Inspection of reinforced concrete structures of the building. Inspection of concrete and reinforced concrete structures. Processing of survey results

Inspection of concrete and iron concrete structures- an important part of the inspection of a building or structure as a whole.

In this article we reveal an approach to the inspection of concrete and reinforced concrete structures. The longevity of the building’s operation depends on the qualified performance of this part of the building inspection.

Inspections of concrete and reinforced concrete structures of a building are carried out both as part of regular inspections during operation, and before the addition or reconstruction of a building, before purchasing a building, or when structural defects are identified.

Correct assessment of the condition of concrete and reinforced concrete structures allows us to reliably assess their load-bearing capacity, which will ensure further safe operation or superstructure/extension.

Evaluation technical condition concrete and reinforced concrete structures according to external characteristics are carried out on the basis of:

determining the geometric dimensions of structures and their sections; This data is necessary for verification calculations. For experienced specialist, sometimes, it is enough to visually assess the clearly insufficient dimensions of the structure.
comparison of actual dimensions of structures with design dimensions; The actual dimensions of the structures play a very important role, because dimensions are directly related to load-bearing capacity calculations. One of the tasks of designers is to optimize dimensions in order to avoid overspending building materials, and, accordingly, increased construction costs. The myth that designers include multiple safety margins in their calculations is actually a myth. Reliability and safety factors are of course present in the calculations, but they are in accordance with SNiP for design 1.1-1.15-1.3. those. not so much.
compliance of the actual static diagram of the operation of structures adopted in the calculation; The actual diagram of the loads of structures is also very important, because If the design dimensions are not observed, due to construction defects, additional loads and bending moments may occur in structures and assemblies, which sharply reduces the load-bearing capacity of structures.
the presence of cracks, spalls and destruction; The presence of cracks, spalls and destruction is an indicator of unsatisfactory performance of structures, or indicates poor quality of construction work.
location, nature of cracks and width of their opening; Based on the location of the cracks, their nature and the width of their opening, a specialist can determine the probable cause of their occurrence. Some types of cracks are allowed by SNiP in reinforced concrete structures, others may indicate a decrease in the load-bearing capacity of the building structure.
state protective coatings; Protective coatings are so called because they must protect building structures from adverse and aggressive influences. external factors. Violation of protective coatings, of course, will not lead to instant destruction of the building structure, but will affect its durability.
deflections and deformations of structures; The presence of deflections and deformations can give a specialist the opportunity to assess the performance of a building structure. Some bearing capacity calculations building structures are carried out according to the maximum permissible deflections.
signs of impaired adhesion of reinforcement to concrete; The adhesion of reinforcement to concrete is very important, because concrete does not work in bending, but only in compression. Bending work in reinforced concrete structures is provided by reinforcement, which can be prestressed. The lack of adhesion between reinforcement and concrete indicates that the flexural load-bearing capacity of the reinforced concrete structure has decreased.
presence of reinforcement rupture; Reinforcement ruptures indicate a decrease in load-bearing capacity up to the category of emergency condition.
anchorage conditions of longitudinal and transverse reinforcement; Anchoring of longitudinal and transverse reinforcement ensures the correct operation of the reinforced concrete building structure. Violation of anchorage can lead to an emergency condition.
degree of corrosion of concrete and reinforcement. Corrosion of concrete and reinforcement reduces the load-bearing capacity of a reinforced concrete structure, because the thickness of concrete and the diameter of reinforcement decrease due to corrosion. The thickness of concrete and the diameter of the reinforcement are one of the important quantities in calculating the load-bearing capacity of a reinforced concrete structure.

The size (width) of the opening of cracks in concrete is measured in areas of their greatest opening and at the level of the reinforcement of the tensile zone of the element, because this gives the most complete idea of the performance of the building structure.

The degree of crack opening is determined in accordance with SNiP 52-01-2003.

Cracks in concrete are analyzed from the point of view of structural features and the stress-strain state of the reinforced concrete structure. Sometimes cracks appear due to violations of manufacturing, storage and transportation technology.

Therefore, the task of a specialist (expert) is to determine probable cause the occurrence of cracks and assessment of the influence of these cracks on the load-bearing capacity of the building structure.

During the inspection of concrete and reinforced concrete structures, specialists determine the strength of concrete. For this purpose methods are used non-destructive testing or conduct laboratory tests and are guided by the requirements of GOST 22690, GOST 17624, SP 13-102-2003. When conducting an inspection, we use several non-destructive testing devices (impulse-impulse method IPS-MG4, ONICS; ultrasonic method UZK MG4.S; tear-off device with chipping POS, and also, if necessary, we use a “Kashkarov hammer”). We give a conclusion about the actual strength characteristics based on the readings of at least two instruments. We also have the opportunity to conduct research on selected samples in the laboratory.

Assessment of the technical condition of structures based on external signs is based on determining the following factors:

geometric dimensions of structures and their sections;
the presence of cracks, spalls and destruction;
condition of protective coatings (paint and varnish, plasters, protective screens, etc.);
deflections and deformations of structures;
violation of the adhesion of reinforcement to concrete;
presence of reinforcement rupture;
anchorage conditions of longitudinal and transverse reinforcement;
degree of corrosion of concrete and reinforcement.

When determining geometric parameters structures and their sections, all deviations from their design position are recorded. Determination of the width and depth of crack opening should be carried out according to the recommendations indicated above.

It is recommended to measure the crack opening width primarily in places of maximum crack opening and at the level of the tensile zone of the element. The degree of crack opening is compared with regulatory requirements according to limit states of the second group, depending on the type and operating conditions of structures. It is necessary to distinguish between cracks, the appearance of which is caused by stresses manifested in reinforced concrete structures during manufacturing, transportation and installation, and cracks caused by operational loads and environmental influences.

Cracks that appeared during the period before the operation of the facility include: technological, shrinkage, caused by rapid drying of the surface layer of concrete and reduction in volume, as well as cracks from concrete swelling; caused by uneven cooling of concrete; cracks that appeared in prefabricated reinforced concrete elements during storage, transportation and installation, in which the structures were subjected to force effects from their own weight according to schemes not provided for by the design.

Cracks that appeared during the operational period include: cracks that arose as a result of temperature deformations due to violations of the device requirements expansion joints; caused by uneven sedimentation of the pound base, which may be due to violation of the requirements of the sedimentary structure expansion joints, carrying out earthworks in close proximity to foundations without security special measures; caused by force impacts exceeding the load-bearing capacity of reinforced concrete elements.

Force-type cracks must be considered from the point of view of the stress-strain state of the reinforced concrete structure.

The most common types of cracks in reinforced concrete structures are:

a) in bending elements operating according to a beam scheme (beams, purlins), cracks appear, perpendicular (normal) to the longitudinal axis, due to the appearance of tensile stresses in the zone of action of maximum bending moments, inclined to the longitudinal axis, caused by the main tensile stresses in the zone of action of shearing forces and bending moments (Fig. 2.32).

Rice. 2.32.

working according to the beam scheme

1 - normal cracks in the zone of maximum bending moment;
2 - inclined cracks in the zone of maximum transverse force;
3 - cracks and crushing of concrete in the compressed zone.

Normal cracks have a maximum opening width in the outermost tensile fibers of the element's cross-section. Oblique cracks begin to open in the middle part of the side faces of the element - in the zone of maximum tangential stresses, and then develop towards the stretched face.

The formation of inclined cracks at the supporting ends of beams and girders is due to their insufficient load-bearing capacity along inclined sections.

Vertical and inclined cracks in the spans of beams and girders indicate their insufficient bearing capacity in terms of bending moment.

The crushing of concrete in the compressed zone of sections of bending elements indicates the exhaustion of the bearing capacity of the structure;

b) cracks may occur in the slabs:

in the middle part of the slab, having a direction across the working span with maximum opening on the lower surface of the slab;

on supporting sections, directed across the working span with maximum opening on the upper surface of the slab;

radial and end, with possible loss of the protective layer and destruction of the concrete slab;

along the reinforcement along the lower plane of the wall.

Cracks in the supporting sections of the slabs across the working span indicate insufficient bearing capacity for bending support moment.

Characteristic is the development of cracks of force origin on the lower surface of slabs with different aspect ratios (Fig. 2.33). In this case, the concrete of the compressed zone may not be damaged. Collapse of concrete in a compressed area indicates danger complete destruction slabs;

Rice. 2.33. Characteristic cracks on the lower surface of the slabs: a - working according to the beam scheme at / 2 //, > 3; b - supported along the contour at / 2 //, 1.5

c) vertical cracks form on the edges of the columns and horizontal cracks in the columns.

Vertical cracks on the edges of columns can appear as a result of excessive bending of reinforcement bars. This phenomenon can occur in those columns and their areas where clamps are rarely installed (Fig. 2.34).

Rice. 2.34.

Horizontal cracks in reinforced concrete columns do not pose an immediate danger if their width is small, however, through such cracks, humidified air and aggressive reagents can enter the reinforcement, causing corrosion of the metal,

The appearance of longitudinal cracks along the reinforcement in compressed elements indicates destruction associated with loss of stability (buckling) of longitudinal compressed reinforcement due to an insufficient amount of transverse reinforcement;

d) the appearance in bending elements of a transverse crack, perpendicular to the longitudinal axis of the element, passing through the entire section (Fig. 2.35) may be associated with the influence of an additional bending moment in horizontal plane, perpendicular to the plane of action of the main bending moment (for example, from horizontal forces arising in crane beams). Cracks in tensile reinforced concrete elements have the same nature, but the cracks are visible on all faces of the element and encircle it;
e) cracks in supporting areas and ends of reinforced concrete structures.

Detected cracks at the ends of prestressed elements, oriented along the reinforcement, indicate a violation of the anchorage of the reinforcement. This is also evidenced by inclined cracks in the support areas, crossing the area where prestressed reinforcement is located and extending to the lower edge of the support edge (Fig. 2.36);

f) lattice elements of braced reinforced concrete trusses can experience compression, tension, and in support nodes - action

cutting forces. Typical damage

Rice. 2.36.

1 - in case of violation of the anchorage of stressed reinforcement;
2 - at

insufficiency

indirect

reinforcement

Rice. 2.35.

planes

The dynamics during the destruction of individual sections of such trusses are shown in Fig. 2.37. In addition to cracks, 2 (Fig. 2.38) damage of types 1, 2, 4 may occur in the support unit. The appearance of horizontal cracks in the lower prestressed belt of type 4 (see Fig. 2.37) indicates the absence or insufficiency of transverse reinforcement in the compressed concrete. Normal (perpendicular to the longitudinal axis) cracks of type 5 appear in tensile rods when the crack resistance of the elements is not ensured. The appearance of damage in the form of type 2 flanges indicates the exhaustion of the concrete strength in certain areas of the compressed belt or on the support.

Rice. 2.37.

pre-stressed belt:

1 - inclined crack at the support unit; 2 - spalling of flanges; 3 - radial and vertical cracks; 4 - horizontal crack; 5 - vertical (normal) cracks in tensile elements; 6 - inclined cracks in the compressed chord of the truss; 7 - cracks in the lower chord assembly

Defects in the form of cracks and concrete spalling along the reinforcement of reinforced concrete elements can also be caused by corrosion destruction of the reinforcement. In these cases, the adhesion of the longitudinal and transverse reinforcement to the concrete is disrupted. Loss of adhesion between reinforcement and concrete due to corrosion can be

Rice. 2.38.

install by tapping the concrete surface (voids can be heard).

Longitudinal cracks along the reinforcement with disruption of its adhesion to concrete can also be caused by temperature stresses during the operation of structures with systematic heating above 300°C or the consequences of a fire.

In bending elements, as a rule, an increase in deflections and rotation angles leads to the appearance of cracks. Deflections of bending elements of more than 1/50 of the span with a crack opening width in the tensile zone of more than 0.5 mm can be considered unacceptable (emergency). Limit values permissible deflections for reinforced concrete structures are given in table. 2.10.

Determination and assessment of the condition of coatings of reinforced concrete structures should be carried out according to the methodology set out in GOST 6992-68. In this case, the following main types of damage are recorded: cracking and peeling, which are characterized by the depth of destruction of the top layer (before the primer), bubbles and corrosion foci, characterized by the size of the foci (diameter), mm. The area of individual types of coating damage is expressed approximately as a percentage relative to the entire painted surface of the structure (element).

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

During visual inspections, an approximate assessment of the strength of concrete is made. The method is based on tapping the surface of the structure with a hammer weighing 0.4-0.8 kg directly on a cleaned mortar area of concrete or on a chisel installed perpendicular to the surface of the element. A louder sound when tapped corresponds to stronger and denser concrete. To obtain reliable data on the strength of concrete, the methods and instruments given in the section on strength control should be used.

If there are wet 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 a visual inspection of reinforced concrete structures are recorded in the form of a map of defects plotted on schematic plans or sections of the building, or tables of defects are drawn up with recommendations for classification.

VALUE OF MAXIMUM ALLOWABLE DEFLECTIONS OF REINFORCED CONCRETE

CONSTRUCTIONS

Table 2.10

Note. Under constant, long-term and short-term loads, the deflection of beams and slabs should not exceed 1/150 of the span and I/75 of the cantilever overhang.

cation of defects and damage with assessment of the category of condition of structures.

To assess the nature of the corrosion process and the degree of exposure to aggressive environments, three main types of concrete corrosion are distinguished.

Type I includes all corrosion processes that occur in concrete under the action of liquid media (aqueous solutions) capable of dissolving the components of cement stone. The constituents of the cement stone are dissolved and removed from the cement stone.

Type II corrosion includes processes in which chemical interactions - exchange reactions - occur between the cement stone and the solution, including the exchange of cations. The resulting reaction products are either easily soluble and removed from the structure as a result of diffusion or filtration flow, or are deposited in the form of an amorphous mass that does not have astringent properties and does not affect the further destructive process.

This type of corrosion is represented by processes that occur when solutions of acids and certain salts act on concrete.

Type III corrosion includes all those concrete corrosion processes, as a result of which reaction products accumulate and crystallize in the pores and capillaries of concrete. At a certain stage of development of these processes, the growth of crystal formations causes the occurrence of increasing stresses and deformations in the enclosing walls, and then leads to destruction of the structure. This type may include corrosion processes under the action of sulfates associated with the accumulation and growth of crystals of hydrosulfoaluminate, gypsum, etc. The destruction of concrete in structures during their operation occurs under the influence of many chemical and physical-mechanical factors. These include heterogeneity of concrete, increased stress in the material of various origins, leading to micro-tears in the material, alternating wetting and drying, periodic freezing and thawing, sudden temperature changes, exposure to salts and acids, leaching, disruption of contacts between cement stone and aggregates, corrosion steel reinforcement, destruction of aggregates under the influence of cement alkalis.

The complexity of studying the processes and factors causing the destruction of concrete and reinforced concrete is explained by the fact that, depending on the operating conditions and service life of structures, many factors simultaneously act, leading to changes in the structure and properties of materials. For most structures in contact with air, carbonization is a characteristic process that weakens the protective properties of concrete. Carbonation of concrete can be caused not only by carbon dioxide in the air, but also by other acidic gases contained in the industrial atmosphere. During the carbonization process, carbon dioxide from the air penetrates into the pores and capillaries of concrete, dissolves in the pore fluid and reacts with calcium oxide hydroaluminate, forming slightly soluble calcium carbonate. Carbonation reduces the alkalinity of the moisture contained in concrete, which leads to a decrease in the so-called passivating (protective) effect alkaline media and corrosion of reinforcement in concrete.

To determine the degree of corrosion destruction of concrete (degree of carbonization, composition of new formations, structural damage to concrete), physicochemical methods are used.

The study of the chemical composition of new formations that have arisen in concrete under the influence of an aggressive environment is carried out using differential thermal and x-ray structural methods, carried out in laboratory conditions on samples taken from operating structures. The study of structural changes in concrete is carried out using a hand-held magnifying glass, which gives a slight magnification. Such an inspection allows you to examine the surface of the sample, identify the presence of large pores, cracks and other defects.

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

The depth of carbonation of concrete is determined by changes in the pH value.

If the concrete is dry, wet the chipped surface clean water, which should be enough so that a visible film of moisture does not form on the surface of the concrete. Excess water is removed 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 pH changes from 8.3 to 14, the color of the indicator changes from colorless to bright crimson. A fresh fracture of a concrete sample in the carbonized zone after applying a phenolphthalein solution to it has a gray color, and in the non-carbonized zone it acquires a bright crimson color.

Approximately a minute after applying 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. The measured value is the depth of carbonation of the concrete. In concretes with a uniform pore structure, the border of the brightly colored zone is usually located parallel outer surface. In concretes with an uneven pore structure, the carbonization boundary may be tortuous. In this case, it is necessary to measure the maximum and average depth of carbonation of concrete. Factors influencing the development of corrosion of concrete and reinforced concrete structures are divided into two groups: those related to the properties external environment- atmospheric and groundwater, industrial environment, etc., and due to the properties of materials (cement, aggregates, water, etc.) of structures.

For operating structures it is difficult to determine how many and what chemical elements remained in the surface layer, and whether they are able to continue their destructive action. When assessing the danger of corrosion of concrete and reinforced concrete structures, it is necessary to know the characteristics of concrete: its density, porosity, number of voids, etc.

The corrosion processes of reinforced concrete structures and methods of protection against it are complex and varied. The destruction of reinforcement in concrete is caused by the loss of protective properties concrete and access to moisture, air oxygen or acid-forming gases. Corrosion of reinforcement in concrete is an electrochemical process. Since reinforcing steel is heterogeneous in structure, as is the medium in contact with it, all conditions are created for the occurrence of electrochemical corrosion.

Corrosion of reinforcement in concrete occurs when the alkalinity of the electrolyte surrounding the reinforcement decreases to a pH equal to or less than 12, due to carbonization or corrosion of concrete.

When assessing the technical condition of reinforcement and embedded parts affected by corrosion, it is first necessary to establish the type of corrosion and the affected areas. After determining the type of corrosion, it is necessary to establish the sources of influence and the causes of corrosion of the reinforcement. The thickness of corrosion products is determined with a micrometer or using instruments that measure the thickness of non-magnetic anti-corrosion coatings on steel (for example, ITP-1, MT-ZON, etc.).

For periodic profile reinforcement, the residual expression of reefs after stripping should be noted.

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

where 8 a. - average depth of continuous uniform corrosion of steel; - thickness of corrosion products.

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

The reinforcement is exposed in places where it is most weakened by corrosion, which are revealed by the peeling of the protective layer of concrete and the formation of cracks and rusty stains located along the reinforcement rods. The diameter of the reinforcement is measured with a caliper or micrometer. In places where the reinforcement has been subjected to intense corrosion, which has caused the protective layer to fall off, it is thoroughly cleaned of rust until a metallic sheen appears.

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

With continuous uniform corrosion, the depth of corrosion lesions is determined by measuring the thickness of the rust layer, with ulcerative corrosion - by measuring the depth of individual ulcers. In the first case, the rust film is separated with a sharp knife and its thickness is measured with a caliper. It is assumed that the depth of corrosion is equal to either half the thickness of the rust layer or half the difference between the design and actual diameters of the reinforcement.

In case of pitting corrosion, it is recommended to cut out pieces of reinforcement, remove rust by etching (immersing the reinforcement in a 10% solution of hydrochloric acid containing 1% urotropine inhibitor) followed by rinsing with water. Then the fittings 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 mounted on a tripod.

The depth of corrosion is determined by the indicator arrow reading as the difference in readings at the edge and bottom of the corrosion pit. When identifying areas of structures with increased corrosive wear associated with local (concentrated) exposure to aggressive factors, it is recommended to first pay attention to the following elements and components of structures:

supporting units of rafter and sub-rafter trusses, near which water inlet funnels are located internal drain;
the upper chords of the trusses at the points where aeration lamps and wind deflector posts are connected to them;
the upper chords of the rafter trusses, along which the roof valleys are located;
support nodes of trusses located inside brick walls;
the upper parts of columns located inside brick walls;
the bottom and bases of columns located at or below the floor level, especially during wet cleaning in the room (hydraulic wash);
sections of columns of multi-storey buildings passing through the ceiling, especially when wet dusting indoors;
sections of covering slabs located along the valleys, at the funnels of the internal drainage system, at the external glazing and the ends of the lanterns, at the ends of the building.

3.2.1. The main objectives of the inspection of load-bearing reinforced concrete structures are to determine the condition of the structures, identifying damage and the causes of its occurrence, as well as the physical and mechanical characteristics of concrete.

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

Inspection and determination of the technical condition of structures based on 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 geometric parameters of structures and their sections is carried out according to the recommendations of this methodology. 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 method. The degree of crack opening is compared with the regulatory requirements for limit states of the second group.

3.2.5. Determination and assessment of paint and varnish coatings of reinforced concrete structures should be carried out according to the methodology set out in GOST 6992. In this case, the following main types of damage are recorded: cracking and peeling, which are characterized by the depth of destruction of the top layer (before the primer), bubbles and corrosion foci, characterized by the size of the source (diameter ) in mm. The area of certain types of coating damage is expressed approximately as a percentage relative to the entire painted surface.

3.2.6. If there are wet areas and surface efflorescence on concrete structures, the size of these areas and the reason for their appearance are determined.

3.2.7. The results of a visual inspection of reinforced concrete structures are recorded in the form of defect maps plotted on 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 condition of the structures.

3.2.8. External signs characterizing the condition 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 standardized strength, controlled according to 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 method and instruments used, indirect characteristics of strength are:

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

Shock pulse parameter (impact energy);

The dimensions of the imprint on the concrete (diameter, depth) or the ratio of the diameters of the imprints on the concrete and the standard sample when the indenter hits or the indenter is pressed into the concrete surface;

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

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

The value of the force of local destruction of concrete when pulling out an anchor device from it.

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

3.2.10. Instruments of the mechanical operating principle include: Kashkarov's standard hammer, Schmidt's hammer, Fizdel's hammer, TsNIISK pistol, Poldi's hammer, etc. These devices make it possible to determine the strength of the material by the amount of penetration of the striker into the surface layer of structures or by the magnitude of the rebound of the striker from the surface of the structure during application calibrated impact (TsNIISK pistol).

3.2.11. The Fizdel hammer is based on the use of plastic deformation of building materials. When a hammer hits the surface of a structure, a hole is formed, the diameter of which is used to evaluate the strength of the material.

The area of the structure on which prints are applied is first cleaned of the plaster layer, grout or paint.

The process of working with a Fizdel hammer is as follows:

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

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

The distance between impact hammer impressions 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. From the total number of measurements taken in a given area, the largest and smallest results are excluded, and the average value is calculated for the rest.

The strength of concrete is determined by the average measured diameter of the imprint and a calibration curve, previously constructed based on a comparison of the diameters of the imprints of the hammer ball and the results of laboratory tests for the strength 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, the same as the materials of the structure being examined.

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

When a Kashkarov hammer hits the surface of a structure, two imprints 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 is practically independent of the speed and force of the blow applied by the hammer. The strength of the material is determined by the average value from the calibration chart.

At least five determinations must be made at the test site with a distance between prints on concrete of at least 30 mm, and on a metal rod - at least 10 mm (Table 3.2).

Table 3.2

Method name	Number of tests per site	Distance between test sites	Distance from the edge of the structure to the test site, mm	Structure thickness, mm
Elastic rebound
Plastic deformation
Impact impulse
		2 disc diameters
Rib chipping
Separation with chipping		5 breakout depths		Double anchor installation depth

3.2.13. Instruments based on the elastic rebound method include the TsNIISK pistol, Borovoy pistol, Schmidt hammer, 6KM sclerometer with a rod striker, etc. The operating principle of these devices is based on measuring the elastic rebound of the striker at a constant value of the kinetic energy of a metal spring. The firing pin is cocked and lowered automatically when the firing pin comes into contact with the surface being tested. The amount of rebound of the striker is recorded by a pointer on the instrument scale.

As a result of the impact, the firing pin bounces off the firing pin. The degree of rebound is marked on the instrument scale using a special pointer. The dependence of the impactor rebound value on the strength of concrete is established according to calibration tests of concrete cubes measuring 15x15x15 cm, and a calibration curve is constructed on this basis. The strength of the structural material is determined by readings on the graduated scale of the device at the moment of striking the element under test.

3.2.14. The peel-off test method is used to determine the strength of concrete in the body of the structure. The essence of the method is to evaluate the strength properties of concrete by the force required to destroy it around a hole of a certain size when pulling out an expansion cone fixed in it or a special rod embedded in the concrete. An indirect indicator of strength is the pullout force required to pull out an anchor device embedded in the body of a structure along with the surrounding concrete at an embedment depth of . When testing by the peel-off method, the sections should be located in the zone of lowest stresses caused by the operational load or the compression force of the prestressed reinforcement.

The strength of concrete on a site can be determined based on the results of one test. Test areas should be selected so that no reinforcement gets into the pullout zone. At the test site, the thickness of the structure must exceed the anchor embedding depth by at least twice. 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 anchor devices are used during testing. Type I anchor devices are installed on structures during concreting; anchor devices of types II and III are installed in pre-prepared holes formed by drilling in concrete. Recommended hole depth: for type II anchor - 30 mm; for type III anchor - 35 mm. The diameter of the hole in concrete should not exceed the maximum diameter of the buried part of the anchor device by more than 2 mm. The embedding of anchor devices in structures should ensure reliable adhesion of the anchor to the concrete. The load on the anchor device should increase smoothly, at a speed of no more than 1.5-3 kN/s, until it breaks out along with the surrounding concrete.

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 each other by more than twice.

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

Compressible stresses in concrete are determined by structural calculations taking into account the actual dimensions of sections and the magnitude of loads (impacts).

where is a 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 when the actual depth differs from by more than 5% must not differ from the nominal value adopted during testing 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 hardening concrete); =0.25 cm (for heat-treated concrete);

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

The strength of compressed concrete is determined from the equation

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

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

The thickness of the tested 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 value by more than 1 mm. The load on the structure under test should increase smoothly, at a rate of no more than (1+0.3) kN/s, until the concrete breaks off. In this case, the loading hook should not slip. The test results, in which the reinforcement was exposed at the chipping site and the actual spalling depth differed from the specified depth by more than 2 mm, are not taken into account.

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

Compressive stresses in concrete acting during the test period are determined by design calculations taking into account the actual cross-sectional dimensions and load values.

The unit value of concrete strength in a section, assuming = 0, is determined by the formula

Where - correction factor, taking into account the aggregate size, taken equal to 1 for a maximum aggregate size of 20 mm or less, and 1.1 for a size greater than 20 to 40 mm;

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 tested by the rib chipping method, there should be no cracks, concrete chips, sagging or cavities on the concrete surface with a height (depth) of more than 5 mm. The sections should be located in the zone of least stress caused by the operational load or the compression force of the prestressed reinforcement.

Ultrasonic method for determining the strength of concrete

3.2.20. The principle of determining the strength of concrete using 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 dependencies "ultrasound propagation speed - concrete strength." or "ultrasound propagation time - concrete strength.". The degree of accuracy of the method depends on the thoroughness of constructing the calibration graph.

3.2.22. To determine the strength of concrete using 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 using through or surface sounding methods. When measuring the speed of ultrasound propagation using the through-sounding method, ultrasonic transducers are installed on opposite sides of the sample or structure. Ultrasound propagation speed, m/s, is calculated using the formula

where is the ultrasound propagation time, μs;

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

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

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

The deviation of an individual result of measuring the speed of ultrasound propagation in each sample from the arithmetic mean value of the measurement results for a given sample should not exceed 2%.

Measuring the propagation time of ultrasound and determining the strength of concrete are carried out in accordance with the instructions in the passport ( technical conditions applications) of this type device and instructions GOST 17624.

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

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

The strength of concrete is determined by the formula

Coefficients are calculated using 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. When the condition is met

it is allowed to approximately determine the strength for concrete of strength classes up to B25 using the formula

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

3.2.28. For concrete strength classes higher than B25, the strength of concrete in operating structures can also be assessed using a comparative method, taking as a basis the characteristics of the structure with the greatest strength.

In this case

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

3.2.30. When tested carefully, this method provides the most reliable information about the strength of concrete in existing structures. Its disadvantage is the high labor intensity of sampling and testing of samples.

Determination of the thickness of the protective layer of concrete and the location of reinforcement

3.2.31. To determine the thickness of the protective layer of concrete and the location of reinforcement in a reinforced concrete structure during inspections, magnetic and electromagnetic methods are used in accordance with GOST 22904 or transillumination and ionizing radiation methods in accordance with GOST 17623 with a spot check of the results obtained by punching furrows and direct measurements.

Radiation methods are usually 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 shining through controlled structures with ionizing radiation and obtaining information about its internal structure using a radiation converter. X-raying of reinforced concrete structures is carried out using radiation from X-ray machines and radiation from sealed radioactive sources.

Transportation, storage, installation and adjustment of radiation equipment is carried out by specialized organizations that have special permission 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 protective layer of concrete and the location of reinforcement in a reinforced concrete structure are determined on the basis of an experimentally established relationship between the instrument readings 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 reinforcement from instruments, in particular, ISM and IZS-10N are used.

The IZS-10N device provides measurement of the thickness of the protective layer of concrete depending on the diameter of the reinforcement within the following limits:

With a diameter of reinforcement bars from 4 to 10 mm, the thickness of the protective layer is from 5 to 30 mm;

With a diameter of reinforcement bars 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 on the concrete surface:

With a diameter from 12 to 32 mm - with a concrete protective layer thickness of no more than 60 mm;

With a diameter of 4 to 12 mm - with a concrete protective layer thickness of no more than 30 mm.

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

3.2.34. Determination of the thickness of the protective layer of concrete and the diameter of the reinforcement 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 reinforcement parameters of the controlled structure, it is necessary to establish an individual calibration dependence in accordance with GOST 22904.

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

Goals and test conditions;

Peculiarities design solution designs;

Technologies for manufacturing or erecting a structure, 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 its operating instructions. At the measurement points on the surface of the structure there should be no sagging heights of more than 3 mm.

3.2.36. If the thickness of the protective layer of concrete is less than the measurement limit of the device used, 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 thickness of the protective layer of concrete 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. To approximately determine the diameter of the reinforcing bar, the location of the reinforcement is determined and recorded on the surface of the reinforced concrete structure using an IZS-10N type device.

The device transducer is installed on the surface of the structure and, using the instrument scales or an individual calibration relationship, several values of the thickness of the protective layer of concrete are determined for each of the expected 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 device transducer and the concrete surface of the structure, measurements are taken again and the distance is determined for each estimated diameter of the reinforcing bar.

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

The actual diameter is taken to be the value for which the condition is met

where is the instrument reading taking into account the thickness of the gasket;

Gasket thickness.

The indices in the formula indicate:

Pitch of longitudinal reinforcement;

Transverse reinforcement spacing;

Availability of gasket.

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

Table 3.3 - Form for recording the results of measurements of the thickness of the protective layer of concrete of reinforced concrete structures

Conventional designation design	Control numbers areas being constructed	Structural reinforcement parameters according to technical documentation			Instrument readings	the specified thickness of the protected concrete layer, mm
		nominal diameter of the reinforcement,	rod position	Thickness of protection concrete layer, mm

3.2.40. The actual values of the thickness of the protective layer of concrete and the location of steel reinforcement in the structure based on the measurement results are compared with the values established in the technical documentation for these structures.

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

Name of the structure being tested;

Batch volume and number of controlled structures;

Type and number of the device used;

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

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

Results of the tests carried out;

Determination of strength characteristics of reinforcement

3.2.42. The calculated resistances of undamaged reinforcement may be taken according to design data or according to design standards for reinforced concrete structures.

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

For reinforcement with a profile whose ridges form a helix 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 from rolled sections is taken into account 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 steel is established by testing samples cut from the structure with a comparison of the yield strength, tensile strength and elongation at break with the data of GOST 380 or approximately according to the type of reinforcement, the profile of the reinforcing bar and the time of construction 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 of 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;

Testing the surface layer of metal for hardness 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 deformation due to damage, and so that after cutting their strength and structural stability are ensured.

3.2.47. It is recommended to select blanks for samples in three similar structural elements (upper chord, lower chord, first compressed brace, etc.) in the amount of 1-2 pieces. from one element. All workpieces must be marked at the places where they were taken and the marks are indicated on the diagrams attached to the materials for examining structures.

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

The determination of the main design resistances of steel structures is made by dividing the average value of the yield strength by the material safety factor = 1.05 or the temporary resistance by the safety factor = 1.05. At the same time, for design resistance the smallest of the values found accordingly is accepted.

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

The data obtained during hardness testing is converted into characteristics of the mechanical properties of the metal using an empirical formula. Thus, the relationship between Brinell hardness and the temporary resistance of the metal is established by the formula

where is the Brinell hardness.

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

Determination of concrete strength by laboratory tests

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

Samples are taken by cutting cores with a diameter of 50 to 150 mm in areas where the weakening of the element does not significantly affect the load-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 sampling and processing of samples.

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

The essence of the method is to measure the minimum forces that destroy concrete samples drilled or cut from a structure when they are statically loaded with a constant rate of load growth.

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 locations should be designated after a visual inspection of structures, depending on their stress state, taking into account the minimum possible reduction in their load-bearing capacity.

It is recommended to take samples from places away from joints and edges of structures. After sampling, the sampling sites should be sealed fine-grained concrete. Sites for drilling or cutting out concrete samples should be selected in areas free of reinforcement.

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

For cutting samples from concrete structures, they use sawing machines types URB-175, URB-300 with cutting tools in the form of cutting diamond discs of the AOK type.

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 testing and loading schemes, is also carried out in accordance with GOST 10180.

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

3.2.55. The strength of the concrete of the test sample with an accuracy of 0.1 MPa during compression tests and with an accuracy of 0.01 MPa during tensile tests is calculated using the formulas:

for compression

for axial tension

tensile bending

Working section area of the sample, mm;

Accordingly, the width and height of the cross section of the prism and the distance between the supports when testing samples for tensile bending, mm.

To bring the strength of concrete in the tested sample to the strength of concrete in a sample of the basic size and shape, the strength obtained using the specified formulas is recalculated using the formulas:

for compression

for axial tension

tensile splitting

tensile bending

where and are coefficients taking 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 samples of other shapes;

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

Table 3.4

From 0.85 to 0.94

From 0.95 to 1.04

From 1.05 to 1.14

From 1.15 to 1.24

From 1.25 to 1.34

From 1.35 to 1.44

From 1.45 to 1.54

From 1.55 to 1.64

From 1.65 to 1.74

From 1.75 to 1.84

From 1.85 to 1.95

Table 3.5

	1.04 or less

Table 3.6

		Splitting Tension		Bending stretch	Axial tension
Sample dimensions: edge of a cube or side of a square prism, mm	All types of concrete	Heavy concrete	granular concrete	Heavy concrete

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

3.2.57. If there are wet areas and surface efflorescence on concrete structures, the size of these areas and the reason for their appearance are determined.

3.2.58. The results of a visual inspection of reinforced concrete structures are recorded in the form of a map of defects plotted on 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 condition of the structures.

Determination of the degree of corrosion of concrete and reinforcement

3.2.59. To determine the degree of corrosion destruction of concrete (degree of carbonization, composition of new formations, structural damage to concrete), physicochemical methods are used.

The study of structural changes in concrete is carried out using a hand-held magnifying glass. Such an inspection allows you to examine the surface of the sample, identify the presence of large pores, cracks and other defects.

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

3.2.60. The depth of carbonation of concrete is determined by changes in the pH value.

If the concrete is dry, moisten the chipped surface with clean water, which should be enough so that a visible film of moisture does not form on the surface of the concrete. Excess water is removed 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 color of the indicator changes from colorless to bright crimson. A fresh fracture of a concrete sample in the carbonized zone after applying a phenolphthalein solution to it has a gray color, and in the non-carbonized zone it acquires a bright crimson color.

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

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

3.2.61. Factors influencing the development of corrosion of concrete and reinforced concrete structures are divided into two groups: those related to the properties of the external environment (atmospheric and groundwater, industrial environment, etc.) and those caused by the properties of materials (cement, aggregates, water, etc.). ) structures.

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

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

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

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

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

For periodic profile reinforcement, the residual expression of reefs after stripping should be noted.

In places where steel corrosion products are well preserved, their thickness can be used to roughly judge the depth of corrosion by the ratio

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

Thickness of corrosion products.

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

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

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

With continuous uniform corrosion, the depth of corrosion lesions is determined by measuring the thickness of the rust layer, with ulcerative corrosion - by measuring the depth of individual ulcers. In the first case, the 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% solution of hydrochloric acid containing 1% urotropine inhibitor) followed by rinsing with water.

Then the fittings 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 mounted on a tripod. The depth of corrosion is determined by the indicator arrow reading as the difference in 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 pay attention to the following elements and components of structures:

Support units of rafter and sub-rafter trusses, near which the water inlet funnels of the internal drainage are located:

The upper chords of the trusses at the nodes for connecting light aeration lamps and racks of various shields to them;

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

Support nodes of trusses located inside brick walls;

The upper parts of columns located inside brick walls.

Assessment of the technical condition of structures based on external signs is based on determining the following factors:

- geometric dimensions of structures and their sections;
- presence of cracks, spalls and destruction;
- condition of protective coatings (paint and varnish, plasters, protective screens, etc.);
- deflections and deformations of structures;
- violation of the adhesion of reinforcement to concrete;
- presence of reinforcement rupture;
- state of anchoring of longitudinal and transverse reinforcement;
- degree of corrosion of concrete and reinforcement.

Determination and assessment of the condition of paint and varnish coatings of reinforced concrete structures should be carried out according to the methodology set out in GOST 6992-68. In this case, the following main types of damage are recorded: cracking and peeling, which are characterized by the depth of destruction of the top layer (before the primer), bubbles and corrosion foci, characterized by the size of the foci (diameter), mm. The area of individual types of coating damage is expressed approximately as a percentage relative to the entire painted surface of the structure (element).

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

In progress visual examinations an approximate assessment of the strength of concrete is made. In this case, you can use the tapping method. The method is based on tapping the surface of the structure with a hammer weighing 0.4-0.8 kg directly on a cleaned mortar area of concrete or on a chisel installed perpendicular to the surface of the element. In this case, to assess the strength, the minimum values obtained as a result of at least 10 impacts are accepted. A louder sound when tapped corresponds to stronger and denser concrete.

If there are wet areas and surface efflorescence on concrete structures, the size of these areas and the reason for their appearance are determined.

The results of a visual inspection of reinforced concrete structures are recorded in the form of a map of defects plotted on 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 condition of the structures.

External signs characterizing the states 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

	Signs of structural condition

I - normal	On the surface of concrete of unprotected structures there are no visible defects or damage or there are small individual potholes, chips, hairline cracks (no more than 0.1 mm). Anti-corrosion protection of structures and embedded parts has no violations. When opened, the surface of the reinforcement is clean, there is no corrosion of the reinforcement, the depth of concrete neutralization does not exceed half the thickness of the protective layer. The estimated strength of concrete is not lower than the design strength. The color of the concrete is not changed. The amount of deflection and crack opening width do not exceed the permissible limits
II - satisfactory	Anti-corrosion protection of reinforced concrete elements is partially damaged. In some areas, in places where the protective layer is small, traces of corrosion of distribution fittings or clamps appear, corrosion of working fittings in individual spots and spots; loss of cross-section of working reinforcement no more than 5%; There are no deep ulcers or rust plates. Anti-corrosion protection of embedded parts was not detected. The depth of concrete neutralization does not exceed the thickness of the protective layer. The color of the concrete has changed due to overdrying, and in some places the protective layer of concrete has peeled off when tapped. Peeling of the edges and edges of structures exposed to freezing. The estimated strength of concrete within the protective layer below the design value is no more than 10%. The requirements of current standards relating to limit states of group I are met; the requirements of the standards for limit states of group II may be partially violated, but normal operating conditions are ensured
III - unsatisfactory	Cracks in the tensile zone of concrete that exceed their permissible opening. Cracks in the compressed zone and in the zone of main tensile stresses, deflections of elements caused by operational impacts exceed the permissible limits by more than 30%. Concrete in the stretched zone at the depth of the protective layer between the reinforcement bars easily crumbles. Lamellar rust or pitting on the rods of exposed working reinforcement in the area of longitudinal cracks or on embedded parts, causing a reduction in the cross-sectional area of the rods from 5 to 15%. Reduction of the estimated strength of concrete in the compressed zone of bending elements to 30 and in other areas - to 20%. Sagging of individual rods of distribution reinforcement, bulging of clamps, rupture of individual ones, with the exception of clamps of compressed truss elements due to steel corrosion (in the absence of cracks in this area). The support area of prefabricated elements, reduced against the requirements of the standards and the design, with a drift coefficient K=1.6 (see note). High water and air permeability of wall panel joints
IV - pre-emergency or emergency	Cracks in structures experiencing alternating loads, cracks, including those crossing the support zone for anchoring tensile reinforcement; rupture of stirrups in the zone of an inclined crack in the middle spans of multi-span beams and slabs, as well as layered rust or pitting, causing a decrease in the cross-sectional area of the reinforcement by more than 15%; buckling of reinforcement in the compressed zone of structures; deformation of embedded and connecting elements; waste of anchors from plates of embedded parts due to corrosion of steel in welds, breakdown of joints of prefabricated elements with mutual displacement of the latter; displacement of supports; significant (more than 1/50 of the span) deflections of bending elements in the presence of cracks in the tension zone with an opening of more than 0.5 mm; rupture of clamps of compressed truss elements; rupture of clamps in the area of an inclined crack; rupture of individual rods of working reinforcement in the tension zone; crushing of concrete and crumbling of aggregate in a compressed zone. Reduction in concrete strength in the compressed zone of bending elements and in other areas by more than 30%. The support area of prefabricated elements is reduced against the requirements of the standards and the design. Existing cracks, deflections and other damage indicate the danger of destruction of structures and the possibility of their collapse

Notes: 1. To classify a structure into the condition categories 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 condition category II, belong to category III, and those having signs of category III - respectively, to categories IV or V, depending on the danger of collapse. 3. If the supporting area of prefabricated elements is reduced against the requirements of the standards and the design, it is necessary to carry out an approximate calculation of the supporting element for shear and crushing of concrete. The calculation takes into account the actual loads and strength of concrete. 4. In complex and critical cases, the assignment of the structure under examination to one or another condition category in the presence of signs not noted in the table should be made on the basis of an analysis of the stress-strain state of structures carried out by specialized organizations

Determination of concrete strength by mechanical methods

Mechanical methods of non-destructive testing when examining structures are used to determine the strength of concrete of all types of standardized strength, controlled according to GOST 18105-86.

Depending on the method and instruments used, indirect characteristics of strength are:

- the value of the rebound of the striker from the concrete surface (or the striker pressed against it);
- shock pulse parameter (impact energy);
- dimensions of the imprint on concrete (diameter, depth) or the ratio of the diameters of imprints on concrete and standard sample when the indenter hits 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 tearing force divided by the projection area of the concrete tearing surface onto the plane of the disk;
- the value of the force required to chip off 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 using mechanical non-destructive testing methods, one should be guided by the instructions of GOST 22690-88.

Instruments of the mechanical operating principle include: Kashkarov's standard hammer, Schmidt's hammer, Fizdel's hammer, TsNIISK pistol, Poldi's hammer, etc. These devices make it possible to determine the strength of the material by the amount of penetration of the striker into the surface layer of structures or by the magnitude of the rebound of the striker from the surface of the structure during application calibrated impact (TsNIISK pistol).

The Fizdel hammer (Fig. 1) is based on the use of plastic deformations of building materials. When a hammer hits the surface of a structure, a hole is formed, the diameter of which is used to evaluate the strength of the material. The area of the structure on which prints are applied is first cleared of the plaster layer, grout or paint. The process of working with a Fizdel hammer is as follows: right hand take the end of the wooden handle, rest your elbow on the structure. With an elbow blow of medium strength, 10-12 blows are applied on each section of the structure. The distance between impact hammer impressions 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. From the total number of measurements taken in a given area, the largest and smallest results are excluded, and the average value is calculated for the rest. The strength of concrete is determined by the average measured diameter of the imprint and a calibration curve, previously constructed based on a comparison of the diameters of the imprints of the hammer ball and the results of laboratory tests for the strength 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 technology that the materials of the structure being examined.

Methods for monitoring concrete strength

Method, standards, instruments

Test scheme

Ultrasonic

GOST 17624-87

Devices: UKB-1, UKB-1M UKB16P, UV-90PTs Beton-8-URP, UK-1P

Plastic deformation

Devices: KM, PM, DIG-4

Elastic rebound

Devices: KM, Schmidt sclerometer

GOST 22690-88

Plastic deformation

Kashkarov's hammer

GOST 22690-88

Separation with discs

GOST 22690-88

Device GPNV-6

Chipping of a structural rib

GOST 22690-88

GPNS-4 device with URS device

Separation with chipping

GOST 22690-88

Devices: GPNV-5, GPNS-4

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

Rice. 2. Calibration chart for determining the tensile strength of concrete when compressed with a Fizdel hammer

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

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

In Fig. Figure 2 shows a calibration curve for determining the compressive strength with a Fizdel hammer.

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

A distinctive feature of the Kashkarov hammer (Fig. 3) from the Fizdel hammer is that between the metal hammer and the rolled ball there is a hole into which a control metal rod is inserted. When you hit the surface of a structure with a hammer, two impressions are made: on the surface of a material with a diameter d and on a control (reference) rod with a diameter d uh . The ratio of the diameters of the resulting prints depends on the strength of the material being examined and the reference rod and is practically independent of the speed and force of the blow applied by the hammer. By average value d/d uh The strength of the material is determined from the calibration chart (Fig. 4).

At least five determinations must be made at the test site with a distance between imprints on concrete of at least 30 mm, and on a metal rod - at least 10 mm.

Instruments based on the elastic rebound method include the TsNIISK pistol (Fig. 5), Borovoi pistol, Schmidt hammer, KM sclerometer with a rod striker, etc. The operating principle of these devices is based on measuring the elastic rebound of the striker at a constant value of the kinetic energy of a metal spring. The firing pin is cocked and lowered automatically when the firing pin comes into contact with the surface being tested. The amount of rebound of the striker is recorded by a pointer on the instrument scale.

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

Modern means for determining the compressive strength of concrete using the non-destructive shock-pulse method include the ONIX-2.2 device, the principle of which is to record by a transducer the parameters of a short-term electrical pulse that occurs in the sensitive element when it hits concrete, with its conversion into a strength value. After 8-15 hits, the average strength value is displayed on the scoreboard. The series of measurements ends automatically after the 15th blow and the average strength value is displayed on the instrument display.

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

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

The strength of the structural material is determined by readings on the graduated scale of the device at the moment of striking the element under test.

The peel-off test method is used to determine the strength of concrete in the body of the structure. The essence of the method is to evaluate the strength properties of concrete by the force required to destroy it around a hole of a certain size when pulling out an expansion cone fixed in it or a special rod embedded in the concrete. An indirect indicator of strength is the pullout force required to pull out the anchor device embedded in the body of the structure along with the surrounding concrete at the embedment depth h(Fig. 6).

Rice. 6. Scheme of testing by the peel-off method using anchor devices

When testing by the peel-off method, the sections should be located in the zone of lowest stresses caused by the operational load or the compression force of the prestressed reinforcement.

Three types of anchor devices are used during testing (Fig. 7). Type I anchor devices are installed on structures during concreting; anchor devices of types II and III are installed in pre-prepared holes drilled into concrete. Recommended hole depth: for type II anchor - 30 mm; for type III anchor - 35 mm. The diameter of the hole in concrete should not exceed the maximum diameter of the buried part of the anchor device by more than 2 mm. The embedding of anchor devices in structures should ensure reliable adhesion of the anchor to the concrete. The load on the anchor device should increase smoothly at a speed of no more than 1.5-3 kN/s until it breaks out along with the surrounding concrete.

Rice. 7. Types of anchor devices:1 - working rod; 2 - working rod with expansion 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 each other by more than twice.

When determining the class of concrete by chipping the edges of a structure, a device of the GPNS-4 type is used (Fig. 8). The test diagram is shown in Fig. 9.

Loading parameters should be accepted: A=20 mm; b=30 mm, =18.

At least two concrete chips must be carried out at the test site. The thickness of the tested 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 value by more than 1 mm. The load on the structure under test should increase smoothly at a speed of no more than (1±0.3) kN/s until the concrete breaks off. In this case, the loading hook should not slip. The test results, in which the reinforcement was exposed at the chipping site and the actual spalling depth differed from the specified depth by more than 2 mm, are not taken into account.

Rice. 8. Device for determining the strength of concrete using the rib chipping method:1 - test structure, 2 - chipped concrete, 3 - URS device, 4 - device GPNS-4

Rice. 9. Scheme for testing concrete in structures using the method of chipping the edge of the structure

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

Compressive stresses in concrete b, valid during the test period, are determined by design calculations taking into account the actual cross-sectional dimensions and load values.

Single value R i 0 concrete strength at the site, assuming b=0 is determined by the formula

Where T g- correction factor taking 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- conditional strength of concrete, determined according to the graph (Fig. 10) based on the average value of the indirect indicator R

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

When testing by the rib chipping method, there should be no cracks, concrete chips, sagging or cavities in the test area with a height (depth) of more than 5 mm. The sections should be located in the zone of least stress caused by the operational load or the compression force of the prestressed reinforcement.

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

Ultrasonic method for determining the strength of concrete. The principle of determining the strength of concrete using 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 using the established calibration relationships “ultrasound propagation speed - concrete strength V=f(R)" or "ultrasound propagation time t- concrete strength t=f(R)" The degree of accuracy of the method depends on the thoroughness of constructing the calibration graph.

The calibration schedule is constructed based on sounding and strength testing data of control cubes made from concrete of the same composition, using the same technology, under the same hardening regime as the products or structures to be tested. When constructing a calibration schedule, you should follow the instructions of GOST 17624-87.

To determine the strength of concrete using the ultrasonic method, the following devices are used: UKB-1, UKB-1M, UK-16P, “Beton-22”, etc.

Ultrasonic measurements in concrete are carried out using through or surface sounding methods. The concrete testing scheme is shown in Fig. eleven.

Rice. 11. Methods of ultrasonic sounding of concrete:A- testing scheme using the through-sounding method; b- the same, superficial sounding; UP- ultrasonic transducers

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

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

Where t- ultrasound propagation time, μs;

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

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

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

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

Measuring the propagation time of ultrasound and determining the strength of concrete are carried out in accordance with the instructions in the passport (technical conditions of 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 strength of concrete of operating structures in the absence or impossibility of constructing a calibration table. In this case, the determination of the strength of concrete is carried out in areas of structures made of concrete using one type of coarse aggregate (structures of one batch). Ultrasound propagation speed V determined in at least 10 sections of the examined zone of structures, for which the average value is determined V. Next, we outline areas in which the speed of propagation of ultrasound has a maximum V max and minimum V min values, as well as the area where the speed has a value V n closest to the value V, and then drill out at least two cores from each targeted area, from which the strength values in these areas are determined: R max, R min, R n respectively. Strength of concrete R H determined by the formula

R max /100. (5)

Odds A 1 and a 0 is calculated using the formulas

When determining the strength of concrete using samples taken from the structure, one should follow the instructions of GOST 28570-90.

If the 10% condition is met, it is possible to approximately determine the strength: for concrete of strength classes up to B25, according to the formula

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

For concrete strength classes higher than B25, the strength of concrete in operating structures can also be assessed using a comparative method, taking as a basis the characteristics of the structure with the greatest strength. In this case

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

When tested carefully, this method provides the most reliable information about the strength of concrete in existing structures. Its disadvantage is the high labor intensity of sampling and testing of samples.

Determination of the thickness of the protective layer of concrete and the location of reinforcement

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

The radiation method is based on x-raying of controlled structures ionizing radiation and obtaining information about its internal structure using a radiation converter. X-raying of reinforced concrete structures is carried out using radiation from X-ray machines and radiation from sealed radioactive sources.

Transportation, storage, installation and adjustment of radiation equipment is carried out only by specialized organizations that have special permission 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

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 provides measurement of the thickness of the protective layer of concrete depending on the diameter of the reinforcement within the following limits:

- with a diameter of reinforcement bars from 4 to 10 mm, the thickness of the protective layer is from 5 to 30 mm;
- with a diameter of reinforcement bars 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 on the concrete surface:

- with diameters from 12 to 32 mm - with a concrete protective layer thickness of no more than 60 mm;
- with diameters from 4 to 12 mm - with a concrete protective layer thickness of no more than 30 mm.

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

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

- before testing, compare the technical characteristics of the device used with the corresponding design (expected) values of the geometric parameters of the reinforcement of the controlled reinforced concrete structure;
- in case of inconsistency technical characteristics device, it is necessary to establish an individual calibration dependence for the reinforcement parameters of the controlled structure in accordance with GOST 22904-93.

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

- purpose and test conditions;
- features of the design solution of the structure;
- technologies for manufacturing or erecting 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 its operating instructions. At the measurement points on the surface of the structure there should be no sagging heights of more than 3 mm.

If the thickness of the protective layer of concrete is less than the measurement limit of the device used, 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 thickness of the protective layer of concrete 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.

To approximately determine the diameter of the reinforcing bar, the location of the reinforcement is determined and recorded on the surface of the reinforced concrete structure using an IZS-10N type device.

The device transducer is installed on the surface of the structure, and several values of the thickness of the protective layer of concrete are determined using the scales of the device or according to an individual calibration dependence pr for each of the expected reinforcing bar diameters that could be used to reinforce a given structure.

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- instrument reading 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- presence of gasket;

e- 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 thickness of the protective layer of concrete and the location of steel reinforcement in the structure based on the measurement results are compared with the values established in the technical documentation for these structures.

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

- name of the structure being tested (its symbol);
- batch size and number of controlled structures;
- type and number of the device used;
- numbers of controlled sections of structures and the diagram of their location on the structure;
- design values of the geometric parameters of the reinforcement of the controlled structure;
- results of tests performed;
- a link to the instructional and regulatory document regulating the test method.

Form for recording the results of measurements of the thickness of the protective layer of concrete of reinforced concrete structures

Determination of strength characteristics of reinforcement

The calculated resistances of undamaged reinforcement may be taken according to design data or according to design standards for reinforced concrete structures.

- for smooth reinforcement - 225 MPa (class A-I);
- for reinforcement with a profile whose ridges form a helix 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 from rolled sections is taken into account in calculations with a design resistance in tension, compression and bending equal to 210 MPa.

In the absence of the necessary documentation and information, the class of reinforcing steel is established by testing samples cut from the structure and comparing the yield strength, tensile 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 of 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*;
- testing 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 deformation due to 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 of the same type structural elements: trusses, beams, columns, etc.

All workpieces must be marked at the places where they were taken and the marks are indicated on the diagrams attached to the materials for examining structures.

The characteristics of the mechanical properties of steel - yield strength t, tensile strength and elongation at break are obtained by tensile testing of samples 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 strength by the reliability factor for the material m = 1.05 or the temporary resistance by the reliability factor = 1.05. In this case, the smallest of the values is taken as the calculated resistance R T, R, which are found according to m and.

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

3,5H b ,

Where N- Brinell hardness.

The identified actual characteristics of the valves are compared with the requirements of SNiP 2.03.01-84* and SNiP 2.03.04-84*, and on this basis an assessment of the serviceability of the valves is made.

Determination of concrete strength by laboratory tests

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

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

The essence of the method is to measure the minimum forces that destroy concrete samples drilled or cut from a structure when they are statically loaded with a constant rate of load growth.

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 compressive strength, from 0.4 to 2 diameters when determining tensile strength during splitting, and from 1.0 to 4 diameters when determining strength when axial tension.

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

Concrete sampling locations should be designated after a visual inspection of structures, depending on their stress state, taking into account the minimum possible reduction in their load-bearing capacity. It is recommended to take samples from places away 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.

Sites for drilling or cutting out concrete samples should be selected in areas free of reinforcement.

Used for drilling samples from concrete structures. drilling machines type IE 1806 according to TU 22-5774 with cutting tools in the form of annular diamond drills type SKA 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 cutting tools in the form of cutting diamond discs of the AOK type according to GOST 10110-87E or TU 2- 037-415.

It is allowed to use other equipment and tools for the production of samples from concrete structures that ensure 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 testing and loading schemes, is carried out in accordance with GOST 10180-90.

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

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

The strength of the concrete of the test sample with an accuracy of 0.1 MPa during compression tests and with an accuracy of 0.01 MPa during tensile tests is calculated using the formulas:

for compression;

for axial tension;

tensile bending,

A- sample working cross-section area, 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 samples for tensile bending, mm.

for compression;

for axial tension;

for 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 for compression tests according to the table, for tensile splitting tests according to the table. And equal to one for samples of other shapes;

Scale factors that take into account the shape and cross-sectional dimensions of the tested samples are determined experimentally according to GOST 10180-90.

from 0.85 to 0.94

from 0.95 to 1.04

from 1.05 to 1.14

from 1.15 to 1.24

from 1.25 to 1.34

from 1.35 to 1.44

from 1.45 to 1.54

from 1.55 to 1.64

from 1.65 to 1.74

from 1.75 to 1.84

from 1.85 to 1.95

from 1.95 to 2.0

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

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

To assess the current condition of a building or structure, an inspection of reinforced concrete structures is carried out, determining:

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 obvious and hidden deformations of structures.
The condition of the reinforcement regarding the violation of its adhesion to concrete, the presence of ruptures in it and the manifestation of the corrosion process.

Most corrosion defects visually have similar signs; only a qualified examination can be the basis for prescribing methods for repairing and restoring structures.

Carbonation is one of the most common reasons 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 able to absorb carbon dioxide, oxygen and moisture with which the atmosphere is saturated. This not only significantly affects the strength of the concrete structure, changing its physical and chemical properties, but also negatively affects the reinforcement, which, when the concrete is damaged, gets into acidic environment and beginning to collapse under the influence of harmful corrosive phenomena.

Rust, which is formed 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. When exposed, they wear out even faster, which leads to even faster destruction of concrete. Using dry mixtures specially developed for this purpose and paint coatings, it is possible to significantly increase the corrosion resistance and durability of the structure, but before this it is necessary to carry out its technical examination.

Inspection of reinforced concrete structures consists of several stages:

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

All this helps to establish the strength characteristics of reinforced concrete, the chemical composition of aggressive environments, the degree and depth of corrosion processes. To inspect reinforced concrete structures, they are used necessary tools and certified devices. The results, in accordance with current regulations and standards, are reflected in a well-written final conclusion.

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