Waterproofness of concrete: what it depends on and how to achieve it. Waterproof concrete W6 - classification, application and production. Marking. Compressive strength and frost resistance How is the water resistance of concrete indicated?
The water resistance of concrete is a technical characteristic of artificial stone, which shows how it does not allow moisture to pass under pressure. This is determined by the letter W. The indicator can be from 2 to 20.
Characteristics of concrete grades for water resistance
To determine the water resistance of concrete, it is recommended to first familiarize yourself with its grades:
- W2. Water penetrates into this composition very quickly. That is why it is recommended to install special waterproofing film for his protection.
- W4. Compared to the previous material, w4 concrete is less waterproof. But, it needs waterproofing protection. In order to improve the performance, it is recommended to add various reagents to the mixture.
- W6. Concrete w6 is similar in its technical characteristics to M350. It is characterized by relative resistance to water permeation. The mixture is used in the construction of buildings that have commercial or civil purposes. The solution is resistant to water, so it is used to seal gaps between reinforced concrete slabs, repair monolithic buildings, and create hydraulic reservoirs. The mixture is used to fill the foundation.
- W8. For its production, high-quality cement is used, which contains large quantities of clinker. With its use, foundations are laid, containers and reservoirs are erected, which are used in the economic and industrial spheres. W8 concrete is used for structures that will be operated in conditions of high humidity.
- Concrete W10 - W20. This brand of concrete does not require the use of additional waterproofing layer. Concrete grades w 10 and w20 are used for pouring foundations in multi-story construction. The use of w10 concrete is recommended for the construction of hydraulic buildings, which must be strong and reliable. This waterproof concrete has a high level of frost resistance, which makes it possible to use it for the construction of buildings in the most severe climatic conditions.
There are different grades of concrete for water resistance, which allows you to choose the most appropriate option depending on the tasks.
Concrete grades
Concrete is considered waterproof if it meets the standards of GOST 12730. In this case, grade W2 is not considered, since the mixture does not perform its functions.
W4 concrete has a water absorption value of 4.7-5.7 percent depending on its mass. The w6 material in Moscow has indicators of 4.2-4.7. W8 concrete is characterized by an index of up to 4.2. W10-W20 is a waterproof concrete that has excellent technical characteristics.
Proportions for concrete mixture
Before making concrete waterproof, it is recommended to determine the proportions. When manufacturing the material, they must be strictly adhered to, since when deviating from the norms, quality deterioration is observed. concrete mixture.
Particular attention should be paid to the water/cement ratio. It is recommended to use cement grade M300-M400. In rare cases, building material grade M200 is used.
A good middle option is class 15. Before using cement, it is sifted through a sieve. Obtaining a hydrophobic effect is achieved by varying components such as sand and gravel. To prepare waterproof concrete with your own hands, you need to make sure that there is half as much sand as gravel. Gravel, cement and sand can be used in the following proportions:
- 3:1:2;
- 4:1:1;
- 5:1:2,5.
Compliance with these proportions will ensure high-quality hardening of the mixture. It is also recommended to use various additives that will ensure the waterproofness of concrete (w6 or another brand).
Methods for determining water resistance
The water resistance of artificial stone depends on various factors. This property is influenced by the specific capillary-porous structure of the building material. If the concrete is dense, then it has minimal pores, which leads to an increase in water resistance.
A large volume of pores is observed due to shrinkage, insufficiently compacted composition or the presence of water. As the concrete mixture dries and hardens, it shrinks and its volume decreases. Excessively intense shrinkage is observed with insufficient reinforcement and evaporation of water. This is influenced external factors atmospheres in which the concrete mixture is dried.
A change in the nature of porosity is observed with changes in air-entraining additives. After closing the pores, an increase in water resistance is observed. To obtain high performance, it is recommended to make a concrete mixture from aluminous and high-strength cement. During hydration, these materials add a large amount of water and form a dense stone.
Water resistance is influenced by the properties of the additives used. To increase the degree of compaction of the mixture, it is recommended to use sulfates of materials such as aluminum and iron. In order to delete excess water and ensure waterproofness, it is recommended to use a vacuum. the mixture is carried out by vibration and pressing. If used, then you need to ensure that its composition contains optimal quantity included pozzolanic additives, which will have a positive effect on the performance.
The water resistance indicator depends on the age of the artificial stone. The older the concrete, the better its hydration formation.
In order to determine the water resistance of concrete w4, 6, 8, 10-20, the use of basic and auxiliary methods is recommended.
Basic methods
The main methods for determining the water resistance of a concrete mixture are:
- Wet spot method. It is necessary to measure the maximum pressure at which concrete does not allow water to pass through.
- Filtration coefficient. An indicator is determined that determines the constant pressure and the time period of the filtration process.
Helper Methods
Auxiliary methods are determined in accordance with appearance substance that is used to bind the solution. These substances include Portland cement and hydrophobic cement. The content of chemical additives is also determined. Auxiliary methods involve determining the structure of pores, with a decrease in the number of pores, the indicator increases.
How to waterproof concrete mix
In order to increase the water resistance of a concrete mixture, it is recommended to use a large number of methods. When making the mixture with your own hands, it is recommended to eliminate the shrinkage of concrete, as well as provide a temporary effect on it.
Elimination of composition shrinkage
According to the properties of the material of medium grades, it contains pores in sufficient quantities. They promote the penetration of moisture into the material. This is explained by the fact that during the hardening process, gradual shrinkage of concrete is observed.
In order to reduce the degree of concrete shrinkage, it is recommended to follow certain rules:
- In order to increase the class of concrete, the use of special compounds is recommended. With their help, a special film is formed, with the help of which the possibility of shrinkage is limited. The addition of compounds must be carried out in strict accordance with the instructions, which will ensure excellent technical characteristics. Otherwise, the opposite effect will be diagnosed.
- After preparing the solution, it should be sprinkled with water every 4 hours. The procedure should be carried out no more than 4 days. After this time, the concrete should harden naturally.
- After pouring, the material should be covered with plastic film. This will provide the opportunity for the formation of slight condensation, which will prevent shrinkage of the concrete. During the manipulation, it is recommended to ensure that the film does not touch the concrete.
Temporary impact
In order to increase the water resistance of concrete, it is recommended to provide temporary exposure. The material must be kept dry for a long period, which will lead to improvement technical characteristics. To promote a high filtration rate, the concrete mixture must be stored properly.
The material should be stored in a dark and warm place characterized by a high level of moisture. An increase in the quality of artificial stone several times is observed after 6 months of storage.
other methods
In order to create waterproof concrete with a solution of hydrophobic cement, it is recommended to apply coating materials to the surface. For this purpose, mastic or hot bitumen is used. Before applying to the surface, you need to clean the concrete structure and prime it. This ensures high-quality adhesion between coating materials and concrete. At the final stage, mastic or bitumen is applied in several layers. The thickness of one layer must be at least 2 millimeters. A few minutes after applying the composition, a protective crust forms on the surface.
This method has a certain disadvantage. When artificial stone is deformed, the coating layer is destroyed. If you choose the wrong mastic protective layer may drain.
In order to create a protective layer, it is recommended to use paint-based waterproofing, which improves the waterproof qualities concrete structure. The technique involves applying an emulsion, heated bitumen or mastic to the surface. After this, primer or paint is applied in several layers.
To increase the moisture resistance of concrete, it is recommended to use special additives, which in modern construction market presented in a wide range. The use of ferric chloride and silicate glue is recommended. The cheapest supplement option is calcium nitrate. It has excellent resistance to moisture. The product dissolves well in water, which simplifies the process of its use. To provide high level For moisture resistance, the use of sodium oleate is recommended. Thanks to all of the above additives, an increase in the indicator is ensured. The choice of supplement depends on the financial capabilities of the user.
Water resistance is an important indicator used to determine the quality of concrete. In accordance with this value, brands of artificial stone are provided. Not only the amount of moisture passed through, but also the amount of loads it can withstand depends on them. fake diamond. To increase the moisture resistance at home, it is recommended to use polyethylene film to cover the surface. Coating or paint materials can also be applied to concrete.
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
Item number, application |
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Appendix 4 |
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1.1, Appendix 4 |
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Appendix 4 |
|
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
Largest aggregate grain size | Minimum sample height |
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 structure that has at least six sockets for attaching samples and provides the ability to supply water to the bottom end surface samples at increasing pressure, as well as the ability to monitor the state 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 relative humidity air 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
Sample height, mm | ||||
Holding time at each stage, h |
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 by the maximum water pressure at which it has not yet been observed to leak through the sample.
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
Water resistance of a series of samples, MPa | ||||||
________________
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) internal diameter 150 mm and height 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
Water temperature, °C | |||
Coefficient |
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
Sample diameter, mm | ||||||
Correction factor |
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
Filtration coefficient, cm/s | Concrete grade for water resistance |
||||
________________
*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
A method of compacting the side surface of a sample by compressing the samples with a set of alternating rubber and metal rings or a vulcanized steel spring with a rubber ring | A method of compacting the side surface of a sample by filling the gap between the samples and the holder with special mastics | |||
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 the 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 air permeability surface layers 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
Concrete air permeability parameter, cm/s | Concrete resistance to air penetration, s/cm | Concrete grade for water resistance |
0,105-0,0728 | ||
0,0727-0,0510 | ||
0,0509-0,0345 | ||
0,0344-0,0238 | ||
0,0237-0,0164 | ||
0,0163-0,0113 | ||
0,0112-0,0077 |
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 a given value () and rounded to the nearest even integer is taken as the concrete grade for water resistance when using the calibration dependence.
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 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 of which 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
Series index | |||||
8.3. According to equation (1) the corresponding calibration dependence has the form:
Table 9
Series number | (according to equation (5) | |||
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
Waterproof concrete refers to the ability of a hardened mortar to resist the penetration of water under pressure. Permeability is measured by either the filtration coefficient (the mass of water passed through a sample of material at constant pressure) or the ultimate pressure that a sample can withstand when exposed to pressurized water for a specified period of time.
The water resistance of materials in SI is measured in meters (m) or pascals (Pa). Waterproofness of concrete and mortar mixtures is estimated in kgf/cm 2 or MPa and means the water pressure at which standard concrete samples.
To indicate the water resistance of concrete and mortar mixtures, a water resistance coefficient is used, denoted by the letter “W”, which characterizes the grade of concrete in terms of water resistance (W2 - W20).
Properties
The water resistance of concrete depends on the W/C ratio (water-cement ratio), the type of binder, as well as the content of finely ground and chemical additives in the concrete, hardening conditions and the age of the concrete. The water resistance of concrete is also affected by the pore structure. By lowering the W/C, we reduce macroporosity and increase the water resistance of concrete. In Fig. Figure 1 shows the graphical dependence of the permeability constant of concrete on W/C. The higher the W/C, the greater the permeability of concrete and, accordingly, the lower the grade of concrete for water resistance.
The W/C can be reduced by increasing the cement consumption at a constant water consumption, using plasticizing additives (for example, KT tron-5) and other methods.
Increases the degree of compaction of the concrete mixture and increases water resistance different kinds machining: vibration, pressing, centrifugation, etc. or removing water by vacuuming.
Testing concrete for water resistance
Determination of the water resistance of concrete is carried out according to GOST 12730.5-84 using the following methods:
- "wet spot" method
- determination of water resistance by filtration coefficient;
- accelerated method for determining the filtration coefficient (filtrate meter);
- an accelerated method for determining the waterproofness of concrete based on its air permeability.
Example. Determination of water resistance using the “wet spot” method:
- Samples are prepared in cylindrical molds with an internal diameter of 150 mm and a height of 150; 100; 50 and 30 mm. The height of the samples is selected depending on the size of the filler grains.
- The prepared samples are stored in a normal hardening chamber at a temperature of 20°C and a relative air humidity of at least 95%. Before testing, the samples are kept in the laboratory for 24 hours.
- An installation of any design is used that has at least six slots 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.
- Place the samples in the holder into the sockets of the test setup and securely fasten them.
- The water pressure is increased in steps of 0.2 MPa and maintained at each step for 4-16 hours (depending on the height of the samples).
- Tests are 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. The waterproof grade of concrete is taken for the pressure at which no signs of water filtration were observed, according to the table:
|
Water resistance of a series of samples, MPa |
||||||||||
|
Concrete grade for water resistance |
Despite the diversity of modern building materials, concrete continues to maintain a leading position among competing options, as it has such important characteristics as strength, reliability and durability. It is an integral component of mortars for creating foundations, laying walls, plastering and other construction operations.
The water resistance of concrete, as well as its ability to withstand harsh weather conditions, are the main qualities that ensure a long service life of the finished products. These criteria are the main ones when choosing a brand of this building material.
And the water resistance of which is at a high level is the key to the quality and excellent performance of any design. These properties mean the ability concrete products resist the negative impact of such natural phenomena, like moisture, water and negative temperatures.
Currently, there are various grades of concrete for frost resistance and water resistance, differing in quality, price and technological capabilities. This classification helps to choose the optimal suitable material to create structures intended for operation in certain conditions.
by water resistance
Depending on the degree of water resistance, concrete is divided into ten main grades (GOST 26633). They are designated by the Latin letter W with a specific digital value, indicating the maximum water pressure, which the test concrete sample can withstand cylindrical 15 cm high during special tests.
The water resistance of concrete is determined by direct and indirect indicators of its interaction with water. Direct indicators are the brand of concrete and its filtration coefficient, and indirect indicators are indicators of the water-cement ratio and water absorption by mass.
In private and commercial construction practice, to find out the water resistance of concrete, they pay attention to its brand, and other criteria are important mainly in the production of this building material.
Characteristic features of concrete grades in terms of water resistance
When choosing the required grade of concrete to perform a certain type construction work are guided by digital indices after the letter W, characterizing the degree of interaction of the material with moisture and water. For example, grade W2 has the lowest water resistance of concrete and, therefore, low quality. Solutions on this basis are strictly not recommended for use in environments with even low levels of humidity.
Concrete grade W4 has a normal degree of water permeability. This means that this composition has the ability to absorb a normal amount of water, so its use is possible only if good waterproofing is provided.
The next position in the quality scale is the W6 brand, which is characterized by reduced water permeability. belongs to compositions of average quality and low price category, which explains the popularity of its use in construction.
Concrete grade W8 has low permeability, as it absorbs moisture in an amount of only about 4.2% of its mass. It is a higher quality and more expensive option compared to the W6 brand.
This is followed by concrete grades with indices 10, 12, 14, 16, 18 and 20. The higher the digital indicator, the lower the water permeability of the material. According to this classification, the most waterproof concrete is grade W20, but it is not often used due to its rather high price.
Practical use of certain grades of concrete for water resistance
The type of concrete should be selected depending on the operating conditions of the objects. For example, the W8 brand is quite suitable for pouring a foundation, provided that additional waterproofing is installed. Walls are plastered using concrete grades W8-W14. However, to equip sufficiently damp and cold rooms, the water resistance of concrete must be maximum, so it is recommended to use the highest quality solutions, and it will also be necessary additional processing walls with special soil compounds.
For high quality and durable exterior finishing walls, pouring garden areas and paths should also use concrete with maximum water resistance, since these areas will be systematically exposed to the negative effects of external weather factors.
Do-it-yourself concrete additives for waterproofing
The need to use high-quality objects or their elements in the production is obvious, but this requires significant financial investments due to the high cost of such materials. But what to do if the construction budget is limited, and violation technological process unacceptable? The answer is simple: you can use a compromise option, namely, increase the water resistance of concrete yourself.
Today there are several effective ways increasing the resistance of concrete mixtures to water, but two of them have gained the most popularity: by eliminating concrete shrinkage and by temporarily affecting the concrete composition.
Elimination of concrete shrinkage process
Low and medium grade concretes are quite porous materials, easily absorbing moisture. This negative property increases during the process of shrinkage of the solution during solidification. Thus, the quality and waterproofness of a concrete mixture can be improved by reducing the degree of its shrinkage.
An integrated approach will help you achieve the desired result:
- It is necessary to use special additives in concrete for waterproofing. The principle of their action is that when the solution hardens, they form protective film, preventing its shrinkage. Today, there are various concrete additives on the market for waterproofing, and although they have the same task, each individual option has its own characteristics, so before purchasing you should carefully read the manufacturer’s instructions.
- In addition to adding special additives to concrete to make it waterproof, it is also recommended to water it. This procedure is performed during the first four days at intervals of 4 hours. Next, the concrete structure must dry under natural conditions.
- With the rapid evaporation of moisture from the solution during hardening, unwanted shrinkage also occurs. To slow down this process, after pouring a concrete structure, it must be immediately covered with a special film, under which condensation will form, preventing shrinkage and helping to increase the strength of concrete. The coating is positioned so that it does not touch the fill. Small gaps are left along the edges for air ventilation.
Temporary effect on concrete composition
This method involves letting the dry solution “sit” for a certain time. The main requirement is compliance the right conditions storage The mixture should be kept warm dark room and be constantly moistened. Thus, in just six months its water resistance can increase several times.
Frost resistance of concrete
This indicator means the ability of concrete mixtures to maintain their physical and mechanical properties under conditions of repeated freezing and thawing. This characteristic plays a priority role when choosing concrete for the construction of bridge supports, airfield and road surfaces, buildings and other objects operated in middle and northern latitudes.
Determination of the frost resistance of concrete is carried out through laboratory tests using two methods: basic and accelerated. If the results of studies differ, the data obtained using the base method will be considered as the final version.
Study of concrete resistance to low temperatures
Tests are carried out using basic and control samples, which are made from concrete various brands on water resistance for serial testing. Control concrete blanks are used to determine their compressive strength. This procedure is carried out before testing the main samples, which will be subjected to alternate freezing and thawing in different water saturation regimes that occur in natural climatic conditions.
For example:
- in the presence of the highest possible level groundwater;
- during seasonal thawing of permafrost;
- when exposed to precipitation;
- in the complete absence of periodic water saturation, when the concrete is reliably protected from groundwater and precipitation.
Classification of the frost resistance level of concrete by grade
According to the latest edition of GOST, concrete grades for frost resistance are designated by the Latin letter F. This value characterizes the maximum number of freezing/thawing cycles that can be withstood by samples of a certain design age, taking into account the reduction in tensile strength and reduction in the mass of the material by its value, provided for by the norms of current standards.
To determine the level of frost resistance of concrete, digital indicators from 25 to 1000 are used. The more given value, the higher the quality and reliability of the material.
Rules for choosing concrete mixtures
The choice of the required brand of concrete mixtures for frost-resistant properties should be made taking into account the climatic characteristics of the area, as well as the number of freezing and thawing cycles during the cold period of the year. It should be noted that concrete with high densities has the greatest frost resistance.
Concrete is a universal building material, widely used during various construction works. Traditionally, floors between floors are made from it, capital walls buildings, reinforced concrete structures. The material has a lot positive qualities, one of the main ones is the excellent water resistance of concrete.
Conventional cement composition can allow water to pass through it. But situations arise when increased moisture resistance of concrete is required to ensure the necessary operating conditions of the structure. The main representatives of these structures, which are used in traditional construction, are:
- floors in the building that are below zero;
- basement walls;
- strip foundations.
At the same time, during the construction of a basement or pouring a foundation, thanks to the increased water resistance of concrete, you can significantly save on installing waterproofing or choose a more budget-friendly type.
The water resistance of this material is also relevant for industrial hydraulic structures. having direct contact with
water and taking increased loads:
- dams;
- dams;
- underwater tunnels;
- special tanks.
General description of the indicator
Resistance to the ingress of water under pressure is determined by the water resistance index of the concrete mixture, which is designated by the letter W simultaneously with a digital value in the range of 2−20 and changes with a factor of two.
The digital designation determines the permissible water pressure in kg/cm² on a reference standard of a cubic shape, where the sides are 15 cm. For example, the water resistance of W6 concrete is the pressure of a water mass per one square centimeter 6 kg. Moreover, water does not penetrate through this building material.
With an increase in the numerical index that describes the brand cement composition in terms of water resistance, the ability of the concrete mass to withstand water pressure increases.
Features of different brands
The permeability of a concrete mixture is expressed by indirect and direct parameters. The latter includes the filtration coefficient and the grade of concrete for water resistance. Indirect indicators are the water-cement ratio and water absorption. Thus, There is a specific table for the water resistance of concrete:
- Concrete, which is marked W2, corresponds to M150-M250 cement, which quickly absorbs moisture and, regardless of the thickness of the layer, requires the application of waterproofing.
- Concrete composition W4 corresponds to the cement grade M250-M350. It is less susceptible to moisture, unlike W2, but is quite hygroscopic. Recommended for use with a waterproofing layer. The material is used in traditional construction. The water resistance indicator increases during the introduction of ingredients and additives into the prepared concrete composition, which cause compaction of the mass, as well as the use of cements with high rate extensions.
- Concrete mortar W6 (corresponds to M350) is characterized by lower moisture permeability, which makes it possible to widely use it during construction. Excellent water resistance allows the composition to be used for sealing cracks in reinforced concrete and monolithic structures for waterproofing tanks. It is also used for the construction of basements on the ground where underground water is close.
- The W8 concrete composition is made from high-quality M400 cement. The W8's water resistance is approximately 5% moisture by weight. Concrete has shown itself to be excellent during the work of pouring the foundation, constructing tanks and containers that are used for storing liquids, bomb shelters, as well as various hydraulic structures. It is used in traditional construction if it is necessary to carry out work on the construction of a structure that will be operated in high humidity.
- Solutions W10−20 (M450−600) are characterized by maximum water resistance and do not require a waterproofing layer during application. The scope of use of these compounds is the construction of hydraulic structures, liquid storage tanks, as well as other special tanks. Concrete W20 has the greatest resistance to water; it is not used in private construction. The solution is characterized by high frost resistance F250-F350, which allows it to withstand significant temperature differences.
The water resistance of a concrete composition marked “W” depends on several factors. The main points that influence this characteristic are:
Porosity and Density
The concrete composition, being a porous-capillary body, is permeable to moisture during the presence of appropriate pressure. Water resistance depends significantly on the porosity of the material.
Causes of pores:
- reducing the volume of concrete when drying;
- the presence of an excessive amount of water in the solution;
- bad seal.
The required compaction of the solution is achieved through careful vibration and stirring of the cement composition.
The chemical reaction of concrete components with water, which takes place in the mass during strength gain, is called hydration. Moreover, the reaction lasts for a long time.
For complete hydration of cement particles, the volume of water must be at the level of 45% of the total mass of concrete, this corresponds to the water-cement ratio W/C = 0.45. Moreover, it is connected chemically only 55% of the total amount of water in the solution, this corresponds to W/C = 0.20.
In theory, W/C = 0.20 is enough to hydrate concrete, but at the same time the hardness of the solution increases significantly, therefore in practice a concrete mixture with a W/C ratio of approximately 0.5 is used, this completely ensures convenient delivery and pouring of the solution.
Water that has not entered into the hydration reaction forms many pores in the mass after solidification. Some of which are closed, and some create through tunnels through which moisture subsequently begins to pass.
To improve water resistance, the amount of moisture during mixing must be minimized (W/C = 0.45 is the optimal value).
A reduction in the water-cement ratio (for example, from W/C = 0.6 to W/C = 0.45, i.e. by 25%) with a certain mobility of the cement composition is achieved through the use of plasticizers, and the number of pores is significantly reduced.
To obtain the most dense solution with a high level of water resistance, various waterproofing additives are used.
Improved performance
The task of increasing the water resistance of a concrete mixture is relevant both during civil and industrial construction, and during the corresponding work in private buildings. Since not all the time, when carrying out concrete work, it is possible to purchase high-quality cement.
Eat effective methods, which make it possible to achieve increased stability, complicating the penetration of moisture through hardened concrete:
Control methods
Options for determining indicators are specified by GOST. This document specifies the following methods for testing the watertightness of a concrete mixture:
When there is an urgent need to determine water resistance, accelerated testing options are used, since accurate laboratory methods will require at least one week for testing.
Selecting the required brand concrete solutions frost resistance and water resistance must be carried out taking into account climatic conditions your region, and the number of freeze and thaw cycles throughout the winter. We must not forget that compositions with increased density characteristics have the best performance.
