspools, treatment plant tanks, concrete collectors;
• dams, dikes, walls and galleries in them, concrete conduits, cooling towers, fountains;
• underground and buried structures and structures (including warehouses, trading floors, basements, shelters, ground floors, underground garages, parking lots, cellars, foundations, sewage pumping stations), damp, wet and freezing walls.

To obtain waterproof concrete, methods are used to reduce its porosity, for example, clogging.

When a waterproofing additive is introduced into a concrete mixture, the entire thickness of the concrete becomes waterproof.

Example of a waterproof concrete recipe:

The main characteristic of waterproof concrete is its waterproof grade. For example, adding Dehydrol Lux grade 10-2 to a concrete mixture allows you to obtain concrete with water resistance up to grade W20.

It would seem that concrete with water resistance grade W20 can withstand 200 meters of water column without filtration - an excessive value for conventional construction, but this is not the case. The fact is that tests of concrete for water resistance in accordance with GOST 12730.5-84 (from 09/01/2019 GOST 12730.5-2018) are carried out on samples with a thickness of no more than 150 mm, and the samples are kept under a given water pressure for no more than 16 hours. This gives a common standard for determining and fixing the water resistance of concrete. Naturally, in practice, conditions may differ radically from GOST standards, in particular:

• groundwater backs up concrete basement structures in spring and autumn not for 16 hours, but tens and hundreds of times longer;
• the thickness of most foundation blocks is 400 or 600 mm, and the thickness of monolithic walls is 100 mm or more;
• concrete may contain porous (insufficiently compacted) areas.

The task of the civil engineer is precisely to take into account the complex influence of various factors and ensure the watertightness of the concrete structure.

Source

Water absorption and permeability of concrete

Thanks to its capillary-porous structure, concrete can absorb moisture both upon contact with it and directly from the air. Hygroscopic moisture absorption in heavy concrete is insignificant, but in lightweight concrete (and especially in cellular concrete) it can reach 7.8 and 20.25%, respectively.

Water absorption characterizes the ability of concrete to absorb moisture in a drop-liquid state; it depends mainly on the nature of the pores. The greater the number of capillary interconnected pores in the concrete, the greater the water absorption. The maximum water absorption of heavy concrete with dense aggregates reaches 4.8% by weight (10.20% by volume). For lightweight and cellular concrete this figure is significantly higher.

High water absorption negatively affects the frost resistance of concrete. To reduce water absorption, they resort to hydrophobization of concrete, as well as vapor and waterproofing of structures.

The water permeability of concrete is determined mainly by the permeability of the cement stone and the contact zone “cement stone - aggregate”; In addition, microcracks in the cement stone and defects in the adhesion of reinforcement to concrete can be the paths for filtration of liquid through concrete. The high water permeability of concrete can lead to its rapid destruction due to corrosion of the cement stone.

To reduce water permeability, it is necessary to use fillers of appropriate quality (with a clean surface), as well as use special compacting additives (liquid eraser, ferric chloride) or expanding cements. The latter are used for concrete waterproofing.

Based on water resistance, concrete is divided into grades W2; W4; W6; W8 and W12. The mark indicates the water pressure (kgf/cm2), at which a 15 cm high cylinder sample does not allow water to pass through during standard tests.

Preventing moisture evaporation from the surface of a concrete structure and from the concrete mixture

Why is there a need to protect freshly poured and compacted concrete mixtures from moisture evaporation not only from its surface, but also from the concrete mixture itself?

First, let's define what concrete is? The structural elements of the concrete mixture are: cement stone, coarse aggregate and sand.

After the concrete mixture has hardened, the structure of heavy concrete is a cement stone with aggregate grains embedded in it, which has many pores and voids of different sizes and origins.

To make cement stone, you need to mix cement with water. Moreover, there must be enough water for the cement to hydrate , and therefore for the concrete to gain strength.

Let's look at what cement hydration is and what role it plays in concrete production.

Cement hydration is a chemical reaction of cement with water, during which liquid or plastic cement glue (cement + water) turns into cement stone. The first stage of this process is called thickening or setting, the second is called hardening or hardening.

The process of cement hydration is the most important and decisive in the entire production of a concrete structure. The change in any property of concrete is determined precisely by this process. The conditions under which the hydration process occurs determines the change in both the structure of concrete and its properties.

As the hydration process fades and ends, all changes in the properties of concrete fade and stabilize over time.

The cement paste itself, which turns into cement stone, is a hygroscopic substance (capable of absorbing water vapor from the air) since the cement particles are hydrophilic in nature (the ability to absorb water well), and the cement paste itself contains micropores.

During the process of cement hydration, large capillary pores appear in the cement stone, formed during the preparation of cement paste.

Why do pores appear in cement stone?

The fact is that for complete hydration of all cement minerals, that is, for cement to completely react with water, approximately 18% of the mass of cement is required (water-cement ratio W/C = 0.18). But in order to obtain a mobile, and therefore workable, mixture, much more water is added, and the value of the water-cement ratio in most cases varies from 0.4 to 1 (W/C = 0.4 ÷ 1). That is, 2 ÷ 4 times more water is added than is needed for normal mixing of cement.

What happens to the excess water that is not used to hydrate the cement? It evaporates, and in place of the evaporated water, capillary pores are formed, available for moisture migration. And the basic law of the strength of stone materials: the curve of the dependence of strength on porosity is hyperbolic in nature - the greater the porosity, the lower the strength.

In addition, during the process of hydration, a redistribution of water quality occurs: due to a decrease in the amount of free or capillary water, the amount of chemically and physico-chemically bound water increases. That is, in order for cement hydration to occur normally, a sufficient amount of free water is necessary.

GOST provides for determining the standard strength of concrete at the age of 28 days. In this case, it must harden at a normal temperature of 20 ± 2 ° C and a relative humidity of 90-100%.

How to make concrete waterproof

Currently, the construction business is developing at a very rapid pace throughout the world. Every year thousands of buildings and structures are erected and reconstructed, new building materials and substances (additives) are synthesized that improve the quality of structures and increase their strength. Much attention in this area is paid to the foundation. It is the basis of any building or home. The durability of the structure itself largely depends on its strength and durability. A mixture is most often used to make the foundation. Concrete is an artificial building material with high strength, obtained by mixing various ingredients: sand, crushed stone, cement powder and water.

The mixture is used at any stage of construction - from pouring the foundation to screeding the floor and leveling the walls.

Often some special additives are introduced into it, which increase its strength and wear resistance. These include water repellents, which increase resistance to moisture. Hygroscopicity is an important property that protects the structure from water. But not all building materials meet such requirements. Let's take a closer look at how to make concrete waterproof, the necessary materials, mixtures and solutions.

Mold and mildew thrive in finished basements!

Moisture promotes the formation of mold, mildew, dust mites and other biological air pollutants that cause allergies, asthma or other health problems. Ventilation distributes moisture and bio-pollutants throughout the house.

Harmful microorganisms need high humidity, porous materials (concrete). They develop in carpeting, upholstered furniture, drywall, wood paneling and damp fiberglass insulation. In the presence of mold, volatile organic compounds (such as aldehydes) are formed on cellulose, which we recognize as a musty odor.

The destructive effect of moisture

Making concrete waterproof with your own hands is not difficult. But before that, you need to know for what purpose all this is used. To make it waterproof means to waterproof it.

Waterproofing can be of various types: pasting, coating, using roll materials.

Waterproofing a concrete foundation must be carried out using one of the following methods in order to prevent premature destruction of the building structure.

In addition, it is carried out both at the stage of laying the foundation and during its operation. Its main goal is to ensure the hygroscopicity of the foundation. The latter is laid below the ground level, as a result of which it comes into contact with groundwater. How can water destroy concrete?

This will undoubtedly happen within a few years or even decades. Poor quality has the ability to absorb moisture, as it has micropores. In the winter season, the water freezes, and its volume increases sharply in size. As a result, the pores expand and cracks may appear. The next year, water again enters the micropores, but in larger quantities. Thus, every year the concrete absorbs more and more liquid and gradually deteriorates. In addition, water can penetrate into the foundation of the building.

How is it different from ordinary ones?

Surface primers, penetrating into the pores of concrete, create a kind of protective film.
It prevents surface cracking, protects against moisture and the development of pathogenic flora. Deep penetration impregnation has the following differences:

1. More liquid, which makes it easier to penetrate into the thickness of concrete.
2. Contains polymers and active substances that increase the wear resistance of concrete.
3. Increases impact resistance, which is especially necessary in those rooms where there is an increased load on the concrete surface.
4. It does not require grinding or polishing, since it is completely absorbed and creates a glossy coating on the surface.
5. Prevents the absorption of moisture by the pores of the concrete structure, and accordingly there is no development of bacterial flora.
6. Dries relatively quickly under any microclimatic conditions.

Impregnation prevents the formation of cracks and dust during the operation of the concrete coating. It has a prolonged service life, but can be reused if there is a need to strengthen the structure. In addition to strengthening concrete, impregnation also plays a decorative role, creating a glossy finish.

Brand meaning

Waterproofing of concrete can be carried out both at the stage of preparing the mixture, and with the help of special protective agents applied to the hardened concrete surface.

It is possible to make concrete waterproof with your own hands, knowing that its properties are influenced by the quality of the raw materials. Water resistance is determined by the so-called water-cement ratio, which directly depends on the water content in concrete and the brand of cement used. As the amount of cement increases, the water-cement ratio decreases. This ensures that the concrete does not delaminate, increases its strength and, as a result, resistance to moisture. The brand of cement itself is also of great importance. In most cases, manufacturers do not use expensive cement because it is not profitable.

Finely ground cement is well suited for these purposes, as it promotes the formation of smaller pores that are evenly distributed throughout the entire volume and reduces the sedimentation of particles. Higher water content increases filtration and thereby increases the water load. Portland cement is very widespread. Based on these data, we can say: the lower the water-cement ratio in concrete, the better.

Methods for determining the resistance of concrete to moisture penetration

Water resistance is characterized by direct and indirect indicators. The main indicators include:

• Brand determined using the “wet spot” technology . This determines the maximum pressure under which the sample remains impenetrable to water. Tests are carried out on a special installation with nests for 6 samples, which can have a height of 30, 50, 100, 150 mm. The load applied to the samples is gradually increased until a “wet spot” appears. The maximum pressure is considered to be at which a “wet spot” appears on two out of six samples.
• Filtration coefficient . Calculation of the filtration coefficient of concrete of various waterproof grades is carried out using a special installation that supplies water to the samples under a pressure of 1.3 MPa.

Table of direct and indirect indicators of concrete water permeability

Indirect indicators (relevant for heavy concrete)

Waterproof grade

Maximum pressure, MPa

Filtration coefficient, cm/s

Water-cement ratio (water/cement)

Painting waterproofing

Painting waterproofing of concrete is a rather complex and labor-intensive process that requires the use of special equipment. This method is more often used in the construction of large industrial facilities.

It is possible to make concrete waterproof using surfactants. They form a waterproof layer (film) on the concrete surface. These substances are applied using special equipment: pistols, sprayers. Most often, bitumen heated to high temperatures, mastics, emulsions and other mixtures are used. Some of them are not able to withstand low temperatures and often become covered with cracks. To give concrete special properties, its surface is carefully processed and cleaned before applying the painting material.

Then a layer of paint or any other mixture is applied, its thickness can be different, on average several millimeters. A layer of primer is placed on it. Currently, hydrophobic solutions based on organosilicate compounds are widely used. But they do not completely close the pores in concrete; therefore, they are only relevant for protection from precipitation and low water pressure. Fluates, salts of fluoric acid, are also highly effective. But they are only suitable for finely porous concrete. The use of bitumen mastic can give good results. It consists of bitumen and a mineral component (limestone, clay). Their ratio varies. The percentage of bitumen in the mixture ranges from 30 to 45%. Moreover, such a coating material has high frost resistance.

Work with concrete in water for private housing construction

The above methods are of little use in private residential buildings, since they are very expensive and difficult to implement. But there are other ways to pour concrete into water, if necessary.

Construction of the foundation using bags

The simplest way to arrange the foundation of a house is “bag technology”, similar to that used with the caisson method. First, prepare a saturated concrete solution, fill bags with it, then put them in a trench or pit. The pit is filled with bags so that they exceed the groundwater level. The structure is allowed to harden for a month, and then the formwork is installed and the foundation is poured in the usual way.

Coating option

To waterproof concrete surfaces, they are coated with special waterproofing compounds that penetrate into the thickness of the concrete and clog the pores.

Waterproof concrete can be obtained by applying coating materials to its surface. They can be used as hot mixtures based on bitumen and mastic. To do this, it is important to prepare the concrete surface for processing. She is being cleansed. Then 2 layers of primer are applied. The first includes a slow-acting solvent, the second - a fast-acting one. These layers contribute to better adhesion of the coating solution and the concrete surface. The coating material is applied in two layers. First one, then the second. Within a few minutes you can observe how a special protective film forms on the concrete.

This method is better than painting, as it is more durable. But it also has a number of disadvantages. The most important of them is that even with slight deformation of the concrete and its surface, the coating can collapse. In addition, there are often cases of coating dripping. The reason for this is the incorrect selection of mastic. It is very important to know that the coating is applied in 2 layers, each about 2 mm thick. After applying the feather coat, you need to carefully check the quality of the coating and only then continue working.

Waterproofness of concrete: what is it and what does it depend on?

Concrete is one of the most common materials in construction work.

Since it is used to make objects that come into direct contact with adverse environmental conditions, the ability of concrete to resist water permeation is of great importance.

Why can concrete allow water to pass through, and what are the consequences?

The fact is that, although concrete looks very dense and invulnerable, it has a large number of pores and capillaries in its structure.

Water enters the concrete through capillaries. As a result, the vital activity of bacteria and fungi can develop there, the spores of which are always present in the air and water. These microorganisms and microflora can seriously harm concrete, since their metabolic products contain acids and alkalis that are harmful to it.

During cold seasons, when the air temperature drops below zero, the water in the pores of concrete freezes and, according to the laws of physics, expands. Repeated cycles of freezing and thawing lead to the appearance of microcracks, which allow even more water to enter. This is how the durable and strong material gradually breaks down.

The water resistance of concrete is especially important for structures that will become wet during operation: facades of buildings that become wet from precipitation and can absorb moisture from the air; foundations, especially on wet soils in which water easily moves both up and down the ground near walls and under the basement floor; hydraulic structures; floors in industrial premises, etc.

Application of plaster

Today, the use of plaster as a waterproofing material is widely used in construction. It is prepared from fatty cement mortars. It may contain various additives. Some of them help fill pores and cracks in concrete with small particles, others are needed for the formation of crystalline substances as a result of chemical reactions with concrete.

The water resistance of concrete is ensured by various additives and plasticizers that compact the material and change its properties.

A special place is occupied by plasticizers or foaming agents, which reduce the water-cement ratio, change the shape of the surface and prevent the penetration of liquid.

Compacting additives include ceresite, cerolite, stone flour, ground sand and others.

Plasticizers include rosin soap, wood pitch, and oleates. The technique for applying the solution is as follows: first, clean the surface, then, following the instructions for use, apply a layer of plaster at least 2.5 cm thick, otherwise it will not be effective. It is very important to ensure good grip on the surface. For this purpose, the solution is applied only mechanically.

To increase the water resistance of the concrete mixture, aluminate is added to it at the stage of preparing the solution.

In manufactured concrete you can often find various types of impurities - additives. In recent years, a compound that imparts hygroscopicity, such as sodium aluminate, has been valued. When it is contained in the solution (from 3 to 5%), water resistance increases, and concrete can better withstand high pressure. Another very valuable property is that sodium aluminate does not cause corrosion of reinforcement. Solutions based on it are very stable and do not smear when exposed to water and high pressure. But besides the positive aspects, there are also negative ones.

Aluminate speeds up the setting time of the solution to 10 - 15 minutes, which is inconvenient in most cases. You can increase the time by using sulfite-alcohol stillage. But it will slightly reduce the water resistance. It is also of great practical importance that aluminate-based solutions can be widely used during repair work to seal cracks and seams. It is recommended to work with these additives only at positive temperatures, and the concrete and mortars are kept in a wet state for several days.

Penetrating waterproofing Kalmatron

Kalmatron is a well-known brand of waterproofing products that provide reliable protection of concrete surfaces from moisture.

Waterproofing material Kalmatron has found wide application as a means of increasing the hygroscopicity of structures and frost resistance during their repair and new construction of buildings and structures. This is a complex preparation that includes purified quartz sand, Portland cement and mineral additives. The mechanism of its action is based on the fact that when the mixture interacts with the surface of concrete, chemical reactions begin to take place, resulting in the formation of an electrolytic solution. Thanks to the laws of osmotic pressure, it penetrates deep into the structure and contributes to the filling of larger pores with crystalline structures.

This increases the strength of the structure, reduces porosity, but maintains vapor permeability, which is very important for future operation. Its service life increases sharply, the water resistance class of products increases, resistance to low and high temperatures and their differences increases, and mechanical strength increases. A characteristic feature is that minor damage can heal on its own, but only in the presence of moisture.

Other Supplements

Various additives and pigments significantly improve its performance characteristics: they increase frost resistance, water resistance, hygroscopicity, anti-corrosion, etc.

Today, in times of scientific and technological progress, there are many different additives that are included in mixtures. This includes the well-known potash, ferric chloride, and sodium abietate. Ferric chloride is introduced into concrete in an amount of 2-5% by weight of cement. Its mechanism of action is based on the synthesis of aluminum hydroxide, which increases the hygroscopicity of the structure and solution. A special place is occupied by those substances that increase resistance to low temperatures. These include sodium bienate and calcium chloride.

As mentioned above, frost resistance of building materials is an important property, especially for our country. In winter, the soil can freeze to a considerable depth. The foundation is laid shallow, so the water that is at this level during the cold season freezes and gradually destroys the coating.

Preparatory work

Before you begin laying concrete directly into the water, you need to draw up a project that describes the order and progress of the work, the volume of material, the necessary equipment and accessories. As a rule, at significant depths, divers are required to outline a plan for clearing the concrete area or clear it manually, install the formwork, and regulate the placement of pipes and hoses through which the pouring mixture flows.

The concrete solution is prepared at the factory in accordance with a certain recipe. For different methods involving pouring into water, the grade of concrete should be 10-20% higher than if laying was carried out under normal conditions; in this case, it is necessary to reduce the ratio of water and cement in the finished solution. Water slows down the hardening process, so it is advisable to introduce accelerators and plasticizers. Anti-erosion additives increase the resistance of structures to erosion.

Special requirements are also imposed on formwork. She must be:

1. impermeable to the concrete mixture, including at joints;
2. holds its shape well despite the water pressure;
3. easy to install.

From the outside, the formwork is additionally reinforced with stone or sandbags.

Waterproof concrete

The water resistance of concrete is one of the main qualities of a building material. It has no voids in its structure and is dense. The seams between the sections are filled with a waterproofing substance. Concrete has specific characteristics, has a number of advantages and is widely used. Waterproof concrete is used only in monolithic structures (for foundations), because prefabricated buildings have many seams, which makes it impossible to achieve moisture impermeability.

Waterproof concrete is designated by the letter W, even numbers from two to twenty. They mean the level of pressure (measured in MPa x 10 -1 degrees), at which waterproof concrete can withstand water pressure and prevent the passage of moisture.

What affects the waterproof rating?

The water resistance of concrete is a specific characteristic that a concrete solution has. It is influenced by a large number of factors, including:

• the age of the concrete itself. The older it is, the better it is protected from the damaging effects of moisture;
• environmental influences;
• use of additive. For example, aluminum sulfate increases the density of concrete. Builders achieve this using vibration, press action, and vacuum removal of moisture.

As concrete hardens, pores may form. Reasons for this:

• insufficient mixture density;
• presence of excess water;
• reduction in the volume of building materials during shrinkage.

Shrinkage should be minimal for this type of concrete mixture. To avoid problems, follow these steps:

1. moistening fresh concrete every three hours for the first three days;
2. cover the concrete-filled area with damp burlap or film;
3. do not forget about a special product that forms a film.

Characteristics of concrete grades for water resistance

Table for selecting concrete grades based on frost resistance and water resistance.
The market offers a huge selection of building materials. And it is not always possible for an ordinary consumer to determine the brand he needs. Therefore, you should familiarize yourself with the possible labeling and use of these brands of mixtures in practice. There is a table corresponding to the strength class of concrete and its brand.

According to GOST, there are requirements for brands that are necessary to achieve the desired result. The most commonly used grades of concrete are waterproof grades no lower than W6. Every brand has limitations. It is thanks to the brands that you can understand what water pressure the concrete solution can withstand.

Indicators that determine the interaction of concrete with water are identified. This:

• straight (the level of water resistance that corresponds to the brand, and the coefficient of possible filtration);
• indirect (the ratio of water and cement, its absorption in accordance with mass).

In everyday life, attention is often paid to the first indicator - the water resistance of concrete; it is considered indicative. The remaining three components are used less frequently, and then only in the process of producing the mixture or in scientific experiments. Each grade characterizes the degree of interaction of moisture with concrete, which can be either less or more. The main brands are considered to be:

1. W4. She has a normal degree of permeability. This means that the absorbed level of moisture is within normal limits, but use for buildings with a good level of waterproofing is not suitable.
2. W6. Moisture permeability is reduced. Unlike the previous one, it is of average quality, more moisture-proof, and is used most often in construction work.
3. W8. Mixture with low water resistance. Permits moisture in small quantities. The mixture turns out more expensive than the previous one.

Brands that go further down the line become more hydrophobic. The most resistant to moisture is the W20 mixture, but it is rarely used due to its high price. Therefore, W10-W20 is used for the construction of reservoirs, bunkers or hydraulic structures. They have one more, rather positive, quality - frost resistance.

It is important to be able to select the class of concrete and its purpose. So, in order to fill the foundation, it is necessary to make W8, and at the same time make additional waterproofing. You can plaster walls in a room with normal humidity using W8-W14. When the room is cold and damp, it is better to use higher markings, while doing additional treatment with a special primer composition.

When finishing the external walls of a house, it is necessary to use the highest grades to ensure the best level of waterproofing. This is important because there will be constant changes in the environment and dampness should not enter the house.

Proportions for concrete mixture

To make the desired concrete mixture, it is necessary to strictly adhere to the proportions, because deviation to the side will worsen the properties.
This will prevent unnecessary translation of material. You can prepare it either with your own hands or using a special mixer. The main focus is on the proportion between water and cement. The cement must be taken fresh, marked M300-M400, less often M200 (b15). Class B15 is a good average option. Before use, it is imperative to sift B15 through a sieve. The hydrophobic effect can be achieved by varying the amount of sand and gravel. So, there should be 2 times less sand than gravel.

Possible proportions of gravel, cement, sand are as follows: 4:1:1, 3:1:2, 5:1:2.5. The mass of water should be somewhere around 0.5-0.7. Thanks to these proportions, the mixture hardens well. Various additives are also used to achieve waterproofness.

Methods for determining water resistance

To determine the level of waterproof indicator, basic and auxiliary methods are used. The main ones include:

• “wet spot” method (measurement of the maximum pressure during which the sample does not allow water to pass through);
• filtration coefficient (calculation of the coefficient associated with constant pressure and time period of the filtration process).

The auxiliary methods include:

• determination by the type of substance that binds the solution (the content of a waterproof solution of hydrophobic cement, Portland cement);
• by the content of chemical additives (the use of special attachments makes the mixtures more waterproof);
• according to the pore structure of the materials (the number of pores decreases - the indicator increases, increasing the moisture-resistant quality with the help of sand, gravel).

How to treat concrete

To prevent the mixture from allowing water and evaporation to pass through during operation, special additives are added to the composition. You can increase resistance to moisture using liquid glass (silicate glue), which covers the surface of the pouring with an elastic film.

An effective remedy is mastic, which is evenly applied to the hardening surface after the concrete has set. Before applying the waterproofing layer, the surface is cleared of debris and a primer is applied. Depending on the recipe, hot or cold mastic is applied in a thin layer, 2 mm thick several times. To complete the treatment of the object, you can apply a concrete emulsion, primer and the selected paint coating to enhance the waterproof effect.

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What is added to concrete to make it waterproof?

The principle of action of additives in concrete.
Additives are the main component in a concrete mixture, increasing its waterproofing properties. Concrete becomes moisture resistant and durable. But this mixture should only be used on horizontal surfaces, since on vertical surfaces it simply slides down. Of course, this can be avoided by using a special protective film that presses the solution against the structure. But it will take a lot of time and effort.

The market puts forward a huge number of different additives, with different prices. There are several substances that are most commonly used as additives. This:

1. silicate glue;
2. ferric chloride;
3. calcium nitrate. Perhaps the cheapest option, which has excellent resistance to moisture. It dissolves well in water, is not toxic, however, it can cause a fire;
4. sodium oleate and many other additives that increase moisture-resistant quality.

You must add the component following the instructions!

There are discussions about what additives are best added to the concrete mixture: domestic or imported from abroad? A definite answer has not yet been found, since they all have good quality brands. But they still insist that domestic ones are better because they are distinguished by their low price, which means they can be used for mass use.