Inspection of concrete structures. Inspection of reinforced concrete structures. Prices for inspection of reinforced concrete structures

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 in reinforced concrete structures, unacceptable deflections, cracks, and damage occur. 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 physical condition of the structure, to establish the causes of damage, to determine the real strength, crack resistance and rigidity of the structure, the examination of iron concrete structures. It is important to properly assess bearing capacity structures and develop recommendations for their further operation. And this is possible only as a result of a detailed natural study.

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

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

The next step is 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 structures and their operation under operating conditions. Depending on the tasks set, the concrete strength can be assessed by non-destructive methods, as well as the actual reinforcement, which consists in collecting data on the actual state of the reinforcement, and comparing them with the parameters contained in the working drawings, as well as in a selective check of the compliance of the actual reinforcement with the design one.

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

We work according to this principle:

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

2 After analyzing your situation, we define a list of questions that our experts should answer. A contract for the inspection of reinforced concrete structures can be concluded both in our office and immediately at your site.

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

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

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

The terms for obtaining the conclusion are from 3 working days.

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

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

5 We have designers and constructors in our company who, based on our opinion, can develop a project to eliminate deficiencies and a project to strengthen structures.

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

• Compliance of the actual dimensions of structures with their design values;
• The presence of destruction and cracks, their location, nature and causes of occurrence;
• The presence of obvious and hidden deformations of structures.
• The condition of the reinforcement for violation of its adhesion to concrete, the presence of gaps 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 repair and restoration of structures.

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

Concrete can absorb carbon dioxide, oxygen, and moisture in the atmosphere. This not only significantly affects the strength of the concrete structure, changing its physical and Chemical properties, but has a negative effect on the reinforcement, which, if the concrete is damaged, enters the acidic environment and begins to break down under the influence of harmful corrosion phenomena.

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

Inspection of reinforced concrete structures consists of several stages:

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

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

Grade technical condition designs according to outward signs is made on the basis of determining the following factors:

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

Definition and assessment of the state coatings reinforced concrete structures should be produced according to the methodology set forth in GOST 6992-68. In this case, the following main types of damage are recorded: cracking and delamination, which are characterized by the depth of destruction of the upper layer (before the primer), bubbles and corrosion centers, characterized by the size of the focus (diameter), mm. Square certain types coating damage is expressed approximately as a percentage in relation to the entire painted surface of the structure (element).

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

In the process 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 the cleaned mortar section of concrete or on a chisel installed perpendicular to the surface of the element. At the same time, to assess the strength, minimum values resulting from at least 10 hits. A louder sound when tapped corresponds to a stronger and denser concrete.

In the presence of wet areas and surface efflorescence on the 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 applied to the schematic plans or sections of the building, or tables of defects are compiled with recommendations for the classification of defects and damages with an assessment of the category of the condition of the structures.

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

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

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

Notes: 1. To assign a structure to the categories of state 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 having signs of III category - respectively to IV or V categories, depending on the danger of collapse. 3. When the area of ​​support of prefabricated elements is reduced against the requirements of the norms and the project, it is necessary to carry out an approximate calculation support element for shearing and crushing concrete. The calculation takes into account the actual loads and strength of concrete. 4. Assignment of the examined structure to one or another category of state in the presence of signs not noted in the table, in complex and critical cases, should be made on the basis of an analysis of the stress-strain state of structures performed by specialized organizations

Determination of concrete strength mechanical methods

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

Depending on the method and instruments used indirect characteristics strengths are:

• - the value of the rebound of the striker from the surface of the concrete (or the striker pressed against it);
• - shock impulse parameter (impact energy);
• - the dimensions of the imprint on concrete (diameter, depth) or the ratio of the diameters of imprints on concrete and standard sample when the indenter strikes or the indenter is pressed into the concrete surface;
• - the value of the stress required for the local destruction of concrete when it is torn off glued to it metal disc, equal to the tear force divided by the projection area of ​​the concrete tear surface on the disc plane;
• - 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 testing by mechanical methods of non-destructive testing, one should be guided by the instructions of GOST 22690-88.

The devices of the mechanical principle of operation include: the reference hammer of Kashkarov, the Schmidt hammer, the Fizdel hammer, the TsNIISK pistol, the Poldi hammer, etc. These devices make it possible to determine the strength of the material by the amount of penetration of the striker into surface layer structures or by the magnitude of the rebound of the striker from the surface of the structure when applying a calibrated blow (TsNIISK pistol).

Fizdel's hammer (Fig. 1) is based on the use of plastic deformations building materials. When a hammer strikes the surface of the structure, a hole is formed, according to the diameter of which the strength of the material is estimated. The place of the structure, on which the imprints are applied, is preliminarily cleaned of the plaster layer, grouting or painting. The process of working with Fizdel's hammer is as follows: with the right hand they take the end of the wooden handle, the elbow is supported on the structure. An elbow blow of medium strength is applied 10-12 blows on each section of the structure. The distance between the impressions of the impact hammer must be at least 30 mm. The diameter of the formed hole is measured with a vernier caliper with an accuracy of 0.1 mm in two perpendicular directions and the average value is taken. From total number measurements taken in this area, exclude the largest and smallest results, and calculate the average value for the rest. The strength of concrete is determined by the average measured diameter of the imprint and the calibration curve, previously constructed on the basis of 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 surveyed design.

Concrete Strength Control Methods

Method, standards, devices	Test scheme
Ultrasonic GOST 17624-87 Devices: UKB-1, UKB-1M UKB16P, UF-90PC Beton-8-URP, UK-1P
plastic deformation Devices: KM, PM, DIG-4 elastic rebound Devices: KM, Schmidt sclerometer GOST 22690-88
plastic deformation Kashkarov's hammer GOST 22690-88
Detachment with discs GOST 22690-88 GPNV-6 device
Structural rib shearing GOST 22690-88 GPNS-4 device with URS device
Breakaway with chipping GOST 22690-88 Devices: GPNV-5, GPNS-4

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

Rice. 2. Calibration chart for determining the compressive strength of concrete with a Fizdel hammer

Rice. 3. Determination of the strength of the material, using a hammer K.P. 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

On fig. 2 shows a calibration curve for determining the ultimate 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 there is a hole between the metal hammer and the rolled ball, into which a control metal rod is inserted. When a hammer strikes the surface of the structure, two imprints are obtained: on the surface of the material with a diameter d and on the 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. According to the average value of the value d/d uh from the calibration graph (Fig. 4) determine the strength of the material.

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

The devices based on the elastic rebound method include the TsNIISK pistol (Fig. 5), the Borovoy pistol, the Schmidt hammer, the KM sclerometer with a rod striker, etc. The principle of operation of these devices is based on measuring the elastic rebound of the striker at a constant value of the kinetic energy of a metal spring. The platoon and descent of the striker are carried out automatically when the striker comes into contact with the surface being tested. The rebound value of the striker is fixed by the pointer on the scale of the device.

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

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

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

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

The strength of the material of construction is determined by the readings of the graduated scale of the device at the moment of impact on the tested element.

The shearing shear test method determines the strength of concrete in the body of the structure. The essence of the method is to evaluate the strength properties of concrete according to the force required for its destruction around a hole of a certain size when pulling out an expansion cone fixed in it or a special rod embedded in concrete. An indirect indicator of strength is the pull-out force required to pull out the anchor device embedded in the body of structures together with the surrounding concrete at a depth of embedment h(Fig. 6).

Rice. 6. Schematic of the pull-off test using anchor devices

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

The strength of concrete on the site is allowed to be determined by the results of one test. The test sites should be selected so that the reinforcement does not fall into the pull-out zone. At the test site, the thickness of the structure should exceed the depth of anchoring by at least two times. When punching a hole with a jumper 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.

When testing, three types of anchor devices are used (Fig. 7). Anchor devices of type I are installed on structures during concreting; anchor devices of types II and III are installed in pre-prepared holes, punched in concrete by drilling. Recommended hole depth: for type II anchor - 30 mm; for anchor type III - 35 mm. The diameter of the borehole in concrete must 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 must ensure reliable adhesion of the anchor to concrete. The load on the anchor device should increase smoothly at a speed of no more than 1.5-3 kN / s until it is pulled out together with the surrounding concrete.

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

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

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

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

At the test site, at least two concrete chips must be carried out. The thickness of the structure to be tested shall 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 shall increase smoothly at a rate not exceeding (1 ± 0.3) kN/s until the concrete is chipped. In this case, the load hook must not slip. The test results, in which reinforcement was exposed at the cleavage site, and the actual cleavage depth differed from the specified one by more than 2 mm, are not taken into account.

Rice. 8. Device for determining the strength of concrete by rib shearing:1 - test design, 2 - chipped concrete, 3 - URS device, 4 - device GPNS-4

Rice. 9. Scheme of testing concrete in structures by the method of chipping the ribs of the structure

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

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

single value R i 0 strength of concrete in the area assuming b=0 is determined by the formula

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

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

P i- the force of each of the chipping performed on the test site.

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

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

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

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

The strength of concrete in structures is determined experimentally according to the established calibration dependencies "velocity of propagation of ultrasound - strength of concrete V=f(R)” or “ultrasound propagation time t- strength of concrete t=f(R)". The degree of accuracy of the method depends on the thoroughness of the construction of the calibration graph.

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

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

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

Rice. 11. Ways of ultrasonic sounding of concrete:a- scheme of testing by the method of end-to-end sounding; b- the same, superficial sounding; UP- ultrasonic transducers

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

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

where t- propagation time of ultrasound, μs;

l- distance between transducer installation centers (sound base), mm.

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

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

Deviation of an individual measurement of the propagation time of ultrasound in each sample from the average arithmetic value measurement results for a given sample, should not exceed 2%.

The measurement of the propagation time of ultrasound and the determination of the strength of concrete are carried out in accordance with the instructions of the passport ( specification applications) of this type instrument and instructions GOST 17624-87.

In practice, there are often cases when it becomes necessary to determine the strength of concrete of operated 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 the areas of structures made of concrete on one type of coarse aggregate (structures of one batch). Ultrasound propagation speed V are determined in at least 10 sections of the surveyed zone of structures, for which the average value is determined v. Next, the areas are marked in which the propagation velocity of ultrasound has a maximum V max and minimum V min values, as well as the section where the speed has the value V n closest to the value V, and then at least two cores are drilled from each designated area, which determine the strength values ​​in these areas: R max , R min , R n respectively. Concrete strength R H determined by the formula

R max /100. (5)

Odds a 1 and a 0 is calculated by the formulas

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

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

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

For concrete of strength classes higher than B25, the strength of concrete in structures in operation can also be evaluated by a comparative method, taking into account the characteristics of the structure with the greatest strength. In this case

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

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

Determining the thickness of the concrete cover and the location of the reinforcement

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

Radiation methods, as a rule, are used to examine the condition and quality control 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 the transillumination of controlled structures ionizing radiation and obtaining information about it internal structure using a radiation converter. The translucence of reinforced concrete structures is carried out using radiation from X-ray machines, radiation from sealed radioactive sources.

Transportation, storage, installation and adjustment of radiation equipment is carried out only by specialized organizations who have a special permit to carry out the specified work.

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

The thickness of the protective layer of concrete and the location of the reinforcement in the reinforced concrete structure is determined on the basis of the experimentally established relationship between the readings of the device and the indicated controlled parameters of the structures.

To determine the thickness of the protective layer of concrete and the location of reinforcement from modern appliances in particular, ISM, IZS-10N (TU25-06.18-85.79) are used. The device IZS-10N 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 - from 5 to 30 mm;
• - with a diameter of reinforcement bars from 12 to 32 mm, the thickness of the protective layer - 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 not more than 60 mm;
• - with diameters from 4 to 12 mm - with a concrete protective layer thickness of not more than 30 mm.

When the distance between the reinforcement bars is less than 60 mm, the use of devices of the IZS type 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 non-compliance specifications of the device, it is necessary to establish an individual calibration dependence in accordance with GOST 22904-93 to the parameters of the reinforcement of the controlled structure.

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

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

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

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

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

When controlling 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, the layout of the reinforcement is determined and its diameter is measured by opening the structure.

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

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

Between the transducer of the device and the concrete surface of the structure, a gasket of the appropriate thickness (for example, 10 mm) is installed, measurements are taken again and the distance is determined for each expected reinforcing bar diameter.

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

as actual diameter d take the value for which the condition is satisfied

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

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

The indices in the formula mean:

s- step of longitudinal reinforcement;

R- step of transverse reinforcement;

e- the presence of a gasket;

e- gasket thickness.

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

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

The results of measurements are drawn up in a protocol, which should contain the following data:

• - name of the tested structure (its symbol);
• - batch size and number of controlled structures;
• - type and number of the device used;
• - numbers of controlled sections of structures and a diagram of their location on the structure;
• - design values geometric parameters of the reinforcement of the controlled structure;
• - the results of the tests;
• - a link to the instructive-normative 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 design resistance of undamaged reinforcement is allowed to be taken according to design data or according to the design standards for reinforced concrete structures.

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

Rigid reinforcement from rolled profiles taken in calculations with a design resistance in tension, compression and bending equal to 210 MPa.

With absence necessary documentation and information, the class of reinforcing steels is established by testing specimens cut out of the structure with a comparison of the yield strength, tensile strength and relative 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, according to the instructions of GOST 7564-73*;
• - tests of the surface layer of metal for hardness according to the instructions of GOST 18835-73, GOST 9012-59* and GOST 9013-59*.

Sample blanks from damaged elements are recommended to be cut in places that have not received plastic deformations during damage, and that after cutting their strength and stability are ensured.

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

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

Characteristics of the mechanical properties of steel - yield strength t, tensile strength and relative elongation at break are obtained by tensile testing of samples according to GOST 1497-84 *.

The determination of the basic design resistances of steel structures is carried out by dividing the average value of the yield strength by the material safety factor m = 1.05 or the temporary resistance by the safety factor = 1.05. In this case, the smallest of the values ​​is taken as the design resistance R t, R, which are found, respectively, for m and.

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

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

3,5H b ,

where H- Brinell hardness.

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

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.

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

When determining the strength of 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 minimum effort, destroying concrete samples drilled or sawn from the structure under their static loading with a constant load growth rate.

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

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

For the base for all types of tests, a sample with a working section size of 150150 mm is taken.

Concrete sampling sites should be assigned after a visual inspection of the structures, depending on their stress state, taking into account the minimum possible decrease in their bearing capacity. Samples are recommended to be taken from places remote from the joints and edges of structures.

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

Sites for drilling or sawing concrete samples should be selected in places free from reinforcement.

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

For sawing samples from concrete structures, they are used sawing machines types URB-175 according to TU 34-13-10500 or URB-300 according to TU 34-13-10910 with a cutting tool 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 making samples from concrete structures that ensure the production of samples that meet the requirements of GOST 10180-90.

Testing specimens for compression and all types of tension, as well as the choice of testing and loading scheme, is carried out in accordance with GOST 10180-90.

The bearing surfaces of the samples tested for compression, in the case when their deviations from the surface of the press plate are more than 0.1 mm, must be corrected by applying a layer of leveling compound. As standard, cement paste should be used, 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 tested sample, with an accuracy of 0.1 MPa in compression tests and with an accuracy of 0.01 MPa in tensile tests, is calculated by the formulas:

for compression;

for axial tension;

tensile bending,

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

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

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

for compression;

for axial tension;

tensile when splitting;

tensile bending,

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

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

The test report shall consist of a sampling protocol, the test results of the samples and an appropriate reference to the standards against 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 disclose an approach to the inspection of concrete and reinforced concrete structures. The longevity of the building operation depends on the qualified performance of this part of the building survey.

Inspection of the concrete and reinforced concrete structures of the building is carried out both as part of regular inspections during operation, and before the superstructure or reconstruction of the building, before purchasing the building or when structural defects are detected.

A correct assessment of the state of concrete and reinforced concrete structures allows you to reliably assess their bearing capacity, which will provide further safe operation or add-on/add-on.

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

1. determination of the geometric dimensions of structures and their sections; These data are necessary for verification calculations. For an experienced specialist, sometimes it is enough to visually assess the obviously insufficient dimensions of the structure.
2. comparison of the actual dimensions of structures with design dimensions; The actual dimensions of the structures play a very important role, as the dimensions are directly related to the bearing capacity calculations. One of the tasks of designers is to optimize the dimensions in order to prevent overspending of building materials, and, accordingly, increase in the cost of construction. 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 with the actual static scheme of the structures adopted in the calculation; The actual scheme of the loads of the structures is also very important, because if the design dimensions are not observed due to construction defects, additional loads and bending moments in structures and nodes may occur, which sharply reduces the bearing capacity of structures.
4. the presence of cracks, spalls and destruction; The presence of cracks, spalls and destruction is an indicator of unsatisfactory operation of structures, or indicates poor quality construction works.
5. location, nature of cracks and the width of their opening; According to the location of the cracks, their nature and the width of their opening, the 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 bearing capacity building structure.
6. state of protective coatings; Protective coatings are called so because they must protect building structures from adverse and aggressive external factors. Violation of protective coatings, of course, will not lead to instant destruction of the building structure, but it will affect durability.
7. deflections and deformations of structures; The presence of deflections and deformations can give the specialist the opportunity to assess the performance of the building structure. Some calculations of the bearing capacity of building structures are carried out according to the maximum allowable deflections.
8. signs of violation of the adhesion of reinforcement with concrete; The adhesion of reinforcement to concrete is very important, because Concrete does not work in bending, but only works in compression. Bending work in reinforced concrete structures is provided by reinforcement, which is prestressed. The lack of adhesion of reinforcement to concrete indicates that the bearing capacity of the reinforced concrete structure for bending has decreased.
9. the presence of a rupture of reinforcement; Breaks in the reinforcement indicate a decrease in the bearing capacity up to the emergency category.
10. state of anchoring of longitudinal and transverse reinforcement; Anchoring of longitudinal and transverse reinforcement provides correct work reinforced concrete building structure. Violation of the anchorage can lead to an emergency condition.
11. degree of corrosion of concrete and reinforcement. Corrosion of concrete and reinforcement reduces the bearing capacity of a reinforced concrete structure, because. the thickness of the concrete and the diameter of the reinforcement are reduced due to corrosion. The thickness of concrete and the diameter of the reinforcement are one of the important values ​​in calculating the bearing capacity of a reinforced concrete structure.

The size (width) of the opening of cracks in concrete is measured in the areas of their greatest opening and at the level of the reinforcement of the tension zone of the element, because this most fully gives an 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 occurrence of cracks and assessment of the impact of these cracks on the bearing capacity of the building structure.

During the inspection of concrete and reinforced concrete structures, specialists determine the strength of concrete. For this, non-destructive testing methods are used or laboratory tests are carried out and guided by the requirements of GOST 22690, GOST 17624, SP 13-102-2003. During the survey, we use several non-destructive testing devices (shock-pulse method IPS-MG4, ONIKS; ultrasonic method UT MG4.S; tear-off device with chipping POS, and also, if necessary, use the "Kashkarov's hammer"). We give a conclusion about the actual strength characteristics according to the readings of at least two instruments. We also have the opportunity to conduct research on selected samples in the laboratory.