Determination of strength by mechanical methods of non-destructive testing. Peel-off method with shearing Concrete peel strength

Testing of concrete by the method of separation with shearing at correct use gives the most accurate results compared to other non-destructive methods. Employees of the "Standard" laboratory conduct it using equipment that meets established requirements. After the verification is completed, our specialists calculate desired values, draw up a report and provide the client with all the data received.

We are confident in the qualifications of our employees and high quality equipment - the accuracy of the results is guaranteed.

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Preparatory work and testing

It is important to consider that the tear-off method is not the fastest verification option. Before starting research, you need to prepare a device with petal anchors and holes for its installation. To achieve maximum measurement accuracy, the holes drilled in the structure are cleaned and dedusted. If the concrete temperature is below -10°C, the boreholes must also be heated along the entire length.

The location of the anchor is easy to choose, since the surface does not have to be flat. The curvature of the structure can be any, unless it prevents the installation of the device on the draft. This is one of the most important advantages of the method.

When the boreholes are warmed up and the anchors are installed, the tests begin. The bottom line is simple: the anchor device is pulled out of the structure along with a piece of concrete using a special device. The load is increased slowly and smoothly, at a speed of about 1.5-3.0 kN / s - this is necessary for greater accuracy of the results. Specialists register the force that had to be applied to destroy the structure, as well as the depth of the pull-out with an error of no more than 1 mm.

After the end of the tests, the laboratory staff analyze the data obtained. To calculate the strength of concrete, they use the formula R=m1*m2*P (explanation is given below). The analysis of the obtained results makes it possible to determine whether the concrete has sufficient strength and whether its characteristics meet the established requirements and standards.

Method features

Advantages:

• High measurement accuracy.
• Strength range from 5 to 100 MPa. This is the widest range available using non-destructive methods.
• The concrete tear test is the only non-destructive method for which calibration dependencies are prescribed. Their construction in accordance with GOST 22690 is not required. You can use the calibration dependence in the form of the formula R=m1*m2*P, where

P is the breaking force;
m1 - coefficient determined taking into account maximum size filler and equal to 1 if this size does not exceed 50 mm and 1.1 if it does;
m2 is the coefficient of conversion to compressive strength. Determined by the table:

Disadvantages:

• Not suitable for use in heavily reinforced and thin-walled structures. Optimal Performance buildings: reinforcement cells from 150 mm, concrete layer thickness from 100 mm.
• The need to check at least 1 time every 2 months.
• Labor intensity, additional preparatory work.
• Difficulty checking at temperatures below -10°C. The hole for the anchor in such cases must be heated to at least 0 ° C along the entire length.

Additional terms:

When testing concrete with shearing, it is necessary to lay the anchor at a distance of at least 150 mm from the edge of the structure. The thickness of the structure must be at least twice the depth of the anchor.

The distance between the areas where the tests are carried out should exceed five times the depth of the anchor.

The maximum anchor slippage is 10% of the installation depth.

Let us consider some basic methods and instruments for determining the strength of concrete in structures that are used in practice. The determination of strength by mechanical methods of non-destructive testing is carried out according to, the determination of strength by the ultrasonic method of non-destructive testing is carried out according to, the determination of strength from concrete samples drilled or sawn from structures is carried out according to.

Non-destructive methods determination of the compressive strength of concrete structures are based on indirect characteristics of instrument readings based on the methods of elastic rebound, shock impulse, plastic deformation, separation, shearing of the rib and separation with shearing, the speed of passage of ultrasound. Determining the compressive strength of samples taken from structures involves testing them on a press.

To determine the class and grade of concrete, depending on the compressive or tensile strength, you can use Table 6, Appendix 1,

RELATIONSHIP BETWEEN THE CLASSES OF CONCRETE IN COMPRESSION AND TENSION STRENGTH AND GRADES

Table 6

Strength class of concrete	Average strength of concrete () *, kgf / cm2	The nearest brand of concrete in terms of strength M	Deviation of the nearest concrete grade from the average strength of the class, % ,

Average strength of concrete R calculated with coefficient of variation V, equal to 13.5%, and security - 95% for all types of concrete, and for massive hydraulic structures - with a coefficient of variation V, equal to 17% , and security - 90%.

Methods and devices for non-destructive testing

To determine the compressive strength of concrete, these readings must be converted using pre-established calibration dependencies between the strength of concrete and an indirect strength characteristic (in the form of a graph, table or formula), according to the methods specified in GOST 22690-88 and according to the attached graphs of calibration dependencies for instruments set at the instrument's factory.

Strength testing with non-destructive testing devices is performed directly at the locations of structures, however, it is also possible to test concrete samples from structures. Testing of concrete in samples is recommended to determine its strength in hard-to-reach areas of structures and in structures located at negative temperature. The sample is monolithic in a solution, the strength of which on the day of testing must be at least half the strength of the sample concrete (to prevent sample destruction during testing). It is convenient to monolithize samples into a solution using standard forms for the manufacture of concrete control samples according to. The location of the samples after stripping is shown in Fig.1.

Fig.1. one- concrete sample; 2 - the most convenient side of the sample for testing 3 - the solution in which the sample is fixed

Instruments are usually supplied with calibration curves or with basic settings for heavy concrete medium brands. To examine structures, it is allowed to use the methods of elastic rebound, shock impulse or plastic deformation, using the calibration dependence established for concrete that differs from the tested one (in composition, age, hardening conditions, humidity), with its refinement in accordance with the method given in () . Ultrasonic instruments require calibration and adjustment according to , and guidelines for concrete strength control monolithic structures ultrasonic method of surface sounding.

The calibration dependence "speed - strength" is established when testing structures by the method of through sounding. The calibration dependence "time - strength" is established when testing structures by the method of surface sounding.

When testing structures by the method of surface sounding, it is allowed to use the calibration dependence "speed - strength" taking into account the transition coefficient determined in accordance with Appendix 3.

Measurement of the propagation time of ultrasound in concrete structures should be carried out in the direction perpendicular to the compaction of concrete. The distance from the edge of the structure to the installation site of the ultrasonic transducers must be at least 30 mm. Measurement of the propagation time of ultrasound in concrete structures should be carried out in the direction perpendicular to the direction of the working reinforcement. The concentration of reinforcement along the selected sounding line should not exceed 5%. It is allowed to sound along a line parallel to the working reinforcement, if the distance from this line to the reinforcement is at least 0.6 of the base length.

Pulsar 1.2.

Rice. 2. Appearance instrument
Pulsar-1.2: 1 - receiver input;
2 - emitter output

The device consists of an electronic unit (see Fig. 3.2) and ultrasonic transducers - separate or combined into a surface sounding sensor. On the front panel the electronic block are located: 12-key keyboard and the graphic display. Connectors for connecting a surface sounding sensor or individual ultrasonic transducers for through sounding are installed in the upper end part of the case. The USB interface connector is located on the right side of the device. The batteries are accessed through the cover. battery compartment on the bottom wall of the case.

The operation of the device is based on measuring the transit time of an ultrasonic pulse in the product material from the emitter to the receiver. The speed of ultrasound is calculated by dividing the distance between transmitter and receiver by the measured time. To increase reliability, 6 measurements are automatically performed in each measurement cycle and the result is formed by their statistical processing with rejection of outliers. The operator performs a series of measurements (from 1 to 10 measurements of his choice), which is also subjected to mathematical processing with the determination of the average value, coefficient of variation, coefficient of heterogeneity and rejection of outliers.

The speed of propagation of an ultrasonic wave in a material depends on its density and elasticity, on the presence of defects (cracks and voids), which determine strength and quality. Therefore, sounding the elements of products, structures and structures, you can get information about:

• strength and uniformity;
• modulus of elasticity and density;
• the presence of defects and their localization.
• A-signal form

Sounding options with lubrication and dry contact are possible (protectors, cone nozzles), see fig. 3.1.

Rice. 3. Sound options

The instrument performs entry and visualization of received ultrasonic waves, has built-in digital and analog filters that improve the signal-to-noise ratio. The oscilloscope mode allows you to view the signals on the display (in a specified time and gain scales), manually set the cursor to the position of the first break control mark. The user has the ability to manually change the gain of the measuring path and shift the time axis to view and analyze the first break and envelope signals.

Registration of results for methods for determining the strength of non-destructive testing

The results of concrete strength tests are recorded in a log, which should indicate:

• design name, batch number;
• type of controlled strength and its required value;
• type of concrete;
• name of the non-destructive method, instrument type and serial number;
• the average value of the indirect strength characteristic and the corresponding value of the concrete strength;
• information on the use of correction factors;
• results of concrete strength assessment;
• surname and signature of the person who conducted the test, date of the test.

For the ultrasonic method for determining the strength, you need to use the form of the journal established in appendices No. 8-9,

The shearing method is one of the most common and reliable methods for assessing the strength of concrete structures.

The method belongs to direct, non-destructive testing methods and allows you to immediately, on the spot, evaluate the strength concrete structure, both at the intermediate age and upon reaching the design age of concrete.

The essence of the method consists in drilling a hole in concrete, fixing a special anchor in this hole (if an anchor of the second and third types is used) and then tearing off this anchor from concrete special device with pull-out force measurement. If the test is carried out correctly, there remains at the place of separation correct form funnel, with a depth in the middle equal to the working height of the anchor.

When the anchor is torn off, the corresponding force is displayed on the scale of the device. After several measurements (at least three tests for flat structures; for elongated horizontal structures one test in four running meters length, but not less than three tests), it is possible to recalculate the test results using a special formula and draw a conclusion about the concrete compression class (GOST 18105 schemes C, D).

The shear-off method is well-deservedly popular among methods for controlling the strength of concrete, such as independent method and duplicating other test methods. It is much faster and cheaper than core drilling, it is indispensable in cases where sample cubes are not made or parallel tests are required.

In addition, according to GOST 18105, complete control of concrete structures is required. And the shearing method is the most suitable strength control method for this.

When controlling the strength of concrete by the method of separation with chipping, one should be guided by the instructions of GOST 22690.

16 and 24 what are these numbers.

Three types of anchors are used for the shear-off method.

difference anchors of the first type from the rest lies in the fact that it is embedded in the structure when laying concrete mix its separation is carried out at the design (or intermediate) age with the same device as the anchors of the second and third types, otherwise the tests do not differ.

Anchors of the second type comes in two sizes: ø16x25mm and ø24x48mm.

Anchor size ø24x48mm is used if the approximate strength of concrete in the structure is 5-100 MPa.

Anchor size ø16x25mm it is used if the approximate strength of concrete in the structure is 40-100 MPa. The use of an anchor ø16mm for testing low-grade concrete is unacceptable without building a calibration dependence.

The photo shows an anchor of the second type with a special nut that measures the slip of the anchor.

In order to conduct the tests correctly and obtain the most accurate data, you need to pay attention to the following points:

1. Before drilling a hole for the anchor, it is necessary to find and mark the reinforcement mesh with a reinforcement search device (so that the drill does not get into the reinforcement), if a reinforcing mesh comes across in the way of the drill, it is necessary to drill into the middle of the cell.
2. You need to drill a hole, departing from the edge of a flat structure of at least 0.5 m.
3. The hole is drilled strictly perpendicular to the concrete surface.
4. Do not drill structures in places of maximum stress.
5. The number of test points is determined as follows: three test points per flat design(wall, floor slab, grillage), poured into one grip. One point per 4 linear meters of an elongated structure (column, crossbar), also filled in one grip, but not less than three points. Under one grip it should be understood the pouring of the concrete mix from one concrete unit, one class of concrete in one working day without a break in concreting until a cold joint is formed. Those. if the class of concrete, the date of concreting or the plant supplier of the mixture changes, this is a new grip that requires a strength test.
6. The drilled hole should be thoroughly cleaned of concrete dust. Only after that you need to place the assembled anchor in the hole and tighten it as well as possible. wrench to maximum expansion.
7. When breaking out of concrete, the anchor must cling to concrete for at least 9/10 of its length immersed in the thickness of concrete. The length of the clutch is clearly visible in the pull-out funnel after the test and can be measured with a ruler. If by such a measurement it turns out that the anchor clings to less than 9/10 of its length, this means that the cutting of the jaws of the anchor is licked and the jaws must be replaced with new ones.
8. If, during the tear-off, the anchor began to slip and crawl out, it is necessary to measure the slip length, this length is included in the adjustment of the test results. To measure the slip, use a special nut (see photo above).

Examples of instruments used for testing:

In addition to the two presented, many other models can be used.

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

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

The procedure for testing concrete structures for separation with chipping

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

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

Study of this building material by tearing off the anchor with shearing is carried out in the manner prescribed by the current GOST:

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

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

Preparatory work

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

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

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

Procedure for Conducting Concrete Strength Studies

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

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

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

Results processing

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

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

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

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

Advantages and features of the research method

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

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

In this article, we will look at several instruments that are used in construction in order to determine the strength of concrete using the “Peel-off” method.

This method allows you to determine the strength of any concrete from an unknown composition in the strength range from 5 to 100 MPa.

Method " Breakaway with chipping» based on local destruction concrete structure, which uses the relationship between the applied force and the strength of the structure. For this in concrete an anchor device is installed during pouring, or after curing, into a drilled hole. After that, this anchor device breaks out of the structure with a small piece concrete and at the moment of separation, the applied force is measured, after which, according to the data obtained, concrete structure strength.

Despite the fact that with this method of measuring strength, a small part of the material breaks out of the structure, this method " Breakaway with chipping» belongs to the type non-destructive methods for assessing the strength of concrete structures, although in fact local destruction of the structure still occurs. And destructive methods include, for example, strength measurement concrete cubes under a special press, during which the test cube is completely destroyed.

And just on the basis of the fact that the measurement of strength occurs during direct destruction, this method allows you to obtain the most accurate results, on the basis of which tables are later compiled for subsequent construction of dependencies with the results of other tests.

For strength testing concrete constructions according to the method Breakaway with chipping", one of the following devices is used:

Each of these devices differs from each other not only in design, but also in the field of application. Let's consider each of them.

This device is designed to determine the strength of both light concrete, and heavy. Lungs concretes are determined in the strength range from 5 to 40 MPa, and heavy in the range from 10 to 100 MPa.

In order to use this device, you need to connect its working part with the anchor installed in the structure to a depth of about 5.5 centimeters and turn the handle, which activates piston pump. The pump, in turn, pulls the anchor out of the structure and at the moment of destruction, readings are taken from the pressure gauge installed on the device, which, in turn, can be either analog or electronic. In this case, the standard pressure division value is 0.5 MPa.

This instrument is most commonly used to test the strength of honeycomb concrete any building structures, as well as to check the strength penositalla and polystyrene concrete.

The strength measurement range of this device is from 0.5 to 8 MPa, which is much less than the previous device and that is why it is used only in rare cases.

This is a microprocessor-based instrument for measuring shear strength of concrete.

The device is used both directly during construction and when measuring the strength of already constructed buildings.

This device differs from the first two in that it has a built-in electronic force meter with subsequent fixation of the maximum value, digital indication of force and pressure in kN and MPa, as well as a load rise rate meter during operation.

Another important distinguishing feature of this instrument is that it provides parameter settings concrete, such as the heavy or easy and expected strength, more or less than 50 MPa. These settings allow you to increase the accuracy of measurements and ease of use.

This device, in terms of its characteristics and scope, almost completely coincides with, but with some differences.

Firstly, it has a completely different design, in which the working cylinder and pump are axially located. And secondly, it has a built-in device for measuring anchor slippage, and it is also possible to transfer the obtained measurements to a stationary PC.

And just like in the previous device, it is possible to enter the parameters of the subject concrete such as: type and hardening conditions concrete, aggregate size, anchor size and control product type.

POS 50MG4 "Skol" (POS 30MG4 "Skol")

Another variety of the two previous devices is a variety of " Skol».

This device has interchangeable nozzles that allow you to measure the strength, both by breaking off the anchor, and by chipping off the rib of the structure.

For all other parameters of this device, it coincides with the device.

This device has almost the same characteristics as the one, but at the same time it has a completely different technical design.

It is a device made of lightweight materials, has two working legs and a two-cylinder design with automatic installation pullout axis. As well as a device that prevents the anchor from slipping.