How to use a sclerometer for concrete: application features, tables with indications

Any construction project must ensure that the concrete is of the highest quality and durability, and testing the concrete’s hardness is an important way to do this. A useful instrument for determining the surface hardness of concrete is a sclerometer, sometimes referred to as a rebound hammer. This non-destructive testing technique offers important information about the consistency and strength of concrete constructions.

Sclerometers are a common tool among engineers and construction workers because they are simple to use. Utilizing a spring-loaded hammer to strike the concrete surface and measuring the rebound distance is how the tool operates. Concrete’s hardness is correlated with its compressive strength, and this can be ascertained with the help of a scale that displays the rebound value.

To ensure accurate results, it is imperative to adhere to proper procedures when applying a sclerometer test. To obtain a trustworthy average reading, the test should be run in several locations on a clean, smooth concrete surface. It’s crucial to take into account additional elements that may have an impact on the readings, such as the age of the concrete and any current damage.

Standard indication tables are used to interpret the results. These tables serve as a guide for estimating compressive strength from rebound values. Experts can determine whether the concrete satisfies the project’s specifications by comparing the measurements to these standards.

Sclerometer testing can be incorporated into your concrete evaluation process to greatly improve on-site quality control measures. It contributes to the early detection of possible problems, guaranteeing the construction’s longevity and safety. For those working in concrete construction, the sclerometer is still a vital tool due to its dependability and simplicity of use.

Operating principle of the device

A sclerometer is a tool used to measure the strength of concrete. It works by capturing an electrical shock wave. Since the turn of the 20th century, when the Schmidt hammer and other antiquated tools were employed everywhere, technology has been widely employed in the construction industry.

With sclerometers, you can accomplish the following objectives:

  • Control of the strength of concrete and reinforced concrete structures.
  • Identification of cracks, large pores, non-vibrated areas and other defects on the surface of the material.
  • Checking the homogeneity of the structure of concrete placed in the structure after hardening.

Sclerometers do not require surface damage to the structure and do not require subsequent restoration, in contrast to many other non-destructive methods of testing the strength and hardness of concrete, such as tearing with chipping.

How the device works?

Sclerometers can be broadly classified into three categories based on their design, method of operation, and final result accuracy. A detailed description of each of these control device categories can be found below.

Ultrasonic

The UK sclerometer is a cutting-edge, contemporary instrument that doesn’t make contact with concrete.

The following algorithm serves as the foundation for the device’s operation:

  • The device consists of two main elements – a transmitter that generates an ultrasonic wave, which propagates in the structure of the structure, and a receiver that registers the signal.
  • The receiver and transmitter can be located in a single housing, or manufactured as two independent devices.
  • To measure the strength and uniformity of a structure using two separate devices, each of them is applied to the surface on both sides of a wall, ceiling, pylon, column or beam.
  • The transmitter sends a signal to the body of the structural element, and the receiver on the reverse side registers it.
  • When determining strength, the speed of wave propagation through the structure is taken into account, as well as losses due to signal absorption in the presence of inhomogeneities inside the reinforced concrete element.
  • In the case of using a compact sclerometer with a transmitter and receiver in a single housing, the pulse is recorded by reflecting the wave from obstacles, voids and seals.
  • Devices from among the increased price category are equipped with a wide-format liquid crystal display, which displays a defectoscopy graph, allowing you to get a complete picture and assess the condition of the structure.

Increased accuracy and dependability are the hallmarks of ultrasonic devices, which enable up to 10–15 iterations per minute in various structural element regions.

Electronic

A processor with a display on which the results are shown and an impact spring block make up the control device known as an electronic sclerometer. The fundamental idea behind how electronic devices work is:

  • The impact block is made in the form of a pen or a gun.
  • To activate the equipment, it is necessary to cock the spring until the lock is triggered.
  • The recording module is turned on by holding the power button for a long time.
  • The device sets different boundary parameters, depending on the design class of concrete, type of structure and ultimate resistance of the surface of the solid material.
  • The gun has a support plane with contact points that are applied to the concrete surface.
  • The impact of a solid steel ball is produced after the operator presses the trigger with the gun in a fixed position.
  • During an impact, an elastic rebound occurs, the magnitude of which is recorded by the processor.
  • The screen displays the rebound value in mm, or already processed results reduced to calculated values ​​- kgf/cm 2 or MPa.

Due to the heterogeneity of concrete, control measurements must be taken simultaneously in multiple zones on the same structure. This tool works best when working with fine-grained concrete. Significant errors may arise when testing the strength of heavy materials with large aggregate, the fraction of which exceeds 70 mm.

Mechanical

An upgraded Schmidt hammer is the most basic tool for non-destructive concrete surface strength testing.

The application of a straightforward algorithm forms the foundation of the working principle:

  • The device consists of a single impact block with a powerful spring and a recording scale.
  • Before use, the spring is brought to a stressed state.
  • The device is applied to the surface of the concrete structure.
  • By pressing the button, the spring is released, and a hard ball strikes the test material with force.
  • The scale records the value of the elastic rebound in mm.
  • The obtained readings are deciphered using a graph of the non-linear dependence of the rebound value and the strength of the structure in kgf/cm2 or MPa.

Experts advise against using a mechanical device to reach an official conclusion because the device’s readings could contain an error depending on its design, brand, and retail price.

Concrete can be tested with a sclerometer, which is a simple yet important tool for determining the material’s hardness and quality. This convenient tool offers accurate and timely measurements, assisting in ensuring that concrete structures adhere to regulations. This post will go over how to use a sclerometer correctly, provide important application hints, and provide simple-to-read tables with standard indications so you can accurately interpret your results. Your concrete projects’ longevity and integrity can be greatly improved by knowing how to use this tool properly, whether you’re a professional builder or a do-it-yourself enthusiast.

Table with transcripts of readings

The amount of elastic rebound in millimeters is the sclerometer’s absolute result, which is the foundation for the indicator decoding process.

You can accomplish this by applying a sophisticated formula that shows the readings’ indirect dependence. Nevertheless, using the unit conversion table below or a pre-made nonlinear dependence graph will suffice to get an accurate result:

Material strength’s dependence on mechanical sclerometer scale readings

Grade of cement binder (M) and concrete compression class (B) Vertical impact of a sclerometer on the surface being examined at a control point, when impacted from above Vertical impact of a sclerometer on the surface being examined at a control point, when impacted from below Horizontal impact of the sclerometer on the surface being examined at the control point
M100 (B7.5) 9-11 19-21 12-14
M100 (B10) 11-13 22-24 17-19
M150 (B12.5) 19-21 27-29 23-25
M200 (B15) 23-25 31-33 27-29
M250 (B20) 29-31 37-39 33-35
M300 (B22.5) 33-35 40-42 36-38
M350 (B27.5) 37-39 44-46 40-42
M400 (B30) 40-42 46-48 42-44
M450 (B35) 43-45 49-51 46-48
M500 (B40) 46-48 51-53 48-50
M600 (B45) 48-50 54-56 51-53

Contrary to popular belief, the strength of concrete can be expressed using a sclerometer as either grade or class:

  1. The grade represents surface strength, characterizing the hardness of a concrete structure in the range from 50 to 1000 kgf/cm2 .
  2. Class is a value that determines the structural strength of concrete when crushing prototypes – cubes with dimensions of 100x100x100 mm or 150x150x150 mm in order to determine the ultimate resistance of the material before destruction.

The brand and class dependence for various material categories is provided in the following table:

Material grade determined by a sclerometer under the surface impact of an impact block Comparison of the actual concrete grade obtained from the results of measurements and the material class based on the determination of physical and mechanical characteristics by a destructive method
Concrete class, according to tables SP 63.13330.2012 Relative concrete grade obtained by interpolating adjacent values ​​for each iteration, corresponding to the standard class of material
Heavy and lightweight concretes with large aggregate of different density Variation coefficient between concrete class and grade, % Indications for cellular concrete, without large aggregate Variation coefficient between concrete class and grade, %
M15 B1 14.47 -3.5
M25 B1.5 21.70 -13.2
M25 B2 28.94 15.7
M35 B2.5 32.74 -6.5 36.17 3.3
M50 B3.5 45.84 -8.1 50.64 1.3
M75 B5 65.48 -12.7 72.34 -3.5
M100 B7.5 98.23 -1.8 108.51 8.5
M150 B10 130.97 -12.7 144.68 -3.55
M150 B12.5 163.71 9.1 180.85
M200 B15 196.45 -1.8 217.02
M250 B20 261.93 4.8
M300 B22.5 294.68 -1.8
M300 B25 327.42 9.1
M350 B25 327.42 -6.45
M350 B27.5 360.18 2.9
M400 B30 392.90 -1.8
M450 B35 458.39 1.9
M500 B40 523.87 4.8
M600 589.35 1.8
M700 B20 654.84 -6.45
M700 B21 720.32 2.9
M800 B22 785.81 -1.8

The computed values in the tables only apply when assessing a concrete structure’s strength 28 days after the liquid material was placed and after it has completely hardened.

Possible errors and what they depend on?

There is no metrology apparatus on the field that can provide measurement results that are 100% accurate. In this sense, manufacturers establish allowable mistakes that don’t compromise a capital structure’s ability to operate safely.

Variations rely on the following elements:

  • Type of sclerometer – ultrasonic and electronic devices have an extremely low error of up to 1.5% -2.0%. Mechanical instruments with a conventional analogue scale may exhibit discrepancies of 5% to 10%.
  • Climatic conditions and temperature and humidity conditions – most factories allow additional errors that do not exceed normal limits, up to 0.5% for every 10 o C. As a rule, ultrasonic and electronic devices can operate in the temperature range from –10 to +40 o C.
  • Type of surface and quality of concrete – in the presence of inhomogeneities and a large number of defects, readings for each iteration may vary by 10% or more. In such cases, experts recommend not taking into account measurements that clearly stand out from the average values, provided that there are no more than 10% of such zones on the surface of the structure.

Sclerometers are among the most accurate instruments in use. The majority of Russian electronic or ultrasonic models are registered in the State Register and are available for use by official expert bodies to provide official opinions. These opinions can then be supplied to various authorities that are qualified to receive them, such as courts.

Topic Details
Using a Sclerometer A sclerometer, also known as a rebound hammer, is used to measure the surface hardness of concrete. It"s a simple and quick test that provides an indication of the compressive strength of the concrete.
Application Features To use a sclerometer, press it against the concrete surface and release the hammer. The rebound value, which shows how far the hammer bounces back, indicates the surface hardness. This value can then be converted to an estimated compressive strength using standard tables.
Indication Tables The tables with indications convert the rebound values to approximate compressive strength. These tables are essential for interpreting the sclerometer results and ensuring accurate assessments of the concrete"s condition.

Sclerometers, also known as rebound hammers, are a useful and simple tool for determining the hardness of concrete. It is incredibly useful for both construction and maintenance work because it provides a rapid and non-destructive method of evaluating the strength and quality of concrete surfaces. Professionals are able to guarantee that concrete structures fulfill the required safety and performance standards by comprehending the particular application features and correctly interpreting the readings.

When using a sclerometer, it’s imperative to follow the right procedures in order to get accurate results. This entails appropriately prepping the concrete surface, running several tests in different places, and averaging the results to get a representative value. Maintaining the accuracy of the measurements also requires routine sclerometer calibration.

An essential component of efficiently using a sclerometer is utilizing tables with indications. These tables aid in converting rebound values into compressive strength values, giving a clear picture of the state of the concrete. Users can determine whether concrete is suitable for its intended use or pinpoint areas that might need more research or maintenance by consulting these tables.

All things considered, any construction professional’s toolkit should include the sclerometer. It is a practical choice for on-site testing due to its simplicity of use and quick results. Users can get the most out of this instrument in their concrete assessment processes by using the supplied tables and following the suggested application practices.

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Dmitry Sokolov

Chief engineer in a large construction company. I have extensive experience in managing construction projects and implementing modern technologies.

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