Determination of strength by mechanical methods of non-destructive testing. Concrete strength determination by pull-off method with shearing Rib shearing method

Building construction based on a mixture of binder, sand and aggregate need testing for reliability and safety. However, such studies should not cause an interruption in the operation of the tested object, therefore, non-destructive method. This reduces costs, reduces labor intensity and eliminates localized damage.

Direct methods of control

These methods are necessary for the formation of calibration dependencies and their subsequent correction for indirect methods carried out on the same sections of the structure. The technology can be applied in the survey at various stages of building construction, as well as in the operation and reconstruction of finished facilities.

Breakaway with chipping

This operation is carried out in accordance with state standards, which reflects the basic information about the method of carrying out. The results are not affected by the state of the surface.

Three types of anchor devices are used for research.

Working rod equipped with an anchor head.
A device with an expanding cone and corrugated 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 fixture and the depth of penetration of the anchor, the expected strength of the composition and the dimensions of the aggregate should be taken into account, which is reflected in the table below.

Conditions for drying the mixture	Applicable device type	Anchor insertion depth in mm	Estimated strength in MPa	Coefficient value
Conditions for drying the mixture	Applicable device type	Anchor insertion depth in mm	Estimated strength in MPa	Light composition	heavy mortar
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 curing	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, the strength of concrete is tested by a non-destructive method, which involves separation with chipping, is carried out immediately in three sections. When adjusting the calibration dependences, together with this method, three indirect tests are carried out.

Rib chipping

This method involves cutting off the edge of the structure under test. It is primarily used to inspect linear segments such as girders, 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.

Tearing off metal discs

Another measure that allows the implementation of a non-destructive method of testing concrete has not found wide distribution in our country, which is associated with a limited temperature regime. Another negative factor is the need to make a furrow with a drill, and this reduces the productivity of the study.

The method itself involves the removal of stress registration, which is required for local destruction of the hardened composition when the steel disk is torn off. When determining the strength properties, the applied force and the surface projection area are taken into account.

Indirect methods of control

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 the structure. The result obtained is not allowed to be used if the partial calibration dependence () has not been determined.

Ultrasonic Testing

The method of testing concrete by a non-destructive method, which involves the use of ultrasonic waves, has become widespread. During the operation, a connection is established between the speed of oscillations and the density of the hardened mixture.

Dependence can be influenced by a variety of factors.

Aggregate fraction and its amount in the solution.
The selected method of preparation of the composition.
The degree of compaction and stress.
Change in binder consumption by more than 30 percent.

Addition! Ultrasonic surveys provide an opportunity to perform mass testing of almost any structure an unlimited number of times. The main disadvantage lies in the margin of error.

elastic rebound

Non-destructive control of the strength of concrete by this method allows you to establish the relationship between compressive strength and elasticity of the material. In the study, the metal striker of the main device after the impact moves away to a certain distance, which is an indicator of the strength qualities of the structure.

During the test, the fixture 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 snaps directly into the trigger.

Having attached the device perpendicular to the plane, pull the trigger. The striker cocks automatically, after which it releases itself and makes a blow under the action of a special spring. The metal element bounces over a certain distance, which is measured by a special scale.

As the main instrument for testing, a device of the KISI system is used, which has a rather complex structure. The strength of the hardened mixture can be determined based on the device data after 6-7 tests according to a special schedule.

Giving shock impulse

Thanks to this method of research, it is possible to fix the impact energy released at the moment of contact of the striker with the concrete structure. A positive point is the fact that the devices for non-destructive testing of concrete, operating on the principle of a shock pulse, are compact in size. However, their price is quite high.

Plastic deformation

During the operation, the size of the trace 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 impact, the remaining prints are measured.

Devices for determining the strength of this type are based on the indentation of the rod directly into the plane by static pressure of the desired force or a conventional impact. Pendulum, hammer and spring products are used as the main devices.

Below are the conditions for the operation.

Tests should be carried out on a site 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 shall be perpendicular to the plane being tested.
To determine the strength characteristics, a smooth surface is required, which is achieved by molding in a metal formwork.

Important! If non-destructive concrete strength measurements are made using hammer-type devices, then the samples must be installed on a perfectly level base.

Comparative characteristics by example

A well made of monolithic reinforced concrete is taken as an object. Its depth is 8 m, and the radius is 12 m. The filling of the side surfaces was carried out 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		shock impulse		elastic rebound		Press test
	Wed value in m/s	Percentage	Wed value in MPa	Percentage	Wed value in u. units	Percentage	Wed value 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 value V		≈4,26		≈32,2		≈8,14

Output! From the above table, it becomes clear that the minimum error during research is characteristic of the ultrasonic method. The scatter when checking with a shock pulse is maximum.

Instrumentless Testing

Above, studies conducted using special devices were considered, however, if necessary, simple tests can be done by hand. 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 tool is prepared: a chisel and a hammer, the weight of which varies between 400-800 g. The impact-cutting device is installed perpendicular to the surface.

Medium-strength blows are applied to it, in the wake of which the analysis will be carried out.

A barely noticeable imprint may indicate that the hardened mixture is classified as B25 or higher.
Strongly visible marks on the surface of the structure are usually left with B15 concrete.
Significant depressions and the presence of crumbs make it possible to attribute the composition used to class B10.
If the tip of the tool entered the plane to a depth of more than 1 cm, then B5 concrete was probably used for the work.

Attention! It is possible to carry out a check in this way within a few minutes without any equipment. After that, there will already be an idea of \u200b\u200bwhat strength the hardened composition has.

State standard

Non-destructive methods for controlling the strength of concrete are regulated in accordance with GOST 22690-88, the points 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

For the formation of structures based on the building mixture, a 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, fastened by welding or wire, is placed in the composition. Usually 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.. A similar operation can be carried out using water to avoid heavy dusting.
The filling of the solution is carried out, as a rule, at positive temperatures. However, if there is 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 an attic), diamond drilling of holes in concrete is carried out.
It is allowed to load the finished structure only after the final hardening of the mixture, that is, after 28 days.

INTERSTATE COUNCIL FOR STANDARDIZATION, METROLOGY AND CERTIFICATION

INTERSTATE

STANDARD

CONCRETE

Determination of strength by mechanical methods of non-destructive testing

(EN 12504-2:2001, NEQ)

(EN 12504-3:2005, NEQ)

Official edition

Stand rtinform 2016

Foreword

The goals, basic principles and basic procedure for carrying out work on the interstate camp, darting 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 the development, adoption, application, updating and cancellation "

About the standard

1 DEVELOPED by the Structural Subdivision of JSC "NIC "Construction" Research. Design and Technological Institute of Concrete and Reinforced Concrete. A.A. Gvozdev (NIIZhB)

2 INTRODUCED by the Technical Committee for Standardization TC 465 "Construction"

3 ADOPTED by the Interstate Council for Standardization, Metrology and Certification (Minutes of June 18, 2015 No. 47)

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 the national standard of the Russian Federation from April 1, 2016.

5 8 this standard takes into account the main regulatory provisions regarding the requirements for mechanical methods of non-destructive testing of the strength of concrete of the following European regional standards:

EN 12504-2:2001 Testing concrete in structures - Part 2: Non-destructive testing - Determination of rebound number

EN 12504-3:2005 Testing concrete in structures - Determination of pull-out force.

Degree of conformity - non-equivalent (NEQ)

6 83AMEN GOST 22690-88

Information about changes to this standard is published in the annual information index "National Standards", and the text of changes and amendments - in the monthly information index "National Standards". In case of revision (replacement) or cancellation of this standard, a corresponding notice will be published in the monthly information index *National Standards. Relevant information, notification 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

In the Russian Federation, this standard may not be fully or partially reproduced. replicated and distributed as an official publication without the permission of the Federal Agency for Technical Regulation and Metrology

Annex A (normative) Standard design for the pull-and-shear test. . . 10

INTERSTATE STANDARD

Determination of strength by mechanical methods of non-destructive testing

Determination of strength by mechanical methods of nondestructive testing

Introduction date - 2016-04-01

1 area of use

This standard applies to structural heavy, fine-grained, light and tension concrete of monolithic, prefabricated and precast-monolithic 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, shock impulse, plastic deformation, separation, chipping of the rib and tearing with chipping.

8 of this standard, normative references to the following interstate standards are used:

GOST 166-89 (ISO 3599-76) Calipers. Specifications

GOST 577-68 Clock-type indicators with a division stage of 0.01 mm. Specifications

GOST 2789-73 Surface roughness. Parameters and characteristics

GOST 10180-2012 Concrete. Methods for determining the strength of control samples

GOST 18105-2010 Concrete. Strength control and assessment rules

GOST 28243-96 Pyrometers. General technical requirements

GOST 28570-90 Concrete. Methods for determining strength from samples taken from structures

GOST 31914-2012 High-strength heavy and fine-grained concrete for monolithic structures. Rules for quality control and evaluation

Note - When using this standard, it is advisable to check the validity of reference standards in the public information system - not the official website of the Federal Agency for Technical Regulation and Metrology on the Internet or according to the annual information index "National Standards", which was published as of January 1 of the current year, and on issues of the monthly information index "National Standards" for the current year. If the reference standard is replaced (modified), then when using this standard, you should be guided by the replacing (modified) standard. If the referenced standard is canceled without replacement, the provision in which the reference to it is given applies to the extent that this reference is not affected.

3 Terms and definitions

8 of this standard, the terms are used in accordance with GOST 18105. as well as the following terms with the corresponding definitions:

Official edition

destructive methods for determining the strength of concrete: Determination of the strength of concrete according to control samples made from a concrete mixture in accordance with GOST 10180 or selected from structures in accordance with GOST 28570.

[GOST 18105-2010. article 3.1.18]

3.2 non-destructive mechanical methods for determining the strength of concrete: Determination of the strength of concrete directly in the structure under local mechanical action on concrete (impact, separation, chipping, indentation, separation with chipping, elastic rebound).

3.3 indirect non-erosion methods for determining the strength of concrete: Determination of the strength of concrete according to pre-established calibration dependencies.

3.4 direct (standard) non-destructive methods for determining the strength of concrete: Methods that provide standard test schemes (tearing off with shearing and shearing of the rib) and allowing the use of known calibration dependencies without reference and adjustment

3.5 calibration dependence: Graphical or analytical dependence between the indirect strength characteristic and the compressive strength of concrete, determined by one of the destructive or direct non-destructive methods.

3.6 indirect strength characteristics (indirect indicator): The magnitude of the applied force during local destruction of concrete, the magnitude of the rebound, the impact energy, the size of the imprint or other indication of the device when measuring the strength of concrete by non-destructive mechanical methods.

4 General provisions

4.1 Non-destructive mechanical methods are used to determine the compressive strength of concrete at the intermediate and design age established by the design documentation and at an age exceeding the design age when examining structures.

4.2 Non-destructive mechanical methods for determining the strength of concrete, established by this standard, are divided according to the type of mechanical action or determined indirect characteristic per method:

Elastic rebound;

plastic deformation;

> shock impulse:

Breakaway with chipping:

Rib chipping.

4.3 Non-erosion mechanical methods for determining the strength of concrete are based on the relationship between the strength of concrete and indirect strength characteristics:

The method of elastic rebound on the relationship between the strength of concrete and the value of the rebound of the striker from the surface of the concrete (or the striker pressed against it);

The method of plastic deformation in relation to the strength of concrete with the dimensions of the imprint on the concrete of the structure (diameter, depth, etc.) or the ratio of the diameter of the imprint on concrete and a standard metal sample when the indenter is struck or the indenter is pressed into the concrete surface;

Impact impulse method on the relationship between the strength of concrete and the energy of impact and its changes at the moment of impact of the striker with the concrete surface;

The method of tearing off the tension bond required for local destruction of concrete when a metal disk glued to it is torn off, equal to the tearing force divided by the projection area of the concrete tearing surface onto the plane of the disk;

Method of detachment with shearing on the connection of the strength of concrete with the value of the force of local destruction of concrete when the anchor device is excavated from it;

Rib shearing method on the relationship of concrete strength with the value of the force required to shear a section of concrete on a structure edge.

4.4 In general, non-destructive mechanical methods for determining the strength of concrete are indirect non-destructive methods for determining strength. The strength of concrete in structures is determined by experimentally established calibration dependencies.

4.5 The tear-off method with shearing during testing in accordance with the standard scheme in Appendix A and the method of shearing off the rib during testing in accordance with the standard scheme in Appendix B are direct non-destructive methods for determining the strength of concrete. For direct non-destructive methods, it is allowed to use the calibration dependences established in Appendixes b and D.

Note - Standard test schemes are applicable for a limited range of concrete strength (see Annexes A and B). 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 Table 1. and additional restrictions established by manufacturers of specific measuring instruments. The use of methods outside the concrete strength ranges recommended in Table 1 is allowed with scientific and technical justification based on the results of studies using measuring instruments that have passed metrological certification for an extended concrete strength range.

Table 1

4.7 Determination of the strength of heavy concrete of design classes B60 and higher or with an average compressive strength of concrete R m i 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 sections of structures that do not have visible damage (peeling of the protective layer, cracks, cavities, etc.).

4.9 The age of concrete of controlled structures and its sections should not differ from the age of concrete of structures (sections, samples) tested to establish calibration dependence, by more than 25%. The exceptions are the control of strength and the construction of a calibration dependence for concrete whose age exceeds two months. In this case, the difference in the age of individual structures (sections, samples) is not regulated.

4.10 Tests are carried out at a positive temperature of concrete. It is allowed to conduct 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 of 6.2.4. The temperature of the concrete during testing must correspond to the temperature provided for by the operating conditions of the devices.

Calibration dependencies established at a concrete temperature 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 a surface temperature T to 40 * C (to control the tempering, transfer and stripping strength of concrete), the calibration dependence is established after determining the strength of concrete in the structure by an indirect non-destructive method at a temperature (t (T ± 10) *C, and testing of concrete by a direct non-destructive method or testing of samples - after cooling at normal temperature.

5 Measuring instruments, equipment and tools

5.1 Measuring instruments and devices for mechanical testing, designed to determine the strength of concrete, must be certified and verified in the prescribed manner and must comply with the requirements of Appendix D.

5.2 Readings of instruments calibrated in units of concrete strength should be considered as an indirect indicator of concrete strength. These devices should only be used after

establishing a calibration dependence "instrument reading - concrete strength" or linking the dependence established in the device in accordance with 6.1.9.

5.3 A tool for measuring the diameter of indentations (caliper according to GOST 166) used for the plastic deformation method should provide measurement with an error of no more than 0.1 mm. a tool for measuring the depth of an imprint (a dial indicator according to GOST 577, etc.) - with an error of no more than 0.01 mm.

5.4 Standard schemes for testing the method of separation with shearing and spalling of the rib provide for the use of anchor devices and grips in accordance with Annexes A and B.

5.5 For the chipping method, anchor devices should be used. the embedment depth of which shall not be less than the maximum size of the coarse concrete aggregate of the structure being tested.

5.6 For the pull-off method, steel discs with a diameter of at least 40 mm should be used. not less than 6 mm thick and not less than 0.1 diameter, with the roughness parameters of the bonded surface not less than Ra = 20 µm according to GOST 2789. The adhesive for gluing the disc must provide adhesion to concrete, at which destruction occurs along concrete.

6 Test preparation

6.1 Procedure for preparing for testing

6.1.1 Preparation for testing includes checking the instruments used in accordance with the instructions for their operation and establishing calibration dependencies between the concrete strength and the indirect strength characteristic.

6.1.2 The calibration dependence is established on the basis of the following data:

The results of parallel tests of the same sections of structures by one of the indirect methods and the direct non-destructive method for determining the strength of concrete;

The results of testing sections of structures by one of the indirect non-destructive methods for determining the strength of concrete and testing core samples taken from the same sections of the structure and tested in accordance with GOST 28570:

The results of testing standard concrete samples by 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, the calibration dependence is established for each type of normalized strength specified in 4.1 for concretes of the same nominal composition.

It is allowed to build one calibration dependence for concrete of the same type with one type of coarse aggregate, with a single production technology, differing in nominal composition and normalized strength value, subject to the requirements of 6.1.7

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 a controlled structure is taken according to 4.9.

6.1.5 For direct non-destructive methods according to 4.5, it is allowed to use the dependencies given in Appendices C and D for all types of normalized concrete strength.

6.1.6 The calibration dependence must have a standard (residual) deviation S T n m not exceeding 15% of the average concrete strength of the sections or samples used in the construction of the dependence, and the correlation coefficient (index) of at least 0.7.

It is recommended to use a linear relationship of the form R * a * bK (where R is the strength of concrete. K is an indirect indicator). The methodology for establishing, estimating parameters and determining the conditions for applying a linear calibration dependence is given in Appendix E.

6.1.7 When constructing the calibration dependence of the deviation of individual values of concrete strength R^ from the average value of the concrete strength of sections or samples R f. used to build the calibration dependence should be within:

> from 0.5 to 1.5 average concrete strength Rf at Rf £20 MPa;

From 0.6 to 1.4 average concrete strength R, f at 20 MPa< Я ф £50 МПа;

From 0.7 to 1.3 average concrete strength R f at 50 MPa<Я Ф £80 МПа;

From 0.8 to 1.2 the average value of concrete strength R f at R f > 80 MPa.

6.1.8 Correction of the established dependence for concretes of intermediate and design age should be carried out at least once a month, taking into account additionally obtained test results. The number of samples or areas of additional tests during the adjustment should be at least three. The correction method is given in Appendix E.

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 tested one in composition, age, hardening conditions, moisture content, with reference in accordance with the method according to the assumption Zh.

6.1.10 Without reference to specific conditions according to Appendix G, the calibration dependences established for concrete that differs from the tested one can only be used to obtain approximate strength values. It is not allowed to use approximate strength values without reference to specific conditions to assess the strength class of concrete.

6.2 Construction of a calibration dependence based on the results of concrete strength tests

in designs

6.2.1 When constructing a calibration dependence based on the results of testing the strength of concrete in structures, the dependence is established by single values of the indirect indicator and concrete strength of the same sections of structures.

For a single value of the indirect indicator, the average value of the indirect indicator in the area is taken. For a single value of the strength of concrete, the strength of the concrete of the site, determined by a direct non-destructive method or testing of selected samples, is taken.

6.2.2 The minimum number of single values for constructing a calibration dependence based on the results of testing the strength of concrete in structures is 12.

6.2.3 When constructing a calibration dependence based on the results of testing the strength of concrete in structures not subject to testing, structures or their zones, preliminary measurements are carried out by an indirect non-destructive method in accordance with the requirements of Section 7.

Then, sections are selected in the number provided for in 6.2.2, on which the maximum is obtained. minimum and intermediate values of the indirect indicator.

After testing by an indirect non-destructive method, the sections are tested by a direct non-destructive method or samples are taken for testing in accordance with GOST 26570.

6.2.4 To determine the strength at a negative temperature of concrete, the sections selected for constructing or linking the calibration dependence are first tested by an indirect non-erosion method, and then samples are taken for subsequent testing at a positive temperature or heated by external heat sources (infrared emitters, heat guns and etc.) to a depth of 50 mm to a temperature not lower than 0 * C and tested by a direct non-destructive method. The temperature control of the heated concrete is carried out at the installation depth of the anchor device in the prepared hole or along the chip surface in a non-contact way using a pyrometer according to GOST 28243.

Rejection of the test results used to build the calibration dependence 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 should be replaced by the results of a repeated test in the same area of the structure.

6.3 Construction of a calibration dependence on control samples

6.3.1 When constructing a calibration dependence on control samples, the dependence is established by single values of the indirect indicator and concrete strength of standard cube samples.

For a single value of the indirect indicator, the average value of the indirect indicators for a series of samples or for one sample (if the calibration dependence is established for individual samples) is taken. For a single value of the strength of concrete, the strength of concrete in a series according to GOST 10180 or one sample (calibration dependence for individual samples) is taken. Mechanical testing of samples according to GOST 10180 is 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 sample cubes, at least 15 series of sample cubes according to GOST 10180 or at least 30 individual sample cubes are used. 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, according to the same technology, with the same hardening mode as the structure to be controlled.

The unit values of the concrete strength of the sample cubes used to build the calibration dependence must correspond to the deviations expected in production, while being within the ranges established in 6.1.7.

6.3.3 The calibration dependence for the methods of elastic rebound, shock impulse, plastic deformation, separation and chipping of the rib is established on the basis of the results of testing the manufactured sample cubes, first by the non-destructive method, and then by the destructive method in accordance with GOST 10180.

When establishing a calibration dependence for the tear-off method with shearing, the main and control samples are made according to 6.3.4. An indirect characteristic is determined on the main samples. control samples are tested in accordance with GOST 10180. The main and control samples must be made from 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 in accordance with GOST 10180. but not less than:

100* 100* 100 mm for rebound, shock impulse, plastic deformation methods. as well as for the method of separation with chipping (control samples);

200*200*200mm for design rib chipping method:

300*300*300mm. but with a rib size of at least six anchor device installation depths for the pull-off method with shearing (basic samples).

6.3.5 To determine the indirect strength characteristics, tests are carried out in accordance with the requirements of Section 7 on the side (in the direction of concreting) faces of the sample cubes.

The total number of 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 Table 2. and the distance between the impact points must be at least 30 mm (15 mm for the shock impulse method). For the indentation plastic deformation method, the number of tests on each face must be at least two, and the distance between the test points must be at least two indent diameters.

When establishing a calibration dependence for the rib shearing method, one test is carried out on each side rib.

When establishing the calibration dependence for the method of separation with shearing, 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, plastic deformation upon impact, the specimens shall be clamped in the press with a force of not less than (30 ± 5) kN and not more than 10% of the expected value of the breaking load.

6.3.7 The specimens tested by the pull-off method are mounted on the press as follows. so that the surfaces on which the pull-out was carried out do not adjoin to the base plates of the press. The test results according to GOST 10180 are increased by 5%.

7 Testing

7.1 General requirements

7.1.1 The number and location of controlled sections in structures must comply with the requirements of GOST 18105 and be indicated in the design documentation for structures or be set taking into account:

Control tasks (determining the actual class of concrete, stripping or tempering strength, identifying areas of reduced strength, etc.);

Type of construction (columns, beams, slabs, etc.);

Placement of grips and pouring order:

Structural reinforcement.

The rules for assigning the number of test sites for monolithic and prefabricated structures in the control of concrete strength are given in Appendix I. When determining the strength of concrete of the examined structures, the number and location of the sections should be taken according to the survey program.

7.1.2 Tests are carried out on a construction site with an area of 100 to 900 cm2.

7.1.3 The total number of measurements in each area, the distance between the measurement points in the area and from the edge of the structure, the thickness of the structures in the measurement area should not be less than the values given in Table 2, depending on the test method.

Table 2 - Requirements for test sites

Method name	Total number of measurements per plot	Minimum distance between measurement points on the site, mm	Minimum distance from the edge of the structure to the measurement point, mm	Minimum construction thickness, mm
Elastic Bounce
shock impulse
Plastic deformation
Rib digging
		2 disc diameters
Detachment with chipping at the working depth of the anchor L: * 40mm< 40мм

7.1.4 The deviation of individual measurement results in each section from the arithmetic mean of the measurement results for this section should not exceed 10%. The results of measurements that do not meet the specified condition are not taken into account when calculating the arithmetic mean of the indirect indicator for this area. The total number of measurements in each section when calculating the arithmetic mean must comply with the requirements of Table 2.

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 dependence established in accordance with the requirements of Section 6. provided that the calculated value of the indirect indicator is within the established (or tied) dependence (between the smallest and largest values strength).

7.1.6 The surface roughness of the structure concrete section when tested by the methods of rebound, impact impulse, plastic deformation should correspond to the surface roughness of the structure sections (or cubes) tested when establishing the calibration dependence. In necessary cases, it is allowed to clean the surfaces of the structure.

When using the indentation plastic deformation method, if the zero reading is taken after the application of the initial load, there are no requirements for the roughness of the concrete surface of the structure.

7.2 Rebound method

7.2.1 Tests are carried out in the following sequence:

The position of the device when testing the structure relative to the horizontal is recommended to be taken the same. as well as when establishing the calibration dependence. In a different position of the device, it is necessary to make a correction for the indicators in accordance with the instruction manual for the device:

7.3 Plastic deformation method

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 instructions for use of the device;

When using a spherical indemtor to facilitate measurements of the diameters of prints, the test can be carried out through sheets of carbon paper and white paper (in this case, tests to establish the calibration dependence should be carried out using the same paper);

Fix the values of the indirect characteristic in accordance with the instruction manual for the device;

Calculate the average value of the indirect characteristic on the construction site.

7.4 Shock pulse method

7.4.1 Tests are carried out in the following sequence:

The device is placed like this. so that the force is applied perpendicular to the surface under test * in accordance with the instructions for use of the device:

The position of the device when testing a structure relative to the horizontal is recommended to be taken the same as when testing when establishing a calibration dependence. In a different position of the device, it is necessary to make a correction for the readings in accordance with the instruction manual for the device;

The value of the indirect characteristic is fixed in accordance with the instruction manual for the device;

Calculate the average value of the indirect characteristic on the construction site.

7.5 Pull-off method

7.5.1 When testing by the pull-off method, the sections should be located in the zone of the 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:

At the place where the disk is glued, a surface layer of concrete with a depth of 0.5-1 mm is removed and the surface is cleaned of dust;

The disk is glued to the concrete by pressing the disk and removing excess adhesive outside the disk;

The ribs are connected to the disk;

The load is smoothly increased with a speed of (1 ± 0.3) kN / s;

Record the reading of the force meter of the device;

Measure the projection area of the separation surface on the plane of the disk with an error of iO.Scm 2 ;

The value of the conditional stress in the concrete at separation is determined as the slope of the maximum separation force to the area of the projection of the separation surface.

7.5.3 The test results are not taken into account if the reinforcement was exposed during the detachment of concrete or the projection area of the detachment surface was less than 80% of the disk area.

7.6 Pull-off method with shear

7.6.1 When testing by the pull-off method with shearing, the sections should be located in the zone of the 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 device operating instructions, depending on the type of anchor device;

An anchor device is fixed in the hole to the depth provided for in the instruction manual for the device, depending on the type of anchor device;

The device is connected with a sunker device;

The load is increased at a rate of 1.5-3.0 kN / s:

The reading of the force meter of the P 0 device and the amount of slippage of the anchor LP (the difference between the actual depth of the pull-out and the depth of the anchor device) are recorded with an accuracy of not less than 0.1 mm.

7.6.3 The measured value of the pull-out force P 4 is multiplied by the correction factor y. determined by the formula

where L is the working depth of the anchor device, mm;

DP - anchor slippage, mm.

7.6.4 If the largest and smallest dimensions of the torn out part of the concrete from the anchor device to the boundaries of destruction along the surface of the structure differ by more than two times, and also if the depth of the torn out differs from the depth of the anchor device by more than 5% (DL > 0.05ft, y > 1.1), then the test results can only be taken into account for an approximate assessment of the strength of concrete.

Note - Approximate values of the strength of concrete are not allowed to be used to assess the class of concrete in terms of strength and build calibration dependencies.

7.6.5 The test results are not taken into account if the pull-out depth differs from the anchoring device embedment depth by more than 10% (dL > 0.1 A) or the reinforcement was exposed at a distance from the anchor device less than its embedment depth.

7.7 Rib chipping method

7.7.1 When testing by the rib shearing method, there should be no cracks, concrete rims, sags or shells with a height (depth) of more than 5 mm in the test area. The sections should be located in the zone of the least stresses 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 fastened to the structure. apply a load at a speed of no more than (1 ± 0.3) kN/s;

Record the reading of the instrument's force meter;

Measure the actual depth of chipping;

Determine the average value of the chipping force.

7.7.3 The test results are not taken into account if the reinforcement was exposed when concrete was chipped or the actual chipping depth differed from the specified one by more than 2 mm.

8 Processing and presentation of results

8.1 The test results are presented in a table indicating:

Type of construction;

Design class of concrete;

Age of concrete;

The strength of the concrete of each controlled area according to 7.1.5;

The average strength of the concrete structure;

Zones of the structure or its parts subject to the requirements of 7.1.1.

The form of the test results presentation table is given in Annex K.

8.2 The processing and assessment of compliance with the established requirements of the actual strength of concrete obtained using the methods given in this standard is carried out according to GOST 18105.

Note in h in n and in - Statistical assessment of the concrete class according to the test results is carried out in accordance with GOST 18105 (schemes "A", "B" or "C") in cases where the strength of concrete is determined by the calibration dependence built in in accordance with section 6. When using previously established dependencies by linking them (according to Appendix G), statistical control is not allowed, and the assessment of the concrete class is carried out only according to the “G” scheme of GOST 18105.

8.3 The results of determining the strength of concrete by mechanical methods of non-destructive testing are drawn up in a conclusion (protocol), in which the following data are given:

About the tested structures indicating the design class, the date of concreting and testing, or the age of concrete at the time of testing;

On the methods used to control the strength of concrete;

About the types of devices with serial numbers, information about the verification of devices;

On the accepted calibration dependences (dependence equation, dependence parameters, compliance with the conditions for applying the calibration dependence);

Used to build a calibration dependence or its binding (date and results of tests by non-destructive indirect and direct or destructive methods, correction factors);

On the number of sites for determining the strength of concrete in structures, indicating their location;

Test results;

Methodology, results of processing and evaluation of the obtained data.

Standard Shear-Pull Test Design

A.1 The standard shear-pull test scheme provides for tests subject to the requirements of A.2 to A.6.

A.2 The standard test scheme is applicable in the following cases:

Tests of heavy concrete with compressive strength from S to 100 MPa:

Tests of lightweight concrete with compressive strength from S to 40 MPa:

The maximum fraction of coarse concrete aggregate is not more than the working depth of anchor devices.

A.3 The supports of the loading device must evenly adjoin the concrete surface at a distance of at least 2h from the axis of the anchor device, where L is the working depth of the anchor device. The test scheme is shown in Figure A.1.

1 - a device with a loading device and a measuring force; 2 - support of the loading device: 3 - grip of the loading device: 4 - transition elements, rods, S - anchor device. 6 - torn-out concrete (tear cone): 7 - tested structure

Figure A.1 — Schematic of the pull-out and shear test

A.4 The standard shearing test scheme provides for the use of three types of anchor devices (see Figure A.2). Anchor device type I is installed in the structure during concreting. Anchor devices of types II and ill are installed in holes previously prepared in the structure.

1 - working rod: 2 - working rod with frames of a different cone: 3 - segmented corrugated sheets: 4 - support rod: 5 - working rod with a ripe expanding cone: b - leveling washer

Figure A.2 — Types of anchor devices for a standard test scheme

A.5 The parameters of anchor devices and the permissible ranges of measured concrete strength for them under the standard test scheme are indicated in Table A.1. For lightweight concrete, in the standard test scheme, only anchor devices with a embedment depth of 48 mm are used.

Table A.1 - Parameters of anchor devices for a standard test scheme

Type of anchor device	Anchor device diameter tf. mm	Embedment depth of anchor devices, mm		Permissible range of concrete compressive strength measurements for the anchor device. MPa
Type of anchor device	Anchor device diameter tf. mm	working hours h	fattening L"	severe

A.b Anchor designs of types II and III must provide preliminary (before applying the load) compression of the hole walls at the working depth of embedding l and slip control after the test.

Standard Rib Shearing Test Arrangement

B.1 The standard scheme of testing by the rib shearing method provides for testing subject to the requirements of B.2-B.4.

B.2 The standard test scheme is applicable in the following cases:

The maximum fraction of coarse concrete aggregate is not more than 40 mm:

Tests of heavy concrete with compressive strength from 10 to 70 MPa on crushed granite and limestone. B.3 For testing, a device is used, consisting of a power exciter with a force-measuring unit

crossbar and gripper with a bracket for local shearing of the structure rib. The test scheme is shown in Figure B.1.

1 - device with a loading device and a sipo-meter. 2 - support frame: 3 - chipped concrete: 4 - tested

construction^ - grip with bracket

Figure B.1 - Schematic of the rib shear test

B.4 In case of local shearing of the rib, the following parameters should be provided:

Depth of chipping a ■ (20 a 2) mm.

Cleaving width 0 "(30 and 0.5) mm;

The angle between the direction of the load and the normal to the loaded surface of the structure p "(18 a 1) *.

Calibration dependence for the pull-off method with shearing in the standard test scheme

When carrying out tests by the method of separation with squealing according to the standard scheme in accordance with Appendix A, the cubic strength of concrete is not compressive R. MPa. it is allowed to calculate according to the gravity dependence according to the formula

R*P)|P>^. (IN 1)

where m, is a coefficient that takes into account the maximum size of coarse aggregate in the pull-out zone and is taken equal to 1 when the aggregate size is less than 50 mm:

t 2 - coefficient of proportionality for the transition from the pull-out force in kilonewtons to the strength of concrete in megapascals:

P is the pull-out force of the anchor device. kN.

When testing heavy concrete with a strength of 5 MPa or more and light concrete with a strength of 5 to 40 MPa, the values of the proportionality factor m2 are taken from Table B.1.

Table 8.1

Type of anchor device	Range of measured concrete compressive strength. MPa	Anchor device diameter d. neither	Depth of embedding of the anchor device, mm	The value of the coefficient w^ for concrete
Type of anchor device	Range of measured concrete compressive strength. MPa	Anchor device diameter d. neither	Depth of embedding of the anchor device, mm	severe

The coefficients m 3 when testing heavy concrete with an average strength above 70 MPa should be taken according to GOST 31914.

Calibration dependence for the rib shearing method with a standard test scheme

When performing the test by chipping the ribs according to the standard scheme in accordance with Appendix B, the cubic compressive strength of concrete on granite and lime rubble R. Mla. it is allowed to calculate according to the calibration dependence according to the formula

R - 0.058m (30R + PJ). (D.1)

where m is a coefficient that takes into account the maximum size of coarse aggregate and is taken equal to:

1.0 - with aggregate size less than 20 mm:

1.05 - with aggregate size from 20 to 30 mm:

1.1 - aggregate size from 30 to 40 mm:

P - chipping force. kN.

Annex D (mandatory)

Requirements for instruments for mechanical testing

Table E.1

Name of characteristics of devices

Characteristics of devices for the method

elastic

shock

momentum

plastic

deformations

otryaa with skapyaa * and it

The hardness of the striker, striker or indenter of the NYaSe. at least

The roughness of the contact part of the striker or indenter. µm. no more

Impactor or indenter diameter. mm. at least

The thickness of the edges of the disk indenter. mm. at least

Conical indenter angle

Indentation diameter, % of indenter diameter

Tolerance of perpendicularity when applying a load not at a height of 100 mm. mm

Impact energy. J. no less

Load increase rate. kN/s

Load measurement error, H. no more

5 here RjN - see the explication to the formula (£.3).

After rejection, the calibration dependence is established again according to the formulas (£.1) - (E.S) according to the remaining test results. The rejection of the remaining test results is repeated, considering the fulfillment of condition (E.6) when using a new (corrected) calibration dependence.

Particular values of concrete strength must meet the requirements of 6.1.7.

£.3 Parameters of the calibration dependence

For the accepted calibration dependence, determine:

Minimum and maximum value indirect characteristics H gave.

Root-mean-square deviation ^ n m of the constructed calibration dependence according to the formula (E.7);

Correlation coefficient of the calibration dependence r according to the formula

where the average value of concrete strength according to the calibration dependence is calculated according to the form

here are the values of R (H. I f.Ya f. N - see the explications to the formulas (E.E.). (E.b).

E.4 Correction of the calibration dependence

Adjustment of the established calibration dependence, taking into account additionally obtained test results, should 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 indirect indicator.

With the accumulation of data to build a calibration dependence, the results of previous tests. starting from the very first, they 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 set again according to formulas (E.1) - (E.9).

E.S Conditions for applying the calibration dependence

The use of a calibration dependence to determine the strength of concrete according to this standard is allowed only for values of an indirect characteristic falling in the range from N tl to n tad.

If the correlation coefficient r< 0.7 или значение 5 тнм "Я ф >0.15. then the control and evaluation of the strength according to the obtained dependence is not allowed.

The method of binding the calibration dependence

G.1 The value of the strength of concrete, determined using the calibration dependence established for concrete that differs from that tested, is multiplied by the coefficient of coincidence K s. The value is calculated according to the form

where is the strength of concrete in t-th section, determined by chipping or core testing

according to GOST 26570;

I msa, - concrete's strength<-м участке, опредепяемвя пюбым косвенным методом по используемой градуировочной зависимости: л - число участков испытаний.

G.2 When calculating the coefficient of coincidence, the following conditions must be met:

The number of test sites taken into account when calculating the coefficient of coincidence, n i 3;

Each private value R k, / R (0ca ^ should be at least 0.7 and not more than 1.3:

Each particular value R^. , should differ from the average value by no more than 15%:

The Yade values do not satisfy the conditions (G.2). (G.Z). should not be taken into account when calculating

coefficient of coincidence K with.

Assignment of the number of test sites for prefabricated and monolithic structures

I.1 In accordance with GOST 18105, when testing the strength of concrete of prefabricated structures (tempering or transferring), the number of controlled structures of each type is taken at least JC and at least ^ structures from the batch. If the batch consists of 12 structures or less, complete control is carried out. In this case, the number of sections must be at least:

1 not 4 m length linear structures:

1 by 4 m 2 area of flat structures.

I.2 In accordance with GOST 18105, when testing the strength of concrete of monolithic structures at an intermediate age, at least one structure of each type (column, wall, ceiling, crossbar, etc.) from the controlled batch is controlled by non-erosion methods.

I.Z In accordance with GOST 18105, when controlling the strength of concrete of monolithic structures at the design age, continuous nerve-breaking control of the strength of concrete of all structures of the controlled batch is carried out. In this case, the number of test sites must be at least:

3 for each grip for flat structures (wall, floor, foundation slab);

1 per 4 m length (or 3 per grip) for each linear horizontal structure (beam, crossbars);

6 for each structure - for linear vertical structures (column, pylon).

The total number of measurement sites for calculating the characteristics of the uniformity of the strength of concrete of a batch of structures should be at least 20.

I.4 The number of single measurements of the strength of concrete by mechanical methods of nerve-destructive testing in each section (the number of measurements in the section) is taken according to table 2.

Test result presentation table form

Best structures (batch of structures), design class of concrete strength, date concreting or concrete age of tested structures	Designation”	1# uchasg * according to the scheme ipi location about the axes 21	Strength of concrete. MPa		Concrete strength class*’
			plot 9"	medium 4'






” Mark, symbol and (or) location of the structure in the axes, the zone of the structure, or part of the monolithic and prefabricated-monolithic structure (grip), for which the concrete strength class is determined. 11 Total number and location of sites in accordance with 7.1.1. 11 Strength of site concrete in accordance with 7.1.5. 41 Average strength of concrete of a structure, a zone of a structure or a part of a monolithic and precast-monolithic structure with the number of sections that met the requirements of 7.1.1. *" The actual strength class of concrete of a structure or part of a monolithic and precast-monolithic structure in accordance with clauses 7.3-7.5 of GOST 16105, depending on the selected control scheme. Note - The presentation in the column "Concrete strength class" of the estimated values of the class or values \u200b\u200bof the required concrete strength for each section separately (estimation of the strength class for one section) is not allowed.

UDC 691.32.620.17:006.354 MKS 91.100.10 NEQ

Keywords: structural heavy and light concretes, monolithic and prefabricated concrete and reinforced concrete products, structures and structures, mechanical methods for determining compressive strength, elastic rebound, shock impulse, plastic deformation, separation, rib shearing, separation with shearing

Editor T.T. Martynova Technical editor 8.N. Prusakova Proofreader M 8. Vuchiaya Computer Layout I.A. Napaykina

Handed over to the set 12/29/201S. Signed and stamped 06.02.2016. Format 60 «64^. Arial headset. Uel. oven l. 2.7V. Uch.-iad. l. 2.36. Tira” 60 eq. Zach. 263.

Published and printed by FSUE STANDARTINFORM, $12399 Moscow. Garnet lane.. 4.

Put into effect by order of the Federal Agency for Technical Regulation and Metrology dated September 25, 2015 N 1378-st

Interstate standard GOST 22690-2015

"CONCRETE. DETERMINATION OF STRENGTH BY MECHANICAL METHODS OF NON-DESTRUCTIVE TESTING"

Concretes. Determination of strength by mechanical methods of nondestructive testing

Instead of GOST 22690-88

Foreword

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 the development, adoption, application, renewal and cancellation

About the standard

1 Developed by the Structural Subdivision of JSC "NRC "Construction" Research, Design and Technological Institute of Concrete and Reinforced Concrete named after A.A. Gvozdev (NIIZhB)

2 Introduced by the Technical Committee for Standardization TC 465 "Construction"

3 Adopted by the Interstate Council for Standardization, Metrology and Certification (Minutes of June 18, 2015 N 47)

Short name of the country according to MK (ISO 3166) 004-97	Country code according to MK (ISO 3166) 004-97	Abbreviated name of the national standards body
		Ministry of Economy of the Republic of Armenia
Belarus		State Standard of the Republic of Belarus
Kazakhstan		State Standard of the Republic of Kazakhstan
Kyrgyzstan		Kyrgyzstandart
		Moldova-Standard
		Rosstandart
Tajikistan		Tajikstandart

4 By order of the Federal Agency for Technical Regulation and Metrology dated September 25, 2015 N 1378-st, the interstate standard GOST 22690-2015 was put into effect as the national standard of the Russian Federation from April 1, 2016.

5 This standard takes into account the main regulatory provisions regarding the requirements for mechanical methods for non-destructive testing of the strength of concrete of the following European regional standards:

EN 12504-2:2001 Testing concrete in structures - Part 2: Non-destructive testing - Determination of rebound number

EN 12504-3:2005 Testing concrete in structures - Determination of pull-out force.

Degree of conformity - non-equivalent (NEQ)

6 Instead of GOST 22690-88

1 area of use

This standard applies to structural heavy, fine-grained, light and tension concrete of monolithic, prefabricated and precast-monolithic 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, shock impulse , plastic deformation, separation, rib shearing and separation with shearing.

2 Normative references

This standard uses normative references to the following interstate standards:

GOST 166-89 (ISO 3599-76) Calipers. Specifications

GOST 577-68 Dial gauges with division value 0.01 mm. Specifications

GOST 2789-73 Surface roughness. Parameters and characteristics

GOST 10180-2012 Concrete. Methods for determining the strength of control samples

GOST 18105-2010 Concrete. Strength control and assessment rules

GOST 28243-96 Pyrometers. General technical requirements

GOST 28570-90 Concrete. Methods for determining strength from samples taken from structures

GOST 31914-2012 High-strength heavy and fine-grained concrete for monolithic structures. Rules for quality control and evaluation

Note - When using this standard, it is advisable to check the validity of reference standards in the public information system - on the official website of the Federal Agency for Technical Regulation and Metrology on the Internet or according to the annual information index "National Standards", which was published as of January 1 of the current year, and on issues of the monthly information index "National Standards" for the current year. If the reference standard is replaced (modified), then when using this standard, you should be guided by the replacing (modified) standard. If the referenced standard is canceled without replacement, the provision in which the reference to it is given applies to the extent that this reference is not affected.

3 Terms and definitions

This standard uses the terms according to GOST 18105, as well as the following terms with their respective definitions;

3.3 indirect non-destructive methods for determining the strength of concrete: Determination of the strength of concrete according to pre-established calibration dependencies.

3.4 direct (standard) non-destructive methods for determining the strength of concrete: Methods that provide for standard test schemes (tearing with shearing and shearing of the rib) and allowing the use of known calibration dependencies without reference and adjustment.

4 General provisions

Elastic rebound;

plastic deformation;

shock impulse;

Breakaway with chipping;

Rib chipping.

4.3 Non-destructive mechanical methods for determining the strength of concrete are based on the relationship between the strength of concrete and indirect strength characteristics:

The method of elastic rebound on the relationship between the strength of concrete and the value of the rebound of the striker from the surface of the concrete (or the striker pressed against it);

Impact impulse method on the relationship between the strength of concrete and the energy of impact and its changes at the moment of impact of the striker with the concrete surface;

The method of detachment with chipping on the connection of the strength of concrete with the value of the force of local destruction of concrete when the anchor device is pulled out of it;

Rib shearing method on the relationship of concrete strength with the value of the force required to shear a section of concrete on a structure edge.

NOTE Standard test schemes are applicable to a limited range of concrete strengths (see Annexes A and B). 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 Table 1 and additional restrictions established by manufacturers of specific measuring instruments. The use of methods outside the concrete strength ranges recommended in Table 1 is allowed with scientific and technical justification based on the results of studies using measuring instruments that have passed metrological certification for an extended concrete strength range.

Table 1

4.7 Determination of the strength of heavy concrete of design classes B60 and higher or with an average compressive strength of concrete R m ≥ 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 sections of structures that do not have visible damage (peeling of the protective layer, cracks, cavities, etc.).

4.9 The age of concrete of controlled structures and its sections should not differ from the age of concrete of structures (sections, samples) tested to establish a calibration dependence by more than 25%. The exceptions are the control of strength and the construction of a calibration dependence for concrete whose age exceeds two months. In this case, the difference in the age of individual structures (sections, samples) is not regulated.

4.10 Tests are carried out at a positive temperature of concrete. It is allowed to conduct tests at a negative temperature of concrete, but not lower than minus 10°C, when establishing or linking the calibration dependence, taking into account the requirements of 6.2.4. The temperature of the concrete during testing must correspond to the temperature provided for by the operating conditions of the devices.

Calibration dependencies established at a concrete temperature 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 a surface temperature T≥40°C (to control the tempering, transfer and stripping strength of concrete), the calibration dependence is established after determining the strength of concrete in the structure by an indirect non-destructive method at a temperature t = (T ± 10) °C, and testing of concrete by a direct non-destructive method or testing of samples - after cooling at normal temperature.

5 Measuring instruments, equipment and tools

5.2 Readings of instruments calibrated in units of concrete strength should be considered as an indirect indicator of concrete strength. These devices should be used only after establishing the calibration dependence "instrument reading - concrete strength" or linking the dependence set in the device in accordance with 6.1.9.

5.3 A tool for measuring the diameter of indentations (caliper according to GOST 166) used for the plastic deformation method must provide measurement with an error of not more than 0.1 mm, a tool for measuring the depth of an indentation (caliper type according to GOST 577, etc.) - with an error no more than 0.01 mm.

5.4 Standard schemes for testing the method of separation with shearing and spalling of the rib provide for the use of anchor devices and grips in accordance with Annexes A and B.

5.5 For the shear pull method, anchor devices should be used, the insertion depth of which should not be less than the maximum size of the coarse concrete aggregate of the structure being tested.

5.6 For the tear-off method, steel discs with a diameter of at least 40 mm, a thickness of at least 6 mm and at least 0.1 diameter should be used, with the roughness parameters of the glued surface not less than Ra = 20 µm according to GOST 2789. The adhesive for gluing the disc must ensure adhesion with concrete, in which the destruction occurs along the concrete.

6 Test preparation

6.1 Procedure for preparing for testing

6.1.2 The calibration dependence is established on the basis of the following data:

The results of parallel tests of the same sections of structures by one of the indirect methods and the direct non-destructive method for determining the strength of concrete;

Results of testing sections of structures by one of the indirect non-destructive methods for determining the strength of concrete and testing core samples taken from the same sections of the structure and tested in accordance with GOST 28570;

The results of testing standard concrete samples by one of the indirect non-destructive methods for determining the strength of concrete and mechanical tests in accordance with GOST 10180.

6.1.5 For direct non-destructive methods according to 4.5, it is allowed to use the dependencies given in Appendices C and D for all types of normalized concrete strength.

6.1.6 The calibration dependence must have a standard (residual) deviation S T . H. M , not exceeding 15% of the average concrete strength of the sections or samples used in the construction of the dependence, and the correlation coefficient (index) of at least 0.7.

It is recommended to use a linear relationship of the form R = a + b K (where R is the strength of concrete, K is an indirect indicator). The methodology for establishing, estimating parameters and determining the conditions for applying a linear calibration dependence is given in Appendix E.

6.1.7 When constructing a calibration dependence, the deviations of individual values of concrete strength R i f from the average value of the concrete strength of sections or samples R̅ f used to construct the calibration dependence must be within:

From 0.5 to 1.5 average concrete strength R̅ f at R̅ f ≤ 20 MPa;

From 0.6 to 1.4 average concrete strength R̅ f at 20 MPa< R̅ ф ≤ 50 МПа;

From 0.7 to 1.3 average concrete strength R̅ f at 50 MPa< R̅ ф ≤ 80 МПа;

From 0.8 to 1.2 average concrete strength R̅ f at R̅ f > 80 MPa.

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 tested one in composition, age, hardening conditions, humidity, with reference in accordance with the methodology in Appendix G.

6.2 Construction of a calibration dependence based on the results of testing the strength of concrete in structures

6.2.2 The minimum number of single values for constructing a calibration dependence based on the results of testing the strength of concrete in structures is 12.

Then the sites are selected in the number provided for in 6.2.2, on which the maximum, minimum and intermediate values of the indirect indicator are obtained.

After testing by an indirect non-destructive method, the sections are tested by a direct non-destructive method or samples are taken for testing in accordance with GOST 28570.

6.2.4 To determine the strength at a negative temperature of concrete, the sections 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 warmed up 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 by a direct non-destructive method. The temperature control of the heated concrete is carried out at the installation depth of the anchor device in the prepared hole or along the chip surface in a non-contact way using a pyrometer according to GOST 28243.

6.3 Construction of a calibration dependence on control samples

6.3.1 When constructing a calibration dependence on control samples, the dependence is established by single values of the indirect indicator and concrete strength of standard cube samples.

When establishing a calibration dependence for the tear-off method with shearing, the main and control samples are made according to 6.3.4. An indirect characteristic is determined on the main samples, control samples are tested in accordance with GOST 10180. The main and control samples must be made from 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 in accordance with GOST 10180, but not less than:

100 x 100 x 100 mm for the methods of rebound, shock impulse, plastic deformation, as well as for the method of separation with chipping (control samples);

200 x 200 x 200 mm for the method of chipping the rib of the structure;

300 x 300 x 300 mm, but with a rib size of at least six anchor device installation depths for the pull-out method with shearing (basic samples).

The total number of 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 Table 2, and the distance between the impact points must be at least 30 mm (15 mm for the shock impulse method). For the indentation plastic deformation method, the number of tests on each face must be at least two, and the distance between the test points must be at least two indent diameters.

When establishing a calibration dependence for the rib shearing method, one test is carried out on each side rib.

When establishing the calibration dependence for the method of separation with shearing, 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, plastic deformation upon impact, the specimens shall be clamped in a press with a force of not less than (30 ± 5) kN and not more than 10% of the expected value of the breaking load.

6.3.7 The samples tested by the pull-off method are installed on the press so that the surfaces on which the pull-out was carried out do not adjoin the press base plates. The test results according to GOST 10180 are increased by 5%.

7 Testing

7.1 General requirements

Control tasks (determining the actual class of concrete, stripping or tempering strength, identifying areas of reduced strength, etc.);

Type of construction (columns, beams, slabs, etc.);

Placement of grips and order of concreting;

Structural reinforcement.

7.1.2 Tests are carried out on a section of the structure with an area of 100 to 900 cm 2 .

7.1.3 The total number of measurements in each section, the distance between the measurement points in the section and from the edge of the structure, the thickness of the structures in the measurement section should not be less than the values \u200b\u200bgiven in Table 2, depending on the test method.

Table 2 - Requirements for test sites

Method name	Total number of measurements per site	Minimum distance between measurement points on the site, mm	Minimum distance from the edge of the structure to the measurement point, mm	Minimum construction thickness, mm
elastic rebound
shock impulse
Plastic deformation
Rib chipping
		2 disc diameters
Breakaway with shearing at working depth h: ≥ 40 mm

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 dependence established in accordance with the requirements of Section 6, provided that the calculated value of the indirect indicator is within the established (or tied) dependence (between the smallest and largest values strength).

7.2 Rebound method

7.2.1 Tests are carried out in the following sequence:

The position of the device when testing the structure relative to the horizontal is recommended to be taken the same as when establishing the calibration dependence. In a different position of the device, it is necessary to make a correction for the indicators in accordance with the instruction manual for the device;

7.3 Plastic deformation method

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 instructions for use of 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);

Fix the values of the indirect characteristic in accordance with the instruction manual for the device;

Calculate the average value of the indirect characteristic on the construction site.

7.4 Shock pulse method

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 instructions for use of the device;

The value of the indirect characteristic is fixed in accordance with the instruction manual for the device;

Calculate the average value of the indirect characteristic on the construction site.

7.5 Pull-off method

7.5.1 When testing by the pull-off method, the sections should be located in the zone of the 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:

At the place where the disk is glued, the surface layer of concrete is removed with a depth of 0.5 - 1 mm and the surface is cleaned of dust;

The disk is glued to the concrete by pressing the disk and removing excess adhesive outside the disk;

The device is connected to the disk;

The load is smoothly increased at a rate of (1±0.3) kN/s;

Measure the projection area of the separation surface on the plane of the disk with an error of ±0.5 cm 2 ;

The value of the conditional stress in concrete at separation is determined as the ratio of the maximum separation force to the area of the projection of the separation surface.

7.6 Pull-off method with shear

7.6.2 Tests are carried out in the following sequence:

An anchor device is fixed in the hole to the depth provided for in the instruction manual for the device, depending on the type of anchor device;

The device is connected to the anchor device;

The load is increased at a rate of 1.5 - 3.0 kN/s;

Record the reading of the force meter of the device P 0 and the value of the anchor slip Δh (the difference between the actual pull-out depth and the depth of the anchor device) with an accuracy of at least 0.1 mm.

7.6.3 The measured value of the pull-out force P 0 is multiplied by the correction factor γ, determined by the formula

where h is the working depth of the anchor device, mm;

Δh - anchor slippage, mm.

7.6.4 If the largest and smallest dimensions of the torn out part of the concrete from the anchor device to the boundaries of destruction along the surface of the structure differ by more than two times, and also if the depth of the torn out differs from the depth of the anchor device by more than 5% (Δh > 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 the strength of concrete are not allowed to be used to assess the class of concrete in terms of strength and build calibration dependencies.

7.6.5 The results of the test are not taken into account if the pull-out depth differs from the depth of anchor device embedment by more than 10% (Δh > 0, 1h) or the reinforcement was exposed at a distance of the tanker device less than its embedment depth.

7.7 Rib chipping method

7.7.2 The test is carried out in the following sequence:

The device is fixed on the structure, load is applied at a speed of not more than (1±0.3) kN/s;

Record the reading of the force meter of the device;

Measure the actual depth of chipping;

Determine the average value of the chipping force.

7.7.3 The test results are not taken into account if the reinforcement was exposed during concrete shearing or the actual shearing depth differed from the specified one by more than 2 mm.

8 Processing and presentation of results

8.1 The test results are presented in a table indicating:

Type of construction;

Design class of concrete;

Age of concrete;

The strength of the concrete of each controlled area according to 7.1.5;

The average strength of the concrete structure;

Zones of the structure or its parts subject to the requirements of 7.1.1.

The form of the test results presentation table is given in Annex K.

8.2 The processing and assessment of compliance with the established requirements of the values 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 concrete class based on test results is carried out in accordance with GOST 18105 (schemes "A", "B" or "C") in cases where the strength of concrete is determined by the calibration dependence constructed in accordance with Section 6. When using previously established dependencies by linking them (according to Appendix G), statistical control is not allowed, and the assessment of the concrete class is carried out only according to the "D" scheme of GOST 18105.

8.3 The results of determining the strength of concrete by mechanical methods of non-destructive testing are drawn up in a conclusion (protocol), in which the following data are given:

About the tested structures indicating the design class, the date of concreting and testing, or the age of concrete at the time of testing;

On the methods used to control the strength of concrete;

About the types of devices with serial numbers, information about the verification of devices;

On the accepted calibration dependences (dependence equation, dependence parameters, compliance with the conditions for applying the calibration dependence);

Used to build a calibration dependence or its binding (date and results of tests by non-destructive indirect and direct or destructive methods, correction factors);

On the number of sites for determining the strength of concrete in structures, indicating their location;

Test results;

Methodology, results of processing and evaluation of the obtained data.

Annex A
(mandatory)

Standard Shear-Pull Test Design

A.1 The standard shearing test scheme provides for tests subject to the requirements of A.2 to A.6.

A.2 The standard test scheme is applicable in the following cases:

Tests of heavy concrete with compressive strength from 5 to 100 MPa;

Tests of 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 anchor devices.

A.3 The supports of the loading device must evenly adjoin the concrete surface at a distance of at least 2h from the axis of the anchor device, where h is the working depth of the anchor device. The test scheme is shown in Figure A.1.

1 - device with a loading device and a force meter; 2 - support of the loading device; 3 - capture of the loading device; 4 - transitional elements, traction; 5 - anchor device; 6 - tear-out concrete (separation cone); 7 - test design

"Figure A.1 - Schematic of the shear-pull test"

A.4 The standard shearing test scheme provides for the use of three types of anchor devices (see Figure A.2). Anchor device type I 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 expanding cone; 3 - segmented corrugated cheeks; 4 - support rod; 5 - working rod with a hollow expanding cone; 6 - leveling washer

"Figure A.2 - Types of anchor devices for a standard test scheme"

Table A.1 - Parameters of anchor devices for a standard test scheme

Type of anchor device	Embedment depth of anchor devices, mm	Permissible range of concrete compressive strength measurements for the anchor device, MPa
Type of anchor device	working h	severe

A.6 Anchor designs of types II and III should provide preliminary (before applying the load) compression of the hole walls at the working embedment depth h and slip control after the test.

Annex B
(mandatory)

Standard Rib Shearing Test Arrangement

B.1 The standard scheme of testing by the rib shearing method provides for testing subject to the requirements of B.2 - B.4.

B.2 The standard test scheme is applicable in the following cases:

The maximum fraction of coarse concrete aggregate is not more than 40 mm;

Tests of heavy concrete with compressive strength from 10 to 70 MPa on crushed granite and limestone.

B.3 For testing, a device is used, consisting of a power exciter with a force measuring unit and a gripper with a bracket for local shearing of the structure rib. The test scheme is shown in Figure B.1.

1 - device with a loading device and a force meter; 2 - support frame; 3 - chipped concrete; 4 - test design. 5 - grip with bracket

"Figure B.1 - Scheme of the rib shearing test"

B.4 In case of local shearing of the rib, the following parameters should be provided:

Depth of chipping 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)°.

Calibration dependence for the pull-off method with shearing in the standard test scheme

When carrying out tests by the method of separation with shearing according to the standard scheme in accordance with Appendix A, the cubic compressive strength of concrete R, MPa, can be calculated from the calibration dependence according to the formula

where m 1 is the coefficient that takes into account the maximum size of the coarse aggregate in the pull-out zone and is taken equal to 1 when the aggregate size is less than 50 mm;

m 2 - coefficient of proportionality for the transition from the pull-out force in kilonewtons to the strength of concrete in megapascals;

P - pull-out force of the anchor device, kN.

When testing heavy concrete with a strength of 5 MPa or more and lightweight concrete with a strength of 5 to 40 MPa, the values of the proportionality factor m 2 are taken from Table B.1.

Table B.1

Type of anchor device	Range of measured concrete compressive strength, MPa	Anchor device diameter d, mm	Depth of embedding of the anchor device, mm	The value of the coefficient m 2 for concrete
Type of anchor device	Range of measured concrete compressive strength, MPa	Anchor device diameter d, mm	Depth of embedding of the anchor device, mm	severe

The coefficients m 2 when testing heavy concrete with an average strength above 70 MPa should be taken according to GOST 31914.

Calibration dependence for the rib shearing method with a standard test scheme

When performing a rib shearing test according to the standard scheme in accordance with Appendix B, the cubic compressive strength of concrete on granite and lime rubble R, MPa, can be calculated from the calibration dependence according to the formula

R=0.058m(30P+P2),

where m is a coefficient that takes into account the maximum size of coarse aggregate and is 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;

P - shearing force, kN.

Annex D
(mandatory)

Requirements for instruments for mechanical testing

Table E.1

Name of characteristics of devices	Characteristics of devices for the method
Name of characteristics of devices	elastic rebound	shock impulse	plastic deformation	chipping ribs	breakaway with chipping
Hardness of striker, striker or indenter HRCe, not less than
Roughness of the contact part of the striker or indenter, µm, not more than
Impactor or indenter diameter, mm, not less than
Thickness of disk indenter edges, mm, not less than
Conical indenter angle
Indentation diameter, % of indenter diameter
Perpendicularity tolerance when applying a load at a height of 100 mm, mm
Impact energy, J, not less than
Load increase rate, kN/s
Load measurement error, %, no more
* When pressing the indenter into the concrete surface.

Method for establishing, correcting and evaluating the parameters of calibration dependencies

E.1 Calibration equation

The equation of dependence "indirect characteristic - strength" is taken as linear by the formula

E.2 Rejection of test results

After constructing the calibration dependence according to formula (E.1), it is corrected by rejecting single test results that do not satisfy the condition:

where R i n is the strength of concrete in the i-th section, determined by the considered calibration dependence;

S - residual standard deviation, calculated by the formula

here R i f, N - see the explication to the formula (E.3).

After rejection, the calibration dependence is established again according to formulas (E.1) - (E.5) according to the remaining test results. The rejection of the remaining test results is repeated, considering the fulfillment of condition (E.6) when using a new (corrected) calibration dependence.

Particular values of concrete strength must meet the requirements of 6.1.7.

E.3 Parameters of calibration dependence

For the accepted calibration dependence, determine:

Minimum and maximum values of the indirect characteristic H min , H max ;

Standard deviation S T . H. M of the constructed calibration dependence according to the formula (E.7);

Correlation coefficient of the calibration dependence r according to the formula

where the average value of concrete strength according to the calibration dependence R̅ n is calculated by the formula

here the values R i n, R i f, R̅ f, N - see the explications to formulas (E.3), (E.6).

E.4 Correction of the calibration dependence

Adjustment of the established calibration dependence, taking into account additionally obtained test results, should 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 to build the calibration dependence, the results of previous tests, starting from the very first ones, 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 set again according to the formulas (E.1) - (E.9).

E.5 Conditions for applying the calibration dependence

The use of a calibration dependence to determine the strength of concrete according to this standard is allowed only for values of an indirect characteristic that falls in the range from H min to H max.

If the correlation coefficient r< 0, 7 или значение S T . H . M / R̅ ф >0, 15, then control and strength assessment based on the obtained dependence are not allowed.

Annex G
(mandatory)

The method of binding the calibration dependence

G.1 The value of the strength of concrete, determined using the calibration dependence established for concrete that differs from the test, is multiplied by the coefficient of coincidence K c. The value of K with is calculated by the formula

where R os i is the strength of concrete in the i-th section, determined by the method of separation with chipping or testing of cores according to GOST 28570;

R cos i - strength of concrete in the i-th section, determined by any indirect method according to the calibration dependence used;

n is the number of test sites.

G.2 When calculating the coefficient of coincidence, the following conditions must be met:

The number of test sites taken into account when calculating the coefficient of coincidence, n ≥ 3;

Each private value R os i /R cos i must be at least 0.7 and not more than 1.3:

;

Each private value R os i /R cos i must differ from the average value by no more than 15%:

Values R os i /R cos i that do not satisfy the conditions (G.2), (G.3) should not be taken into account when calculating the coefficient of coincidence K with.

Assignment of the number of test sites for prefabricated and monolithic structures

I.1 In accordance with GOST 18105, when testing the strength of concrete of prefabricated structures (tempering or transfer), the number of controlled structures of each type is taken at least 10% and at least 12 structures from the batch. If the batch consists of 12 structures or less, complete control is carried out. In this case, the number of sections must be at least:

1 per 4 m length of linear structures;

1 by 4 m 2 area of flat structures.

I.3 In accordance with GOST 18105, when controlling the strength of concrete of monolithic structures at the design age, continuous non-destructive testing of the strength of concrete of all structures of the controlled batch is carried out. In this case, the number of test sites must be at least:

3 for each grip for flat structures (wall, floor, foundation slab);

1 per 4 m length (or 3 per grip) for each linear horizontal structure (beam, crossbars);

6 for each structure - for linear vertical structures (column, pylon).

The total number of measurement sites for calculating the characteristics of the uniformity of the strength of concrete of a batch of structures should be at least 20.

I.4 The number of single measurements of the strength of concrete by mechanical methods of non-destructive testing in each section (the number of measurements in the section) is taken according to table 2.

Test result presentation table form

Name of structures (batch of structures), design class of concrete strength, date of concreting or age of concrete of tested structures	Designation(1)	N plot according to the scheme or location in the axes (2)	Strength of concrete, MPa		Concrete strength class(5)
			plot(3)	medium(4)






(1) The brand, symbol and (or) location of the structure in the axes, the zone of the structure, or part of the monolithic and precast-monolithic structure (grip), for which the concrete strength class is determined. (2) Total number and location of sites in accordance with 7.1.1. (3) Strength of site concrete in accordance with 7.1.5. (4) The average strength of the concrete of a structure, a zone of a structure, or a part of a monolithic and cast-in-place structure for the number of sections that meet the requirements of 7.1.1. (5) The actual strength class of concrete of a structure or part of a monolithic and precast-monolithic structure in accordance with paragraphs 7.3 - 7.5 of GOST 18105, depending on the selected control scheme. Note - The presentation in the column "Concrete strength class" of the estimated values of the class or values \u200b\u200bof the required concrete strength for each section separately (estimation of the strength class for one section) is not allowed.

The strength of load-bearing and enclosing structures largely depends on the characteristics of the building materials used. Comprehensive testing of concrete for separation with chipping belongs to the category of non-destructive and allows you to determine the parameters and quality of the mixtures used with high accuracy. Research is carried out in accordance with the requirements of GOST 22690-2015 with the use of special instruments.

In our country, this concrete testing technique has become widespread due to its versatility and convenience. The strength characteristics of the material are tested by acting directly on the concrete of the structure and causing its partial spalling. In the course of research, the force is determined that allows tearing off a fragment of a building structure using a petal anchor embedded in the hole.

The procedure for testing concrete structures for separation with chipping

The described method of control allows you to set the strength characteristics of the material in the measurement range from 5 to 100 MPa. This test method is applicable to four types of concrete:

lungs;
heavy;
fine-grained;
straining in monolithic and prefabricated reinforced concrete products.

The study of this building material by tearing off the anchor with chipping is carried out in the manner prescribed by the current GOST:

Preparation of equipment and facility.
Conducting research and fixing the results.
Data processing using standard techniques.
Creation of calibration dependence.

To carry out the program, two types of samples are made, control and basic, from materials of that type under study. They must be cured under the same conditions as the products under test. At the same time, the main samples are necessary to determine the indirect characteristics of concrete mixtures.

Preparatory work

Testing building structures and reinforced concrete products using this technique will require considerable time. Before conducting concrete studies by tearing with shearing, a number of preparatory measures are performed:

The device and the anchor device are inspected, their technical condition is checked.
The place of installation of the device is chosen, not necessarily even, the curvature of the surface should not interfere with its use.
In the structure under study, a hole is drilled, from which dust and debris are removed. At an ambient temperature below -10 °C, the hole and the adjacent array are heated along the entire length.

The area under investigation, where it is planned to tear off the concrete with chipping, should be at a sufficient distance from the prestressed reinforcement. In addition, the area under study should not experience large operational loads.

Procedure for Conducting Concrete Strength Studies

Testing of concrete by the detachment method can be carried out, including with the use of anchors laid before the pouring of the structure from cement-sand mixtures.
The described method for checking the strength characteristics of concrete, in which separation and shearing takes place, involves a number of operations:

A flap anchor is inserted into the pre-drilled hole to the full depth and fixed in it.
The device is being installed and the embedded device is connected to it.
Gradually increase the load (rate of increase -1.5 -3 kN / s).
Fixation of indications: forces and values of anchor slippage (difference between the depth of the hole and the hole at which a fragment of material is detached from the array).

The result obtained - the pull-out force is entered into the test report and is used to build a calibration dependence. In this case, the accuracy of measuring the slippage index of the embedded anchor must be at least 0.1 mm.

Results processing

The data recorded in the course of the research make it possible to evaluate the strength of the mentioned material by the magnitude of the applied load at which chipping occurs. The value of the force at which a piece of concrete breaks off as a result of shearing is multiplied by a correction factor. The latter is calculated by the following formula:

γ \u003d h 2 / (h- Δh) 2,
where h is the depth of the anchor,
and Δh is the slip value.

If the maximum length of the part of the material that was torn off during the test is more than twice the minimum length, then the result is considered indicative. The same is done if the depth of the hole exceeds the slippage of the anchor by 5% or more. The use of guide values for determining the property class of a material is not permitted.

The tests are invalidated if the pull-out depth differs from the anchor length by 10% or reinforcement is detected at a distance not exceeding the hole depth.

Advantages and features of the research method

One of the main advantages of the described method is its high accuracy over a wide range of measurements. Moscow is the leader in terms of the number of facilities under construction, and such tests of concrete for separation with subsequent chipping are in demand. This method of assessing the strength of the material is the only one of the methods that allows you to build a calibration dependence without destroying the structure.

When monitoring characteristics using this method, it is necessary to take into account climatic conditions, as well as a number of other factors. In particular, the thickness of the product should be twice the depth of the anchor, and the distance between the measurement points should exceed this value five times. You can order concrete testing by tearing with chipping in Moscow at an affordable price directly on our website or by calling the contact phone.

A. V. Ulybin, Ph.D.; S. D. Fedotov, D. S. Tarasova (PNIPKU "Venture", St. Petersburg)

The proposed article discusses the main methods of non-destructive testing of the strength of concrete, used in the inspection of structures of buildings and structures. The results of experiments on comparison of data obtained by non-destructive methods of control and testing of samples are presented. The advantage of the method of separation with shearing over other methods of strength control is shown. Measures are described, without which the use of indirect non-destructive control methods is unacceptable.

The compressive strength of concrete is one of the most frequently monitored parameters in the construction and inspection of reinforced concrete structures. There are a large number of control methods used in practice. More reliable, from the point of view of the authors, is the determination of strength not by control samples (GOST 10180-90) made from a concrete mix, but by testing the concrete of the structure after it has gained design strength. The method of testing control samples allows you to evaluate the quality of the concrete mix, but not the strength of the concrete structure. This is due to the fact that it is impossible to provide identical conditions for curing (vibration, heating, etc.) for concrete in the structure and concrete sample cubes.

Methods of control according to the classification of GOST 18105-2010 ("Concrete. Rules for the control and evaluation of strength") are divided into three groups:

Destructive;
Direct non-destructive;
Indirect non-destructive.

Table 1. Characteristics of methods for non-destructive testing of concrete strength.

№	Method name	*Application range, MPa**	Measurement error**
1	plastic deformation	5 - 50	± 30 - 40%
2	elastic rebound	5 - 50	±50%
3	shock impulse	10 - 70	±50%
4	separation	5 - 60	No data
5	Breakaway with chipping	5 - 100	No data
6	Rib chipping	5 - 70	No data
7	Ultrasonic	5 - 40	± 30 - 50%

*According to the requirements of GOST 17624-87 and GOST 22690-88;

**According to the source without constructing a private calibration dependence

The methods of the first group include the mentioned method of control samples, as well as the method for determining strength by testing samples taken from structures. The latter is basic and is considered the most accurate and reliable. However, during the examination, they rarely run to him. The main reasons for this are a significant violation of the integrity of structures and the high cost of research.

Methods for determining the strength of concrete by non-destructive testing are mainly used. Most of the work is done by indirect methods. Among them, the most common today are the ultrasonic method according to GOST 17624-87, the shock pulse and elastic rebound methods according to GOST 22690-88. However, when using these methods, the requirements of the standards for the construction of particular calibration dependencies are rarely met. Some performers do not know these requirements.

Others know, but do not understand, how large the error in the measurement results is when using dependencies built into or supplied with the instrument, instead of a dependency built on the specific concrete under study. There are “specialists” who are aware of the specified requirements of the norms, but neglect them, focusing on financial benefits and the customer’s ignorance in this matter.

A lot of works have been written about the factors influencing the error in strength measurement without constructing partial calibration dependences. Table 1 presents data on the maximum measurement error by various methods, given in the monograph on non-destructive testing of concrete.

In addition to the indicated problem of using inappropriate (“false”) dependencies, let us designate another one that arises during the survey. According to the requirements of SP 13-102-2003, providing a sample of measurements (parallel tests of concrete by indirect and direct methods) in more than 30 areas is necessary, but not sufficient for the construction and use of a calibration dependence. It is necessary that the dependence obtained by pairwise correlation-regression analysis has a high correlation coefficient (more than 0.7) and a low standard deviation (less than 15% of the average strength). In order for this condition to be fulfilled, the accuracy of measurements of both controlled parameters (for example, the speed of ultrasonic waves and the strength of concrete) must be sufficiently high, and the strength of concrete, on which the dependence is built, must vary over a wide range.

When examining structures, these conditions are rarely met. First, even the basic method of testing samples is often accompanied by a high error. Secondly, due to the heterogeneity of concrete and other factors, the strength in the surface layer (investigated by an indirect method) may not correspond to the strength of the same section at a certain depth (when using direct methods). And finally, with the normal quality of concreting and the conformity of the concrete class to the design one, it is rare to find structures of the same type with strength varying over a wide range (for example, from B20 to B60) within one object. Thus, the dependence has to be built on a sample of measurements with a small change in the parameter under study.

As an illustrative example of the above problem, consider the calibration dependence shown in Fig. 1. Linear regression dependence is built based on the results of ultrasonic measurements and press tests of concrete samples. Despite the large spread of measurement results, the dependence has a correlation coefficient of 0.72, which is acceptable according to the requirements of SP 13-102-2003. When approximating functions other than linear (power, logarithmic, etc.), the correlation coefficient was less than indicated. If the range of the studied concrete strength were smaller, for example, from 30 to 40 MPa (the area highlighted in red), then the totality of the measurement results would turn into a “cloud” presented on the right side of Fig. 1. This cloud of points is characterized by the absence of a connection between the measured and sought parameters, which is confirmed by the maximum correlation coefficient of 0.36. In other words, the calibration dependence cannot be built here.

RICE. 1. Dependence between the strength of concrete and the speed of ultrasonic waves

It should also be noted that on ordinary objects, the number of strength measurement sections for constructing a calibration dependence is comparable to the total number of measured sections. In this case, the strength of concrete can be determined from the results of only direct measurements, and there will no longer be any sense in the calibration dependence and the use of indirect control methods.

Thus, without violating the requirements of the current standards, in any case, it is necessary to use direct non-destructive or destructive methods of control to determine the strength of concrete during examination. Taking this into account, as well as the problems outlined above, we will further consider direct methods of control in more detail.

This group according to GOST 22690-88 includes three methods:

Pull-off method

The tear-off method is based on measuring the maximum force required to tear off a fragment of a concrete structure. A shear load is applied to the flat surface of the structure under test by gluing a steel disc (Figure 2) with a rod to connect to the instrument. Various epoxy-based adhesives can be used for bonding. GOST 22690-88 recommends ED20 and ED16 adhesives with cement filler.
Today, modern two-component adhesives can be used, the production of which is well established (POXIPOL, Contact, Moment, etc.). In the domestic literature on concrete testing, the testing method involves gluing the disk to the test site without additional measures to limit the separation zone. Under such conditions, the separation area is not constant and must be determined after each test. In foreign practice, before testing, the separation area is limited to a groove created by annular drills (crowns). In this case, the separation area is constant and known, which increases the measurement accuracy.

After tearing off the fragment and determining the force, the tensile strength of the concrete (R(bt)) is determined, from which the compressive strength (R) can be determined by recalculation according to the empirical dependence. For translation, you can use the expression indicated in the manual:

For the detachment method, various devices can be used that are also used for the detachment method with shearing, such as, ONIKS-OS, PIB, DYNA (Fig. 2), as well as old analogues: GPNV-5, GPNS-5. To carry out the test, it is necessary to have a gripping device corresponding to the rod located on the disk.

Rice. 2. Peel-off device with disc for gluing to concrete

In Russia, the separation method has not found wide distribution. This is evidenced by the absence of mass-produced devices adapted for fastening to disks, as well as the disks themselves. In the normative documents, there is no dependence for the transition from the pull-out force to the compressive strength. In the new GOST 18105-2010, as well as the previous GOST R 53231-2008, the tear-off method is not included in the list of direct non-destructive testing methods and is not mentioned at all. The reason for this, apparently, is the limited temperature range of application of the method, which is associated with the duration of hardening and (or) the impossibility of using epoxy adhesives at low air temperatures. Most of Russia is located in colder climatic zones than European countries, so this method, which is widely used in European countries, is not used in our country. Another negative factor is the need to drill a furrow, which further reduces the inspection performance.

Rice. 3. Testing of concrete by the method of detachment with shearing

This method has much in common with the detachment method described above. The main difference is the method of fastening to concrete. Lobe anchors of various sizes are used to apply the tearing force. When examining structures, anchors are placed in a hole drilled in the measurement area. As with the tear-off method, the breaking force (P) is measured. The transition to the compressive strength of concrete is carried out according to the dependence specified in GOST 22690: R=m1 .m2 .P, where m 1- coefficient taking into account the maximum size of coarse aggregate, m2- coefficient of transition to compressive strength, depending on the type of concrete and hardening conditions.

In our country, this method has found, perhaps, the widest distribution due to its versatility (Table 1), the relative ease of attachment to concrete, and the possibility of testing on almost any part of the structure. The main limitations for its use are the dense reinforcement of the concrete and the thickness of the structure being tested, which must be greater than twice the length of the anchor. The instruments mentioned above may be used to carry out the tests.

Table 2. Comparative characteristics of direct methods of non-destructive testing

Advantages	Method
Advantages	Separation	Breakaway with chipping	Rib chipping
Determination of the strength of concrete with a class of more than B60	-	+	-
Possibility of installation on uneven concrete surface (irregularities more than 5 mm)	-	+	-
Possibility of installation on a flat section of the structure (without a rib)	+	+	-
No power supply required for installation	+*	-	+
Fast installation time	-	+	+
Operation at low air temperatures	-	+	+
Availability in modern standards	-	+	+

*Without drilling a furrow limiting the separation area.

In addition to being easier and faster to attach the structure to the concrete than with the tear-off method, it is not necessary to have a flat surface. The main condition is the need for the curvature of the surface to be sufficient to install the device on the anchor rod. As an example, in fig. 3 shows the POS-MG4 device installed on the destructed surface of the abutment of a hydraulic structure.

Rib chipping method

The last direct method of non-destructive testing is a modification of the tear-off method - the rib shearing method. The main difference is that the strength of concrete is determined by the force (P) required to chip off a section of the structure located on the outer edge. In our country, for a long time, devices of the type GPNS-4 and POS-MG4 Skol were produced, the design of which assumed the obligatory presence of two adjacent outer corners of the structure.

The grips of the device, like a clamp, were attached to the element under test, after which a force was applied through the gripping device to one of the ribs of the structure. Thus, the test could only be carried out on linear elements (columns, beams) or in openings at the edges of flat elements (walls, ceilings). A few years ago, the design of the device was developed, which allows it to be installed on the element under test with only one external rib. Fastening is carried out to one of the surfaces of the element under test using an anchor with a dowel. This invention somewhat expanded the range of application of the device, but at the same time destroyed the main advantage of the chipping method, which was the absence of the need for drilling and the need for a power source.

The compressive strength of concrete when using the rib shearing method is determined by the normalized dependence: R=0.058 .m .(30P+P2) ,

where m- coefficient taking into account the fineness of the aggregate.

For clarity of comparison, the characteristics of direct control methods are presented in Table. 2.

According to the data in the table, it can be seen that the method of separation with shearing is characterized by the largest number of advantages.

However, despite the possibility of using this method according to the instructions of the norms without constructing a partial calibration dependence, many specialists have a question about the accuracy of the results obtained and the conformity of their concrete strength, determined by the method of testing samples. To study this issue, as well as to compare the results of measurements obtained by the direct method with the results of measurements by indirect methods, the experiment described below was carried out.

Method Comparison Results

In the laboratory "Inspection and testing of buildings and structures" of the FGBOU VPO "SPBGPU" studies were carried out using various control methods. A fragment of a concrete wall cut with a diamond tool was used as an object of study. Concrete sample dimensions - 2.0 × 1.0 x 0.3 m.

Reinforcement is made with two meshes of reinforcement with a diameter of 16 mm, located with a step of 100 mm with a protective layer of 15-60 mm. In the sample under study, heavy concrete was used on aggregate from crushed granite fraction 20-40.

The basic destructive control method was used to determine the strength of concrete. 11 cores of various lengths with a diameter of 80 mm were drilled from the sample using a diamond drilling machine. From the cores, 29 cylinder samples were made, meeting the requirements of GOST 28570-90 (Concrete. Methods for determining strength from samples taken from structures) in terms of their dimensions. According to the results of testing samples for compression, it was revealed that the average value of concrete strength was 49.0 MPa. The distribution of strength values obeys the normal law (Fig. 4). At the same time, the strength of the studied concrete has a high heterogeneity with a coefficient of variation of 15.6% and an RMS equal to 7.6 MPa.

For non-destructive testing, the methods of detachment, detachment with shearing, elastic rebound and shock impulse were applied. The rib shearing method was not used due to the close location of the reinforcement to the ribs of the sample and the impossibility of performing tests. The ultrasonic method was not used, since the strength of concrete is above the permissible range for the application of this method (Table 1). Measurements by all methods were performed on the edge of the sample cut with a diamond tool, which provided ideal conditions in terms of surface evenness. To determine the strength by indirect methods of control, we used the calibration dependencies available in the passports of the devices, or included in them.

On fig. 5. Demonstrates the pull-off measurement process. The results of measurements by all methods are presented in table. 3.

Table 3. Results of strength measurements by various methods

№ p/n	Control method (instrument)	Number of measurements, n	Average value of concrete strength, Rm, MPa	Coefficient of variation, V, %
1	Compression test in a press (PGM-1000MG4)	29	49,0	15,6
2	Breakaway method with shearing (POS-50MG4)	6	51,1	4,8
3	Pull-off method (DYNA)	3	49,5	-
4	shock pulse method (Silver Schmidt)	30	68,4	7,8
5	shock pulse method (IPS-MG4)	7 (105)*	78,2	5,2
6	Rebound method (Concrete Control)	30	67,8	7,27

*Seven plots with 15 measurements each.

According to the data presented in the table, the following conclusions can be drawn:
the average value of the strength obtained by compression testing and direct methods of non-destructive testing differs by no more than 5%;
according to the results of six tests by the method of separation with shearing, the spread of strength is characterized by a low value of the coefficient of variation of 4.8%;
the results obtained by all indirect control methods overestimate the strength by 40-60%. One of the factors that led to this overestimation is the carbonization of concrete, the depth of which on the test surface of the sample was 7 mm.

conclusions

1. The imaginary simplicity and high productivity of indirect methods of non-destructive testing are lost when the requirements for constructing a calibration dependence are met and taking into account (eliminating) the influence of factors that distort the result. If these conditions are not met, these methods can only be used for a qualitative assessment of strength on the principle of "more - less" when examining structures.
2. The results of strength measurements by the basic method of destructive testing by compressing the selected samples can also be accompanied by a large scatter caused by both the non-homogeneity of concrete and other factors.
3. Taking into account the increased labor intensity of the destructive method and the confirmed reliability of the results obtained by direct methods of non-destructive testing, it is recommended to use the latter during the examination.
4. Among the direct methods of non-destructive testing, the method of separation with chipping is optimal in terms of most parameters.

Rice. 4. Distribution of strength values according to the results of compression tests.

Rice. 5. Measurement of strength by the pull-off method.

A. V. Ulybin, Ph.D.; S. D. Fedotov, D. S. Tarasova (PNIPKU "Venture", St. Petersburg), magazine "World of construction and real estate, No. 47, 2013

Determination of strength by mechanical methods of non-destructive testing. Concrete strength determination by pull-off method with shearing Rib shearing method

Direct methods of control

Breakaway with chipping

Rib chipping

Tearing off metal discs

Indirect methods of control

Ultrasonic Testing

elastic rebound

Giving shock impulse

Plastic deformation

Comparative characteristics by example

Instrumentless Testing

State standard

Working with concrete

CONCRETE

Determination of strength by mechanical methods of non-destructive testing

1 area of ​​use

2 Normative references

3 Terms and definitions

4 General provisions

5 Measuring instruments, equipment and tools

6 Test preparation

7 Testing

Table 2 - Requirements for test sites

8 Processing and presentation of results

Standard Shear-Pull Test Design

Table A.1 - Parameters of anchor devices for a standard test scheme

Standard Rib Shearing Test Arrangement

Calibration dependence for the pull-off method with shearing in the standard test scheme

Calibration dependence for the rib shearing method with a standard test scheme

Requirements for instruments for mechanical testing

Method for establishing, correcting and evaluating the parameters of calibration dependencies

The method of binding the calibration dependence

Assignment of the number of test sites for prefabricated and monolithic structures

Test result presentation table form

The procedure for testing concrete structures for separation with chipping

Preparatory work

Procedure for Conducting Concrete Strength Studies

Results processing

Advantages and features of the research method

Pull-off method

Rib chipping method

Method Comparison Results

conclusions

1 area of use