Inspection of reinforced concrete structures of buildings. Inspection of monolithic reinforced concrete structures How we work

Research Group "Safety and Reliability"

Construction expertise, Building inspection, Energy audit, Land management, Design

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.

An inspection is called upon to assess the physical condition of the structure, establish the causes of damage, and determine the actual strength, crack resistance and rigidity of the structure. iron concrete structures. It is important to correctly assess the load-bearing capacity of structures and develop recommendations for their further operation. And this is only possible as a result of detailed field study.

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

The inspection of reinforced concrete structures consists of several stages. On initial stage a preliminary inspection of structures is carried out to identify the presence of completely or partially destroyed areas, ruptures of reinforcement, damage to concrete, displacement of supports and elements in prefabricated structures.

At the next stage, familiarization with the design technical documentation, followed by a direct examination of reinforced concrete structures, which makes it possible to obtain a real picture of the state of the structures and their performance under operating conditions. Depending on the tasks, the strength of concrete can be assessed non-destructive methods, as well as clarifying the actual reinforcement, which consists of collecting data on the actual state of the reinforcement and comparing them with the parameters contained in the working drawings, as well as selectively checking the compliance of the actual reinforcement with the design one.

Because the effective loads may differ significantly from the design ones, the stress state of structures is analyzed. For this purpose, actual loads and impacts are determined. If necessary, the continuation may be full-scale tests. Upon completion, a construction and technical conclusion is issued.

We work according to this principle:

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

2 After analyzing your situation, we determine a list of questions that our experts should answer. An agreement to conduct an inspection of reinforced concrete structures can be concluded either in our office or directly at your site.

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

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

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

The time frame for receiving the conclusion is from 3 working days.

4 Many clients require a visit from a specialist without a subsequent conclusion. A construction and technical expert will conduct an inspection of reinforced concrete structures, based on the results of which he will give an oral report with conclusions and recommendations on site. You can decide whether to draw up a written conclusion based on the results of the study later.

The cost of our expert’s visit starts from 7,000 rubles.

5 We have designers and constructors in our company who, based on our conclusion, can develop a project for eliminating deficiencies and a project for strengthening structures.

Cost of inspection of reinforced concrete structures
from 17,000 rub.

Structures built from reinforced concrete are strong and durable objects. If they are built in strict accordance with the project, then in the future there should be no problems with their operation. Even if you are sure that the object is impeccable in terms of the materials used, it is worth regularly monitoring it. The fact is that even the most durable buildings are exposed to aggressive factors and their resistance to corrosion begins to decline.

Our experts at professional level examine civil and industrial buildings and structures in Moscow and recommend ordering an inspection of reinforced concrete structures of buildings:

• Before commissioning.
• Within 2 years after commissioning.
• At least once every 10 years.
• Before the purchase.
• Before redevelopment, reconstruction.
• If the service life of the object has expired.
• After natural Disasters and man-made accidents.

Prices for inspection of reinforced concrete structures

In all these situations, the purpose of the survey is to determine technical condition, identifying defects, establishing their causes. Only a detailed study of reinforced concrete objects will achieve these goals. Inspection of the condition of objects should be carried out only by experts who have the right to work in this area, that is, they have received SRO access to carry out activities in the field of construction expertise.

Our advantages

Experienced specialists

Our specialists, who have been working in this field for many years, have a full range of practical knowledge

Quality of work

The work takes a minimum of time, while the quality always remains at its best

Wide range of services

Our company specializes in providing a range of services

Affordable prices

Affordable prices with high quality work

How we are working?

Although reinforced concrete structures are varied, their examination is carried out according to a single algorithm:

• Preparation and study of technical and design documentation.
• Field work. They are carried out directly on site. Experts conduct a visual, detailed examination. At this stage, they use ultra-precise equipment, which allows them to determine the strength and other characteristics of materials.
• Laboratory tests of those samples that were taken at the previous stage.
• Analytical work with the results obtained, identifying the causes of defects. Note that the most common causes of destruction of reinforced concrete structural elements is leaching, carbonation, rust, etc.
• Drawing up a technical report and issuing it to the customer.

By calling our experts, you will clarify the prices for the service: they will name preliminary tariffs for the inspection of reinforced concrete structures of buildings. The exact amount will be calculated after reviewing the terms of reference.

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 has a negative effect on the reinforcement, which, when the concrete is damaged, enters an acidic environment and begins 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. By using dry mixtures and paint coatings specially developed for this purpose, 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, chemical composition aggressive environments, 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.

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

• - geometric dimensions structures and their sections;
• - presence of cracks, spalls and destruction;
• - states 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.

Definition and assessment of condition paint coatings 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. More ringing sound when tapped, it 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%. Requirements are met current standards related to limit states Group I; the requirements of the standards for limit states of group II may be partially violated, but are ensured normal conditions operation
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.

To devices mechanical principle actions 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 a 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 when applying a calibrated blow (gun TsNIISK).

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 imprints are obtained: 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.

To devices based on the method elastic rebound, include the TsNIISK pistol (Fig. 5), Borovoy 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

TO modern means To determine the compressive strength of concrete using the non-destructive shock-pulse method, the ONIX-2.2 device is used, the operating principle of which is to record by a converter 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 prestress, 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 the readings of 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.

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.

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 maximum diameter recessed 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

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 with opposite sides sample or design.

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 application) of this type of device and 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 be guided by 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.

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 only by specialized organizations that have special permission to carry out these works.

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

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.

To determine the thickness of the protective layer of concrete and the location of reinforcement from modern devices used in particular ISM, IZS-10N (TU25-06.18-85.79). 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 geometric parameters reinforcement of controlled reinforced concrete structures;
• - 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.

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 ​​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 made of rolled profiles is accepted 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).

For determining mechanical properties steel 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.

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

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.

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 28570-90.

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 from 44 to 150 mm, a height from 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 s cutting tool 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 should be used as a standard cement-sand mortar or epoxy compositions.

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- width and height respectively cross section prisms and distance between supports when testing specimens 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;

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.

Inspection of concrete and reinforced concrete structures is 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.

Assessment of the technical condition of concrete and reinforced concrete structures based on external signs is carried out on the basis of:

1. determining the geometric dimensions of structures and their sections; This data is necessary for verification calculations. For an experienced specialist, sometimes it is enough to visually assess the clearly insufficient dimensions of the structure.
2. comparison of actual dimensions of structures with design dimensions; The actual dimensions of the structures play a very important role 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 prevent overconsumption of building materials and, accordingly, increase in 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.
3. 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.
4. 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.
5. 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 load-bearing capacity building structure.
6. condition of 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.
7. 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 calculations of the load-bearing capacity of building structures are performed based on maximum permissible deflections.
8. 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.
9. presence of reinforcement rupture; Reinforcement ruptures indicate a decrease in load-bearing capacity up to the category of emergency condition.
10. 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.
11. 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, non-destructive testing methods are used or laboratory tests are carried out 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.