Control of the strength of concrete by the method of separation with shearing. The main methods for determining the compressive strength of heavy concrete in prefabricated and monolithic concrete and reinforced concrete structures and products
The proposed article discusses the main methods of non-destructive testing of the strength of concrete used in the inspection of structures of buildings and structures. The results of experiments on comparison of data obtained by non-destructive methods of control and testing of samples are presented. The advantage of the method of separation with shearing over other methods of strength control is shown. Measures are described, without which the use of indirect non-destructive control methods is unacceptable.
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The compressive strength of concrete is one of the most frequently monitored parameters in the construction and inspection of reinforced concrete structures. Available big number control methods used in practice. More reliable, from the point of view of the authors, is the determination of strength not according to control samples () made from concrete mix, and for testing the concrete of the structure after it has gained design strength. The method of testing control samples allows you to evaluate the quality of the concrete mix, but not the strength of the concrete structure. This is due to the fact that it is impossible to provide identical conditions for strength development (vibration, heating, etc.) for concrete in the structure and concrete sample cubes.
Classification control methods are divided into three groups:
- Destructive;
- Direct non-destructive;
- Indirect non-destructive.
The methods of the first group include the mentioned method of control samples, as well as the method for determining strength by testing samples taken from structures. The latter is basic and is considered the most accurate and reliable. However, when examining it, they resort to it quite rarely. The main reasons for this are a significant violation of the integrity of structures and the high cost of research.
Table 1. Characteristics of methods for non-destructive testing of concrete strength.
| № | Method name | Application range*, MPa | Measurement error** |
|---|---|---|---|
| 1 | plastic deformation | 5 ... 50 | ± 30 ... 40% |
| 2 | elastic rebound | 5 ... 50 | ±50% |
| 3 | shock impulse | 10 ... 70 | ±50% |
| 4 | separation | 5 ... 60 | there is no data |
| 5 | Breakaway with chipping | 5 ... 100 | there is no data |
| 6 | Rib chipping | 10 ... 70 | there is no data |
| 7 | Ultrasonic | 10 ... 40 | ± 30 ... 50% |
| * according to the requirements of GOST 17624 and GOST 22690; ** according to the source without constructing a particular calibration dependence |
|||
Mostly non-destructive testing methods are used. Most of the work is done by indirect methods. Among them, the most common today are the ultrasonic method for , the shock pulse and elastic rebound methods for . However, when using these methods, the requirements of the standards for the construction of particular calibration dependencies are rarely met. Some performers do not know these requirements. Others know, but do not understand, how large the error in the measurement results is when using dependencies built into or supplied with the instrument, instead of a dependency built on the specific concrete under study. There are "specialists" who know about specified requirements norms, but they are neglected, focusing on the financial benefit and ignorance of the customer in this matter.
Many works have been written about the factors influencing the error in strength measurement without constructing partial calibration dependencies, including those listed in the list of references. In table. 1 shows data on the maximum measurement error various methods given in the monograph on non-destructive testing of concrete.
In addition to the indicated problem of using inappropriate (“false”) dependencies, we will designate another one that arises during the survey. According to the requirements, providing a sample of measurements (parallel tests of concrete by indirect and direct methods) in more than 30 areas is necessary, but not sufficient for the construction and use of a calibration dependence. It is necessary that the dependence obtained by pairwise correlation-regression analysis has a high correlation coefficient (more than 0.7) and a low standard deviation (less than 15% of the average strength). In order for this condition to be fulfilled, the accuracy of measurements of both controlled parameters (for example, the speed of ultrasonic waves and the strength of concrete) must be sufficiently high, and the strength of concrete, on which the dependence is built, must vary over a wide range.
When examining structures, these conditions are rarely met. First, even the basic method of testing samples is often accompanied by a high error. Secondly, due to the heterogeneity of concrete and other factors, the strength in surface layer(explored by an indirect method) may not correspond to the strength of the same area at a certain depth (when using direct methods). And finally, with the normal quality of concreting and the conformity of the concrete class to the design one, it is rare to find structures of the same type with strength varying over a wide range (for example, from B20 to B60) within one object. Thus, the dependence has to be built on a sample of measurements with a small change in the parameter under study.
Rice. one . The relationship between the strength of concrete and the speed of ultrasonic waves As good example of the above problem, consider the calibration dependence presented in Fig.1. Linear regression dependence is built according to the results ultrasonic measurements and press tests of concrete samples. Despite the large scatter of measurement results, the dependence has a correlation coefficient of 0.72, which is acceptable according to the requirements. When approximating functions other than linear (power, logarithmic, etc.), the correlation coefficient was less than indicated. If the range of the studied concrete strength were smaller, for example, from 30 to 40 MPa (the area highlighted in red), then the totality of the measurement results would turn into a “cloud” presented on the right side of Fig. 1. This cloud of points is characterized by the absence of a connection between the measured and sought parameters, which is confirmed by the maximum correlation coefficient of 0.36. In other words, the calibration dependence cannot be built here.
It should also be noted that on ordinary objects, the number of strength measurement sections for constructing a calibration dependence is comparable to the total number of measured sections. In this case, the strength of concrete can be determined from the results of only direct measurements, and there will no longer be any sense in the calibration dependence and the use of indirect control methods.
Thus, without violating the requirements of the current standards, in any case, it is necessary to use direct non-destructive or destructive methods of control to determine the strength of concrete during examination. Taking this into account, as well as the problems identified above, we will further consider direct methods of control in more detail.
The method of detachment with shearing occupies a special place among the methods for determining the strength of concrete. Considered a non-destructive method, the shearing method is inherently a destructive concrete testing method, as the strength of concrete is estimated by the force required to break a small volume of concrete, which allows the most accurate assessment of its actual strength. Therefore, this method is used not only to determine the strength of concrete of unknown composition, but can also be used to build calibration dependencies for other non-destructive testing methods. This method is applied to heavy concretes and structural concretes on lightweight aggregates in monolithic and precast concrete and reinforced concrete products, structures and structures and establishes a method for testing concrete and determining its compressive strength by local destruction of concrete when a special anchor device is pulled out of it. This method of testing concrete with shearing makes it possible to determine the compressive strength for concrete in the strength range from 5.0 to 100.0 MPa. When developing the standard, materials GOST 22690-88 were used.
One of the most common and effective ways a quick measurement of the compressive strength of concrete or its grade is a measurement with a sclerometer, or as it is also called, a Schmidt hammer.
Conformity of the Grade and Class of concrete to the readings of the scale of the sclerometer (Schmidt hammer) in the direction of impact in accordance with the chart of the calibration curve
Concrete brand, M Concrete class,
B Vertical top, u Horizontal, u Vertically from below, unit
M100 7.5 10 13 20
- 10 12 18 23
M150 12.5 20 24 28
M200 15 24 28 32
М250 20 30 34 38
M300 22.5 34 37 41
M350 27.5 38 41 45
М400 30 41 43 47
М450 35 44 47 50
М500 40 47 49 52
M600 45 49 52 55
GOST 10180-90 Concrete. Methods for determining the strength of control samples
GOST 18105-86 Concrete. Strength control rules
GOST 22690-88 Concrete. Strength definitions mechanical methods non-destructive testing
Another method for testing concrete is shearing. This method consists in determining the degree of force that is necessary to chip off a section of concrete on the edge of the structure. Sometimes this method consists in the local destruction of concrete: within the framework of this method, the anchor device breaks out. The chipping method is the most accurate, but also the most time-consuming method of control, since the preparation of special holes is required for the installation of the anchor. Moreover, this method is not universal enough: it is not applicable in series of structures.
"Prometheus" recommends a method for determining the strength of concrete by separation with shearing in field surveys. Such methods of testing concrete by detachment are also ideal for surveying at the stages of construction, acceptance, operation and reconstruction of building objects, as well as for the manufacture of prefabricated products at enterprises producing reinforced concrete products.
Testing the mechanical properties of concrete in the laboratory
For materials such as concrete, the determination of strength by mechanical methods of non-destructive testing is desirable to control the reliability of the results by comparing data obtained directly and indirectly. This kind of research is carried out by the mechanical testing laboratory at Prometey LLC.
AT laboratory conditions physical and mechanical tests of concrete samples are carried out using all known approaches, including the basic destructive method of concrete control, methods of shock impulse and elastic rebound. It is important that the measurements are carried out by a qualified mechanical test technician - the influence of the human factor should be minimized.
As shown by mechanical testing of materials, indirect methods of mechanical testing overestimate the strength characteristics of carbonized concrete by 40–60%, and the method of separation with chipping is recognized as the most reliable.
Sheared pull-off method: advantages and limitations
All modern standards include in the program of full-scale inspections of reinforced concrete structures mechanical tests of concrete with shearing.
In practice, shear-off provides a number of advantages:
- the ability to install devices on flat areas without a rib;
- independence from power supply;
- tolerance for low temperatures;
- control of the strength of concrete class B50 and above;
- fast and convenient mounting of equipment.
If the curvature of the block does not prevent the connection of the device to the anchor, the determination of the strength of concrete by detachment with shearing can also be carried out on uneven concrete surfaces(from 5 mm). The dense reinforcement of concrete makes it difficult to test for mechanical strength using this method; at the same time, the thickness of the concrete in the measurement area should not be less than twice the length of the anchor.
Used equipment
POS-50MG4 "Skol" is designed for non-destructive testing of concrete strength by methods of rib chipping, tearing with chipping and tearing of steel disks according to GOST 22690-88.
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 get the most accurate results, on the basis of which tables are later compiled for the 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 test 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, which allow measuring the strength, both by the method of breaking off the anchor, and by the method of 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.
The ability of concrete to withstand mechanical and thermal stress is called strength. This is the most important characteristic that affects operating parameters designs.
All rules relating to testing concrete for tension, compression and bending are prescribed in GOST 18105-86. An important characteristic The reliability of the material is the coefficient of variation, which characterizes the homogeneity of the mixture (Vm).
where S m- quadratic deviation of strength, Rm is the strength of the concrete in the batch.
According to GOST 10180-67, the cubic compressive strength of the material is determined. It is calculated by compressing control cube samples with stiffeners at the age of 28 days. For class B25 and above, the prismatic index should be 0.75, for compositions with a class below B25 - 0.8.
Requirements for design strength, in addition to GOSTs, are also spelled out in SNiPs. For example, the stripped indicator of unloaded horizontal structures, having a span of less than 6 meters, should be at least 70% of the design strength, if the span exceeds 6 meters - 80%.
Sample testing makes it possible to determine the quality of the mixture, but not the characteristics of the concrete in the structure. Such studies are carried out in accordance with GOST 18105-2010 and the following methods are used:
- destructive,
- indirect destructive,
- direct destructive.
Direct methods of non-destructive testing enjoy considerable popularity. The main methods of this type include ultrasonic or mechanical.
Concrete strength control methods according to GOST22690-88
- separation;
- separation with chipping;
- rib chipping.
Tools needed for research
- the electronic unit;
- device for tearing off with a device for gluing to concrete;
- sensors;
- dowels and anchors;
- standard metal rod.
The graph reflects the strength gain of the material over time, while line A is vacuum processing, B is natural hardening, C is the change in the index after vacuum processing.
Testing the strength of concrete by pull-off method
The basis of this type of study is the measurement of the maximum force to tear off a part of a concrete structure. Moreover, the tearing load should be applied to a flat surface by gluing the device disk. Adhesives are used for bonding epoxy based. GOST22690-88 specifies adhesives ED16 and ED20 with cement filler. You can also apply two-component formulations. The separation area is determined after each test. After pull-off and force calculation, the concrete tensile strength (Rbt) is measured. Using the empirical dependence and this indicator, you can calculate the indicator R - compressive strength. To do this, use the formula:
Rbt = 0.5∛ (R^2)
Breakaway with chipping
After the concrete has hardened, an anchor device is placed in a pre-drilled hole, after which it is pulled out with a part of the concrete. This method is very similar to the one described earlier. The main difference is the way the tool is attached to the surface. The tearing force is generated by flap anchors. The anchor is placed in the hole and measured P - breaking force. GOST 22690 indicates the transition of strength concrete composition for compression according to the formula:
R = m1 * m2 *P,
where m2 is the coefficient of compressive strength transition, depending on the conditions of hardening and the type of concrete, m1 is the coefficient reflecting the maximum parameters of large aggregate (loose stone materials).
The limitations for using this research method are thick reinforcement and insignificant thickness of the structure. The surface thickness must be more than twice the length of the anchor.
Rib chipping method
The strength of concrete with this method is determined by the force (P) required to chip off a part of the structure placed on the edge outside. The instrument is fixed to the surface with anchor bolt with dowel. The following formula is used to determine the indicator:
R = 0.058 * m * (30P + P2),
where m is a coefficient reflecting the fineness of the aggregate.
Ultrasonic method
The action of ultrasonic testing devices is based on the relationship between the speed with which waves propagate through the structure and its strength. Based on this method, it was determined that the speed, as well as the time of wave propagation, correspond to the strength of concrete.
For prefabricated linear structures, the through-transmission method is used. In this case, ultrasonic transducers are located on opposite sides of the structure. Flat, hollow and ribbed plates coverings, and Wall panels are examined by surface transillumination, in which a wave transducer (flaw detector) is placed on one side of the structure.
To ensure maximum acoustic contact with working surface choose viscous contact materials (for example, grease). A dry version is possible with the use of protectors and cone nozzles. Installation of ultrasonic devices is carried out at a distance of at least 3 cm from the edge.
Tests are carried out in accordance with GOST22690.2-77. Determination of the strength of concrete is carried out within 5-50 MPa. An impact is applied to a flat surface to be tested, as a result of which two indentations are formed: on the reference metal rod and on the surface of the base. With each blow, the rod is moved 10 mm into the hole in the hammer body. The base is struck through white carbon paper. An angular scale is used to measure prints on paper.
For studies based on elastic rebound, a Schmidt hammer, pistols from Borovoy, TsNIISK, and a KM sclerometer with a rod striker are used. The cocking and start-up of the striker occur automatically at the moment the striker touches the tested base. The rebound value of the striker is fixed by a special pointer on the scale of the apparatus.
5.1. Preparation of Products and Anchor Device for Pull-Pull Tests
5.1.1. The marking of the product area for testing is carried out after visual inspection concrete surface (the presence of visible cracks, the boundaries of the tiers of concreting, chips and sagging of concrete) and determining the location and depth of the reinforcement.
5.1.2. An anchor hole is drilled in the centers of the reinforcing cells after the reinforcement mesh is detected at a distance of at least 150 mm from the boundaries of the concreting tiers, provided that there are no visible defects (cracks, chips and sagging of concrete) within a radius of 90 mm from the center of the hole.
The hole for laying the anchor must be no closer than 150 mm from the edge of the product and no closer than 70 mm from the nearest reinforcing bar or embedded part.
The distance between the holes (test points) must be at least 200 mm, and the depth of the anchor must exceed the dimensions of the coarse filler by at least 1.2 times.
5.1.3. Holes (holes) are made with a drilling, impact-rotary or impact tool with an impact energy of not more than 2 J using a guide that ensures the verticality of the hole to the reference plane. Permissible deviation from perpendicularity is not more than 1:25.
The diameter of the drill (drill) should be 16+0.5 mm for anchors ø 16x35 mm and 24...25 mm for anchors ø 24x30 mm, ø 24x48 mm.
After drilling, if necessary, calibrate the hole (hole) with a jumper of the appropriate diameter, blow it thoroughly compressed air, having cleaned of dust and concrete residues, after which the hole diameter should be 16 + 1 mm (24 + 1 mm).
For the formation of holes, it is allowed to use embedded plugs.
The depth of the hole must be for an anchor device type II, not less than:
55 mm (embedding depth 48 mm);
45 mm (embedding depth 35 mm);
40mm (embedding depth 30mm).
5.1.4. Screw a rod with a micrometer nut onto the threaded shank of the anchor device.
5.1.5 Lay the anchor device with the rod in the prepared hole until the leveling washer stops against the concrete surface (Fig. 5.1) and create a prestress in the anchor installation area, for which, with a 19 mm wrench, tighten the rod clockwise, preventing the anchor from being pulled out of the hole . Tighten with force (tightening torque 45...50 kg-m).
5.2. Preparation of the instrument for the pull-prick test
5.2.1. Install the exciter in base plate, aligning the hole in the exciter with the axis of the latch, and screw the fork into the rod of the exciter.
5.2.2. By turning the loading handle counterclockwise, bring the exciter to its original state, while the protrusion of the exciter screw in should be 99 ± 1 mm.
5.2.3. Install the device with supports on the surface of the product, insert the fork under the traction head and align its axis with thrust axis.
5.2.4. Turning the device around the rod, find a stable position of the supports, if necessary, unscrew one or two adjusting screws until they touch the surface of the product.
5.2.5. Select the gaps between the supporting surfaces of the link and the fork, for which turn the fork into the exciter rod.
5.2.6. Screw the micrometer nut all the way into the surface of the product and apply a visible mark on the concrete opposite the zero scale division of the nut.
5.2.7 Connect the electronic unit to the power exciter connector located in the power exciter cover ( connection cable supplied) and turn on the power. The indicator looks like this:
5.2.8 Use the buttons ,↓ to move the blinking to the required test method - "Cleavage with chipping" and press the button ENTER,
with a blinking value of the type of large placeholder.
5.2.9 Use the buttons ,↓ to display the required type of aggregate (granite, limestone, gravel) on the indicator and press the button ENTER.
AT On this screen, the user has the option of selecting the type of item to be tested to be archived along with the measurement result.
Then, by blinking, with the buttons ,↓and ENTER enter the type of product to be tested and then the type of anchor device used (ø 24x48, ø 24x30, ø16x35). In this case, the value of the coefficient is automatically entered into formula (3.1) for calculating the strength of concrete t 2
5.3 Performing a pull-off test
5.3.1 Perform a test, for which, uniformly rotating the loading handle clockwise, load the anchor to the control force or until the concrete fragment breaks off and fix the load R. Then tighten the micrometric nut until it stops at the concrete surface and determine the amount of anchor slippage ∆h with an accuracy of ± 0.1 mm (division value of the micrometric nut is 0.1 mm)
During testing, the loading rate must be maintained within 1.5 ... 3 kN / s.
5.3.2 The loading speed is displayed in the upper line of the indicator as symbols >>>>>□□□□□□<<<<<.
The illumination of the >>> symbols indicates the need to increase the loading rate, since it is less than 1.5 kN/sec. At a loading speed of more than 3 kN / s, the symbols are lit<<<.
The illumination of the leftmost symbol □ corresponds to the loading speed of 1.5 kN/s, the rightmost symbol □ corresponds to 3 kN/s.
5.3.3 To obtain the appropriate concrete strength, press the button ENTER, in this case, the concrete strength is automatically calculated according to the formula (3.1), and the indicator has the form, for example:
5.3.6 By pressing the buttons (↓) enter the value ∆h read from the micrometric nut, for example 3.6 mm and by pressing the button ENTER, make the adjustment.
The indicator looks like this:
| R k \u003d 26.8 MPa 0.9 R k \u003d 33.69 kN |
The values of Rk and Rk are stored in the device memory and marked with the type of product, date and time of testing.
5.3.7 The required number of tests in one area:
For anchors with an insertion depth of 48 mm and 35 mm, one test;
For anchors with an insertion depth of 30 mm, three tests.
5.3.8. To conduct repeated tests on the same product without changing the initial data, you must press the button again ENTER, perform auto-tuning in accordance with clause 6.2.10. and perform tests in accordance with sp. 5.3.1. ..5.3.6.
5.3.9. Record the test results in the protocol in accordance with Appendix 2 of this Guide.
5.4. Performing pull-off tests with shearing according to individual calibration dependencies
5.4.1. Enter Mode 2, for which, after turning on the device, press the button MODE, use the or ↓ buttons to set the flashing message "Ind. dependent" and press the button ENTER. The indicator looks like:
5.4.2. Use the buttons (↓) to set the flashing of the required method - "Separation"(separation with chipping) and press the button ENTER, after which the indicator looks like:
5.4.4. Prepare the device for operation in accordance with p.p. 6.2.1.. .6.2.7 and connect the electronic unit to the exciter.
5.4.5. Push button ENTER perform auto-tuning of the device, after which the indicator looks like, for example:
| >>> 04 P=00.00 kN |
indicating that the device is ready for operation.
5.4.6. Carry out tests in accordance with p.p. 5.3.1 ... 5.3.6.
Rib chipping method
5.5. Preparation of the product for testing by the rib shearing method.
5.5.1. 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.
5.6. Preparing the device for rib shearing tests
Attention! Before starting each test, it is necessary to bring the power exciter to its initial state by turning the loading handle counterclockwise (extension of the power exciter screw θ = 100 ± 1 mm).
Significant resistance to rotation may indicate that the piston of the working cylinder is in extreme positions when the exciter may break.
The use of extension arms is prohibited.
5.6.1. Insert the power exciter into the body of the power frame, aligning the hole in the power exciter with the axis of the latch and, turning the loading handle counterclockwise, bring the power exciter to its original state, while the protrusion of the screw of the power exciter in should be 100 ± 1 mm.
5.6.2. Turning the steering wheel counterclockwise, unscrew the clamping screw until the heel stops in the bracket.
5.6.3. Insert the extension rods in the holes of the grips and fix them with a lock so that the size With exceeded the size of the face of the controlled product by no more than 45 mm.
5.6.4. Install the power frame with the power exciter on the controlled product (see Fig. 5.2) and, turning the steering wheel clockwise until the heel stops against the product, fix it on the product.
5.6.5. Insert the rod with the bracket into the fork grip of the exciter.
5.6.6. Check the position of the bracket. If the gap between the chipping plate and the workpiece is more than 3 mm, it is necessary to tighten the rod with the bracket into the rod (one turn of the rod corresponds to moving the clip by 1 mm), if there is no gap between the chipping plate and the workpiece, or the size a less than 20 ± 2 mm, it is necessary to unscrew the rod with the bracket for one turn to check the appearance of a gap and match the size a with the required value - 20 ± 2mm.
5.6.7. Use buttons , ↓ to move the blinking to the required test method - “Skol ribs" and press the button ENTER, after which the maximum size of coarse aggregate (fractional) in the concrete of the controlled product is displayed on the indicator, with a flashing value of 20 mm.
5.6.8. By pressing the buttons , ↓ set the blinking to the required (suggested) size of the filler and press the button ENTER. In this case, the value of the coefficient m = 1.0 (1.05 or 1.1) is entered into the formula (3.2) for calculating the strength of concrete. After that, the indicator looks like, for example:
In this screen, the user has the option of selecting the type of product to be tested to be stored in memory along with the measurement result.
Use the buttons , ↓ to display the type of product being tested and press the button ENTER.
5.6.9. At the end of the input of the initial data, the indicator displays the message:
If the electronic unit is connected by cable to the exciter, by pressing the button ENTER perform auto-tuning of the device, after which the indicator looks like, indicating the readiness of the device for testing:
| >>> 0.2 P= 00.00 kN |
Rice. 5.2. General form device POS-50MG4 "Skol" in the configuration "Chipping the rib"
5.7. Performing Rib Shearing Tests
5.7.1. Perform a test, for which rotate the loading handle clockwise so that the loading speed is within the limits established by GOST 22690 (from 0.5 to 1.5 kN / s).
Loading is carried out until the destruction of concrete, or until the control force.
5.7.2. The loading speed is displayed in the top line of the indicator during testing, simultaneously with the load.
5.7.3. To obtain the appropriate concrete strength, press the button ENTER. In this case, the concrete strength is calculated according to the formula (3.2) and the test result is stored. The indicator looks like this:
| ↗ R k = 38.3 MPa 0.2 P k = 18.74 kN |
The values of R k and R k are stored in the device memory and marked with the type of product, date and time of testing.
5.7.4. To conduct repeated tests on the same product without changing the initial data, you must press the button again ENTER, perform auto-tuning in accordance with clause 5.6.10. and perform tests in accordance with paragraphs. 5.7.1...5.7.3.