All ways to improve the water resistance of concrete: from the right choice of brand to the insulation of the finished surface. Overview of brands of concrete mixes for water resistance What is the water resistance of concrete

Technologies in construction allow us to implement more and more daring projects today. The safety of buildings and structures under construction is designed to ensure construction control.

One of the important factors in determining the quality of the finished structure is the assessment of the water resistance of concrete when constructing underground parts of buildings and individual structures that are below the horizon level in conditions of high humidity.

The durability of monolithic reinforced concrete structures depends on the ability of the material to resist the influence of various atmospheric factors and aggressive environments, including moisture and freezing.

The permeability of structures depends on the porosity of the concrete, the structure of the pores and the properties of the binder and aggregates. Small pores and capillaries, which include the pores of the cement gel, are practically impermeable to water. In larger pores, water is filtered due to pressure, moisture gradient or osmotic effect, for these reasons, wet spots and leaks are observed in structures.

According to GOST 26633-2012 “Concrete is heavy and fine-grained. Specifications” for monolithic structures, requirements are imposed to limit the permeability of concrete and the following water resistance grades are established: W2, W4, W6, W8, W10, W12, W14, W16, W18, W20.

The water resistance grade of concrete is determined by the water pressure at which no seepage is observed on four out of six samples when tested using the Wet Spot method. The obtained values ​​determine the maximum water pressure at which the concrete is waterproof and will not let moisture through.

There are several methods for determining the water resistance of concrete:

Determination of water resistance by the "Wet spot" method. The method is based on measurements of the maximum pressure at which water does not pass through the sample;

Determination of water resistance by filtration coefficient. The method is based on determining the filtration coefficient at constant pressure from the measured amount of filtrate and filtration time;

An accelerated method for determining the water resistance of concrete by the value of resistance to air penetration (air permeability).

The widespread use of the accelerated method is due to the fact that standard tests take a lot of time, for example, the test of B10 concrete using the “wet spot” method lasts more than 10 days, and when tested by the accelerated method for determining the water tightness in the structure, it will take no more than 2 hours.

It should also be taken into account that during the hardening of monolithic structures in air-dry conditions, the permeability of concrete is 10 times greater than during the hardening of control concrete samples in a normal storage chamber at a humidity of (95 ± 5)% and a temperature of (20 ± 5) 0 C.

In most cases, concrete watertightness requirements are imposed on vertical structures of underground structures, parts of buildings exposed to groundwater, and structures in contact with atmospheric precipitation. When inspecting buildings and structures, engineers of the Laboratory for Testing Building Materials and Structures conduct tests to determine the water resistance of concrete in existing structures using an accelerated method.

In the fourth quarter of 2014, in addition to the existing devices "Agama 2RM", for the needs of the Laboratory for Testing Building Materials and Structures of the State Budgetary Institution "CEIIS", a VIP 1.3 device was purchased, which today is one of the most modern developments of the Research and Production Enterprise "Interpribor".

The use of the VIP 1.3 device in the laboratory is due to the following objective indicators:

Possibility of testing on vertical surfaces and places with limited access;

Carrying out tests on sample cubes 150x150 mm and cores ø150 mm;

Ease of testing and automatic calculation by the device of the water resistance grade of concrete;

The device has two chambers: the central one is measuring, the outer one serves as a security zone for reliable isolation of the measuring chamber from the environment;

Measuring range of waterproof marks up to W20.

Tests to determine the water resistance grade of concrete are carried out by laboratory engineers at construction sites in the structure and in the laboratory on selected core samples.

Tests are carried out in strict accordance with the requirements of GOST 12730.5-84 "Methods for determining water resistance", the instrument's instructions and the approved method for performing work, developed by the Laboratory for Testing Building Materials and Structures of the State Budgetary Institution "CEIIS".

The quality and durability of concrete products largely depends on the brand of concrete chosen. It must comply with the operating conditions of the product. In particular, if constant contact of the material with water is implied, then it is necessary to use waterproof concrete, for example, grade W6, to which, in fact, this article is devoted.

Waterproof concrete

Marking waterproof concrete

The water resistance of concrete, as you might guess, is its ability to prevent water from passing under a certain pressure. As a rule, such material is used in the construction of various hydraulic structures, including water tanks. However, it should be noted that it comes in a variety of types and is designed for different purposes.

In particular, hydraulic concrete is primarily divided according to the degree of water resistance into:

• Underwater;
• Designed to be permanently in the water;
• For operation in the zone of variable water horizon;
• Subject to occasional water washing.

In addition, it is distinguished into the following types:

• Massive and non-massive;
• Designed for pressure and non-pressure structures.

To choose the right material, you need to understand its designations, which we will consider below.

In the photo - a hydraulic structure

Waterproof designation

As for water resistance, the material is divided into the following grades - W2, W4, W6, W20. The numbers indicate at what pressure it does not let water through. Thus, the water resistance of W6 concrete is 0.6 MPa.

Compressive strength

Another important indicator is compressive strength. This material parameter is determined at the age of 180 days. For construction, concrete of classes B10, B40 is used. For example, class B10 corresponds to the M150 concrete grade, B20 to the M250 grade, and B30 to M400.

Frost resistance

Hydroconcrete is also divided according to the degree of frost resistance. There are five of its brands - F50, F100, F150, F200 and F300. In this case, the numbers indicate the number of freezing and thawing cycles, after which its strength will decrease by no more than 25 percent.

Advice!
The requirement of frost resistance is imposed only on those hydraulic materials that are exposed to the simultaneous action of water and frost during operation.
Since the price of the solution depends on this indicator, it does not always make sense to purchase it.

Now, having understood the features of the marking, you can easily determine the characteristics of W6 concrete. That will allow you to choose the most suitable material for operation in certain conditions.

For example, concrete B20 W6 F150:

• Corresponds to the brand M250;
• Able to withstand water at a pressure of 0.6 MPa;
• Withstands 150 freeze and thaw cycles.

Pouring the foundation with concrete W6

Application

At first glance, it may seem that when building private houses with your own hands and for other domestic purposes, there is no need for waterproof concrete, since hydraulic structures are built very rarely. However, in reality this is not the case.

For example, the foundation of a house has to be constantly in contact with moisture. Therefore, for its construction, at least concrete B25 W6 F150 is needed. Moreover, in order to make the concrete foundation airtight, it is necessary not only to use a waterproof material for it, but also to provide waterproofing of the seams.

pool bowl

Also, the characteristics of concrete B25 W6 F100 allow it to be used in the construction of:

• Socles of houses;
• Piling manufacturing;
• Overlappings;
• Pool bowls;
• columns;
• Balok;
• Rigelei;
• Monolithic walls, etc.

Foundation blind area

Concrete B20 W6 F200 can be used when performing:

• Foundation blind areas;
• garden paths;
• Screeds in open gazebos, etc.

Advice!
Durable concrete grades are difficult to process.
Therefore, diamond tools are used for these purposes, for example, diamond drilling of holes in concrete or cutting of reinforced concrete with diamond wheels is often used.

How to make waterproof concrete

Concrete is a capillary-porous material, as a result of which, under a certain pressure, it becomes permeable to water. It follows that the permeability depends on the nature and degree of porosity of the massif. The denser the structure, the higher the water resistance, respectively.

Here are the main reasons why pores occur:

• The solution is not sufficiently compacted. To prevent this drawback, vibration installations are used.
• Presence of excess water.
• Excessive array shrinkage, i.e. when dried, it decreased in volume.

To obtain a material with a high degree of water resistance, the amount of water must be minimized. The optimal value is W/C=0.4.

Waterproofing additive

Reducing the water-cement ratio, for example, from W/C=0.5 to W/C=0.40, i.e. by 20 percent, achieved with the help of plasticizers or, in other words, waterproofing additives.

Thus, it is quite possible to obtain, for example, concrete in 25 f200 w6 on your own, even without vibration. The instructions for using these additives may be different, so you should read the instructions from the manufacturer on the package before use.

The use of waterproof concretes, such as W6, in construction can significantly extend the life of concrete structures. The only thing, when choosing a material, it is necessary to pay attention to its other characteristics, such as strength and frost resistance.

See the video in this article for more information on this topic.

The resistance of concrete to moisture and low temperatures is an important indicator of its quality and durability. A material capable of withstanding the negative effects of external factors for a long time is in great demand in construction, especially when erecting monolithic reinforced concrete structures.

The resistance of the surface of concrete products to water penetration makes it possible to use these materials in the construction of hydraulic and underground structures, bridges, embankments, foundation supports and other structures. The water resistance of concrete is denoted by the letter "W" and indicates the external pressure of water at which it begins to penetrate through the pores on the surface into the body of the concrete monolith. The value of this indicator determined by the standard may be in the range of W2-W20. For most buildings and structures, the resistance to moisture penetration of concrete elements, the water resistance grade of concrete does not exceed W6.

Characteristics of various concrete mixtures according to GOST

The definitions of the standard show that concretes with F150 - F250 indicators should be attributed to the most common grades in Russia. Classification according to GOST does not apply to concrete used for road construction and airfield runways.

Table of frost resistance and water resistance of concrete of various grades and classes

Methods for determining the frost resistance of concrete

The State Standard 10060-2012 specifies 4 methods of laboratory testing of hardened concrete for frost resistance and one chemical method. For each of them it is necessary to prepare test specimens in the form of concrete cubes with a rib length of 100 mm.

Prior to the start of testing, the samples must gain design. To do this, they are aged in a warm room for 28 days. If an extended study is required, it is possible to conduct intermediate tests 4, 7 and 14 days after pouring concrete into molds.

Testing may require:

• molds for making samples;
• racks for storage of samples;
• containers for water and chemicals.
• freezing equipment;
• thermal oven;

The technology of laboratory testing is that the samples are dipped into water to get wet, and then subjected to repeated freezing with subsequent heating. In this case, cooling occurs at a temperature of -130˚C, heating in an oven at +180˚C. As a result, if concrete samples do not lose strength and cracks do not form on them, then the frost resistance grade meets the stated requirements.

The very principle of laboratory testing is to confirm the declared results. Therefore, in practice, the real frost resistance of materials is always higher. This is due to the forced soaking of the samples and the large difference in cooling and heating rates.

How the tests happen, video

Accelerated chemical and visual methods

To conduct express tests, prepared concrete samples are immersed in sodium sulfate for a day. Then they are dried at a temperature of 100˚C for 4 hours. This procedure is repeated 5 times and then the concrete cubes are examined. If there are no cracks and defects on the surface, then the frost resistance of the material is at least F300.

Sufficient resistance of concrete to low temperatures in private construction can be determined visually by examining the finished concrete sample. Coarse-grained structure, cracks and damages, places of delamination and colored spots should not be visible on it. To check the water absorption rate, dip the sample in water overnight. If the amount of water during this time decreases by more than 5% of the sample volume, then this indicates high porosity and poor frost resistance.

Ways to improve frost resistance

The frost resistance of concrete largely depends on the porosity of the material and the possible penetration of moisture into the structure. Therefore, the indicators of moisture resistance and frost resistance are very strongly related to each other.

In addition, the frost resistance of concrete materials is increased by reducing the fraction of fillers and adding special air-entraining impurities. As a result, the pores acquire a closed structure and do not connect with each other. This can be compared with polystyrene foam - a porous moisture-proof material.

Concrete is widely used in construction due to a number of properties that allow you to build buildings on almost any soil, regardless of the weather. Water resistance is one of the main advantages of the material and is indicated by the letter W and an index from 2 to 20.

What determines the water resistance of concrete

Concrete consists of loose components, which, when solidified, form microscopic pores on the surface of the material. If during the preparation of the mixture mistakes were made in the proportions of sand, crushed stone, cement, then the consistency of the material becomes looser, because of this, liquid-permeable pores appear on the concrete.

Another factor affecting the water resistance of the mixture is the shrinkage that occurs when the reinforced belt is insufficiently sized. The age of the concrete stone passively affects the water tightness, since over time, the amount of hydrate formations in the hardened mixture increases, which leads to an increase in the strength of concrete and a decrease in the number of pores. In conditions of abundant moisture, the waterproof properties of the material increase significantly.

Other common mistakes in construction also affect fluid transmission:

1. Delays en route. Due to the slow delivery speed of the finished mix to the construction site, the material sets prematurely. The hardening process of the mixture can be further accelerated in hot weather;
2. The amount of water. When diluted, concrete becomes much more pliable, but excessive water leads to the formation of voids inside the mortar. They will not disappear even after the water has evaporated;
3. Insufficient compaction of the mixture. If the crushed stone is not distributed tightly to each other and the residual air and liquid are not removed from the concrete, then voids will also form inside the material.

Concrete grade and water resistance class

You can find out the level of water resistance of the material by the grade of concrete: the higher the coefficient, the higher the water resistance of the mixture. Each brand corresponds to a separate class of water resistance; for example, grades M100 - M200 have class W2, which can only be used in conjunction with waterproofing. In the future, when determining the qualities of the material, it should be taken into account that the higher the grade of concrete, the higher the water resistance class.

If you build a basement using a concrete mixture with water resistance W6 - W8, you can further save on waterproofing due to the high hydrophobicity of the material. This is the optimal solution for the construction of durable private buildings.

Mixtures with a class from W10 do not require the use of waterproofing and are used for the construction of structures that are in direct contact with water (pools, technical tanks, bomb shelters located at great depths). The mixture not only does not pass liquid, it also has a high resistance to negative temperatures. The only drawback of the material is the increased price, which makes it unprofitable to use it for the construction of private buildings.

Several methods are used to test the characteristics of purchased concrete and to test the properties of the mixture before construction begins. There are expensive, accurate methods and more affordable ones that are used in the construction of small buildings.

Exact methods according to GOST using special installations:

• By "wet spot". The samples are placed in a device that delivers water at high pressure to the bottom end of the concrete. The test continues until water seepage through the concrete is noticeable;
• By filtration factor. Cylindrical workpieces are placed in a special chamber and subjected to significant pressure.

Since the determination of water resistance takes a significant amount of time (at least a week), before construction, the properties of concrete are most often checked by examining the structure and consistency of the material:

• Binding materials. Hydraulic binders such as hydraulic lime, Portland cement, and sulphate-resistant cement have the highest density;
• Placeholder type. Using river or quartz sand, as well as various gravel from rocks. It is possible to create concrete with pores of a minimum diameter, which will qualitatively protect the hardened mixture from liquid exposure;
• Chemical additives. The main types of additives include plasticizing, polymeric and bridging agents. Plasticizers and polymers act in a similar way and form a thin film on the surface of the mixture that does not absorb liquid. Colmatants significantly compact the concrete mixture, which reduces the number of pores on the surface of the material.

Increasing the water resistance of concrete with your own hands

High-quality concrete with high strength and resistance to moisture is sold at a high price. As a more affordable alternative, you can make your own mixture that will not be inferior in quality to branded brands. To obtain a mixture with the necessary characteristics, you must carefully follow the instructions.

The easiest way is to keep the concrete dry for a long time. If it is stored at stable humidity, minimal lighting and warm temperature, then in a year the quality characteristics of the material will increase several times.

Elimination of shrinkage

In the process of solidification, the volume of the mixture decreases, and an abundant amount of pores begins to form on the surface of the material. Moisture will penetrate through them into the foundation and any other structure made of concrete. Concrete grades with water resistance class W2 and W4 are subject to significant shrinkage.

To prevent shrinkage, several methods are used:

• abundant watering. For several days (10 times a day), it is recommended to water the surface with water;
• shelter. Fix the film on visible areas of concrete. The film should completely cover the concrete, but not touch it directly, due to which condensation will form. This will reduce shrinkage;
• use of additives. Various types of additives are used, which, by forming an elastic film on the surface of the material, lead to a decrease in the degree of shrinkage. The most effective is the addition of liquid glass (silicate glue) to the solution.

Applying mastic

The classic option, in which a waterproofing layer is applied to the surface of the hardened concrete. Before starting work, the surface of the processed material is cleaned of debris and primed. After that, cold or hot mastic is applied in thin layers (up to 2 mm). Hot mastic is more difficult to prepare, but it has excellent waterproofing characteristics and can be applied even at low temperatures. Since over time the concrete will begin to deform, the mastic will have to be reapplied.

To give the coating layer additional protection against moisture and elasticity, the surface of the material is treated with additional means. In addition to mastic, an emulsion is applied to the artificial stone, then covered with a layer of primer and paintwork material.

The ability of concrete and reinforced concrete to resist moisture under a certain pressure is considered one of the main characteristics and is taken into account when choosing a brand along with the strength class and frost resistance. Water tightness directly and indirectly affects their reliability and service life, the maximum requirements are put forward to external and underground structures - building foundations, bridge supports, basements, wells, facades, exploited roofs. The required value is laid down at the design or planning stage of construction work.

This value reflects the maximum water pressure that can be sustained by a cylindrical specimen 15 cm high under other standard conditions. In practice, this means that concrete with water resistance W2 does not pass water at 0.2 MPa or 2 atm, W4 at 0.4, and so on. The W4 grade meets the construction requirements for structures with normal permeability, but when the pressure rises (for example, when groundwater rises to the base of the foundation), moisture begins to accumulate inside them, which is unacceptable.

There is a direct relationship between this characteristic, strength class and frost resistance, the correspondence is shown in the table below:

According to the requirements of GOST 26633, concrete mortars from W2 to W20 are used in the construction of building structures. Of these, mixtures up to W4 inclusive are suitable for pouring objects with normal permeability (symbol - N), up to W6 - reduced (P), from W8 to W20 - especially low (O). In addition to the most direct indicator that reflects water resistance, the marking takes into account other additional characteristics: filtration coefficient, water absorption by mass and water-cement ratio. The relationship between them is shown in the table:

The indicators of concrete in terms of frost resistance and water resistance depend on the density of its structure, the formation of which is influenced by a number of factors:

• The quality of compaction of mixtures during pouring and leveling, the formation of large voids and uneven distribution of components is unacceptable.
• Compound. In addition to maintaining the specified proportions, the water resistance of an artificial stone depends on the presence or absence of air-entraining additives and the ratio of binder and water.
• Environmental parameters at the main stages of cement hydration: temperature, air humidity, other conditions affecting the rate of liquid evaporation.
• Carrying out the correct reinforcement. In the absence of a frame or an insufficient cross section of its rods, the shrinkage of the structure increases, which in turn leads to the formation of large capillaries and a deterioration in its water resistance.

The choice of mortar for the foundation

The foundation of buildings is subjected to intense moisture loads (atmospheric and soil), taking into account the indispensability of this structure, concretes with a low water resistance grade are used. This also applies to W2 and W4, their use for pouring foundations and external walls is limited and requires a number of costly waterproofing measures. The purchase of expensive varieties during the construction of tape or slab systems should be justified; in order to avoid unnecessary expenses, all factors are taken into account in advance: the geological conditions of the site, weight loads, rainfall and the climate of the region.

The minimum allowable brand of concrete for pouring the foundation is:

• W4 - for frame and temporary buildings;
• W4 and W6 - for wooden low-rise buildings during construction on stable and moving soils, respectively;
• W6 - for a cottage from foam blocks, W8 - from structural aerated concrete;
• W8 - when laying foundations of any type under a brick or stone building.

The W8 mixture is considered optimal in terms of "price-result" for foundations and basements, which corresponds to the B25 (M350) strength class. In practice, not every owner of a future home affords the purchase of this variety, which leads to the need to increase water resistance artificially. It should also be remembered that the use of concrete with a high water resistance grade does not mean giving up protection from ground moisture or precipitation, an exception is made only when building in dry areas with low groundwater levels.

Another factor to consider is the type of work. In practice, mixtures of W2 and W4 are quite in demand when preparing a pillow for a strip foundation or areas for a column foundation. When arranging iron-reinforced structures, the recommended minimum is W6. When constructing the foundation, in addition to choosing a brand, it is important to eliminate all risks of water penetration. This variety is poured in a single monolith, without defects, seam protection is provided at the mating areas.

Ways to improve the water resistance of concrete

Conventionally, all measures to protect artificial stone from moisture are divided into primary (control over the composition and stages of hydration, treatment with deep penetration soils and other processes that directly affect the structure of the material) and secondary, aimed at creating a barrier between the surface of the foundation or external walls and the external environment . The maximum effect is achieved if they are observed in a complex, including the stages of preparing the concrete mixture, its laying and compaction, ensuring the necessary setting conditions and waterproofing. There are nuances in each case.

During the kneading phase, it is important to maintain the correct W/C ratio. Water is a prerequisite for the hydration of cement, but only 60% of its total share enters into chemical reactions. In practice, this means that the less liquid there is in the solution, the higher its quality (but not below the minimum established by the standards). Excess leads to the formation of large pores, the penetration of water into them is only a matter of time. A low W/C ratio reduces the mobility of concrete, which is also fraught with a deterioration in its structure and water resistance.

The correct solution is to use precise predetermined proportions of water and cement and to introduce special additives for high mobility requirements (compacting is sufficient for normal applications).

Substances that reduce the water demand of building compositions have a different chemical basis. These include water-soluble sulfates of aluminum and iron, mixtures of sodium salts, organosilicon compounds, polycarboxylate esters and resins. The criterion for the effectiveness of additives is the degree of reduction in water demand, most of them can reduce it by at least half. But their introduction requires caution due to side effects and impact on performance.

Most builders choose preventive measures to ensure good water resistance of concrete, namely high-quality compaction and maintenance. At the preparation stage, concrete mixers are necessarily used, the solution is not mixed for too long and consumed immediately, without dilution with water and re-starting the equipment. Air distillation is carried out when pouring a layer of no more than 20 cm using vibrators or improvised means. After that, the foundation monolith or screed is covered with a film and watered with water for the first 5-7 days. The required water resistance is achieved when creating an artificial environment - with an air humidity of 60% or more and a temperature of about 20 ° C (but not lower than +5).

If it is necessary to increase the water resistance of an already exploited or hardened base, treatment with penetrating or film-type waterproofing compositions is selected. When selecting them, the drying speed, application method, washout resistance, cost and degree of protection enhancement are taken into account. The best results are achieved when using multi-component polymer primers and penetrating compounds, which increase the water resistance of building foundations and external walls several times.