Inspection of reinforced concrete structures. Inspection of reinforced concrete structures of buildings Inspection of reinforced concrete structures of a building

In civil and industrial construction, reinforced concrete structures are among the most used. During the construction, operation of various buildings, structures, their various damages are often found in the form of cracks, deflections, and other defects. This happens due to deviations from the requirements of design documentation during their manufacture, installation, or caused by mistakes of designers.

The Konstruktor company has in its staff a group of expert engineers with deep knowledge in various areas of construction and the peculiarities of technological processes in industrial buildings, which is especially important when examining reinforced concrete structures. The main goal for which the inspection of reinforced concrete structures is carried out is to establish the current state of these elements with the identification of the causes of the identified deformations, to establish the degree of wear of its individual elements. During the examination, the real strength, stiffness of concrete, its physical and technical condition are determined, damage is identified, and the reasons for their occurrence are determined. The task is not only to search for various defects in concrete and reinforced concrete structures, but also to prepare recommendations for the customer to correct the situation for the normal further operation of the facility. This becomes possible only after a detailed study of structures made of reinforced concrete and concrete.

Reasons for the need for examination

To determine the bearing capacity of structures, their condition, a survey of buildings and structures is carried out at the request of the customer. They can be carried out according to a certain schedule or the need for their implementation arises after man-made accidents, natural disasters.

Inspection of structures made of concrete, reinforced concrete is required if:

• reconstruction of the building, structure is planned, if necessary, its re-profiling, changing the functional purpose of the premises, which can increase the load on the supporting structures;
• there are deviations from the project (discrepancies were found between the real project and the erected object);
• there were obvious deformations of elements of buildings, structures that exceed the permissible, according to the standards, values;
• the standard service life of buildings has been exceeded;
• structures are physically worn out;
• structures, buildings have been exposed to natural, man-made impacts;
• there was a need to study the features of the work of reinforced concrete structures in difficult conditions;
• any kind of examination is carried out.

Survey stages

Concrete and reinforced concrete structures can be of different types and shapes, however, the methods of their research remain the same for everyone, and the work carried out has a clear sequence. The survey is aimed at identifying the strength of concrete, the extent of the spread of corrosion processes in metal reinforcement.

For a complete inspection of structures, specialists must step by step perform:

• preparatory work (study of documentation);
• field work (visual, detailed study directly at the site using special tools);
• laboratory tests of taken samples;
• analysis of the results, carrying out calculations, determining the causes of defects;
• delivery of survey results to the customer with recommendations.

The work of specialists for the inspection of reinforced concrete structures begins with a study of all available project documentation, the service provided by the customer, analysis of the raw materials used at the facility.

Further, a direct examination of the object is carried out, which makes it possible to get an idea of ​​its real state. A preliminary external examination of prefabricated structures is carried out for the detection of their obvious defects.

At the stage of visual inspection of buildings and structures, the following can be identified:

• visible defects (cracks, spalling, destruction, damage);
• breaks of reinforcement, the real state of its anchorage (longitudinal, transverse);
• the presence of complete or partial destruction in various areas in concrete, reinforced concrete;
• displacement of individual elements, supports in structures;
• structural deflections, deformations;
• corrosive places of concrete, reinforcement, violation of their adhesion to each other;
• damage to protective coatings (screens, plaster, paintwork);
• areas with changed concrete color.

Instrumental examination

With a detailed examination in the process of work, specialists carry out the following actions:

• the geometric parameters of structures and their sections, the dimensions of external damage, defects are measured;
• detected defects are registered with marks of their characteristic features, location, width, depth of damage;
• strength, characteristic deformations of concrete, reinforcement are checked by instrumental or laboratory examination method;
• calculations are carried out;
• structures are tested for strength by load (if necessary).

In the course of a detailed examination, the characteristics of concrete are assessed in terms of frost resistance, strength, abrasion, density, uniformity, water permeability, and the degree of its corrosion damage.

These properties are defined in two ways:

• laboratory tests of concrete samples taken from the structure in violation of its integrity;
• inspection by ultrasonic, mechanical testers, moisture meters, other instruments using non-destructive testing methods.

For testing the strength of concrete, areas of visible damage are usually selected. In order to measure the thickness of the protective concrete layer during a detailed examination, non-destructive testing technologies are also used with the help of electromagnetic testers or its local opening is done.

The level of corrosion of concrete, reinforcement and its elements is determined by chemical-technical and laboratory methods for studying the samples taken. It is installed according to the type of concrete destruction, the spread of the process on surfaces, the capture of reinforcement with steel elements by rust.

The actual state of the reinforcement is also found out after collecting data about it and comparing them with the design parameters of the working drawings. Inspection of the condition of the reinforcement is carried out by removing the concrete layer to gain access to it. For this, places are selected where there are clear signs of corrosion in the form of rusty spots, cracks in the area of ​​reinforcing bars.

Inspection of structural elements is carried out by opening it in several places, depending on the area of ​​the object. If there are no obvious signs of deformations, then the number of openings is small or they are replaced by engineering sounding. The survey may include the determination of loads and their effects on structures.

Processing of examination results

At the end of the examination of concrete and reinforced concrete structures, the results are processed as follows:

1. Diagrams, statements are drawn up, where the deformations of the building, structures are recorded, indicating their characteristic features (deflections, rolls, faults, distortions, etc.).
2. The reasons for the appearance of deformations in concrete and structures are analyzed.
3. Based on the results of the survey, the bearing capacity of the structure is calculated, which will show the real state of the object and the likelihood of its trouble-free operation in the future. In the laboratory, samples of materials taken from structures of structures, buildings are tested, on the basis of which a test report is drawn up.

After that, a Technical Opinion is drawn up with the conclusions of specialists, which are presented to the customer:

• an estimated opinion on the technical condition of structures, determined by the degree of their damage, the characteristics of the defects identified;
• defective statements, tables, descriptions, results of instrumental and laboratory tests of samples taken during the examination;
• a new technical passport or an updated old document for a building, structure;
• conclusions on the probable causes of damage to structures made of concrete, reinforced concrete (if found);
• conclusions about the possibility to operate the building, the structure further;
• recommendations for the elimination of defects (if possible) in several options (restoration, reinforcement of structures).

Reinforced concrete structures are strong and durable, but it is no secret that in the process of erecting and operating buildings and structures in reinforced concrete structures, unacceptable deflections, cracks, and damage occur. These phenomena can be caused either by deviations from the design requirements in the manufacture and installation of these structures, or by design errors.

To assess the current state of a building or structure, a survey of reinforced concrete structures is carried out, which determines:

• Correspondence of the actual dimensions of structures to their design values;
• The presence of destruction and cracks, their location, nature and reasons for their appearance;
• The presence of explicit and hidden deformations of structures.
• The state of the reinforcement for a violation of its adhesion to concrete, the presence of ruptures in it and the manifestation of the corrosion process.

Most of the corrosion defects visually have similar signs, only a qualified inspection can be the basis for the appointment of methods of repair and restoration of structures.

Carbonation is one of the most common causes of destruction of concrete structures of buildings and structures in environments with high humidity, it is accompanied by the transformation of calcium hydroxide of cement stone into calcium carbonate.

Concrete is capable of absorbing carbon dioxide, oxygen and moisture, which are saturated with the atmosphere. This not only significantly affects the strength of the concrete structure, changing its physical and chemical properties, but has a negative effect on the reinforcement, which, when concrete is damaged, gets into an acidic environment and begins to collapse under the influence of harmful corrosion phenomena.

Rust, which forms during oxidation processes, contributes to an increase in the volume of steel reinforcement, which, in turn, leads to fractures of reinforced concrete and exposure of rods. Bare, they wear out even more rapidly, this leads to an even faster destruction of concrete. Using specially developed dry mixes and paint-and-lacquer coatings, it is possible to significantly increase the corrosion resistance and durability of the structure, but before that it is necessary to conduct its technical expertise.

Inspection of reinforced concrete structures consists of several stages:

• Identification of damages and defects by their characteristic features and their thorough examination.
• Instrumental and laboratory studies of the characteristics of reinforced concrete and steel reinforcement.
• Carrying out verification calculations based on the results of the survey.

All this contributes to the establishment of the strength characteristics of reinforced concrete, the chemical composition of aggressive media, the degree and depth of corrosion processes. The necessary tools and calibrated devices are used to inspect reinforced concrete structures. The results, in accordance with the applicable regulations and standards, are reflected in a well-written final conclusion.

3.2.1. The main tasks of examining load-bearing reinforced concrete structures are to determine the state of structures with the identification of damage and the causes of their occurrence, as well as the physical and mechanical characteristics of concrete.

3.2.2. Field surveys of concrete and reinforced concrete structures include the following types of work:

Inspection and determination of the technical condition of structures by external signs;

Instrumental or laboratory determination of the strength of concrete and reinforcing steel;

Determination of the degree of corrosion of concrete and reinforcement.

Determination of technical condition by external signs

3.2.3. Determination of the geometric parameters of structures and their sections is carried out according to the recommendations of this method. In this case, all deviations from the design position are recorded.

3.2.4. Determination of the width and depth of crack opening should be carried out in accordance with this technique. The degree of crack opening is compared with the normative requirements for the limiting states of the second group.

3.2.5. The determination and assessment of paint-and-lacquer coatings of reinforced concrete structures should be carried out according to the method described in GOST 6992. The following main types of damage are recorded: cracking and delamination, which are characterized by the depth of destruction of the upper layer (before the primer), bubbles and corrosion foci, characterized by the size of the focus (diameter ) in mm. The area of ​​certain types of damage to the coating is expressed as an approximate percentage in relation to the entire painted surface.

3.2.6. In the presence of wetted areas and surface efflorescence on the concrete of structures, the size of these areas and the reason for their appearance are determined.

3.2.7. The results of visual inspection of reinforced concrete structures are recorded in the form of defect maps, plotted on the schematic plans or sections of the building, or tables of defects with recommendations for the classification of defects and damages with an assessment of the category of the state of structures are drawn up.

3.2.8. External signs characterizing the state of reinforced concrete structures in 5 categories are given in the table (Appendix 1).

Determination of concrete strength by mechanical methods

3.2.9. Mechanical methods of non-destructive testing during the inspection of structures are used to determine the strength of concrete of all types of rated strength, controlled in accordance with GOST 18105 (table 3.1).

Table 3.1 - Methods for determining the strength of concrete depending on the expected strength of the elements

Depending on the applied method and devices, indirect strength characteristics are:

The value of the rebound of the striker from the concrete surface (or the striker pressed against it);

Impact impulse parameter (impact energy);

Dimensions of an indentation on concrete (diameter, depth) or the ratio of diameters of indentations on concrete and a standard specimen when the indenter is hit or the indenter is pressed into the concrete surface;

The value of the stress required for local destruction of concrete when tearing off a metal disk glued to it, equal to the pull-off force divided by the projection area of ​​the concrete tear-off surface onto the plane of the disc;

The value of the force required to shear a section of concrete on the edge of the structure;

The value of the force of local destruction of concrete when the anchor device is pulled out of it.

When conducting tests by mechanical methods of non-destructive testing, one should be guided by the instructions of GOST 22690.

3.2.10. Devices of the mechanical principle of operation include: Kashkarov's reference hammer, Schmidt's hammer, Fizdel's hammer, TsNIISK pistol, Poldi's hammer, etc. calibrated blow (TsNIISK pistol).

3.2.11. Fizdel's hammer is based on the use of plastic deformation of building materials. When struck with a hammer on the surface of the structure, a hole is formed, according to the diameter of which the strength of the material is estimated.

The place of the structure, on which the prints are applied, is preliminarily cleaned of the plaster layer, grouting or painting.

The process of working with Fizdel's hammer is as follows:

With the right hand, they take the end of the wooden handle, rest the elbow on the structure;

With an elbow blow of medium strength, 10-12 blows are applied to each section of the structure;

The distance between the impact hammer marks must be at least 30 mm.

The diameter of the formed hole is measured with a caliper with an accuracy of 0.1 mm in two perpendicular directions and the average value is taken. The largest and smallest results are excluded from the total number of measurements made in this area, and the average value is calculated for the rest.

The strength of concrete is determined by the average measured diameter of the indentation and a calibration curve previously constructed based on a comparison of the diameters of the hammer ball indentations and the results of laboratory strength tests of concrete samples taken from the structure according to the instructions of GOST 28570 or specially made from the same components and using the same technology. as the materials of the examined structure.

3.2.12. The Kashkarov hammer (GOST 22690) also belongs to the method for determining the strength of concrete based on the properties of plastic deformations.

When Kashkarov hits the surface of the structure with a hammer, two impressions are obtained on the surface of the material with a diameter and on a control (reference) rod with a diameter.

The ratio of the diameters of the resulting prints depends on the strength of the material being examined and the reference rod and practically does not depend on the speed and force of the blow applied by the hammer. The strength of the material is determined by the average value of the value from the calibration chart.

At the test site, at least five determinations must be made with the distance between the indentations on the concrete not less than 30 mm, and on the metal rod - not less than 10 mm (Table 3.2).

Table 3.2

3.2.13. Devices based on the method of elastic rebound include the TsNIISK pistol, Borovoy's pistol, Schmidt's hammer, 6KM sclerometer with a rod striker, etc. The principle of operation of these devices is based on measuring the elastic rebound of the striker at a constant kinetic energy of a metal spring. The cocking and descent of the striker are carried out automatically when the striker touches the test surface. The magnitude of the striker's rebound is fixed by a pointer on the scale of the device.

As a result of the impact, the striker bounces off the striker. The degree of rebound is marked on the scale of the device using a special pointer. The dependence of the rebound value of the striker on the strength of concrete is established according to the data of calibration tests of concrete cubes 15x15x15 cm in size, and on this basis a calibration curve is constructed. The strength of the material of construction is determined according to the indications of the graduated scale of the device at the time of striking the tested element.

3.2.14. The shear strength test is used to determine the strength of concrete in the body of the structure. The essence of the method consists in assessing the strength properties of concrete by the force required for its destruction around a borehole of a certain size when pulling out an expanding cone fixed in it or a special rod embedded in concrete. An indirect indicator of strength is the breakout force required to pull out the anchor device embedded in the body of the structures together with the surrounding concrete at the embedment depth. In the shear pull test, the sections shall be located in the zone of lowest stresses caused by the service load or the compression force of the prestressed reinforcement.

The strength of concrete on the site is allowed to be determined based on the results of one test. Test areas should be selected so that reinforcement does not fall into the tear-out zone. At the test site, the thickness of the structure should be at least twice the embedment depth of the anchor. When punching a hole with a bolt or drilling, the thickness of the structure in this place must be at least 150 mm. The distance from the anchor device to the edge of the structure must be at least 150 mm, and from the adjacent anchor device - at least 250 mm.

3.2.15. Three types of anchoring devices are used in the tests. Type I anchoring devices are installed on structures during concreting; anchor devices of types II and III are installed in pre-prepared boreholes formed in concrete by drilling. Recommended hole depth: for type II anchor - 30 mm; for anchor type III - 35 mm. The diameter of the borehole in concrete should not exceed the maximum diameter of the recessed part of the anchor device by more than 2 mm. Sealing of anchor devices in structures should ensure reliable adhesion of the anchor to concrete. The load on the anchor device should increase smoothly, at a rate of no more than 1.5-3 kN / s, until it breaks out together with the surrounding concrete.

The smallest and largest dimensions of the torn out part of concrete, equal to the distance from the anchor device to the boundaries of destruction on the surface of the structure, should not differ from one another by more than two times.

3.2.16. The unit value of the concrete strength at the test site is determined depending on the compressive stresses in concrete and the value.

Compressive stresses in concrete are determined by calculating structures taking into account the actual dimensions of the sections and the magnitudes of the loads (actions).

where is the coefficient taking into account the aggregate size, taken equal to: with a maximum aggregate size of less than 50 mm - 1, with a size of 50 mm or more - 1.1;

The coefficient entered at the actual depth, differing from more than 5%, should not differ from the nominal value adopted during the test by more than ± 15%;

The proportionality coefficient, the value of which, when using anchor devices, is taken:

for type II anchors - 30 mm: = 0.24 cm (for naturally hardened concrete); = 0.25 cm (for heat-treated concrete);

for type III anchors - 35 mm, respectively: = 0.14 cm; = 0.17 cm.

The strength of the compressed concrete is determined from the equation

3.2.17. When determining the class of concrete by the method of chipping the rib of the structure, a device of the GPNS-4 type is used.

At the test site, at least two concrete spalls must be carried out.

The thickness of the test structure must be at least 50 mm, and the distance between adjacent chips must be at least 200 mm. The load hook must be installed in such a way that the value does not differ from the nominal by more than 1 mm. The load on the tested structure should increase smoothly, at a rate of no more than (1 + 0.3) kN / s, until the concrete is chipped off. In this case, there should be no slippage of the load hook. The test results, in which the reinforcement was exposed at the site of the spall and the actual spalling depth differed from the specified one by more than 2 mm, are not taken into account.

3.2.18. The unit value of the concrete strength at the test site is determined depending on the compressive stresses of the concrete and the value.

Compressive stresses in concrete, acting during the test period, are determined by calculating the structure, taking into account the actual dimensions of the sections and the magnitudes of the loads.

The unit value of the concrete strength on the site under the assumption = 0 is determined by the formula

where is the correction factor that takes into account the aggregate size, taken equal at a maximum aggregate size of 20 mm or less - 1, with a size of more than 20 to 40 mm - 1.1;

Conditional strength of concrete, determined by the average value of the indirect indicator:

The force of each of the shears performed at the test site.

3.2.19. When testing by spalling ribs on the concrete surface, there should be no cracks, concrete chips, sagging or cavities with a height (depth) of more than 5 mm. 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.

Ultrasonic method for determining the strength of concrete

3.2.20. The principle of determining the strength of concrete by the ultrasonic method is based on the presence of a functional relationship between the speed of propagation of ultrasonic vibrations and the strength of concrete.

The ultrasonic method is used to determine the compressive strength of concrete of classes B7.5 - B35 (grades M100 - M450).

3.2.21. The strength of concrete in structures is determined experimentally using the calibration dependences "ultrasound propagation speed - concrete strength." Or "ultrasound propagation time - concrete strength." The degree of accuracy of the method depends on the accuracy of the calibration schedule.

3.2.22. To determine the strength of concrete by the ultrasonic method, devices UKB-1, UKB-1M, UK-16P, Beton-22, etc. are used.

3.2.23. Ultrasonic measurements in concrete are carried out by means of through or surface sounding. When measuring the propagation velocity of ultrasound by the through sounding method, ultrasonic transducers are installed on opposite sides of the sample or structure. The speed of propagation of ultrasound, m / s, is calculated by the formula

where is the propagation time of ultrasound, μs;

Distance between the centers of installation of transducers (sounding base), mm.

When measuring the speed of propagation of ultrasound by the method of surface sounding, ultrasonic transducers are installed on one side of the sample or structure.

3.2.24. The number of measurements of the propagation time of ultrasound in each sample should be 3 for through sounding, and 4 for surface sounding.

The deviation of a separate measurement result of the ultrasound propagation velocity in each sample from the arithmetic mean of the measurement results for this sample should not exceed 2%.

The measurement of the propagation time of ultrasound and the determination of the strength of concrete are carried out in accordance with the instructions of the passport (technical conditions for use) of this type of device and the instructions of GOST 17624.

3.2.25. In practice, there are often cases when it becomes necessary to determine the concrete strength of the structures in operation in the absence or impossibility of constructing a calibration table. In this case, the determination of the strength of concrete is carried out in the zones of structures made of concrete on one type of coarse aggregate (structures of one batch).

The speed of propagation of ultrasound is determined in at least 10 sections of the inspected area of ​​structures, according to which the average value is found. Next, the areas in which the ultrasound propagation speed has the maximum and minimum values, as well as the area where the speed has a value that is closest to the value, are marked, and then at least two cores are drilled from each target area, according to which the strength values ​​in these areas are determined: ,,respectively.

The strength of concrete is determined by the formula

The coefficients and are calculated by the formulas:

3.2.26. When determining the strength of concrete using samples taken from the structure, one should be guided by the instructions of GOST 28570.

3.2.27. If the condition is met

it is allowed to roughly determine the strength for concretes of strength classes up to B25 according to the formula

where is the coefficient determined by testing at least three cores taken from the structures.

3.2.28. For concretes of strength classes above B25, the strength of concrete in operating structures can also be assessed by a comparative method, taking as a basis the characteristics of the structure with the highest strength.

In this case

3.2.29. Structures such as beams, girders, columns should be sounded in the transverse direction, the slab should be sounded in the smallest size (width or thickness), and the ribbed slab - in the thickness of the rib.

3.2.30. With careful testing, this method provides the most reliable information about the strength of concrete in existing structures. Its disadvantage is the large laboriousness of work on the selection and testing of samples.

Determination of concrete cover and reinforcement location

3.2.31. To determine the thickness of the protective layer of concrete and the location of reinforcement in a reinforced concrete structure, magnetic, electromagnetic methods according to GOST 22904 or methods of transillumination and ionizing radiation according to GOST 17623 are used with selective control verification of the results obtained by punching furrows and direct measurements.

Radiation methods, as a rule, are used to examine the condition and control the quality of prefabricated and monolithic reinforced concrete structures during the construction, operation and reconstruction of especially critical buildings and structures.

The radiation method is based on transillumination of controlled structures with ionizing radiation and at the same time obtaining information about its internal structure using a radiation converter. Transillumination of reinforced concrete structures is carried out using radiation from X-ray machines, radiation from sealed radioactive sources.

Transportation, storage, installation and adjustment of radiation equipment is carried out by specialized organizations that have a special permit to carry out these works.

3.2.32. The magnetic method is based on the interaction of the magnetic or electromagnetic field of the device with the steel reinforcement of a reinforced concrete structure.

The thickness of the concrete cover and the location of the reinforcement in the reinforced concrete structure are determined on the basis of the experimentally established relationship between the readings of the device and the specified controlled parameters of the structures.

3.2.33. To determine the thickness of the protective layer of concrete and the location of the reinforcement from the devices, in particular, ISM and IZS-10N are used.

The IZS-10N device measures the thickness of the concrete cover depending on the reinforcement diameter within the following limits:

When the diameter of the reinforcement rods is from 4 to 10 mm, the thickness of the protective layer is from 5 to 30 mm;

With a diameter of reinforcement rods from 12 to 32 mm, the thickness of the protective layer is from 10 to 60 mm.

The device provides determination of the location of the projections of the axes of the reinforcement bars onto the concrete surface:

Diameter from 12 to 32 mm - with a concrete cover not more than 60 mm thick;

Diameter from 4 to 12 mm - with a concrete cover not more than 30 mm thick.

When the distance between the reinforcement rods is less than 60 mm, the use of devices of the IZS type is impractical.

3.2.34. Determination of the concrete cover thickness and reinforcement diameter is carried out in the following order:

Before testing, the technical characteristics of the device used are compared with the corresponding design (expected) values ​​of the geometric parameters of the reinforcement of the controlled reinforced concrete structure;

If the technical characteristics of the device do not correspond to the parameters of the reinforcement of the controlled structure, it is necessary to establish an individual calibration dependence in accordance with GOST 22904.

The number and location of the controlled sections of the structure are assigned depending on:

Objectives and test conditions;

Features of the design solution of the structure;

Manufacturing or construction technologies taking into account the fixation of reinforcing bars;

Operating conditions of the structure, taking into account the aggressiveness of the external environment.

3.2.35. Work with the device should be carried out in accordance with the instructions for its operation. At the measurement points on the surface of the structure, there should be no sagging with a height of more than 3 mm.

3.2.36. When the thickness of the protective layer of concrete is less than the measurement limit of the device used, the tests are carried out through a pad with a thickness of 10 + 0.1 mm from a material that does not have magnetic properties.

The actual concrete cover in this case is determined as the difference between the measurement results and the thickness of this pad.

3.2.37. When monitoring the location of steel reinforcement in the concrete of a structure, for which there is no data on the diameter of the reinforcement and the depth of its location, determine the layout of the reinforcement and measure its diameter by opening the structure.

3.2.38. For an approximate determination of the diameter of the reinforcing bar, the location of the reinforcement is determined and fixed on the surface of the reinforced concrete structure using an IZS-10N device.

The device transducer is installed on the surface of the structure and, according to the instrument scales or an individual calibration dependence, several values ​​of the concrete cover thickness are determined for each of the assumed diameters of the reinforcing bar that could be used to reinforce this structure.

A spacer of appropriate thickness (for example, 10 mm) is installed between the instrument transducer and the concrete surface of the structure, measurements are taken again and the distance is determined for each assumed diameter of the reinforcing bar.

For each diameter of the reinforcing bar, the values ​​and are compared.

The value for which the condition is fulfilled is taken as the actual diameter

where is the reading of the device, taking into account the thickness of the gasket;

Gasket thickness.

The indices in the formula indicate:

Longitudinal reinforcement pitch;

Step of transverse reinforcement;

The presence of a gasket.

3.2.39. The measurement results are recorded in a journal, the form of which is shown in Table 3.3.

Table 3.3 - Form of recording the results of measuring the thickness of the concrete cover of reinforced concrete structures

3.2.40. The actual values ​​of the concrete cover thickness and the location of the steel reinforcement in the structure according to the measurement results are compared with the values ​​established by the technical documentation for these structures.

3.2.41. The measurement results are documented in a protocol, which should contain the following data:

The name of the tested structure;

Lot size and number of controlled structures;

Type and number of the device used;

Numbers of controlled sections of structures and a diagram of their location on the structure;

Design values ​​of the geometric parameters of the reinforcement of the controlled structure;

The results of the tests carried out;

Determination of strength characteristics of reinforcement

3.2.42. The design resistances of undamaged reinforcement are allowed to be taken according to design data or according to the design standards for reinforced concrete structures.

For smooth reinforcement - 225 MPa (class A-I);

For reinforcement with a profile, the ridges of which form a helical line pattern, - 280 MPa (class A-II);

For reinforcement of a periodic profile, the ridges of which form a herringbone pattern, - 355 MPa (class A-III).

Rigid reinforcement made of rolled profiles is taken in calculations with a design resistance equal to 210 MPa.

3.2.43. In the absence of the necessary documentation and information, the class of reinforcing steels is established by testing samples cut from the structure with a comparison of the yield strength, ultimate strength and elongation at break with the data of GOST 380 or approximately by the type of reinforcement, the profile of the reinforcing bar and the construction time of the object.

3.2.44. The location, number and diameter of reinforcing bars are determined either by opening and direct measurements, or by using magnetic or radiographic methods (according to GOST 22904 and GOST 17625, respectively).

3.2.45. To determine the mechanical properties of steel in damaged structures, it is recommended to use the following methods:

Testing of standard samples cut from structural elements in accordance with the instructions of GOST 7564;

Hardness tests of the surface layer of metal in accordance with the instructions of GOST 18661.

3.2.46. It is recommended to cut blanks for samples from damaged elements in places that have not received plastic deformations in case of damage, and so that after cutting, their strength and stability of the structure are ensured.

3.2.47. It is recommended to select blanks for samples in three structural elements of the same type (upper chord, lower chord, first compressed brace, etc.) in the amount of 1-2 pcs. from one element. All blanks must be marked in the places of their taking and the marks are indicated on the diagrams attached to the materials of the inspection of structures.

3.2.48. The characteristics of the mechanical properties of steel - yield strength, ultimate strength and elongation at break - are obtained by tensile testing of specimens in accordance with GOST 1497.

The determination of the main design resistances of steel of structures is made by dividing the average value of the yield point by the material safety factor = 1.05 or the ultimate strength by the safety factor = 1.05. In this case, the calculated resistance is taken to be the smallest of the values, which are found, respectively, by.

When determining the mechanical properties of metal by the hardness of the surface layer, it is recommended to use portable portable devices: Poldi-Hutta, Bauman, VPI-2, VPI-3L, etc.

The data obtained during the hardness test are converted into characteristics of the mechanical properties of the metal according to the empirical formula. So, the relationship between the Brinell hardness and the temporary resistance of the metal is established by the formula

where is the Brinell hardness.

3.2.49. The revealed actual characteristics of the valves are compared with the requirements of SNiP 2.03.01, and on this basis, an assessment of the serviceability of the valves is given.

Determination of concrete strength by laboratory tests

3.2.50. The laboratory determination of the strength of concrete of structures is carried out by testing samples taken from these structures.

Sampling is carried out by cutting out cores with a diameter of 50 to 150 mm in areas where the weakening of the element does not have a significant effect on the bearing capacity of the structures. This method provides the most reliable information about the strength of concrete in existing structures. Its disadvantage is the high labor intensity of work on the selection and processing of samples.

When determining the strength on samples taken from concrete and reinforced concrete structures, one should be guided by the instructions of GOST 28570.

The essence of the method consists in measuring the minimum forces destroying drilled or sawn concrete samples from a structure under static loading with a constant load growth rate.

3.2.51. The shape and nominal dimensions of the samples, depending on the type of concrete testing, must comply with GOST 10180.

3.2.52. Concrete sampling sites should be designated after visual inspection of structures, depending on their stress state, taking into account the minimum possible reduction in their bearing capacity.

It is recommended to take samples from places far from joints and edges of structures. After sampling, the sampling sites should be filled with fine-grained concrete. Areas for drilling or cutting concrete samples should be selected in places free of reinforcement.

3.2.53. To drill out samples from concrete structures, drilling machines of the IE 1806 type are used with a cutting tool in the form of circular diamond drills of the SKA type or carbide end drills and the "Bur Ker" and "Burker A-240" devices.

Sawing machines of the URB-175, URB-300 types with a cutting tool in the form of cutting diamond disks of the AOK type are used to cut samples from concrete structures.

It is allowed to use other equipment and tools that ensure the production of samples that meet the requirements of GOST 10180.

3.2.54. Testing of samples for compression and all types of tension, as well as the choice of the test and loading scheme, are also performed in accordance with GOST 10180.

The supporting surfaces of the samples tested for compression in the case when their deviations from the plane of the press plate are more than 0.1 mm should be corrected by applying a layer of a leveling compound, which should be cement paste, cement-sand mortar or epoxy compositions. The thickness of the layer of the leveling compound on the sample should be no more than 5 mm.

3.2.55. The strength of concrete of the test specimen with an accuracy of 0.1 MPa in compression tests and with an accuracy of 0.01 MPa in tensile tests is calculated by the following formulas:

for compression

axial tension

tensile bending

Sample working section area, mm;

Correspondingly, the width and height of the cross-section of the prism and the distance between the supports when testing the specimens for tensile bending, mm.

To bring the strength of concrete in a tested sample to the strength of concrete in a sample of the base size and form of strength obtained according to the indicated formulas, recalculate according to the formulas:

for compression

axial tension

tensile splitting

tensile bending

where and are the coefficients that take into account the ratio of the height of the cylinder to its diameter, taken during compression tests according to table 3.4, during tensile splitting tests according to table 3.5 and equal to one for specimens of a different shape;

Scale factors, taking into account the shape and dimensions of the cross-section of the tested samples, which are taken according to table 3.6 or determined experimentally according to GOST 10180.

Table 3.4

Table 3.5

Table 3.6

3.2.56. The test report shall consist of a sampling report, the results of the test of the samples and an appropriate reference to the standards against which the test was carried out.

3.2.57. In the presence of wetted areas and surface efflorescence on the concrete of structures, the size of these areas and the reason for their appearance are determined.

3.2.58. The results of visual inspection of reinforced concrete structures are recorded in the form of a map of defects plotted on the schematic plans or sections of the building, or tables of defects are compiled with recommendations for the classification of defects and damage with an assessment of the category of the state of structures.

Determination of the degree of corrosion of concrete and reinforcement

3.2.59. Physicochemical methods are used to determine the degree of corrosion destruction of concrete (degree of carbonization, composition of neoplasms, structural damage to concrete).

The study of the chemical composition of neoplasms that have arisen in concrete under the influence of an aggressive environment is carried out using differential thermal and X-ray structural methods, performed in laboratory conditions on samples taken from operating structures.

The study of structural changes in concrete is carried out using a handheld magnifier. This inspection allows you to examine the surface of the sample, to reveal the presence of large pores, cracks and other defects.

Using the microscopic method, the relative position and nature of the adhesion of the cement stone and aggregate grains are revealed; the state of contact between concrete and reinforcement; shape, size and number of pores; size and direction of cracks.

3.2.60. Determination of the depth of concrete carbonization is carried out by changing the pH value.

If the concrete is dry, the cleavage surface is moistened with clean water, which should be enough so that a visible moisture film does not form on the concrete surface. Remove excess water with clean filter paper. Wet and air-dry concrete does not require moisture.

A 0.1% solution of phenolphthalein in ethyl alcohol is applied to the concrete chip using a dropper or pipette. When the pH changes from 8.3 to 10, the indicator color changes from colorless to bright crimson. A fresh fracture of a concrete sample in the carbonized zone after applying a solution of phenolphthalein to it has a gray color, and in the non-carbonated zone it acquires a bright crimson color.

To determine the depth of concrete carbonization, approximately one minute after the application of the indicator, measure with a ruler with an accuracy of 0.5 mm the distance from the surface of the sample to the border of the brightly colored zone in the direction normal to the surface. In concretes with a uniform pore structure, the boundary of the brightly colored zone is usually parallel to the outer surface.

In concretes with an uneven pore structure, the carbonization boundary can be tortuous. In this case, it is necessary to measure the maximum and average depth of concrete carbonization.

3.2.61. Factors affecting the development of corrosion of concrete and reinforced concrete structures are divided into two groups: those associated with the properties of the external environment (atmospheric and ground water, industrial environment, etc.) and those caused by the properties of materials (cement, aggregates, water, etc.) ) designs.

When assessing the risk of corrosion of concrete and reinforced concrete structures, it is necessary to know the characteristics of concrete: its density, porosity, the number of voids, etc. When examining the technical condition of structures, these characteristics should be in the focus of the inspector's attention.

3.2.62. Corrosion of reinforcement in concrete is caused by the loss of the protective properties of concrete and the access to it of moisture, air oxygen or acid-forming gases.

Corrosion of reinforcement in concrete occurs when the alkalinity of the electrolyte surrounding the reinforcement decreases to pH equal to or less than 12, during carbonization or corrosion of concrete, i.e. reinforcement corrosion in concrete is an electrochemical process.

3.2.63. When assessing the technical condition of fittings and embedded parts affected by corrosion, it is first of all necessary to establish the type of corrosion and areas of damage. After determining the type of corrosion, it is necessary to establish the sources of exposure and the causes of corrosion of the reinforcement.

3.2.64. The thickness of the corrosion products is determined with a micrometer or with the help of instruments that measure the thickness of non-magnetic anticorrosive coatings on steel (for example, ITP-1, etc.).

For rebated reinforcement, the residual reef expression after stripping should be noted.

In places where steel corrosion products are well preserved, it is possible to roughly judge the depth of corrosion by their thickness by the ratio

where is the average depth of continuous uniform corrosion of steel;

Corrosion products thickness.

3.2.65. Revealing the state of reinforcement of elements of reinforced concrete structures is carried out by removing the protective layer of concrete with exposure of the working and assembly reinforcement.

Reinforcement is exposed in the places of its greatest weakening by corrosion, which are revealed by the detachment of the protective concrete layer and the formation of cracks and rusty stains located along the reinforcement rods.

The diameter of the reinforcement is measured with a vernier caliper or micrometer. In places where the reinforcement has undergone intense corrosion, which caused the protective layer to fall off, it is thoroughly cleaned from rust until a metallic sheen appears.

3.2.66. The degree of corrosion of reinforcement is evaluated according to the following criteria: the nature of corrosion, color, density of corrosion products, the area of ​​the affected surface, the cross-sectional area of ​​the reinforcement, the depth of corrosion damage.

With continuous uniform corrosion, the depth of corrosion damage is determined by measuring the thickness of the rust layer, with ulcerative corrosion - by measuring the depth of individual pits. In the first case, a rust film is separated with a sharp knife and its thickness is measured with a caliper. In case of pitting corrosion, it is recommended to cut out pieces of reinforcement, remove rust by etching (immersing the reinforcement in a 10% hydrochloric acid solution containing 1% urotropin inhibitor) followed by rinsing with water.

Then the reinforcement must be immersed for 5 minutes in a saturated solution of sodium nitrate, removed and wiped. The depth of the ulcers is measured with an indicator with a needle attached to a tripod. The depth of corrosion is determined by the indication of the indicator arrow as the difference between the readings at the edge and bottom of the corrosion pit.

3.2.67. When identifying areas of structures with increased corrosive wear associated with local (concentrated) exposure to aggressive factors, it is recommended to first of all pay attention to the following elements and structural units:

Supporting nodes of rafter and rafter trusses, near which the water intake funnels of the internal drainage are located:

The upper belts of the trusses at the nodes for attaching light-aeration lanterns to them, racks of various shields;

The upper belts of the roof trusses, along which the roof valleys are located;

Truss support nodes located inside brick walls;

The tops of the columns that are inside the brick walls.

Research Group "Safety and Reliability"

Construction Expertise, Building Inspection, Energy Audit, Land Survey, Design

It is no secret that in the process of erecting and operating buildings and structures in reinforced concrete structures, unacceptable deflections, cracks, and damage occur. These phenomena can be caused either by deviations from the design requirements in the manufacture and installation of these structures, or by design errors.

Inspection of reinforced concrete structures is designed to assess the physical state of the structure, to establish the causes of damage, to determine the real strength, crack resistance and rigidity of the structure. It is important to correctly assess the bearing capacity of structures and develop recommendations for their further operation. And this is possible only as a result of a detailed field study.

The need for such an examination arises in cases of studying the features of the operation of structures and structures in difficult conditions, during the reconstruction of a building or structure, in the process of conducting an examination, if there are deviations from the project in the structures, and in a number of other cases.

Inspection of reinforced concrete structures consists of several stages. At the initial stage, a preliminary inspection of structures is carried out in order to identify the presence of completely or partially destroyed sections, breaks in reinforcement, damage to concrete, displacement of supports and elements in prefabricated structures.

At the next stage, there is an acquaintance with the design and technical documentation, followed by a direct examination of reinforced concrete structures, which makes it possible to get a real picture of the state of structures and their operation under operating conditions. Depending on the tasks set, concrete strength assessment can be carried out by non-destructive methods, as well as the determination of the actual reinforcement, which consists in collecting data on the real state of the reinforcement, and comparing them with the parameters contained in the working drawings, as well as in a random check of the compliance of the actual reinforcement with the design one.

Since the acting loads can differ significantly from the design ones, the analysis of the stress state of structures is carried out. For this, the actual loads and actions are determined. If necessary, field tests can be a continuation. Upon completion, a construction and technical conclusion is issued.

We work on the following principle:

1 You dial our number and ask important questions for you, and we give comprehensive answers to them.

2 After analyzing your situation, we define a list of questions, the answers to which must be provided by our experts. The contract for the inspection of reinforced concrete structures can be concluded both in our office and immediately at your facility.

3 We will come to you at a convenient time for you and conduct a survey of reinforced concrete structures.

After carrying out the work, using special devices (destructive and non-destructive testing), you will receive a written construction and technical conclusion on your hands, which will reflect all defects, the reasons for their occurrence, a photo report, design calculations, an assessment of restoration repairs, conclusions and recommendations.

The cost of inspection of reinforced concrete structures is from 15,000 rubles.

The terms for receiving the conclusion in your hands are from 3 working days.

4 Many clients need a visit of a specialist without further drawing up an opinion. The construction and technical expert will conduct a survey of reinforced concrete structures, according to the results of which he will give an oral opinion with conclusions and recommendations on the spot. You can decide on the need to draw up a written opinion on the results of the study later.

The cost of the departure of our expert is from 7000 rubles.

5 We have designers and constructors in our company who, on the basis of our opinion, can develop a design for eliminating deficiencies and a design for reinforcing structures.

Assessment of the technical condition of structures based on external features is based on the determination of the following factors:

• - geometric dimensions of structures and their sections;
• - the presence of cracks, spalling and destruction;
• - condition of protective coatings (paints and varnishes, plasters, protective screens, etc.);
• - deflections and deformations of structures;
• - violations of adhesion of reinforcement to concrete;
• - the presence of a rupture of the reinforcement;
• - state of anchoring of longitudinal and transverse reinforcement;
• - the degree of corrosion of concrete and reinforcement.

Determination and assessment of the state of paint and varnish coatings of reinforced concrete structures should be carried out according to the method described in GOST 6992-68. In this case, the following main types of damage are recorded: cracking and delamination, which are characterized by the depth of destruction of the upper layer (to the primer), bubbles and corrosion foci, characterized by the size of the focus (diameter), mm. The area of ​​certain types of damage to the coating is expressed as an approximate percentage in relation to the entire painted surface of the structure (element).

The effectiveness of protective coatings when exposed to an aggressive industrial environment is determined by the state of the concrete of the structures after removing the protective coatings.

During visual examinations an approximate assessment of the strength of concrete is made. In this case, the tapping method can be used. The method is based on tapping the surface of the structure with a hammer weighing 0.4-0.8 kg directly on the cleaned mortar area of ​​concrete or on a chisel installed perpendicular to the surface of the element. In this case, for assessing the strength, the minimum values ​​obtained as a result of at least 10 impacts are taken. A louder tapping sound corresponds to a harder, denser concrete.

In the presence of wetted areas and surface efflorescence on the concrete of structures, the size of these areas and the reason for their appearance are determined.

The results of visual inspection of reinforced concrete structures are recorded in the form of a map of defects plotted on the schematic plans or sections of the building, or tables of defects are compiled with recommendations for the classification of defects and damage with an assessment of the category of the state of structures.

External signs characterizing the state of reinforced concrete structures in four categories of states are given in table.

Assessment of the technical condition of building structures based on external signs of defects and damage

Assessment of the technical condition of reinforced concrete structures by external signs

Notes: 1. To classify a structure as a condition category listed in the table, it is sufficient to have at least one feature characterizing this category. 2. Prestressed reinforced concrete structures with high-strength reinforcement, having signs of category II of condition, belong to category III, and those with signs of category III - respectively to IV or V categories, depending on the danger of collapse. 3. When the bearing area of ​​precast elements is reduced against the requirements of the norms and the project, it is necessary to carry out an approximate calculation of the support element for shear and crush concrete. The calculation takes into account the actual loads and the strength of the concrete. 4. The assignment of the examined structure to one or another category of state in the presence of signs not noted in the table, in difficult and critical cases, should be made on the basis of analysis of the stress-strain state of structures performed by specialized organizations

Determination of concrete strength by mechanical methods

Mechanical methods of non-destructive testing during the inspection of structures are used to determine the strength of concrete of all types of rated strength, controlled in accordance with GOST 18105-86.

Depending on the applied method and devices, indirect strength characteristics are:

• - the value of the rebound of the striker from the concrete surface (or the striker pressed against it);
• - parameter of the shock impulse (impact energy);
• - the dimensions of the indentation on concrete (diameter, depth) or the ratio of the diameters of the indentations on the concrete and the standard specimen upon impact of the indenter or the indentation of the indenter into the concrete surface;
• - the value of the stress required for local destruction of concrete when tearing off a metal disk glued to it, equal to the pull-off force divided by the projection area of ​​the concrete tear-off surface onto the plane of the disc;
• - the value of the effort required to chip a section of concrete on the edge of the structure;
• - the value of the force of local destruction of concrete when the anchor device is pulled out of it.

When conducting tests by mechanical methods of non-destructive testing, one should be guided by the instructions of GOST 22690-88.

Devices of the mechanical principle of operation include: Kashkarov's reference hammer, Schmidt's hammer, Fizdel's hammer, TsNIISK pistol, Poldi's hammer, etc. calibrated blow (TsNIISK pistol).

Fizdel's hammer (Fig. 1) is based on the use of plastic deformation of building materials. When struck with a hammer on the surface of the structure, a hole is formed, according to the diameter of which the strength of the material is estimated. The place of the structure, on which the prints are applied, is pre-cleaned of the plaster layer, grouting or painting. The process of working with Fizdel's hammer is as follows: the right hand is taken by the end of the wooden handle, the elbow is supported on the structure. With an elbow blow of medium strength, 10-12 blows are applied to each section of the structure. The distance between the impact hammer marks must be at least 30 mm. The diameter of the formed hole is measured with a caliper with an accuracy of 0.1 mm in two perpendicular directions and the average value is taken. The largest and smallest results are excluded from the total number of measurements made in this area, and the average value is calculated for the rest. The strength of concrete is determined by the average measured diameter of the indentation and a calibration curve previously constructed on the basis of a comparison of the diameters of the hammer ball imprints and the results of laboratory strength tests of concrete samples taken from the structure according to the instructions of GOST 28570-90 or specially made from the same components and according to the same technologies that the materials of the surveyed structure.

Concrete strength control methods

Method, standards, devices	Test scheme
Ultrasonic GOST 17624-87 Devices: UKB-1, UKB-1M UKB16P, UF-90PC Beton-8-URP, UK-1P
Plastic deformation Devices: KM, PM, DIG-4 Elastic rebound Instruments: KM, Schmidt sclerometer GOST 22690-88
Plastic deformation Kashkarov's hammer GOST 22690-88
Tear off with discs GOST 22690-88 GPNV-6 device
Chipping the rib of the structure GOST 22690-88 GPNS-4 device with URS device
Chipping off GOST 22690-88 Devices: GPNV-5, GPNS-4

Rice. 1. The hammer I.A. Fizdelya:1 - hammer; 2 - a pen; 3 - spherical socket; 4 - ball; 5 - angular scale

Rice. 2. Calibration chart for determining the ultimate strength of concrete in compression with Fizdel's hammer

Rice. 3. Determination of the strength of the material using a hammer K.P. Kashkarov:1 - frame, 2 - metric handle; 3 - rubber handle; 4 - head; 5 - steel ball, 6 - steel reference bar; 7 - angular scale

Rice. 4. Calibration curve for determining the strength of concrete with Kashkarov's hammer

In fig. 2 shows a calibration curve for determining the ultimate strength in compression with a Fizdel hammer.

The method for determining the strength of concrete, based on the properties of plastic deformations, also includes Kashkarov's hammer GOST 22690-88.

A distinctive feature of Kashkarov's hammer (Fig. 3) from Fizdel's hammer is that there is a hole between the metal hammer and the rolled ball, into which a control metal rod is inserted. When struck with a hammer on the surface of the structure, two impressions are obtained: on the surface of the material with a diameter d and on a control (reference) rod with a diameter d NS . The ratio of the diameters of the resulting prints depends on the strength of the material being examined and the reference rod and practically does not depend on the speed and force of the blow applied by the hammer. Average value d/d NS the strength of the material is determined from the calibration schedule (Fig. 4).

At the test site, at least five determinations must be made with the distance between the indentations on the concrete not less than 30 mm, and on the metal rod - not less than 10 mm.

Devices based on the method of elastic rebound include the TsNIISK pistol (Fig. 5), Borovoy's pistol, Schmidt's hammer, KM sclerometer with a rod impactor, etc. The principle of operation of these devices is based on measuring the elastic rebound of the striker at a constant kinetic energy of a metal spring. The cocking and descent of the striker are carried out automatically when the striker touches the test surface. The magnitude of the striker's rebound is fixed by a pointer on the scale of the device.

Rice. 5. Pistol TsNIISK and S.I. Borovoy to determine the strength of concrete by a non-destructive method: 1 - drummer, 2 - frame, 3 - scale, 4 - fixture of the reading of the device, 5 - handle

One of the modern means for determining the compressive strength of concrete by the non-destructive shock-impulse method is the ONIKS-2.2 device, the principle of which consists in fixing the parameters of a short-term electric pulse by the transducer that occurs in the sensitive element when it hits concrete, with its transformation into a strength value. After 8-15 strokes, the average strength value is displayed on the scoreboard. The series of measurements ends automatically after the 15th impact and the average strength value is displayed on the instrument panel.

A distinctive feature of the KM sclerometer is that a special striker of a certain mass, with the help of a spring with a given stiffness and pre-stress, strikes the end of a metal rod called a striker, pressed by the other end to the surface of the concrete being tested. As a result of the impact, the striker bounces off the striker. The degree of rebound is marked on the scale of the device using a special pointer.

The dependence of the rebound value of the striker on the strength of concrete is established according to the data of calibration tests of concrete cubes with a size of 151515 cm, and on this basis a calibration curve is constructed.

The strength of the material of construction is determined according to the indications of the graduated scale of the device at the time of striking the tested element.

The shear strength test is used to determine the strength of concrete in the body of the structure. The essence of the method consists in assessing the strength properties of concrete by the force required for its destruction around a borehole of a certain size when pulling out an expanding cone fixed in it or a special rod embedded in concrete. An indirect indicator of strength is the breakout force required to pull out the anchor device embedded in the body of the structures together with the surrounding concrete at the embedment depth h(fig. 6).

Rice. 6. Scheme of the test by the method of shearing with shearing when using anchor devices

In the shear pull test, the sections shall be located in the zone of lowest stresses caused by the service load or the compression force of the prestressed reinforcement.

The strength of concrete on the site is allowed to be determined based on the results of one test. Test areas should be selected so that reinforcement does not fall into the tear-out zone. At the test site, the thickness of the structure should be at least twice the embedment depth of the anchor. When punching a hole with a bolt or drilling, the thickness of the structure in this place must be at least 150 mm. The distance from the anchor device to the edge of the structure must be at least 150 mm, and from the adjacent anchor device - at least 250 mm.

Three types of anchor devices are used during the tests (Fig. 7). Type I anchoring devices are installed on structures during concreting; anchor devices of types II and III are installed in previously prepared boreholes, punched in concrete by drilling. Recommended hole depth: for type II anchor - 30 mm; for anchor type III - 35 mm. The diameter of the borehole in concrete should not exceed the maximum diameter of the recessed part of the anchor device by more than 2 mm. Sealing of anchor devices in structures should ensure reliable adhesion of the anchor to concrete. The load on the anchor device should increase smoothly at a rate of no more than 1.5-3 kN / s until it breaks out together with the surrounding concrete.

Rice. 7. Types of anchor devices:1 - working rod; 2 - working rod with expanding cone; 3 - working rod with a full expansion cone; 4 - support rod, 5 - segmented grooved cheeks

The smallest and largest dimensions of the torn out part of concrete, equal to the distance from the anchor device to the boundaries of destruction on the surface of the structure, should not differ from one another by more than two times.

When determining the class of concrete by the method of chipping the rib of the structure, a device of the GPNS-4 type is used (Fig. 8). The test scheme is shown in Fig. nine.

Loading parameters should be taken: a= 20 mm; b= 30 mm, = 18.

At the test site, at least two concrete spalls must be carried out. The thickness of the test structure must be at least 50 mm. The distance between adjacent chips must be at least 200 mm. The load hook must be installed in such a way that the value "a" does not differ from the nominal by more than 1 mm. The load on the tested structure should grow smoothly at a rate of no more than (1 ± 0.3) kN / s until the concrete is chipped off. In this case, there should be no slippage of the load hook. The test results, in which the reinforcement was exposed at the site of the spall, and the actual spalling depth differed from the specified one by more than 2 mm, are not taken into account.

Rice. 8. Device for determining the strength of concrete by spalling ribs:1 - the structure under test, 2 - chipped concrete, 3 - URS device, 4 - device GPNS-4

Rice. 9. Scheme of testing concrete in structures by shearing the rib of the structure

Single value R i the strength of concrete at the test site is determined depending on the compressive stresses of concrete b and values R i 0 .

Compressive stresses in concrete b acting during the test period are determined by the calculation of the structure, taking into account the actual dimensions of the sections and the values ​​of the loads.

Single value R i 0 concrete strength on the site under the assumption b= 0 is determined by the formula

where T g- a correction factor that takes into account the aggregate size, taken equal to: with a maximum aggregate size of 20 mm or less - 1, with a size of more than 20 to 40 mm - 1.1;

R iy- the conditional strength of concrete, determined according to the graph (Fig. 10) by the average value of the indirect indicator R

P i- the effort of each of the shears performed at the test site.

When testing by spalling ribs, there should be no cracks, concrete chips, sagging or cavities with a height (depth) of more than 5 mm in the test area. 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.

Rice. 10. Dependence of the conditional concrete strength Riy on the cleavage force Pi

Ultrasonic method for determining the strength of concrete. The principle of determining the strength of concrete by the ultrasonic method is based on the presence of a functional relationship between the speed of propagation of ultrasonic vibrations and the strength of concrete.

The ultrasonic method is used to determine the compressive strength of concrete of classes B7.5 - B35 (grades M100-M400).

The strength of concrete in structures is determined experimentally according to the established calibration dependences of the "velocity of propagation of ultrasound - strength of concrete V=f (R)"Or" ultrasound propagation time t- concrete strength t=f (R)". The degree of accuracy of the method depends on the accuracy of the calibration schedule.

The calibration schedule is based on the sounding data and strength tests of control cubes made from concrete of the same composition, using the same technology, with the same hardening mode as the products or structures to be tested. When constructing a calibration schedule, one should be guided by the instructions of GOST 17624-87.

To determine the strength of concrete by the ultrasonic method, instruments are used: UKB-1, UKB-1M, UK-16P, "Beton-22", etc.

Ultrasonic measurements in concrete are carried out by means of through or surface sounding. The concrete test scheme is shown in Fig. eleven.

Rice. 11. Methods of ultrasonic sounding of concrete:a- test scheme by the through sounding method; b- the same, superficial sounding; UP- ultrasonic transducers

When measuring the propagation time of ultrasound by the through sounding method, ultrasonic transducers are installed on opposite sides of the sample or structure.

Ultrasound speed V, m / s, calculated by the formula

where t- ultrasound propagation time, μs;

l- distance between the centers of the installation of transducers (sounding base), mm.

When measuring the propagation time of ultrasound by the surface sounding method, ultrasonic transducers are installed on one side of the sample or structure according to the scheme.

The number of measurements of the propagation time of ultrasound in each sample should be: with through sounding - 3, with surface sounding - 4.

The deviation of a separate measurement result of the ultrasound propagation time in each sample from the arithmetic mean of the measurement results for this sample should not exceed 2%.

The measurement of the propagation time of ultrasound and the determination of the strength of concrete are carried out in accordance with the instructions of the passport (technical conditions for use) of this type of device and the instructions of GOST 17624-87.

In practice, there are often cases when it becomes necessary to determine the concrete strength of the structures in operation in the absence or impossibility of constructing a calibration table. In this case, the determination of the strength of concrete is carried out in the zones of structures made of concrete on one type of coarse aggregate (structures of one batch). Ultrasound propagation speed V are determined in at least 10 sections of the surveyed area of ​​structures, according to which the average value is determined V. Next, the areas are marked in which the ultrasound propagation speed has the maximum V max and minimum V min values, as well as the section where the speed has a value V n closest to the value V, and then drilled from each target area at least two cores, which determine the strength values ​​in these areas: R max, R min, R n respectively. Concrete strength R H determined by the formula

R max / 100. (5)

Odds a 1 and a 0 is calculated by the formulas

When determining the strength of concrete from samples taken from the structure, one should be guided by the instructions of GOST 28570-90.

When the 10% condition is met, it is allowed to roughly determine the strength: for concretes of strength classes up to B25 according to the formula

where A- coefficient determined by testing at least three cores cut from structures.

For concretes of strength classes above B25, the strength of concrete in operating structures can also be assessed by a comparative method, taking as a basis the characteristics of the structure with the highest strength. In this case

Structures such as beams, girders, columns should be sounded in the transverse direction, the slab - according to the smallest size (width or thickness), and the ribbed slab - along the thickness of the rib.

With careful testing, this method provides the most reliable information about the strength of concrete in existing structures. Its disadvantage is the large laboriousness of work on the selection and testing of samples.

Determination of concrete cover and reinforcement location

To determine the thickness of the protective layer of concrete and the location of reinforcement in a reinforced concrete structure, magnetic, electromagnetic methods according to GOST 22904-93 or methods of transillumination and ionizing radiation according to GOST 17623-87 are used during inspections with selective control verification of the results obtained by punching furrows and direct measurements.

Radiation methods, as a rule, are used to examine the condition and control the quality of prefabricated and monolithic reinforced concrete structures during the construction, operation and reconstruction of especially critical buildings and structures.

The radiation method is based on transillumination of controlled structures with ionizing radiation and at the same time obtaining information about its internal structure using a radiation converter. Transillumination of reinforced concrete structures is carried out using radiation from X-ray machines, radiation from sealed radioactive sources.

Transportation, storage, installation and adjustment of radiation equipment is carried out only by specialized organizations that have a special permit to carry out these works.

The magnetic method is based on the interaction of the magnetic or electromagnetic field of the device with the steel reinforcement of a reinforced concrete structure. anchor construction concrete reinforcement

The thickness of the concrete cover and the location of the reinforcement in the reinforced concrete structure are determined on the basis of the experimentally established relationship between the readings of the device and the specified controlled parameters of the structures.

To determine the thickness of the protective layer of concrete and the location of reinforcement from modern devices, in particular, ISM, IZS-10N (TU25-06.18-85.79) are used. The IZS-10N device measures the thickness of the concrete cover depending on the reinforcement diameter within the following limits:

• - when the diameter of the reinforcement rods is from 4 to 10 mm, the thickness of the protective layer is from 5 to 30 mm;
• - with a diameter of reinforcement rods from 12 to 32 mm, the thickness of the protective layer is from 10 to 60 mm.

The device provides determination of the location of the projections of the axes of the reinforcement bars onto the concrete surface:

• - with diameters from 12 to 32 mm - with a concrete cover not more than 60 mm thick;
• - with diameters from 4 to 12 mm - with a concrete cover not more than 30 mm thick.

When the distance between the reinforcement rods is less than 60 mm, the use of devices of the IZS type is impractical.

Determination of the concrete cover thickness and reinforcement diameter is carried out in the following order:

• - before testing, the technical characteristics of the device used are compared with the corresponding design (expected) values ​​of the geometric parameters of the reinforcement of the controlled reinforced concrete structure;
• - if the technical characteristics of the device do not correspond to the parameters of the reinforcement of the controlled structure, it is necessary to establish an individual calibration dependence in accordance with GOST 22904-93.

The number and location of the controlled sections of the structure are assigned depending on:

• - the purpose and conditions of the tests;
• - features of the design solution of the structure;
• - technology of manufacturing or erection of a structure, taking into account the fixation of reinforcing bars;
• - operating conditions of the structure, taking into account the aggressiveness of the external environment.

Work with the device should be carried out in accordance with the instructions for its operation. At the measurement points on the surface of the structure, there should be no sagging with a height of more than 3 mm.

When the thickness of the protective layer of concrete is less than the measurement limit of the device used, the tests are carried out through a gasket with a thickness of (10 ± 0.1) mm made of a material that does not have magnetic properties.

The actual concrete cover in this case is determined as the difference between the measurement results and the thickness of this pad.

When monitoring the location of steel reinforcement in the concrete of a structure, for which there is no data on the diameter of the reinforcement and the depth of its location, determine the layout of the reinforcement and measure its diameter by opening the structure.

For an approximate determination of the diameter of the reinforcing bar, the location of the reinforcement is determined and fixed on the surface of the reinforced concrete structure using an IZS-10N device.

The device transducer is installed on the surface of the structure, and several values ​​of the concrete cover thickness are determined using the device scales or an individual calibration dependence. pr for each of the estimated reinforcing bar diameters that could be used to reinforce this structure.

A spacer of appropriate thickness (for example, 10 mm) is installed between the instrument transducer and the concrete surface of the structure, measurements are taken again and the distance is determined for each assumed diameter of the reinforcing bar.

For each diameter of the reinforcing bar, the values ​​are compared pr and ( abs - e).

As actual diameter d take a value for which the condition is satisfied

[ pr -(abs - e)] min, (10)

where abs- indication of the device, taking into account the thickness of the gasket.

The indices in the formula indicate:

s- pitch of longitudinal reinforcement;

R- pitch of transverse reinforcement;

e- the presence of a gasket;

e- the thickness of the gasket.

The measurement results are recorded in a journal, the form of which is shown in the table.

The actual values ​​of the concrete cover thickness and the location of the steel reinforcement in the structure according to the measurement results are compared with the values ​​established by the technical documentation for these structures.

The measurement results are documented in a protocol, which should contain the following data:

• - the name of the tested structure (its symbol);
• - batch size and number of controlled structures;
• - type and number of the device used;
• - numbers of controlled sections of structures and a diagram of their location on the structure;
• - design values ​​of the geometric parameters of the reinforcement of the controlled structure;
• - the results of the tests carried out;
• - reference to the instructive and normative document regulating the test method.

Form of recording the results of measuring the thickness of the protective layer of concrete of reinforced concrete structures

Determination of strength characteristics of reinforcement

The design resistances of undamaged reinforcement are allowed to be taken according to design data or according to the design standards for reinforced concrete structures.

• - for smooth reinforcement - 225 MPa (class A-I);
• - for reinforcement with a profile, the ridges of which form a helical line pattern - 280 MPa (class A-II);
• - for reinforcement of a periodic profile, the ridges of which form a herringbone pattern - 355 MPa (class A-III).

Rigid reinforcement made of rolled profiles is taken in calculations with a design tensile, compression and bending strength of 210 MPa.

In the absence of the necessary documentation and information, the class of reinforcing steels is established by testing samples cut from the structure with a comparison of the yield strength, ultimate strength and elongation at break with the data of GOST 380-94.

The location, number and diameter of reinforcing bars are determined either by opening and direct measurements, or by using magnetic or radiographic methods (according to GOST 22904-93 and GOST 17625-83, respectively).

To determine the mechanical properties of steel in damaged structures, it is recommended to use the following methods:

• - testing of standard samples cut from structural elements in accordance with the instructions of GOST 7564-73 *;
• - tests of the surface layer of metal for hardness in accordance with the instructions of GOST 18835-73, GOST 9012-59 * and GOST 9013-59 *.

It is recommended to cut blanks for samples from damaged elements in places that have not received plastic deformations during damage, and so that after cutting, their strength and stability are ensured.

When selecting blanks for samples, structural elements are divided into conditional batches of 10-15 structural elements of the same type: trusses, beams, columns, etc.

All blanks must be marked in the places of their taking and the marks are indicated on the diagrams attached to the materials of the inspection of structures.

The characteristics of the mechanical properties of steel - yield strength t, ultimate strength and elongation at break - are obtained by tensile testing of specimens in accordance with GOST 1497-84 *.

The determination of the main design resistances of steel structures is made by dividing the average value of the yield point by the material safety factor m = 1.05 or the ultimate strength by the safety factor = 1.05. In this case, the calculated resistance is taken to be the smallest of the values R T, R, which are found, respectively, by m and.

When determining the mechanical properties of metal by the hardness of the surface layer, it is recommended to use portable portable devices: Poldi-Hutta, Bauman, VPI-2, VPI-Zk, etc.

The data obtained during the hardness test are converted into characteristics of the mechanical properties of the metal according to the empirical formula. So, the relationship between the Brinell hardness and the temporary resistance of the metal is established by the formula

3,5H b ,

where H- Brinell hardness.

The revealed actual characteristics of the reinforcement are compared with the requirements of SNiP 2.03.01-84 * and SNiP 2.03.04-84 *, and on this basis the serviceability of the reinforcement is assessed.

Determination of concrete strength by laboratory tests

The laboratory determination of the concrete strength of existing structures is carried out by testing samples taken from these structures.

Sampling is carried out by cutting out cores with a diameter of 50 to 150 mm in areas where the weakening of the element does not have a significant effect on the bearing capacity of the structures. This method provides the most reliable information about the strength of concrete in existing structures. Its disadvantage is the high labor intensity of work on the selection and processing of samples.

When determining the strength on samples taken from concrete and reinforced concrete structures, one should be guided by the instructions of GOST 28570-90.

The essence of the method consists in measuring the minimum forces destroying drilled or sawn concrete samples from a structure under static loading with a constant load growth rate.

The shape and nominal dimensions of the samples, depending on the type of concrete testing, must comply with GOST 10180-90.

It is allowed to use cylinders with a diameter of 44 to 150 mm, a height of 0.8 to 2 diameters when determining the compressive strength, from 0.4 to 2 diameters when determining the tensile strength when splitting, and from 1.0 to 4 diameters when determining the strength when axial tension.

For all types of tests, a sample with a working section size of 150-150 mm is taken as the basic one.

Concrete sampling sites should be designated after visual inspection of structures, depending on their stress state, taking into account the minimum possible reduction in their bearing capacity. It is recommended to take samples from places far from joints and edges of structures.

After sampling, the sampling sites should be sealed with fine-grained concrete or concrete from which the structures are made.

Areas for drilling or cutting concrete samples should be selected in places free of reinforcement.

To drill out samples from concrete structures, drilling machines of the IE 1806 type according to TU 22-5774 are used with a cutting tool in the form of circular diamond drills of the SKA type according to TU 2-037-624, GOST 24638-85 * E or carbide end drills according to GOST 11108-70 ...

To cut samples from concrete structures, sawing machines of the URB-175 type according to TU 34-13-10500 or URB-300 according to TU 34-13-10910 are used with a cutting tool in the form of cutting diamond disks of the AOK type according to GOST 10110-87E or TU 2- 037-415.

It is allowed to use other equipment and tools for making samples of concrete structures, ensuring the production of samples that meet the requirements of GOST 10180-90.

Testing of samples for compression and all types of tension, as well as the choice of test and loading scheme is performed in accordance with GOST 10180-90.

The supporting surfaces of the samples tested for compression, in the case when their deviations from the surface of the press plate are more than 0.1 mm, must be corrected by applying a layer of a leveling compound. As typical, cement paste, cement-sand mortar or epoxy compositions should be used.

The thickness of the layer of the leveling compound on the sample should be no more than 5 mm.

The strength of concrete of the test specimen with an accuracy of 0.1 MPa in compression tests and with an accuracy of 0.01 MPa in tensile tests is calculated by the following formulas:

for compression;

axial tension;

tensile bending,

A- the area of ​​the working section of the sample, mm 2;

a, b, l- respectively, the width and height of the cross-section of the prism and the distance between the supports when testing specimens for tensile bending, mm.

To bring the strength of concrete in a tested sample to the strength of concrete in a sample of the base size and form of strength, obtained according to the indicated formulas, are recalculated according to the formulas:

for compression;

axial tension;

tensile splitting;

tensile bending,

where 1, and 2 are coefficients that take into account the ratio of the height of the cylinder to its diameter, taken during compression tests according to the table, during tensile splitting tests according to table. and equal to one for samples of a different shape;

Scale factors that take into account the shape and dimensions of the cross-section of the tested samples are determined experimentally in accordance with GOST 10180-90.

The test report shall consist of a sampling report, the results of the test of the samples and an appropriate reference to the standards against which the test was carried out.