Decent workmanship and water resistance are not. Waterproofness of concrete: what it depends on and how to achieve it

Concrete is used everywhere to construct a wide variety of structures. It has a lot of specific characteristics that allow you to select the right solution for specific construction conditions in order to obtain the most durable structure. When choosing this building material, it is necessary to take into account its frost resistance and strength. But the waterproofness of concrete, indicated in the marking by the letter “W,” is also important. The higher it is, the longer the monolithic structure will last.

The water resistance of concrete is its ability to prevent moisture under pressure from entering its structure. It is designated by the letter “W” and an even number from 2 to 20. The latter indicates the pressure in MPa x 10 to the “-1” degree at which concrete surface begins to absorb and transmit water.

The higher the water resistance of concrete, the less moisture it will let through and the longer it will last.

Water resistance directly depends on the capillary-porous structure of the building material. If it belongs to dense brands, then it has a minimum of pores and higher water impermeability. The most unstable in this regard are various foam and aerated concrete. They initially have a mass of air cavities formed inside them, which increase thermal insulation characteristics, but reduce water resistance.

After being poured into a mold, ordinary concrete mixture gradually begins to dry out and shrink. However, if the hardening process occurs too quickly, the reinforcement may be weak. As a result, cracks and air bubbles form inside the concrete, which will reduce its water resistance.

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, which, in fact, is the subject of this article.

Waterproof concrete

Marking of waterproof concrete

The water resistance of concrete, as you might guess, is its ability not to allow water to pass through 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 can be the most different types and is designed for different purposes.

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

• Underwater;
• Designed for permanent use in water;
• For operation in the zone of variable water horizon;
• Subject to occasional washing with water.

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 discuss 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 allow water to pass through. Thus, the water resistance of W6 concrete is 0.6 MPa.

Compressive strength

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

Frost resistance

Hydroconcrete is also divided according to the degree of frost resistance. There are five brands of it - 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 frost resistance requirement applies only to those hydraulic materials that are exposed to the simultaneous effects 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 marking features, you can easily determine the characteristics of W6 concrete. What will allow you to choose the most suitable material for use in certain conditions.

For example, concrete B20 W6 F150:

• Corresponds to the M250 brand;
• Able to withstand water at a pressure of 0.6 MPa;
• Withstands 150 freezing and thawing 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 erected very rarely. However, in reality this is not the case.

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

Pool bowl

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

• Basements of houses;
• Manufacturing of piles;
• Floors;
• Pool bowls;
• Columns;
• Beams;
• Crossbars;
• 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 grades of concrete are difficult to process.
Therefore, diamond tools are used for these purposes, for example, diamond drilling of holes in concrete or cutting 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 permeability depends on the nature and degree of porosity of the massif. The denser the structure, the correspondingly higher the water resistance.

Here are the main reasons why pores appear:

• The solution is not compacted enough. To prevent this disadvantage use vibration installations.
• The presence of excess water in the composition.
• Excessive shrinkage of the array, i.e. As it 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 considered to be 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 independently, even without vibration. Instructions for using these additives may vary, so before use you should read the instructions from the manufacturer on the packaging.

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

You can get more information on this topic from the video in this article.

GOST 12730.5-84

Group W19

INTERSTATE STANDARD

CONCRETE

Methods for determining water resistance

Concrete. Methods for determination of watertightness

ISS 91.100.30

Date of introduction 1985-07-01

INFORMATION DATA

1. DEVELOPED by the Research, Design and Technological Institute of Concrete and Reinforced Concrete (NIIZhB) of the USSR State Construction Committee, Donetsk PromstroiNIIproekt of the USSR State Construction Committee, the USSR Ministry of Transport Construction

INTRODUCED by the Research, Design and Technological Institute of Concrete and Reinforced Concrete (NIIZhB) of the USSR State Construction Committee

2. APPROVED and ENTERED INTO EFFECT by the Resolution State Committee USSR for Construction Affairs dated June 18, 1984 N 87

3. INSTEAD GOST 12730.5-78, GOST 19426-74

4. REFERENCE REGULATIVE AND TECHNICAL DOCUMENTS

5. EDITION (June 2007) with Amendment No. 1, approved in June 1989 (IUS 11-89)


This standard applies to all types of concrete with hydraulic binders and establishes methods for determining the water resistance of concrete by testing samples.

1. GENERAL REQUIREMENTS

1. GENERAL REQUIREMENTS

1.1. General requirements- according to GOST 12730.0 and in accordance with the requirements of this standard.

1.2. The height of the control concrete samples, depending on the largest size of the filler grains, can be assigned in accordance with Table 1.

Table 1

1.3. Schemes for fastening and sealing concrete samples in cages are given in Appendix 1.

1.4. Before testing, the end surfaces of the samples are cleaned of the surface film of cement stone and traces of the sealing composition with a metal brush or other tool.

2. DETERMINATION OF WATERPROOFNESS BY "WET SPOT"

2.1. Equipment and materials



- installation of any design that has at least six sockets for fastening samples and provides the ability to supply water to the lower end surface of the samples with increasing pressure, as well as the ability to monitor the condition of the upper end surface of the samples;


- water according to GOST 23732.

2.2. Preparing for the test

2.2.1. The prepared samples are stored in a normal hardening chamber at a temperature of (20±2) °C and a relative air humidity of at least 95%.

2.2.2. Before testing, the samples are kept in the laboratory for 24 hours.

2.2.3. The diameter of the open end surfaces of concrete samples is not less than 130 mm.

2.3. Carrying out the test

2.3.1. The samples in the holder are installed in the test rig sockets and securely fastened.

2.3.2. The water pressure is increased in steps of 0.2 MPa for 1-5 minutes and maintained at each step for the time specified in Table 2. The test is carried out until signs of water filtration in the form of drops or a wet spot appear on the upper end surface of the sample.

table 2

2.3.3. It is allowed to evaluate the water resistance of concrete using the accelerated method given in Appendix 4.

(Introduced additionally, Amendment No. 1).

2.4. Processing the results

2.4.1. The water resistance of each sample is assessed maximum pressure water, at which its percolation through the sample has not yet been observed.

2.4.2. The water resistance of a series of samples is assessed by the maximum water pressure at which no water seepage was observed on four out of six samples.

2.4.3. The grade of concrete for water resistance is taken according to Table 3.

Table 3

________________

2.4.4. The test results are recorded in a journal, which must contain the following columns:

- marking of samples;

- age of concrete and test date;

- water resistance value of individual samples and a series of samples.

3. DETERMINATION OF WATERPROOFNESS BY FILTRATION COEFFICIENT

3.1. Equipment and materials

For testing use:

- installation for determining the filtration coefficient with a maximum test pressure of at least 1.3 MPa according to Appendix 2;

- cylindrical molds (for making concrete samples) with an internal diameter of 150 mm and a height of 150, 100, 50 and 30 mm;

- technical scales according to GOST 24104;

- silica gel according to GOST 3956.

3.2. Preparing for the test

3.2.1. The prepared samples are stored in a normal hardening chamber at a temperature of (20±2) °C and a relative air humidity of at least 95%.

3.2.2. Before testing, concrete samples are kept in the laboratory until the change in sample mass per day is less than 0.1%.

3.2.3. Before starting the test, the samples must be checked for sealing and defects by assessing the nature of the filtration of an inert gas supplied at an excess pressure of 0.1-0.3 MPa to the lower end of the sample, on the upper end of which a layer of water is poured.

If the side surface of the sample is satisfactorily sealed in the cage and there are no defects in it, gas filtration is observed in the form of evenly distributed bubbles passing through the water layer.

If the lateral surface of the samples in the holder is unsatisfactorily sealed or if there are large defects in the samples, gas filtration is observed in the form of abundant local release in defective areas.

Defects in sealing the side surface are eliminated by resealing the samples. If there are separate large filter channels in the sample, the concrete samples are replaced.

3.2.4. Samples drilled from a structure with a diameter of at least 50 mm, after sealing their side surfaces, are tested regardless of the presence of defects in them.

3.2.5. Water according to GOST 23732 used for testing must be previously deaerated by boiling for at least 1 hour. The water temperature during the testing period is (20±5) °C.

3.3. Testing

3.3.1. Six samples are simultaneously tested in the installation.

3.3.2. The pressure of deaerated water is increased in steps of 0.2 MPa for 1-5 minutes with holding for 1 hour at each step until the pressure at which signs of filtration appear in the form of individual drops.

3.3.3. The water (filtrate) that has passed through the sample is collected in a receiving vessel.

3.3.4. The weight of the filtrate is measured every 30 minutes and at least six times on each sample.

3.3.5. If there is no filtrate in the form of drops for 96 hours, the amount of moisture passing through the sample is measured by absorbing it with silica gel or other sorbent in accordance with paragraph 3.3.4.

Silica gel must be pre-dried and placed in a closed vessel, which is hermetically connected to the nozzle for collecting the filtrate into a receiving vessel.

3.3.6. It is allowed to evaluate the filtration coefficient of concrete using the accelerated method given in Appendix 3.

3.4. Processing the results

3.4.1. The weight of the filtrate of an individual sample (H) is taken as the arithmetic mean of the four largest values.

3.4.2. Filtration coefficient, cm/s, of an individual sample is determined by the formula

where is the weight of the filtrate, N;

- sample thickness, cm;

- sample area, cm;

- time of testing the sample, during which the weight of the filtrate is measured, s;

- excess pressure in the installation, MPa;

- coefficient taking into account the viscosity of water at different temperatures, taken according to Table 4.

Table 4

Note. When the water temperature is in the range between those indicated in Table 4, the coefficient is taken by interpolation.

3.4.3. When testing concrete samples with a diameter of less than 150 mm, drilled out of structures, the filtration coefficient obtained using the calculation formula is multiplied by the correction factor, which is taken according to Table 5.

Table 5

3.4.4. To determine the filtration coefficient of a series of samples, the filtration coefficients of individual samples of this series are arranged in increasing order of their values ​​and the arithmetic average of the filtration coefficients of the two middle samples (the third and fourth) is used.

3.4.5. The test results are recorded in a journal, which must contain the following columns:

- marking of samples;

- weight of the filtrate;

- filtration coefficient of each sample and series.

3.5. The resulting filtration coefficient value is compared with the concrete grade for water resistance in accordance with Table 6.

Table 6

________________
*Probably an error in the original. The designation of the concrete grade for water resistance should be read: W2, W4, W6, W8, W10, W12, respectively (Rosstandart letter dated March 16, 2017 N 3849-ОМ/03). - Database manufacturer's note.

APPENDIX 1 (recommended). DIAGRAMS FOR FASTENING AND SEALING CONCRETE SAMPLES IN CELLS

Method for compacting the side surface of a sample
rubber hollow chamber with excess pressure in it

1 - concrete sample; 2 - test clip; 3 - mastic; 4 - a set of rubber and metal rings; 5 - rubber hollow chamber; 6 - removable cover for water supply; 7 - removable cover with a pipe for collecting filtrate

Note. When determining water resistance using the “wet spot” method, remove cover 7.

APPENDIX 2 (recommended). SCHEMATIC DIAGRAM OF THE INSTALLATION FOR DETERMINING THE FILTRATION COEFFICIENT

1 - gas cylinder; 2 - pump; 3 - gearbox; 4 - valve; 5 - pressure gauge; 6 - pressure transmitter; 7 - container with water; 8 - elastic container with deaerated water; 9 - spare container with deaerated water; 10 - test socket; 11 - filtrate weight meter

APPENDIX 3 (recommended). ACCELERATED METHOD FOR DETERMINING FILTRATION COEFFICIENT (FILTRATOMETER)

1. Minimum size concrete samples for testing should be 150 mm.

2. Storage and preparation for testing of concrete samples - in accordance with paragraphs 3.2.1 and 3.2.2 of this standard.

3. The filtrate meter (see Figure 1 of this appendix) is installed on the lower (during molding) surface of the sample and secured (see Figure 2 of this appendix).

Damn.1. Filtratemeter FM-3

Filtratemeter FM-3

1 - hydraulic pump; 2 - pump handle; 3 - working cylinder; 4 - working piston; 5 - sealing washer; 6 - pressure gauge; 7 - valve

Damn.2. Testing a concrete sample with a filtrate meter

Testing a concrete sample with a filtrate meter

1 - filtratemeter; 2 - fastening device; 3 - concrete sample

4. The water pressure in the filtration chamber is raised to 10 MPa by rotating the pump handle and the rate of pressure drop is assessed.

5. If the pressure drops quickly and it is impossible to maintain it by rotating the pump handle, the tests are stopped and the concrete filtration coefficient is assumed to be large highest value, specified in Table 6 of this standard (10 cm/s).

6. When the pressure drops slowly, the position of the pump handle is noted, and the time corresponding to this moment is taken as the beginning of the test.

The pump handle is made six full revolutions, maintaining the pressure within (10±0.5) MPa, and the tests are stopped. This time is taken as the end of the test.

The number of revolutions is used to determine the weight of water absorbed by concrete, based on the calculation that one full revolution of the pump handle is equal to 9.63 10 N.

7. After completing the tests, the filtratemeter is removed from the sample, the wet surface is wiped with a rag and after 2-3 minutes the diameter of the darkened circle is measured. For calculation, the arithmetic mean of six measurements is taken.

8. Concrete filtration coefficient, cm/s, is determined by the formula

where is the filtration path equal to , cm;

- sample testing time, s;

- excess pressure in the filtratemeter, MPa;

- water absorption coefficient, N/cm.

The water absorption coefficient is determined by the formula

where is the weight of water absorbed by concrete, N;

- volume of concrete saturated with water, cm.

The volume of concrete saturated with water is determined by the formula

9. The average value of the concrete filtration coefficient is determined based on six tests in accordance with the requirements of clause 3.4.4 of this standard.

APPENDIX 4 (recommended). ACCELERATED METHOD FOR DETERMINING THE WATERPROOF CONCRETE BY ITS AIR PERMEABILITY

1. General requirements- according to GOST 12730.0.

2. Sampling

2.1. Dimensions of control samples - according to clause 1.2 of this standard. It is allowed to test cube samples with an edge 150 mm long. The number of samples in the series is six.

2.2. Production of control samples - in accordance with GOST 10180, storage and preparation of them for testing - in accordance with clauses 1.4 and 2.2 of this standard.

Note. When storing samples, the possibility of water getting on their surface must be excluded.

3. Equipment and materials

3.1. For testing use:

- a device of the "Agama-2R" type for determining the air permeability of concrete, the schematic diagram of which is shown in Figure 3;

- sealing mastic that meets GOST 14791.

Damn.3. Schematic diagram of a device for determining the air permeability of surface layers of concrete

Schematic diagram devices for determining the air permeability of surface layers of concrete

1 - concrete sample; 2 - device camera; 3 - chamber flange; 4 - vacuum sensor; 5 - vacuum pump; 6 - sealing mastic; 7 - valve

3.2. It is allowed to use other devices that meet the basic requirements:

- the width of the device chamber flange must be at least 25 mm;

- the initial pressure of pressing the chamber flange to the concrete surface of the sample must be at least 0.05 MPa;

- First level the vacuum pressure created inside the chamber must be at least 0.064 MPa;

- the internal volume of the device chamber cavity must be at least 180 cm;

- when installing and sealing the device on the surface of an impermeable material (plexiglass according to GOST 9784, etc.), the drop in vacuum pressure should not exceed 0.002 MPa for 1 hour.

4. Test preparation

4.1. The water resistance of concrete is determined according to Table 7 or, if it is impossible to use the table, according to an experimentally established calibration dependence.

Table 7

4.2. The possibility of using Table 7 is checked in accordance with paragraphs 7.1 and 7.2. Establishment of the calibration dependence - according to paragraphs 7.3-7.6.

4.3. The possibility of using the values ​​in Table 7 is checked before starting to use this accelerated method and each time the type and quality of cement, additives and fillers used changes.

4.4. Before testing, the device is checked for leaks in accordance with the operating instructions.

5. Testing

5.1. When testing, sealing mastic in a rope with a diameter of at least 6 mm is placed on the chamber flange along its midline and connect the ends. The chamber is mounted with a flange on the lower (according to the molding conditions) surface of the sample and a vacuum of at least 0.064 MPa is created in the chamber cavity.

5.2. In accordance with the operating instructions for the device, the value of the concrete air permeability parameter (cm/s) is determined for each sample or the inverse value of the concrete resistance to air penetration (s/cm).

6. Processing of results

6.1. The obtained values ​​() of the concrete samples are recorded in ascending order and the arithmetic mean value () of the two middle samples (third and fourth) is determined as a parameter characterizing the air permeability of concrete in the series.

6.2. Using Table 7 or the established calibration relationship, the grade of concrete by water resistance () is determined, corresponding to the obtained value or. In this case, the value calculated by formula (1) or (2) for given value() and rounded to the nearest even number.

7. Checking the possibility of using Table 7 and establishing the calibration dependence

7.1. The check is carried out in the following sequence:

- according to clauses 2.2, 5.1, 5.2 of this annex, one series of concrete samples of one of the controlled compositions is made and tested;

- determine the value (or) for this series of samples and the waterproof grade of concrete corresponding to it according to Table 7;

- the same series of samples is tested according to Section 2 of this standard and the grade of concrete is determined by water resistance “by a wet spot”.

7.2. Table 7 can be used if the value of the concrete grade for water resistance differs from that obtained from the table by no more than one grade.

7.3. If the requirement of clause 7.2 is not met (Table 7 cannot be used), to determine the grade of concrete for water resistance, use the calibration dependence "" or "":

where and are coefficients determined according to clauses 7.4-7.5.

7.4. Coefficients and are determined based on the test results of a series of samples in accordance with clause 7.1 and two additional series of samples, also manufactured and tested in accordance with clause 7.1.

When making samples of one of the indicated series, a concrete mixture with a water-cement ratio of 0.40-0.42 should be used, the second - 0.52-0.54. The ratios between aggregates and between cement and additives in these concrete mixtures should be the same as in the controlled composition.

7.5. Coefficients and are calculated using the formulas:

where is the value or for individual series of samples (, , or , , );

- values ​​for individual series (, or) concrete grades for water resistance.

8. An example of establishing and using a calibration relationship

8.1. To establish the calibration dependence, the main and two additional series of concrete samples were manufactured and tested at the reinforced concrete plant according to clause 7.1. The test results are given in columns 2 and 3 of Table 8. With further quality control of concrete of various compositions, prepared from the same materials as the samples of the indicated series, three more series of samples were manufactured and tested according to paragraphs 5.1 and 5.2, the average values ​​of the air permeability parameter are indicated in column 2 of Table 9. It is necessary to determine the grade of concrete for water resistance for each of these series.

8.2. The sequence of data processing to find the coefficients is given in Table 8.

Table 8

8.3. According to equation (1), the corresponding calibration dependence has the form:

Table 9

8.4. Substituting into equation (5) the values ​​for series 3-5 (column 3 of table 9), we obtain the values ​​given in column 4 of table 9. By rounding, in accordance with clause 6.2 of this appendix, these values ​​to the nearest even number, we determine the required grades of concrete for water resistance, indicated in column 5 of Table 9.

APPENDIX 4. (Introduced additionally, Amendment No. 1).



Electronic document text
prepared by Kodeks JSC and verified against:
official publication
Concrete. Determination methods
density, humidity, water absorption,
porosity and water resistance:
Sat. GOST. GOST 12730.0-GOST 12730.5. -
M.: Standartinform, 2007

How construction material, concrete has many advantages and useful qualities, which is why it has become widespread. One of them is water resistance, which means the ability not to allow moisture to pass through under a certain pressure. In this article we will look at the types of concrete that can withstand moisture.

Determination methods

According to GOST 12730.5-84, there are several methods for determining the water permeability of concrete W:

Since the first two methods are quite time-consuming (for example, W8 concrete using the “wet spot” method will have to be tested for a week), the last two options are most often used in practice.

Concrete grades based on water resistance

GOST 26633 suggests 10 grades of concrete depending on the degree of their waterproofness (W2, W4, ... W18, W20).

Instructions for identifying each brand are as follows:

• a concrete sample cylinder Ø150 mm is taken;
• water is supplied to it under pressure;
• make observations and measurements.

Each brand must withstand a certain pressure. For example, W6 concrete must be resistant to pressure up to 6 atmospheres (0.6 MPa), and W4 – 0.4 MPa.

Considering the characteristics of W4 concrete, we can note:

• the price of production of the material is low;
• with age, its water resistance increases, in particular, concrete B15 F150 W4 showed a 6-fold increase during the year;
• the material thickness of 200 mm is ideal for creating waterproofing, which has allowed it to become a leader in civil engineering;
• By adding expanding cements or sealing components to B15 F75 W4 concrete, water resistance can be increased without losing the basic characteristics of the material.

To assess the permeability of concrete products, the following can be used:

• direct methods(water resistance or filtration coefficient);
• indirect(water-cement ratio and water absorption).

Effect of material age

An interesting fact is that as the age of concrete increases, its waterproof qualities only increase. However, a significant and intensive increase in such indicators seems possible only if special care behind it (constant hydration).

An example is concrete made with your own hands from Portland cement. If you constantly moisten it or reach a positive temperature at which moisture will not evaporate, its water resistance will rapidly increase for up to six months. This will significantly increase total term operation.

Advice: concretes that harden with constant moisture and compliance with the required temperature conditions have several times higher water resistance than concretes whose hardening process was carried out in an environment with low relative humidity or was accompanied by significant moisture losses.

For example, if you take a material that hardened after stripping with constant moisture for a month, and compare it with one that, after stripping, hardened in conditions of insufficient humidity (at 50-60%), the latter will need about six months to achieve water resistance first.

From this we can conclude that it will happen most quickly in conditions of sufficient humidity.

Moreover, even if watering is rare or completely absent, and the relative humidity of the environment approaches 100%, the waterproof qualities will also increase in the first six months to a year, then their indicator will stabilize. When moisture evaporates from concrete or it hardens in conditions of insufficient relative humidity, the increase in water resistance decreases.

In situations where the base loses a huge amount of moisture, the process may stop altogether or go in the opposite direction. This can lead to the fact that after a certain time the waterproof rating of concrete becomes lower than the original one.

Advice: the characteristics of W8 concrete are fully adequate for constructing a conventional foundation, but only with waterproofing work.

Ways to improve water resistance

Since concrete has a capillary-porous structure, under the influence certain value water, it turns out to be permeable to it. This indicator is influenced by many factors, including nature and degree of porosity. The connection then turns out to be as follows: as porosity increases, water permeability decreases, and vice versa, the more dense the material is, the higher this indicator will be.

Tip: concrete B25 W4 F75 has a frost resistance of 75 cycles.

Pores can appear in a material due to many reasons, the main ones of which are:

• weak seal;
• excess mixing water;
• shrinkage of concrete, which occurs after it dries and is characterized by a decrease in volume.

To achieve the desired effect using a vibrator. It is worth remembering that the process of adding water to cement is called hydration and it can last for a long period of time.

For complete hydration, the proportions must be strictly observed - for every 10 kg of cement, 4 liters of water should be used. However, only a little more than half (60%) of this water enters directly chemical reaction with cement.

Conclusion

Each brand of concrete has its own characteristics, especially waterproof ones. When developing a construction plan, this parameter must be taken into account. The article described in detail what water resistance is and how it is tested.

The video in this article will help you find additional information on this topic.

To lay the foundation, make a foundation, or simply pour concrete on the path from the house to the gate, you need to know the proportions, features and grades. In this article we will look at the main characteristics by which brands differ. After reading the material, you will know how to select water resistance and how they differ from each other.

Tables and graphs will help in studying, with the help of which even a novice builder will be able to choose the right option. The material is divided into different brands, indicating by their designations the ability to resist frost and water. Depending on the brand, concrete can withstand different pressures without allowing liquid to pass through.

Waterproof

There are ten main brands of water resistance, which are regulated in GOST 26633. Belonging to a particular brand is indicated by the letter “W” and a certain number. If the letter remains unchanged, then the number shows how much water pressure a particular type of concrete solution can withstand. The basis is a concrete cylinder with a height of 15 centimeters.

There are direct and indirect properties of a solution in its interaction with a liquid. Water resistance and filtration are direct properties of concrete mortar. Indirect properties are water absorption by mass and the ratio of cement to water. Of all 4 parameters, the main and, accordingly, approximate one is the first one, that is, water resistance.

The remaining indicators are considered additional for buyers or those involved in construction. But these coefficients are important in the concrete production process, as well as for scientific purposes.

Consideration of the three main brands will help you navigate the properties of concrete solutions:

In between these brands there are additional ones. Calculations perfectly show how different brands of waterproofness differ.

Features of brands

It’s worth starting with brand W4, which has a normal liquid permeability indicator. Such a solution will absorb a normal amount of moisture, so it is not recommended to use it in work where the level of waterproofing is low. Below W4 there is concrete grade W2, which absorbs more more water. Accordingly, W2 characterizes a mixture of lower quality.

The W6 mixture has reduced liquid permeability. This is a versatile formulation as it absorbs less water than W4. It is W6 that is most often used in large-scale construction work. But there are no intermediate brands between W4 and W6.

W8 grade solutions have low permeability. Such concrete absorbs about 4% of the total mass. Concrete marked W8 is already significantly different in cost from W6. Next come W10, W12...W20. The higher the number, the less permeability. W20 solution is the most resistant to water, but such concrete is chosen for private purposes or for large and important projects.

Choice suitable brand sometimes complicated, since there are ten of them. Obviously, it is not recommended to buy W2, since it should only be used in places where there is no moisture at all. The following tips will help you make your choice:

1. Brand W8 is often used in construction work, for example, laying foundations. But there is a condition for using W8 concrete - the presence of additional waterproofing.
2. The range from W8 to W14 is suitable for plastering. You need to choose depending on the humidity level in the room. If it is cold or damp, then you should take a brand higher than W14. Required condition For work in cold and damp rooms, use a primer.
3. Exterior finishing of the house should be done with concrete mixtures W18 or W20, since the concrete layer will be regularly exposed to external natural factors. This also applies to outdoor work, which, unfortunately, is often saved on.

Frost resistance

Next to the “W” is the letter “F” with a specific number, which indicates the frost resistance coefficient. Today, concrete mixtures are produced with a coefficient from 25 to 1000. The numbers in the frost resistance coefficient show how many freezing-thaw cycles a particular mixture can withstand. In simple words- this is the number of times of transitions from a defrosted state to a frozen state and back that a structure made of concrete mortar can withstand.

To better understand the characteristics of frost resistance, it is worth considering the foundation of a house as an example. The design constantly absorbs groundwater. The microscopic pores of the material are filled with liquid and remain there. After freezing, water expands these pores, resulting in microcracks. Each subsequent freezing causes these cracks to widen.

Waterproofing has long been used in construction, which prevents the bulk of water from entering micropores. Various additives help increase the frost resistance parameter (for example, air-entraining). But they also have a disadvantage - a decrease in the strength of the mixture. Hydrophobic cement allows you to achieve optimal frost resistance of concrete mortar.

Below are some tips to help you choose the right concrete solution:

1. Less than F50. Rare species, which can be used in places where there is never frost.
2. Moderate grades F50-150. Optimal frost resistance indicators, which allow the use of concrete of these grades for construction.
3. Increased level – F150-F300. Such solutions are used for structures that are located in harsh climatic conditions. Concrete is not afraid of sudden and severe temperature changes.
4. High level F300-F500. Concrete mixtures with this brand are used in exceptional conditions.
5. More than F500. Brands are used only when the structure must last for centuries. Formulations with an index of more than F500 contain various additives that significantly increase the index

Gradation of concrete grades according to frost resistance and water resistance updated: February 26, 2018 by: zoomfund