The ability of concrete to withstand mechanical and temperature stress is called strength. This is the most important characteristic that affects operational parameters designs.
All rules regarding testing of concrete for tension, compression and bending are prescribed in GOST 18105-86. Important characteristic The reliability of the material is determined by the coefficient of variation, which characterizes the homogeneity of the mixture (Vm).
Where S m - standard deviation strength, Rm– strength of concrete in the batch.
According to GOST 10180-67, the cubic strength of the material under compression is determined. It is calculated by compressing control cube samples with stiffeners at the age of 28 days. For class B25 and above, the prism index should be 0.75, for compounds with a class below B25 - 0.8.
In addition to GOSTs, the design strength requirements are also specified in SNiPs. For example, the decking indicator of unloaded horizontal structures with a span of less than 6 meters must be at least 70% of the design strength, if the span length exceeds 6 meters - 80%.
Testing samples makes it possible to determine the quality of the mixture, but not the characteristics of the concrete in the structure. Such studies are carried out in accordance with GOST 18105-2010 and use the following methods:
- destructive,
- indirect destructive,
- direct destructive.
Direct methods are very popular non-destructive testing. To the main methods of this type include ultrasonic or mechanical.
Methods for monitoring the strength of concrete according to GOST 22690-88
- separation;
- separation with chipping;
- rib chipping.
Tools needed for research
- the electronic unit;
- a tear-off device with a device for gluing to concrete;
- sensors;
- dowels and anchors;
- reference metal rod.
The graph shows the increase in strength of the material over time, while line A is vacuum treatment, B is natural hardening, C is the change in the indicator after undergoing vacuum treatment.
Testing the strength of concrete using the pull-out method
This type of study is based on measuring the maximum force to tear off a part. concrete structure. Moreover, the lifting load should be applied to flat surface by gluing the device disk. Used for gluing adhesive compositions epoxy based. GOST 22690-88 specifies adhesives ED16 and ED20 with cement filler. You can also use two-component formulations. The separation area is determined after each test. After lifting and force calculation, the concrete tensile strength (Rbt) is measured. Using empirical dependence and this indicator, you can calculate the R index - compressive strength. To do this, use the formula:
Rbt = 0.5∛ (R^2)
Separation with chipping
After the concrete has hardened, an anchor device is placed in a pre-drilled hole, after which it is pulled out with part of the concrete. This method is in many ways similar to that described earlier. The main difference is the method of attaching the tool to the surface. The tearing force is created by leaf anchors. The anchor is placed in the hole and P is measured - the breaking force. GOST 22690 indicates the transition of strength concrete composition for compression according to the formula:
R = m1 * m2 *P,
where m2 is the coefficient of transition of compressive strength, depending on the hardening conditions and type of concrete, m1 is the coefficient reflecting the maximum parameters of large aggregate (bulk stone materials).
Restrictions for use this method research is dense reinforcement and insignificant thickness of the structure. The thickness of the surface must exceed twice the length of the anchor.
Rib splitting method
The strength of concrete with this method is determined by the force (P) required to break off a part of the structure placed on the edge outside. The device is mounted on the surface using an anchor bolt with a dowel. To determine the indicator, the following formula is used:
R = 0.058 * m * (30P + P2),
where m is understood as a coefficient reflecting the size of the aggregate.
Ultrasonic method
The operation of ultrasonic testing devices is based on the relationship between the speed at which waves propagate through a structure and its strength. Based this method It was determined that the speed, as well as the time of wave propagation, corresponds to the strength of concrete.
For prefabricated linear structures, the through-transmission method is used. In this case, ultrasonic transducers are located on opposite sides of the structure. Flat, hollow-core and ribbed floor slabs, as well as Wall panels They are examined by surface transmission, in which a wave converter (flaw detector) is placed on one side of the structure.
To ensure maximum acoustic contact with work surface choose viscous contact materials (for example, grease). A dry version is possible using protectors and conical nozzles. Installation of ultrasonic devices is carried out at a distance of at least 3 cm from the edge.
Tests are carried out in accordance with GOST 22690.2-77. The strength of concrete is determined within the range of 5-50 MPa. A blow is applied to the flat test surface, resulting in the formation of two imprints: on the reference metal rod and on the surface of the base. With each blow, the rod is moved 10 mm into the hole in the hammer body. The base is struck through white carbon paper. An angular scale is used to measure prints on paper.
For studies based on elastic rebound, a Schmidt hammer, Borovoy and TsNIISK pistols, and a KM sclerometer with a rod striker are used. The firing pin is cocked and launched automatically at the moment the firing pin touches the base being tested. The amount of rebound of the striker is recorded by a special pointer on the scale of the device.
The goals, basic principles and basic procedure for carrying out work on interstate standardization have been established GOST 1.0-92“Interstate standardization system. Basic provisions" and GOST 1.2-2009“Interstate standardization system. Interstate standards, rules and recommendations for interstate standardization. Rules for development, adoption, application, updating and cancellation"
1 DEVELOPED by the structural unit of JSC "Scientific Research Center "Construction" Scientific Research, Design and Technological Institute of Concrete and Reinforced Concrete named after. A.A. Gvozdeva (NIIZhB)
2 INTRODUCED by the Technical Committee for Standardization TC 465 “Construction”
3 ADOPTED by the Interstate Council for Standardization, Metrology and Certification (protocol dated June 18, 2015 No. 47)
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Short name of the country |
Code of the country |
Abbreviated name of the national authority |
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Armenia |
Ministry of Economy of the Republic of Armenia |
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Belarus |
State Standard of the Republic of Belarus |
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Kazakhstan |
Gosstandart of the Republic of Kazakhstan |
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Kyrgyzstan |
Kyrgyzstandard |
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Moldova |
Moldova-Standard |
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Russia |
Rosstandart |
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Tajikistan |
Tajikstandard |
4 By Order of the Federal Agency for Technical Regulation and Metrology dated September 25, 2015 No. 1378-st interstate standard GOST 22690-2015 entered into force as a national standard of the Russian Federation on April 1, 2016.
5 This standard takes into account the main regulatory provisions regarding the requirements for mechanical methods of non-destructive testing of concrete strength of the following European regional standards:
EN 12504-2:2001 Testing concrete in structures - Part2: Non-destructive testing - Determination of rebound number;
EN 12504-3:2005 Testing concrete in structures - Determination of pull-outforce.
Level of conformity - nonequivalent (NEQ)
Information about changes to this standard is published in the annual information index “National Standards”, and the text of changes and amendments is published in the monthly information index “National Standards”. In case of revision (replacement) or cancellation of this standard, the corresponding notice will be published in the monthly information index “National Standards”. Relevant information, notices and texts are also posted in the information system common use- on the official website of the Federal Agency for Technical Regulation and Metrology on the Internet
GOST 22690-2015
Concrete
Determination of strength by mechanical methods of nondestructive testing
Date of introduction - 2016-04-01
1 area of use
This standard applies to structural heavy, fine-grained, lightweight and prestressing concrete of monolithic, prefabricated and prefabricated concrete and reinforced concrete products, structures and structures (hereinafter referred to as structures) and establishes mechanical methods for determining the compressive strength of concrete in structures by elastic rebound, impact impulse , plastic deformation, tearing, rib chipping and tearing with chipping.
2 Normative references
This standard uses normative references to the following interstate standards:
Note - Standard test schemes are applicable over a limited range of concrete strengths (see annexes And ). For cases not related to standard test schemes, calibration dependencies should be established according to general rules.
4.6 The test method should be selected taking into account the data given in the table and additional restrictions established by the manufacturers of specific measuring instruments. The use of methods outside the ranges of concrete strength recommended in the table is permitted with scientific and technical justification based on the results of research using measuring instruments that have passed metrological certification for an extended range of concrete strength.
Table 1
|
Method name |
Limit values of concrete strength, MPa |
|
Elastic rebound and plastic deformation |
5 - 50 |
|
Impact impulse |
5 - 150 |
|
Breakaway |
5 - 60 |
|
Rib chipping |
10 - 70 |
|
Separation with chipping |
5 - 100 |
4.7 Determination of the strength of heavy concrete of design classes B60 and above or with average compressive strength of concrete Rm≥ 70 MPa in monolithic structures must be carried out taking into account the provisions GOST 31914.
4.8 The strength of concrete is determined in areas of structures that do not have visible damage (detachment of the protective layer, cracks, cavities, etc.).
4.9 The age of the concrete of the controlled structures and its sections should not differ from the age of the concrete of the structures (sections, samples) tested to establish the calibration dependence by more than 25%. Exceptions are strength control and the construction of a calibration relationship for concrete whose age exceeds two months. In this case, the difference in the age of individual structures (sites, samples) is not regulated.
4.10 Tests are carried out at positive concrete temperatures. It is allowed to carry out tests at negative temperature concrete, but not lower than minus 10 °C, when establishing or linking the calibration dependence taking into account the requirements. The temperature of the concrete during testing must correspond to the temperature specified by the operating conditions of the devices.
Calibration dependencies established at concrete temperatures below 0 °C are not allowed to be used at positive temperatures.
4.11 If it is necessary to test concrete structures after heat treatment at surface temperature T≥ 40 °C (to control the tempering, transfer and formwork strength of concrete) the calibration dependence is established after determining the strength of concrete in the structure indirectly non-destructive method at a temperature t = (T± 10) °C, and testing concrete by direct non-destructive method or testing samples - after cooling at normal temperature.
5 Measuring instruments, equipment and tools
5.1 Measuring instruments and instruments for mechanical testing intended to determine the strength of concrete must be certified and verified in the prescribed manner and must comply with the requirements of the application.
5.2 The readings of instruments calibrated in units of concrete strength should be considered as an indirect indicator of the strength of concrete. These devices should be used only after establishing the calibration relationship “device reading - concrete strength” or linking the relationship established in the device in accordance with.
5.3 Tool for measuring the diameter of prints (calipers according to GOST 166), used for the plastic deformation method, must provide measurement with an error of no more than 0.1 mm, a tool for measuring the depth of the indentation (a dial indicator according to GOST 577 etc.) - with an error of no more than 0.01 mm.
5.4 Standard testing schemes for the peel-off and rib shear method provide for the use of anchor devices and grips in accordance with the applications and.
5.5 For the peeling method, anchor devices should be used, the embedment depth of which should be no less than the maximum size of the coarse concrete aggregate of the structure being tested.
5.6 For the tear-off method, steel disks with a diameter of at least 40 mm, a thickness of at least 6 mm and a diameter of at least 0.1, with a roughness of the adhesive surface of at least Ra= 20 µm GOST 2789. The adhesive for gluing the disc must ensure adhesion strength to the concrete, at which destruction occurs along the concrete.
6 Preparation for testing
6.1.1 Preparation for testing includes checking the instruments used in accordance with the instructions for their operation and establishing calibration relationships between the strength of concrete and an indirect characteristic of strength.
6.1.2 The calibration dependence is established based on the following data:
The results of parallel tests of the same sections of structures using one of the indirect methods and the direct non-destructive method for determining the strength of concrete;
The results of testing sections of structures using one of the indirect non-destructive methods for determining the strength of concrete and testing core samples selected from the same sections of the structure and tested in accordance with GOST 28570 ;
Standard test results concrete samples one of the indirect non-destructive methods for determining the strength of concrete and mechanical tests according to GOST 10180.
6.1.3 For indirect non-destructive methods for determining the strength of concrete, a calibration dependence is established for each type of standardized strength specified in for concrete of the same nominal composition.
It is allowed to build one calibration relationship for concrete of the same type with one type of coarse aggregate, with a single production technology, differing in nominal composition and value of standardized strength, subject to compliance with the requirements.
6.1.4 The permissible difference in the age of concrete of individual structures (sections, samples) when establishing a calibration dependence on the age of concrete of the controlled structure is taken according to .
6.1.5 For direct non-destructive methods, it is allowed to use the dependencies given in the appendices for all types of standardized strength of concrete.
6.1.6 The calibration dependence must have a standard (residual) deviation S T . H. M , not exceeding 15% of the average value of the concrete strength of the sections or samples used in constructing the relationship, and the correlation coefficient (index) of not less than 0.7.
It is recommended to use a linear relationship of the form R = a + bK(Where R- concrete strength, K- indirect indicator). The methodology for establishing, evaluating parameters and determining the conditions for using a linear calibration relationship is given in the Appendix.
6.1.7 When constructing a calibration dependence of the deviation of unit values of concrete strength R i f from the average value of the concrete strength of the sections or samples used to construct the calibration dependence must be within the limits:
From 0.5 to 1.5 of the average concrete strength at ≤ 20 MPa;
From 0.6 to 1.4 average concrete strength at 20 MPa< ≤ 50 МПа;
From 0.7 to 1.3 average concrete strength at 50 MPa< ≤ 80 МПа;
From 0.8 to 1.2 of the average concrete strength at > 80 MPa.
6.1.8 Correction of the established relationship for concrete at intermediate and design ages should be carried out at least once a month, taking into account additionally obtained test results. The number of samples or areas of additional testing when making adjustments must be at least three. The adjustment method is given in the Appendix.
6.1.9 It is allowed to use indirect non-destructive methods for determining the strength of concrete, using calibration dependencies established for concrete that differs from the test in composition, age, hardening conditions, humidity, with reference in accordance with the methodology in the Appendix.
6.1.10 Without reference to specific conditions of the application, calibration dependencies established for concrete different from the one being tested can only be used to obtain approximate strength values. It is not allowed to use indicative strength values without reference to specific conditions to assess the strength class of concrete.
Then select areas in the quantity provided for, where the maximum, minimum and intermediate values of the indirect indicator are obtained.
After testing by the indirect non-destructive method, areas are tested by the direct non-destructive method or samples are taken for testing according to GOST 28570.
6.2.4 To determine the strength at a negative temperature of concrete, the areas selected for constructing or linking the calibration dependence are first tested by an indirect non-destructive method, and then samples are taken for subsequent testing at a positive temperature or heated by external heat sources (infrared emitters, heat guns, etc. ) to a depth of 50 mm to a temperature not lower than 0 °C and tested using a direct non-destructive method. The temperature of heated concrete is controlled at the depth of installation of the anchor device in a prepared hole or along the surface of a chip in a non-contact manner using a pyrometer according to GOST 28243.
Rejection of test results used to construct a calibration curve at a negative temperature is allowed only if the deviations are associated with a violation of the test procedure. In this case, the rejected result must be replaced by the results of repeated testing in the same area of the structure.
6.3.1 When constructing a calibration dependence based on control samples, the dependence is established using single values of the indirect indicator and the strength of concrete of standard cube samples.
The average value of indirect indicators for a series of samples or for one sample (if the calibration dependence is established for individual samples) is taken as a single value of an indirect indicator. The unit strength of concrete is taken as the strength of concrete in a series according to GOST 10180 or one sample (calibration dependence for individual samples). Mechanical tests samples according to GOST 10180 carried out immediately after testing by an indirect non-destructive method.
6.3.2 When constructing a calibration dependence based on the results of testing cube samples, use at least 15 series of cube samples according to GOST 10180 or at least 30 individual cube samples. Samples are produced in accordance with the requirements GOST 10180 in different shifts, for at least 3 days, from concrete of the same nominal composition, using the same technology, under the same hardening regime as the structure to be controlled.
The unit values of the concrete strength of the cube samples used to construct the calibration relationship must correspond to the deviations expected in production, and at the same time be within the ranges established in.
6.3.3 The calibration dependence for the methods of elastic rebound, shock impulse, plastic deformation, rib separation and spalling is established based on the results of tests of manufactured cube samples, first by a non-destructive method, and then by a destructive method according to GOST 10180.
When establishing the calibration dependence for the tear-off method, the main and control samples By . An indirect characteristic is determined on the main samples, control samples are tested according to GOST 10180. The main and control samples must be made of the same concrete and harden under the same conditions.
6.3.4 Sample sizes should be selected in accordance with the largest aggregate size in concrete mixture By GOST 10180, but not less:
100×100×100 mm for the rebound, shock impulse, plastic deformation methods, as well as for the peeling method (control samples);
200×200×200 mm for the method of chopping the edge of the structure;
300×300×300 mm, but with a rib size of at least six installation depths of the anchor device for the peeling method (main samples).
6.3.5 To determine indirect strength characteristics, tests are carried out in accordance with the requirements of the section on the lateral (in the direction of concreting) faces of cube samples.
Total number measurements on each sample for the method of elastic rebound, shock impulse, plastic deformation upon impact must be at least the established number of tests in the area according to the table, and the distance between the impact points must be at least 30 mm (15 mm for the shock impulse method). For the method of plastic deformation during indentation, the number of tests on each face must be at least two, and the distance between test sites must be at least twice the diameter of the indents.
When establishing a calibration relationship for the rib shearing method, one test is carried out on each side rib.
When establishing the calibration dependence for the peel-off method, one test is carried out on each side face of the main sample.
6.3.6 When tested by the method of elastic rebound, shock impulse, or plastic deformation upon impact, samples must be clamped in a press with a force of at least (30 ± 5) kN and no more than 10% of the expected value of the breaking load.
6.3.7 Specimens tested by the tearing method are installed on the press so that the surfaces on which the tearing was carried out do not adhere to the support plates of the press. Test results for GOST 10180 increase by 5%.
7 Testing
7.1.1 The number and location of controlled areas in structures must comply with the requirements GOST 18105 and be indicated in the design documentation for the structure or installed taking into account:
Control tasks (determining the actual class of concrete, stripping or tempering strength, identifying areas of reduced strength, etc.);
Type of structure (columns, beams, slabs, etc.);
Placement of grips and concreting order;
Reinforcement of structures.
The rules for assigning the number of test sites for monolithic and prefabricated structures when monitoring the strength of concrete are given in the Appendix. When determining the strength of concrete of the structures being surveyed, the number and location of sections should be taken according to the survey program.
7.1.2 Tests are carried out on a section of the structure with an area of 100 to 900 cm2.
7.1.3 The total number of measurements in each section, the distance between the measurement locations in the section and from the edge of the structure, the thickness of the structures in the measurement section must be no less than the values given in the table depending on the test method.
Table 2 - Requirements for test areas
|
Method name |
Total number |
Minimum |
Minimum |
Minimum |
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Elastic rebound |
||||
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Impact impulse |
||||
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Plastic deformation |
||||
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Rib chipping |
||||
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Breakaway |
2 diameters |
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Separation with chipping at working depth of anchor embeddingh: |
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≥ 40mm |
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< 40мм |
7.1.4 The deviation of individual measurement results at each section from the arithmetic mean value of the measurement results for a given section should not exceed 10%. Measurement results not satisfactory specified condition, are not taken into account when calculating the arithmetic mean value of the indirect indicator for a given area. The total number of measurements at each site when calculating the arithmetic mean must comply with the requirements of the table.
7.1.5 The strength of concrete in the controlled section of the structure is determined by the average value of the indirect indicator according to the calibration relationship established in accordance with the requirements of section, provided that the calculated value of the indirect indicator is within the established (or linked) relationship (between the smallest and highest values strength).
7.1.6 The surface roughness of a section of concrete structures when tested by rebound, shock impulse, and plastic deformation methods must correspond to the surface roughness of sections of a structure (or cubes) tested when establishing the calibration relationship. If necessary, it is allowed to clean the surfaces of the structure.
When using the indentation plastic deformation method, if the zero reading is removed after applying the initial load, there are no requirements for the surface roughness of the concrete structure.
7.2.1 Tests are carried out in the following sequence:
It is recommended that the position of the device when testing the structure relative to the horizontal be the same as when establishing the calibration dependence. In a different position of the device, it is necessary to make corrections to the indicators in accordance with the operating instructions for the device;
7.3.1 Tests are carried out in the following sequence:
The device is positioned so that the force is applied perpendicular to the surface under test in accordance with the operating instructions for the device;
When using a spherical indenter to facilitate measurements of the diameters of prints, the test can be carried out through sheets of carbon and white paper (in this case, tests to establish the calibration dependence are carried out using the same paper);
The values of the indirect characteristic are recorded in accordance with the operating instructions for the device;
The average value of the indirect characteristic on the section of the structure is calculated.
7.4.1 Tests are carried out in the following sequence:
The device is positioned so that the force is applied perpendicular to the surface under test in accordance with the operating instructions for the device;
It is recommended to take the position of the device when testing the structure relative to the horizontal the same as during testing when establishing the calibration dependence. In a different position of the device, it is necessary to make corrections to the readings in accordance with the operating instructions for the device;
Record the value of the indirect characteristic in accordance with the operating instructions for the device;
The average value of the indirect characteristic on the section of the structure is calculated.
7.5.1 When testing by the pull-out method, the sections should be located in the zone of lowest stresses caused by the operational load or the compression force of the prestressed reinforcement.
7.5.2 The test is carried out in the following sequence:
In the place where the disc is glued, remove the surface layer of concrete 0.5 - 1 mm deep and clean the surface of dust;
The disc is glued to the concrete by pressing the disc and removing excess glue outside the disc;
The device is connected to the disk;
The load is gradually increased at a speed of (1 ± 0.3) kN/s;
The projection area of the separation surface on the plane of the disk is measured with an error of ± 0.5 cm 2 ;
The value of the conditional stress in concrete during tearing is determined as the ratio of the maximum tearing force to the projected area of the tearing surface.
7.5.3 The test results are not taken into account if the reinforcement was exposed during concrete separation or the projection area of the separation surface was less than 80% of the disk area.
7.6.1 When testing by the peel-off method, the sections should be located in the zone of lowest stresses caused by the operational load or the compression force of the prestressed reinforcement.
7.6.2 Tests are carried out in the following sequence:
If the anchor device was not installed before concreting, then a hole is made in the concrete, the size of which is selected in accordance with the operating instructions for the device, depending on the type of anchor device;
The anchor device is fixed into the hole to the depth specified in the operating instructions for the device, depending on the type of anchor device;
The device is connected to an anchor device;
The load is increased at a speed of 1.5 - 3.0 kN/s;
Record the reading of the force meter of the device R 0 and the amount of anchor slip Δ h(the difference between the actual tear-out depth and the embedding depth of the anchor device) with an accuracy of at least 0.1 mm.
7.6.3 Measured pullout force value R 0 is multiplied by the correction factor γ, determined by the formula
Where h- working depth of the anchor device, mm;
Δ h- the amount of anchor slippage, mm.
7.6.4 If the largest and smallest dimensions of the torn-out part of concrete from the anchor device to the limits of destruction along the surface of the structure differ by more than twice, and also if the depth of the torn-out differs from the depth of embedding of the anchor device by more than 5% (Δ h > 0,05h, γ > 1.1), then the test results can be taken into account only for an approximate assessment of the strength of concrete.
Note - Approximate values of concrete strength are not allowed to be used to assess the strength class of concrete and construct calibration dependencies.
7.6.5 The test results are not taken into account if the depth of the pullout differs from the depth of embedding of the anchor device by more than 10% (Δ h > 0,1h) or the reinforcement was exposed at a distance from the anchor device less than the depth of its embedding.
7.7.1 When tested by the rib shearing method, there should be no cracks, concrete edges, sagging or cavities in the test area with a height (depth) of more than 5 mm. The sections should be located in the zone of least stress caused by the operational load or the compression force of the prestressed reinforcement.
7.7.2 The test is carried out in the following sequence:
The device is fixed to the structure, a load is applied at a speed of no more than (1 ± 0.3) kN/s;
Record the reading of the force meter of the device;
Measure the actual chipping depth;
The average value of the shearing force is determined.
7.7.3 The test results are not taken into account if the reinforcement was exposed during concrete chipping or the actual chipping depth differed from the specified depth by more than 2 mm.
8 Processing and presentation of results
8.1 The test results are presented in a table in which they indicate:
Type of design;
Design class of concrete;
Age of concrete;
The strength of the concrete of each controlled area according to;
Average strength of concrete structure;
Areas of the structure or parts thereof, subject to compliance.
The form of the table for presenting test results is given in the Appendix.
8.2 Processing and assessment of compliance with established requirements for the actual strength of concrete obtained using the methods given in this standard is carried out according to GOST 18105.
Note - Statistical assessment of the class of concrete based on test results is carried out according toGOST 18105 (schemes “A”, “B” or “C”) in cases where the strength of concrete is determined by a calibration relationship constructed in accordance with section . When using previously installed dependencies by linking them (by application ) statistical control is not allowed, and concrete class assessment is carried out only according to the “D” schemeGOST 18105.
8.3 The results of determining the strength of concrete using mechanical non-destructive testing methods are documented in a conclusion (protocol), which provides the following data:
About the tested structures, indicating the design class, the date of concreting and testing, or the age of the concrete at the time of testing;
About the methods used to control the strength of concrete;
About types of devices with serial numbers, information about verification of devices;
About the accepted calibration dependencies (dependence equation, dependency parameters, compliance with the conditions for applying the calibration dependency);
Used to construct a calibration relationship or its reference (date and results of tests using non-destructive indirect and direct or destructive methods, correction factors);
On the number of sections for determining the strength of concrete in structures, indicating their location;
Test results;
Methodology, results of processing and evaluation of the data obtained.
Appendix A
(required)
Standard test scheme for the peel-off test
A.1 The standard test scheme for the peel-off method involves testing subject to the requirements -.
A.2 The standard test scheme is applicable in the following cases:
Testing heavy concrete with compressive strength from 5 to 100 MPa;
Tests lightweight concrete compressive strength from 5 to 40 MPa;
The maximum fraction of coarse concrete aggregate is not more than the working depth of embedding anchor devices.
A.3 The supports of the loading device must be evenly adjacent to the concrete surface at a distance of at least 2 h from the axis of the anchor device, where h- working depth of the anchor device. The test diagram is shown in the figure.
1
2
- support for the loading device;
3
- grip of the loading device; 4
- transition elements, rods; 5
- anchor device;
6
- pulled out concrete (tearout cone); 7
- test structure
Figure A.1 - Scheme of the peel-off test
A.4 The standard testing scheme for the peel-off method provides for the use of three types of anchor devices (see figure). Type I anchor device is installed in the structure during concreting. Anchor devices of types II and III are installed in holes previously prepared in the structure.
1
- working rod; 2
- working rod with expansion cone; 3
- segmented grooved cheeks;
4
- support rod; 5
- working rod with a hollow expansion cone; 6
- leveling washer
Figure A.2 - Types of anchor devices for standard test scheme
A.5 The parameters of anchor devices and their permissible ranges of measured concrete strength under a standard test scheme are indicated in the table. For lightweight concrete, the standard test scheme uses only anchor devices with an embedment depth of 48 mm.
Table A.1 - Parameters of anchor devices for standard test scheme
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Anchor type |
Anchor diameter |
Depth of embedding anchor devices, |
Acceptable for anchor device |
||
|
working h |
full h" |
heavy |
lung |
||
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45 - 75 |
|||||
|
10 - 50 |
10 - 40 |
||||
|
40 - 100 |
|||||
|
5 - 100 |
5 - 40 |
||||
|
10 - 50 |
|||||
A.6 The designs of anchors of types II and III must ensure preliminary (before applying the load) compression of the walls of the hole at the working embedment depth h and post-test slip monitoring.
Appendix B
(required)
Standard rib splitting test scheme
B.1 The standard testing scheme by the rib shearing method provides for testing subject to the requirements -.
B.2 The standard test scheme is applicable in the following cases:
The maximum fraction of coarse concrete aggregate is no more than 40 mm;
Testing of heavy concrete with compressive strength from 10 to 70 MPa on granite and limestone crushed stone.
B.3 For testing, a device is used, consisting of a force exciter with a force measuring unit and a gripper with a bracket for local chipping of the structure edge. The test diagram is shown in the figure.
1
- a device with a loading device and a force meter; 2
- support frame;
3
- chipped concrete; 4
- test structure; 5
- grip with bracket
Figure B.1 - Scheme of testing using the rib shearing method
B.4 When local chipping of a rib occurs, the following parameters must be ensured:
Shearing depth a= (20 ± 2) mm;
Cleaving Width b= (30 ± 0.5) mm;
The angle between the direction of the load and the normal to the loaded surface of the structure β = (18 ± 1)°.
Appendix B
(recommended)
Calibration dependence for the peel-off method
When testing by the peel-off method according to the standard scheme according to the appendix, the cubic compressive strength of concrete R, MPa, can be calculated using the calibration dependence using the formula
|
R = m 1 m 2 P, |
Where m 1 - coefficient taking into account the maximum size of coarse aggregate in the tear-out zone, taken equal to 1 when the aggregate size is less than 50 mm;
m 2 - proportionality coefficient for the transition from tearing force in kilonewtons to concrete strength in megapascals;
R- pullout force of the anchor device, kN.
When testing heavy concrete with a strength of 5 MPa or more and light concrete with a strength from 5 to 40 MPa, the values of the proportionality coefficient m 2 is taken according to the table.
Table B.1
|
Anchor type |
Range |
Anchor diameter |
Anchor embedment depth |
Coefficient valuem 2 for concrete |
|
|
heavy |
lung |
||||
|
45 - 75 |
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|
10 - 50 |
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|
40 - 75 |
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|
5 - 75 |
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|
10 - 50 |
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Odds m 2 when testing heavy concrete with an average strength above 70 MPa should be taken according to GOST 31914.
Appendix D
(recommended)
Calibration dependence for the rib shearing method
with standard test scheme
When testing by the rib shearing method according to the standard scheme according to the appendix, the cubic compressive strength of concrete on granite and crushed limestone R, MPa, can be calculated using the calibration dependence using the formula
|
R = 0,058m(30R + R 2), |
Where m- coefficient taking into account the maximum size of coarse aggregate and taken equal to:
1.0 - with aggregate size less than 20 mm;
1.05 - with aggregate size from 20 to 30 mm;
1.1 - with aggregate size from 30 to 40 mm;
R- shearing force, kN.
Appendix D
(required)
Requirements for instruments for mechanical tests
Table E.1
|
Name of device characteristics |
Characteristics of instruments for the method |
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|
elastic |
percussion |
plastic |
separation |
chipping |
separation from |
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|
Hardness of the striker, striker or indenter HRCе, not less |
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Roughness of the contact part of the striker or indenter, µm, no more |
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Diameter of striker or indenter, mm, not less |
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Thickness of disk indenter edges, mm, not less |
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|
Conical indenter angle |
30° - 60° |
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|
Indentation diameter, % of indenter diameter |
20 - 70 |
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Perpendicularity tolerance when applying a load at a height of 100 mm, mm |
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Impact energy, J, not less |
0,02 |
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|
Rate of load increase, kN/s The equation for the relationship “indirect characteristic - strength” is taken to be linear according to the formula E.2 Rejection of test results After constructing the calibration dependence using formula (), it is adjusted by rejecting individual test results that do not satisfy the condition: where the average value of concrete strength according to the calibration dependence is calculated using the formula here are the meanings R i H, R i f, , N- see explanations for formulas (), (). E.4 Correction of the calibration dependence Correction of the established calibration dependence, taking into account additionally obtained test results, must be carried out at least once a month. When adjusting the calibration dependence, at least three new results obtained at the minimum, maximum and intermediate values of the indirect indicator are added to the existing test results. As data is accumulated for constructing a calibration dependence, the results of previous tests, starting from the very first, are rejected so that the total number of results does not exceed 20. After adding new results and rejecting old ones, the minimum and maximum values of the indirect characteristic, the calibration dependence and its parameters are established again according to the formulas () - (). E.5 Conditions for using the calibration dependence The use of a calibration relationship to determine the strength of concrete according to this standard is allowed only for values of the indirect characteristic falling in the range from H min to N max. If the correlation coefficient r < 0,7 или значение Appendix G
| ||||||||||||||||||||||||||||||||||||||
|
|
Where R OS i- concrete strength in i- section, determined by the tear-off method with chipping or testing of cores along GOST 28570 ;
R kosv i- concrete strength in i- section, determined by any indirect method using the calibration dependence used;
n- number of test sites.
G.2 When calculating the coincidence coefficient, the following conditions must be met:
Number of test sites taken into account when calculating the coincidence coefficient, n ≥ 3;
Each private value R OS i /R kosv i should be no less than 0.7 and no more than 1.3:
|
1 by 4 m length of linear structures; 1 by 4 m2 area of flat structures. Appendix K
| |||||||||||||||||||||||||||||||||
|
Name of structures |
Designation 1) |
Plot number according to the scheme |
Strength of concrete, MPa |
Strength class |
|
|
section 3) |
average 4) |
||||
|
1) Brand, symbol and (or) the location of the structure in the axes, zones of the structure, or part of a monolithic and prefabricated monolithic structure (capture), for which the concrete strength class is determined. 2) The total number and location of plots in accordance with . 3) The strength of the concrete of the site in accordance with . 4) Average strength of concrete of a structure, structure zone or part of a monolithic and prefabricated monolithic structure with the number of sections that meet the requirements . 5) Actual class strength of concrete of a structure or part of a monolithic and prefabricated monolithic structure in accordance with paragraphs 7.3 - 7.5GOST 18105 depending on the selected control scheme. Note - Presentation in the column “Concrete strength class” of estimated class values or values of the required concrete strength for each section separately (assessment of the strength class for one section) is not acceptable. |
|||||
Key words: structural heavy and light concrete, monolithic and prefabricated concrete and reinforced concrete products, structures and structures, mechanical methods for determining compressive strength, elastic rebound, shock impulse, plastic deformation, tearing, rib spalling, tearing with chipping
Building structures based on a mixture of binder, sand and aggregate need to be tested for reliability and safety. However, such studies should not cause interruption in the operation of the tested object, and therefore are carried out using a non-destructive method. This reduces costs, reduces labor intensity and eliminates local damage.
Direct control methods
These methods are necessary for the formation of calibration dependencies and their subsequent adjustment for indirect methods carried out on the same sections of the structure. The technology can be used for inspection at various stages of construction of buildings, as well as for the operation and reconstruction of finished objects.
Separation with chipping
Such an operation is carried out in accordance with state standards, which reflects basic information about the method of implementation. The results obtained are not influenced in any way by the surface condition.
Three types of anchor devices are used for research.
- Working rod equipped with an anchor head.
- A device with an expansion cone and grooved segment cheeks.
- A device with a hollow expanding cone, which has a special rod for fixing the device in one position.
Note! When choosing the type of device and the penetration depth of the anchor, you should take into account the expected strength of the composition and the size of the aggregate, which is reflected in the table below.
| Drying conditions for the mixture | Type of device used | Anchor immersion depth in mm | Estimated strength in MPa | Coefficient value | |
| Light composition | Heavy solution | ||||
| Heat treatment | 1 | 4835 | <50>50 | 1,2 | 1,32,6 |
| 2 | 4830 | <50>50 | 1,0 | 1,12,7 | |
| 3 | 35 | <50 | — | 1,8 | |
| Natural hardening | 1 | 4835 | <50>50 | 1,2 | 1,12,4 |
| 2 | 4830 | <50>50 | 1,0 | 0,92,5 | |
| 3 | 35 | <50 | — | 1,5 | |
In monolithic structures, testing the strength of concrete using a non-destructive method, which involves tearing off with chipping, is carried out in three areas at once. When adjusting calibration dependencies, three indirect tests are carried out together with this method.
Rib chipping
This method involves cutting off the edge of the structure being tested. It is primarily used to control linear segments such as beams, columns, piles, lintels and support beams. The operation does not require additional preparation, however, if there is a protective layer less than 20 mm thick, the method cannot be applied.
Separation of metal discs
Another measure that allows for a non-destructive method of testing concrete has not found widespread use in our country, which is due to the limited temperature regime. Another negative factor is the need to make a groove with a drill, and this reduces the productivity of the study.
The method itself involves recording the stress that is required for local destruction of the hardened composition when the steel disk is torn off. When determining strength properties, the applied force and surface projection area are taken into account.
Indirect control methods
Such studies are carried out when it is necessary to evaluate the value of strength characteristics, using them as one of several factors that give an idea of the technical condition of a structure. The obtained result cannot be used if the private calibration dependence () has not been defined.
Ultrasound testing
The method of testing concrete using a non-destructive method, which involves the use of ultrasonic waves, has become widespread. During the operation, a connection is established between the vibration speed and the density of the hardened mixture.
Addiction can be influenced by a variety of factors.
- Filler fraction and its quantity in the solution.
- The chosen method of preparing the composition.
- Compaction degree and tension.
- Change in binder consumption by more than 30 percent.
Addition! Ultrasonic surveys provide the opportunity to perform mass testing of almost any structure an unlimited number of times. The main disadvantage lies in the permissible error.
Elastic rebound
Non-destructive testing of concrete strength using this method allows us to establish the relationship between compressive strength and elasticity of the material. During the study, the metal striker of the main device after an impact moves away to a certain distance, which is an indicator of the strength qualities of the structure.
During testing, the device is fixed so that the steel element is in close contact with the concrete surface, for which special screws are used. After fastening, the pendulum is installed horizontally. In this case, it is latched directly by the trigger.
Having placed the device perpendicular to the plane, pull the trigger. The firing pin is cocked automatically, after which it is independently released and strikes under the influence of a special spring. The metal element bounces a certain distance, which is measured by a special scale.
The KISI system device, which has a rather complex structure, is used as the main test tool. The strength of the hardened mixture can be determined based on the device data after conducting 6-7 tests according to a special schedule.
Giving impact impulse
Thanks to this research method, it is possible to record the impact energy released at the moment the striker comes into contact with the concrete structure. A positive point is the fact that non-destructive testing of concrete devices, operating on the shock pulse principle, have compact dimensions. However, their price is quite high.
Plastic deformation
During the operation, the size of the mark left on the concrete surface by the steel element is measured. The method is considered somewhat outdated, but due to the low cost of equipment it continues to be actively used in the construction environment. After the blow is applied, the remaining prints are measured.
Devices for determining the strength of this type are based on pressing the rod directly into the plane by static pressure of the required force or a regular blow. Pendulum, hammer and spring products are used as the main devices.
Below are the conditions for the operation.
- Tests should be carried out on an area whose area ranges from 100 to 400 square meters. cm.
- When carrying out this operation, at least five measurements should be taken with high accuracy.
- The impact force must be perpendicular to the plane being tested.
- To determine the strength characteristics, a smooth surface is required, which is achieved by molding in metal formwork.
Important! If the strength of concrete is measured non-destructively using hammer-type devices, then the samples must be installed on a perfectly level base.
Comparative characteristics using an example
The object is a well made of monolithic reinforced concrete. Its depth is 8 m, and its radius is 12 m. The side surfaces were filled with grips that divide the structure into 7 tiers in height.
The research results are presented in the table below.
| Tier | Indirect research methods | ||||||
| Ultrasonic | Impact impulse | Elastic rebound | Press test | ||||
| Wed. meaning in m/s | Percentage | Wed. meaning in MPa | Percentage | Wed. meaning in u. units | Percentage | Wed. meaning in MPa | |
| 1 | 4058 | 3,9 | 41,9 | 23,4 | 46,2 | 7,8 | 41,6 |
| 2 | 4082 | 4,6 | 24,4 | 40,2 | 43,7 | 7,6 | 35,0 |
| 3 | 4533 | 5,2 | 49,6 | 28,7 | 49,7 | 9,9 | 36,5 |
| 4 | 4300 | 3,9 | 38,1 | 36,3 | 46,6 | 8,3 | 40,1 |
| 5 | 4094 | 4,1 | 38,2 | 28,5 | 48,2 | 8,5 | 42,1 |
| 6 | 4453 | 3,6 | 45,5 | 41,6 | 47,6 | 7,6 | 39,3 |
| 7 | 3836 | 4,5 | 42,8 | 26,5 | 44,6 | 7,3 | 30,6 |
| Wed. meaning V | ≈4,26 | ≈32,2 | ≈8,14 | ||||
Conclusion! From the table below it becomes clear that the minimum error in research is characteristic of the ultrasonic method. The spread when testing with a shock pulse is maximum.
Testing without using instruments
Research carried out using special devices was discussed above, but if necessary, simple tests can be carried out with your own hands. It will not be possible to obtain accurate information about the strength properties, but it is quite possible to determine the class of concrete.
First, the necessary tools are prepared: a chisel and a hammer, the weight of which ranges from 400-800 g. The impact-cutting device is installed perpendicular to the surface.
It receives blows of medium strength, the traces of which will be analyzed.
- A barely noticeable mark may indicate that the hardened mixture is class B25 or higher.
- Very noticeable marks on the surface of the structure usually remain when using B15 concrete.
- Significant depressions and the presence of crumbs allow us to classify the composition used as class B10.
- If the tip of the tool entered the plane to a depth of more than 1 cm, then B5 concrete may have been used for the work.
Attention! You can check this way within a few minutes without any equipment. After this, you will already have an idea of what strength the hardened composition has.
State standard
Non-destructive methods for monitoring the strength of concrete are regulated according to GOST 22690-88, the clauses of which apply to light and heavy mixtures. However, it reflects only mechanical methods that do not include ultrasound. Their limit values are presented in the table.
Working with concrete
- To form structures based on a building mixture, wooden or metal formwork is made that can give the desired shape to the material.
- To improve the quality characteristics, a mesh of steel reinforcement is placed in the composition, fastened by welding or wire. Typically, the size of the cells ranges from 10 to 20 centimeters.
- If it is necessary to separate some part from the structure, then cutting of reinforced concrete with diamond wheels is used. This operation can be carried out using water to avoid excessive dust.
- The solution is poured, as a rule, at positive temperatures.. However, if you have special equipment for warming up, it is permissible to carry out work with negative thermometer readings.
- To create ventilation inside a concrete structure (for example, for a foundation or attic), diamond drilling of holes in the concrete is carried out.
- Loading the finished structure is allowed only after the mixture has completely hardened, that is, after 28 days.
The goals, basic principles and basic procedure for carrying out work on interstate standardization are established by GOST 1.0-92 “Interstate standardization system. Basic provisions" and GOST 1.2-2009 "Interstate standardization system. Interstate standards, rules and recommendations for interstate standardization. Rules for development, adoption, application, updating and cancellation"
1 DEVELOPED by the structural unit of JSC "Scientific Research Center "Construction" Scientific Research, Design and Technological Institute of Concrete and Reinforced Concrete named after. A.A. Gvozdeva (NIIZhB)
2 INTRODUCED by the Technical Committee for Standardization TC 465 “Construction”
3 ADOPTED by the Interstate Council for Standardization, Metrology and Certification (protocol dated June 18, 2015 No. 47)
|
Short name of the country |
Code of the country |
Abbreviated name of the national authority |
|
Armenia |
Ministry of Economy of the Republic of Armenia |
|
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Belarus |
State Standard of the Republic of Belarus |
|
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Kazakhstan |
Gosstandart of the Republic of Kazakhstan |
|
|
Kyrgyzstan |
Kyrgyzstandard |
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Moldova |
Moldova-Standard |
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|
Russia |
Rosstandart |
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Tajikistan |
Tajikstandard |
4 By Order of the Federal Agency for Technical Regulation and Metrology dated September 25, 2015 No. 1378-st, the interstate standard GOST 22690-2015 was put into effect as a national standard of the Russian Federation on April 1, 2016.
5 This standard takes into account the main regulatory provisions regarding the requirements for mechanical methods of non-destructive testing of concrete strength of the following European regional standards:
EN 12504-2:2001 Testing concrete in structures - Part2: Non-destructive testing - Determination of rebound number;
EN 12504-3:2005 Testing concrete in structures - Determination of pull-outforce.
Level of conformity - nonequivalent (NEQ)
Information about changes to this standard is published in the annual information index “National Standards”, and the text of changes and amendments is published in the monthly information index “National Standards”. In case of revision (replacement) or cancellation of this standard, the corresponding notice will be published in the monthly information index “National Standards”. Relevant information, notifications and texts are also posted in the public information system - on the official website of the Federal Agency for Technical Regulation and Metrology on the Internet
GOST 22690-2015
Concrete
Determination of strength by mechanical methods of nondestructive testing
Date of introduction - 2016-04-01
1 area of use
This standard applies to structural heavy, fine-grained, lightweight and prestressing concrete of monolithic, prefabricated and prefabricated concrete and reinforced concrete products, structures and structures (hereinafter referred to as structures) and establishes mechanical methods for determining the compressive strength of concrete in structures by elastic rebound, impact impulse , plastic deformation, tearing, rib chipping and tearing with chipping.
2 Normative references
This standard uses normative references to the following interstate standards:
Note - Standard test schemes are applicable over a limited range of concrete strengths (see annexes And ). For cases not related to standard test schemes, calibration dependencies should be established according to general rules.
4.6 The test method should be selected taking into account the data given in the table and additional restrictions established by the manufacturers of specific measuring instruments. The use of methods outside the ranges of concrete strength recommended in the table is permitted with scientific and technical justification based on the results of research using measuring instruments that have passed metrological certification for an extended range of concrete strength.
Table 1
|
Method name |
Limit values of concrete strength, MPa |
|
Elastic rebound and plastic deformation |
5 - 50 |
|
Impact impulse |
5 - 150 |
|
Breakaway |
5 - 60 |
|
Rib chipping |
10 - 70 |
|
Separation with chipping |
5 - 100 |
4.7 Determination of the strength of heavy concrete of design classes B60 and above or with average compressive strength of concrete Rm≥ 70 MPa in monolithic structures must be carried out taking into account the provisions of GOST 31914.
4.8 The strength of concrete is determined in areas of structures that do not have visible damage (detachment of the protective layer, cracks, cavities, etc.).
4.9 The age of the concrete of the controlled structures and its sections should not differ from the age of the concrete of the structures (sections, samples) tested to establish the calibration dependence by more than 25%. Exceptions are strength control and the construction of a calibration relationship for concrete whose age exceeds two months. In this case, the difference in the age of individual structures (sites, samples) is not regulated.
4.10 Tests are carried out at positive concrete temperatures. It is allowed to carry out tests at a negative temperature of concrete, but not lower than minus 10 ° C, when establishing or linking a calibration dependence taking into account the requirements. The temperature of the concrete during testing must correspond to the temperature specified by the operating conditions of the devices.
Calibration dependencies established at concrete temperatures below 0 °C are not allowed to be used at positive temperatures.
4.11 If it is necessary to test concrete structures after heat treatment at surface temperature T≥ 40 °C (to control the tempering, transfer and formwork strength of concrete) the calibration dependence is established after determining the strength of concrete in the structure by an indirect non-destructive method at temperature t = (T± 10) °C, and testing concrete by direct non-destructive method or testing samples - after cooling at normal temperature.
5 Measuring instruments, equipment and tools
5.1 Measuring instruments and instruments for mechanical testing intended to determine the strength of concrete must be certified and verified in the prescribed manner and must comply with the requirements of the application.
5.2 The readings of instruments calibrated in units of concrete strength should be considered as an indirect indicator of the strength of concrete. These devices should be used only after establishing the calibration relationship “device reading - concrete strength” or linking the relationship established in the device in accordance with.
5.3 A tool for measuring the diameter of indentations (calipers according to GOST 166), used for the plastic deformation method, must provide measurement with an error of no more than 0.1 mm, a tool for measuring the depth of an indentation (dial indicator according to GOST 577, etc.) - with an error no more than 0.01 mm.
5.4 Standard testing schemes for the peel-off and rib shear method provide for the use of anchor devices and grips in accordance with the applications and.
5.5 For the peeling method, anchor devices should be used, the embedment depth of which should be no less than the maximum size of the coarse concrete aggregate of the structure being tested.
5.6 For the tear-off method, steel disks with a diameter of at least 40 mm, a thickness of at least 6 mm and a diameter of at least 0.1, with a roughness of the adhesive surface of at least Ra= 20 microns according to GOST 2789. The adhesive for gluing the disc must ensure adhesion strength to the concrete, at which destruction occurs along the concrete.
6 Preparation for testing
6.1.1 Preparation for testing includes checking the instruments used in accordance with the instructions for their operation and establishing calibration relationships between the strength of concrete and an indirect characteristic of strength.
6.1.2 The calibration dependence is established based on the following data:
The results of parallel tests of the same sections of structures using one of the indirect methods and the direct non-destructive method for determining the strength of concrete;
The results of testing sections of structures using one of the indirect non-destructive methods for determining the strength of concrete and testing core samples selected from the same sections of the structure and tested in accordance with GOST 28570;
Results of testing standard concrete samples using one of the indirect non-destructive methods for determining the strength of concrete and mechanical tests in accordance with GOST 10180.
6.1.3 For indirect non-destructive methods for determining the strength of concrete, a calibration dependence is established for each type of standardized strength specified in for concrete of the same nominal composition.
It is allowed to build one calibration relationship for concrete of the same type with one type of coarse aggregate, with a single production technology, differing in nominal composition and value of standardized strength, subject to compliance with the requirements.
6.1.4 The permissible difference in the age of concrete of individual structures (sections, samples) when establishing a calibration dependence on the age of concrete of the controlled structure is taken according to .
6.1.5 For direct non-destructive methods, it is allowed to use the dependencies given in the appendices for all types of standardized strength of concrete.
6.1.6 The calibration dependence must have a standard (residual) deviation S T . H. M , not exceeding 15% of the average value of the concrete strength of the sections or samples used in constructing the relationship, and the correlation coefficient (index) of not less than 0.7.
It is recommended to use a linear relationship of the form R = a + bK(Where R- concrete strength, K- indirect indicator). The methodology for establishing, evaluating parameters and determining the conditions for using a linear calibration relationship is given in the Appendix.
6.1.7 When constructing a calibration dependence of the deviation of unit values of concrete strength R i f from the average value of the concrete strength of the sections or samples used to construct the calibration dependence must be within the limits:
From 0.5 to 1.5 of the average concrete strength at ≤ 20 MPa;
From 0.6 to 1.4 average concrete strength at 20 MPa< ≤ 50 МПа;
From 0.7 to 1.3 average concrete strength at 50 MPa< ≤ 80 МПа;
From 0.8 to 1.2 of the average concrete strength at > 80 MPa.
6.1.8 Correction of the established relationship for concrete at intermediate and design ages should be carried out at least once a month, taking into account additionally obtained test results. The number of samples or areas of additional testing when making adjustments must be at least three. The adjustment method is given in the Appendix.
6.1.9 It is allowed to use indirect non-destructive methods for determining the strength of concrete, using calibration dependencies established for concrete that differs from the test in composition, age, hardening conditions, humidity, with reference in accordance with the methodology in the Appendix.
6.1.10 Without reference to specific conditions of the application, calibration dependencies established for concrete different from the one being tested can only be used to obtain approximate strength values. It is not allowed to use indicative strength values without reference to specific conditions to assess the strength class of concrete.
Then select areas in the quantity provided for, where the maximum, minimum and intermediate values of the indirect indicator are obtained.
After testing by the indirect non-destructive method, sections are tested by the direct non-destructive method or samples are taken for testing according to GOST 28570.
6.2.4 To determine the strength at a negative temperature of concrete, the areas selected for constructing or linking the calibration dependence are first tested by an indirect non-destructive method, and then samples are taken for subsequent testing at a positive temperature or heated by external heat sources (infrared emitters, heat guns, etc. ) to a depth of 50 mm to a temperature not lower than 0 °C and tested using a direct non-destructive method. The temperature of heated concrete is monitored at the depth of installation of the anchor device in a prepared hole or along the surface of a chip in a non-contact manner using a pyrometer in accordance with GOST 28243.
Rejection of test results used to construct a calibration curve at a negative temperature is allowed only if the deviations are associated with a violation of the test procedure. In this case, the rejected result must be replaced by the results of repeated testing in the same area of the structure.
6.3.1 When constructing a calibration dependence based on control samples, the dependence is established using single values of the indirect indicator and the strength of concrete of standard cube samples.
The average value of indirect indicators for a series of samples or for one sample (if the calibration dependence is established for individual samples) is taken as a single value of an indirect indicator. The strength of concrete in a series according to GOST 10180 or one sample (calibration dependence for individual samples) is taken as a single value of concrete strength. Mechanical tests of samples in accordance with GOST 10180 are carried out immediately after testing by the indirect non-destructive method.
6.3.2 When constructing a calibration curve based on the results of testing cube samples, use at least 15 series of cube samples in accordance with GOST 10180 or at least 30 individual cube samples. Samples are made in accordance with the requirements of GOST 10180 in different shifts, for at least 3 days, from concrete of the same nominal composition, using the same technology, under the same hardening regime as the structure to be controlled.
The unit values of the concrete strength of the cube samples used to construct the calibration relationship must correspond to the deviations expected in production, and at the same time be within the ranges established in.
6.3.3 The calibration dependence for the methods of elastic rebound, shock impulse, plastic deformation, rib separation and spalling is established based on the results of tests of manufactured cube samples, first by a non-destructive method, and then by a destructive method according to GOST 10180.
When establishing the calibration dependence for the peeling method, main and control samples are made according to. An indirect characteristic is determined on the main samples, control samples are tested according to GOST 10180. The main and control samples must be made of the same concrete and harden under the same conditions.
6.3.4 The dimensions of the samples should be selected in accordance with the largest aggregate size in the concrete mixture according to GOST 10180, but not less than:
100×100×100 mm for the rebound, shock impulse, plastic deformation methods, as well as for the peeling method (control samples);
200×200×200 mm for the method of chopping the edge of the structure;
300×300×300 mm, but with a rib size of at least six installation depths of the anchor device for the peeling method (main samples).
6.3.5 To determine indirect strength characteristics, tests are carried out in accordance with the requirements of the section on the lateral (in the direction of concreting) faces of cube samples.
The total number of measurements on each sample for the method of elastic rebound, shock impulse, plastic deformation upon impact must be no less than the established number of tests in the area according to the table, and the distance between the impact points must be at least 30 mm (15 mm for the shock impulse method). For the method of plastic deformation during indentation, the number of tests on each face must be at least two, and the distance between test sites must be at least twice the diameter of the indents.
When establishing a calibration relationship for the rib shearing method, one test is carried out on each side rib.
When establishing the calibration dependence for the peel-off method, one test is carried out on each side face of the main sample.
6.3.6 When tested by the method of elastic rebound, shock impulse, or plastic deformation upon impact, samples must be clamped in a press with a force of at least (30 ± 5) kN and no more than 10% of the expected value of the breaking load.
6.3.7 Specimens tested by the tearing method are installed on the press so that the surfaces on which the tearing was carried out do not adhere to the support plates of the press. Test results according to GOST 10180 increase by 5%.
7 Testing
7.1.1 The number and location of controlled sections in structures must comply with the requirements of GOST 18105 and are indicated in the design documentation for the structure or installed taking into account:
Control tasks (determining the actual class of concrete, stripping or tempering strength, identifying areas of reduced strength, etc.);
Type of structure (columns, beams, slabs, etc.);
Placement of grips and concreting order;
Reinforcement of structures.
The rules for assigning the number of test sites for monolithic and prefabricated structures when monitoring the strength of concrete are given in the Appendix. When determining the strength of concrete of the structures being surveyed, the number and location of sections should be taken according to the survey program.
7.1.2 Tests are carried out on a section of the structure with an area of 100 to 900 cm2.
7.1.3 The total number of measurements in each section, the distance between the measurement locations in the section and from the edge of the structure, the thickness of the structures in the measurement section must be no less than the values given in the table depending on the test method.
Table 2 - Requirements for test areas
|
Method name |
Total number |
Minimum |
Minimum |
Minimum |
|
Elastic rebound |
||||
|
Impact impulse |
||||
|
Plastic deformation |
||||
|
Rib chipping |
||||
|
Breakaway |
2 diameters |
|||
|
Separation with chipping at working depth of anchor embeddingh: |
||||
|
≥ 40mm |
||||
|
< 40мм |
7.1.4 The deviation of individual measurement results at each section from the arithmetic mean value of the measurement results for a given section should not exceed 10%. Measurement results that do not satisfy the specified condition are not taken into account when calculating the arithmetic mean value of the indirect indicator for a given area. The total number of measurements at each site when calculating the arithmetic mean must comply with the requirements of the table.
7.1.5 The strength of concrete in the controlled section of the structure is determined by the average value of the indirect indicator using a calibration relationship established in accordance with the requirements of section, provided that the calculated value of the indirect indicator is within the limits of the established (or linked) relationship (between the lowest and highest strength values ).
7.1.6 The surface roughness of a section of concrete structures when tested by rebound, shock impulse, and plastic deformation methods must correspond to the surface roughness of sections of a structure (or cubes) tested when establishing the calibration relationship. If necessary, it is allowed to clean the surfaces of the structure.
When using the indentation plastic deformation method, if the zero reading is removed after applying the initial load, there are no requirements for the surface roughness of the concrete structure.
7.2.1 Tests are carried out in the following sequence:
It is recommended that the position of the device when testing the structure relative to the horizontal be the same as when establishing the calibration dependence. In a different position of the device, it is necessary to make corrections to the indicators in accordance with the operating instructions for the device;
7.3.1 Tests are carried out in the following sequence:
The device is positioned so that the force is applied perpendicular to the surface under test in accordance with the operating instructions for the device;
When using a spherical indenter to facilitate measurements of the diameters of prints, the test can be carried out through sheets of carbon and white paper (in this case, tests to establish the calibration dependence are carried out using the same paper);
The values of the indirect characteristic are recorded in accordance with the operating instructions for the device;
The average value of the indirect characteristic on the section of the structure is calculated.
7.4.1 Tests are carried out in the following sequence:
The device is positioned so that the force is applied perpendicular to the surface under test in accordance with the operating instructions for the device;
It is recommended to take the position of the device when testing the structure relative to the horizontal the same as during testing when establishing the calibration dependence. In a different position of the device, it is necessary to make corrections to the readings in accordance with the operating instructions for the device;
Record the value of the indirect characteristic in accordance with the operating instructions for the device;
The average value of the indirect characteristic on the section of the structure is calculated.
7.5.1 When testing by the pull-out method, the sections should be located in the zone of lowest stresses caused by the operational load or the compression force of the prestressed reinforcement.
7.5.2 The test is carried out in the following sequence:
In the place where the disc is glued, remove the surface layer of concrete 0.5 - 1 mm deep and clean the surface of dust;
The disc is glued to the concrete by pressing the disc and removing excess glue outside the disc;
The device is connected to the disk;
The load is gradually increased at a speed of (1 ± 0.3) kN/s;
The projection area of the separation surface on the plane of the disk is measured with an error of ± 0.5 cm 2 ;
The value of the conditional stress in concrete during tearing is determined as the ratio of the maximum tearing force to the projected area of the tearing surface.
7.5.3 The test results are not taken into account if the reinforcement was exposed during concrete separation or the projection area of the separation surface was less than 80% of the disk area.
7.6.1 When testing by the peel-off method, the sections should be located in the zone of lowest stresses caused by the operational load or the compression force of the prestressed reinforcement.
7.6.2 Tests are carried out in the following sequence:
If the anchor device was not installed before concreting, then a hole is made in the concrete, the size of which is selected in accordance with the operating instructions for the device, depending on the type of anchor device;
The anchor device is fixed into the hole to the depth specified in the operating instructions for the device, depending on the type of anchor device;
The device is connected to an anchor device;
The load is increased at a speed of 1.5 - 3.0 kN/s;
Record the reading of the force meter of the device R 0 and the amount of anchor slip Δ h(the difference between the actual tear-out depth and the embedding depth of the anchor device) with an accuracy of at least 0.1 mm.
7.6.3 Measured pullout force value R 0 is multiplied by the correction factor γ, determined by the formula
Where h- working depth of the anchor device, mm;
Δ h- the amount of anchor slippage, mm.
7.6.4 If the largest and smallest dimensions of the torn-out part of concrete from the anchor device to the limits of destruction along the surface of the structure differ by more than twice, and also if the depth of the torn-out differs from the depth of embedding of the anchor device by more than 5% (Δ h > 0,05h, γ > 1.1), then the test results can be taken into account only for an approximate assessment of the strength of concrete.
Note - Approximate values of concrete strength are not allowed to be used to assess the strength class of concrete and construct calibration dependencies.
7.6.5 The test results are not taken into account if the depth of the pullout differs from the depth of embedding of the anchor device by more than 10% (Δ h > 0,1h) or the reinforcement was exposed at a distance from the anchor device less than the depth of its embedding.
7.7.1 When tested by the rib shearing method, there should be no cracks, concrete edges, sagging or cavities in the test area with a height (depth) of more than 5 mm. The sections should be located in the zone of least stress caused by the operational load or the compression force of the prestressed reinforcement.
7.7.2 The test is carried out in the following sequence:
The device is fixed to the structure, a load is applied at a speed of no more than (1 ± 0.3) kN/s;
Record the reading of the force meter of the device;
Measure the actual chipping depth;
The average value of the shearing force is determined.
7.7.3 The test results are not taken into account if the reinforcement was exposed during concrete chipping or the actual chipping depth differed from the specified depth by more than 2 mm.
8 Processing and presentation of results
8.1 The test results are presented in a table in which they indicate:
Type of design;
Design class of concrete;
Age of concrete;
The strength of the concrete of each controlled area according to;
Average strength of concrete structure;
Areas of the structure or parts thereof, subject to compliance.
The form of the table for presenting test results is given in the Appendix.
8.2 Processing and assessment of compliance with established requirements of the actual strength of concrete obtained using the methods given in this standard is carried out in accordance with GOST 18105.
Note - Statistical assessment of the class of concrete based on test results is carried out according to GOST 18105 (schemes “A”, “B” or “C”) in cases where the strength of concrete is determined by a calibration relationship constructed in accordance with section . When using previously installed dependencies by linking them (by application ) statistical control is not allowed, and concrete class assessment is carried out only according to the “D” scheme GOST 18105.
8.3 The results of determining the strength of concrete using mechanical non-destructive testing methods are documented in a conclusion (protocol), which provides the following data:
About the tested structures, indicating the design class, the date of concreting and testing, or the age of the concrete at the time of testing;
About the methods used to control the strength of concrete;
About types of devices with serial numbers, information about verification of devices;
About the accepted calibration dependencies (dependence equation, dependency parameters, compliance with the conditions for applying the calibration dependency);
Used to construct a calibration relationship or its reference (date and results of tests using non-destructive indirect and direct or destructive methods, correction factors);
On the number of sections for determining the strength of concrete in structures, indicating their location;
Test results;
Methodology, results of processing and evaluation of the data obtained.
Appendix A
(required)
Standard test scheme for the peel-off test
A.1 The standard test scheme for the peel-off method involves testing subject to the requirements -.
A.2 The standard test scheme is applicable in the following cases:
Testing heavy concrete with compressive strength from 5 to 100 MPa;
Testing lightweight concrete with compressive strength from 5 to 40 MPa;
The maximum fraction of coarse concrete aggregate is not more than the working depth of embedding anchor devices.
A.3 The supports of the loading device must be evenly adjacent to the concrete surface at a distance of at least 2 h from the axis of the anchor device, where h- working depth of the anchor device. The test diagram is shown in the figure.
1
2
- support for the loading device;
3
- grip of the loading device; 4
- transition elements, rods; 5
- anchor device;
6
- pulled out concrete (tearout cone); 7
- test structure
Figure A.1 - Scheme of the peel-off test
A.4 The standard testing scheme for the peel-off method provides for the use of three types of anchor devices (see figure). Type I anchor device is installed in the structure during concreting. Anchor devices of types II and III are installed in holes previously prepared in the structure.
1
- working rod; 2
- working rod with expansion cone; 3
- segmented grooved cheeks;
4
- support rod; 5
- working rod with a hollow expansion cone; 6
- leveling washer
Figure A.2 - Types of anchor devices for standard test scheme
A.5 The parameters of anchor devices and their permissible ranges of measured concrete strength under a standard test scheme are indicated in the table. For lightweight concrete, the standard test scheme uses only anchor devices with an embedment depth of 48 mm.
Table A.1 - Parameters of anchor devices for standard test scheme
|
Anchor type |
Anchor diameter |
Depth of embedding anchor devices, |
Acceptable for anchor device |
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|
working h |
full h" |
heavy |
lung |
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|
45 - 75 |
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|
10 - 50 |
10 - 40 |
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|
40 - 100 |
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5 - 100 |
5 - 40 |
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10 - 50 |
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A.6 The designs of anchors of types II and III must ensure preliminary (before applying the load) compression of the walls of the hole at the working embedment depth h and post-test slip monitoring.
Appendix B
(required)
Standard rib splitting test scheme
B.1 The standard testing scheme by the rib shearing method provides for testing subject to the requirements -.
B.2 The standard test scheme is applicable in the following cases:
The maximum fraction of coarse concrete aggregate is no more than 40 mm;
Testing of heavy concrete with compressive strength from 10 to 70 MPa on granite and limestone crushed stone.
B.3 For testing, a device is used, consisting of a force exciter with a force measuring unit and a gripper with a bracket for local chipping of the structure edge. The test diagram is shown in the figure.
1
- a device with a loading device and a force meter; 2
- support frame;
3
- chipped concrete; 4
- test structure; 5
- grip with bracket
Figure B.1 - Scheme of testing using the rib shearing method
B.4 When local chipping of a rib occurs, the following parameters must be ensured:
Shearing depth a= (20 ± 2) mm;
Cleaving Width b= (30 ± 0.5) mm;
The angle between the direction of the load and the normal to the loaded surface of the structure β = (18 ± 1)°.
Appendix B
(recommended)
Calibration dependence for the peel-off method
When testing by the peel-off method according to the standard scheme according to the appendix, the cubic compressive strength of concrete R, MPa, can be calculated using the calibration dependence using the formula
|
R = m 1 m 2 P, |
Where m 1 - coefficient taking into account the maximum size of coarse aggregate in the tear-out zone, taken equal to 1 when the aggregate size is less than 50 mm;
m 2 - proportionality coefficient for the transition from tearing force in kilonewtons to concrete strength in megapascals;
R- pullout force of the anchor device, kN.
When testing heavy concrete with a strength of 5 MPa or more and light concrete with a strength from 5 to 40 MPa, the values of the proportionality coefficient m 2 is taken according to the table.
Table B.1
|
Anchor type |
Range |
Anchor diameter |
Anchor embedment depth |
Coefficient valuem 2 for concrete |
|
|
heavy |
lung |
||||
|
45 - 75 |
|||||
|
10 - 50 |
|||||
|
40 - 75 |
|||||
|
5 - 75 |
|||||
|
10 - 50 |
|||||
Odds m 2 when testing heavy concrete with an average strength above 70 MPa should be taken according to GOST 31914.
Appendix D
(recommended)
Calibration dependence for the rib shearing method
with standard test scheme
When testing by the rib shearing method according to the standard scheme according to the appendix, the cubic compressive strength of concrete on granite and crushed limestone R, MPa, can be calculated using the calibration dependence using the formula
|
R = 0,058m(30R + R 2), |
Where m- coefficient taking into account the maximum size of coarse aggregate and taken equal to:
1.0 - with aggregate size less than 20 mm;
1.05 - with aggregate size from 20 to 30 mm;
1.1 - with aggregate size from 30 to 40 mm;
R- shearing force, kN.
Appendix D
(required)
Requirements for instruments for mechanical tests
Table E.1
|
Name of device characteristics |
Characteristics of instruments for the method |
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|
elastic |
percussion |
plastic |
separation |
chipping |
separation from |
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|
Hardness of the striker, striker or indenter HRCе, not less |
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Roughness of the contact part of the striker or indenter, µm, no more |
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Diameter of striker or indenter, mm, not less |
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Thickness of disk indenter edges, mm, not less |
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Conical indenter angle |
30° - 60° |
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|
Indentation diameter, % of indenter diameter |
20 - 70 |
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Perpendicularity tolerance when applying a load at a height of 100 mm, mm |
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Impact energy, J, not less |
0,02 |
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Rate of load increase, kN/s The equation for the relationship “indirect characteristic - strength” is taken to be linear according to the formula E.2 Rejection of test results After constructing the calibration dependence using formula (), it is adjusted by rejecting individual test results that do not satisfy the condition: where the average value of concrete strength according to the calibration dependence is calculated using the formula here are the meanings R i H, R i f, , N- see explanations for formulas (), (). E.4 Correction of the calibration dependence Correction of the established calibration dependence, taking into account additionally obtained test results, must be carried out at least once a month. When adjusting the calibration dependence, at least three new results obtained at the minimum, maximum and intermediate values of the indirect indicator are added to the existing test results. As data is accumulated for constructing a calibration dependence, the results of previous tests, starting from the very first, are rejected so that the total number of results does not exceed 20. After adding new results and rejecting old ones, the minimum and maximum values of the indirect characteristic, the calibration dependence and its parameters are established again according to the formulas () - (). E.5 Conditions for using the calibration dependence The use of a calibration relationship to determine the strength of concrete according to this standard is allowed only for values of the indirect characteristic falling in the range from H min to N max. If the correlation coefficient r < 0,7 или значение Appendix G
| ||||||||||||||||||||||||||||||||||||||
|
|
Where R OS i- concrete strength in i- section, determined by the tear-off method with chipping or testing of cores according to GOST 28570;
R kosv i- concrete strength in i- section, determined by any indirect method using the calibration dependence used;
n- number of test sites.
G.2 When calculating the coincidence coefficient, the following conditions must be met:
Number of test sites taken into account when calculating the coincidence coefficient, n ≥ 3;
Each private value R OS i /R kosv i should be no less than 0.7 and no more than 1.3:
|
1 by 4 m length of linear structures; 1 by 4 m2 area of flat structures. Appendix K
| |||||||||||||||||||||||||||||||||
|
Name of structures |
Designation 1) |
Plot number according to the scheme |
Strength of concrete, MPa |
Strength class |
|
|
section 3) |
average 4) |
||||
|
1) Brand, symbol and (or) location of the structure in the axes, zones of the structure, or part of a monolithic and prefabricated monolithic structure (capture), for which the strength class of concrete is determined. 2) The total number and location of plots in accordance with . 3) The strength of the concrete of the site in accordance with . 4) Average strength of concrete of a structure, structure zone or part of a monolithic and prefabricated monolithic structure with the number of sections that meet the requirements . 5) Actual strength class of concrete of a structure or part of a monolithic and prefabricated monolithic structure in accordance with paragraphs 7.3 - 7.5 GOST 18105 depending on the selected control scheme. Note - Presentation in the column “Concrete strength class” of estimated class values or values of the required concrete strength for each section separately (assessment of the strength class for one section) is not acceptable. |
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Key words: structural heavy and light concrete, monolithic and prefabricated concrete and reinforced concrete products, structures and structures, mechanical methods for determining compressive strength, elastic rebound, shock impulse, plastic deformation, tearing, rib spalling, tearing with chipping
