A Schmidt hammer, also known as a Swiss hammer or a rebound hammer or concrete hammer test, is a device to measure the elastic properties or strength of concrete or rock, mainly surface hardness and penetration resistance. It was invented by Ernst Schmidt, a Swiss engineer.[1]
Testing the compressive strength of a concrete cube using Schmidt hammer
The hammer measures the rebound of a spring-loaded mass impacting against the surface of a sample. The test hammer hits the concrete at a defined energy. Its rebound is dependent on the hardness of the concrete and is measured by the test equipment. By reference to a conversion chart, the rebound value can be used to determine the concrete's compressive strength. When conducting the test, the hammer should be held at right angles to the surface, which in turn should be flat and smooth. The rebound reading will be affected by the orientation of the hammer: when used oriented upward (for example, on the underside of a suspended slab), gravity will increase the rebound distance of the mass, and vice versa for a test conducted on a floor slab. Schmidt hammer measurements are on an arbitrary scale ranging from 10 to 100.
Schmidt hammers are available from manufacturers in several different energy ranges, including (i) Type L-0.735 Nm impact energy, (ii) Type N-2.207 Nm impact energy, and (iii) Type M-29.43 Nm impact energy.
The test is also sensitive to other factors:
Prior to testing, the Schmidt hammer should be calibrated using a calibration test anvil supplied by the manufacturer. Twelve readings should be taken, dropping the highest and lowest, and then taking the average of the ten remaining. This method of testing is classed as indirect as it does not give a direct measurement of the strength of the material. It simply gives an indication based on surface properties, and as such is suitable only for making comparisons between samples.
This method for testing concrete is governed by ASTM C805. ASTM D5873 describes the procedure for testing of rock.
References[edit]External links[edit]
Retrieved from 'https://en.wikipedia.org/w/index.php?title=Schmidt_hammer&oldid=899368875'
Clegg Impact Tester / Clegg Decelerometer
New for 2019 - Wireless bluetooth display with GPS data logging. The NEWPNCLEGG-S-2.25-A- Clegg Impact Tester 2.25 kg model reads out from 0 to 150 Gravities or 0 to 15 CIT's and has a better accuracy range (+/- 1% or 1.5 G Accuracy) as compared to the 0-1000 Gravity unit (+/- 1% or 10 G Accuracy) for testing soft surfaces like natural and artificial athletic fields, infill products and sports fields. This model is the same model that is used to test all NFL National Football League Stadium Fields before games. Instruction manual comes with conversion formula to convert readings to F355 readings. Note the 150 g maximum reading on this unit is sufficient for maximum impact readings in the ASTM F355 range after using the conversion formula included in the Turf-Tec Instruction manual. 200 g's on F355 impact tester = 135 g's on Clegg Impact Tester.
The principle behind the Clegg Impact Soil Tester, also called the Clegg Hammer and Clegg Decelerometer is used to obtain a measurement of the deceleration of a free falling mass (Hammer) from a set height onto a surface under test to determine hardness. The impact of the hammer produces an electrical pulse, which is converted and displayed on the Control Unit in units of gravities 'G-max' or tens of gravities 'CIT'. Reference ASTM test methods D5874 and F1702.
The standard test protocol developed by Dr. Clegg is to drop the hammer four consecutive times on the same location with the highest value result in the series taken as the Peak Clegg Impact Test result. Since that time, other test protocols have been used based on the materials under test and the application. These other protocols like the ones used for testing artificial turf test the area with a single drop. The Clegg offers the convenience of rapidly scanning compaction variation over large areas. In research studies, 250 tests were performed with the Clegg in a four hour period.
The Clegg may be transported and operated by one person, allowing for low cost, rapid field and laboratory testing and direct readout of the test results. The Clegg can test a full range of natural grass fields & synthetic turf fields, all athletic surfaces, pads, infill materials and amendments where hardness or impact characteristics need to be controlled for safety or playability. The Clegg can also test a full range of soil and stone as encountered in the construction of flexible pavement and earthworks. It is useful for quickly checking variations during construction and monitoring changes over time due to seasonal environmental changes or road traffic as well as testing natural and 'as constructed' conditions. Suggested Reading from Penn State University's Center for Sports Turf Research
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'Surface Hardness (Gmax)' By: Andrew S. McNitt, Thomas Serensits and Dianne M. Petrukak http://cropsoil.psu.edu/ssrc/research/infill/surface-hardness-gmax Also: http://plantscience.psu.edu/research/centers/ssrc/sportsturf-scoop Clegg Impact Tester - 2.25 kg Model shown with Field Scout Moisture Sensor (Not Included) and Turf-Tec Shear Strength Tester (Not Included). These are the three testing equipment that each NFL Field uses before and after games to check for safety and playability PNCLEGG-S-0.5 - Clegg Impact Tester 0.5 kg model PNCLEGG-S-2.25 Clegg Impact Tester 2.25 kg model (0 to 1000 Gravities) (+/- 1% or 10 G Accuracy)
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PNCLEGG-S-2.25-A- Clegg Impact Tester 2.25 kg model (0 to 150 Gravities) For testing Athletic Fields (+/- 1% or 1.5 G Accuracy) Case-Clegg-Tshear - Optional Hard Case for Clegg
Turf-Tec International Terms of Sale and Warranty LIMITED WARRANTY OF TURF-TEC INTERNATIONAL PRODUCTS Turfgrass Products Corporation - dba - Turf-Tec International ('Seller') warrants to the final purchaser, that all Turf-Tec International tools will be free from defects in material or workmanship for a period of one year from date of purchase. SELLER'S SOLE OBLIGATION AND YOUR EXCLUSIVE REMEDY under this Limited Warranty and, to the extent permitted by law, any warranty or condition implied by law, shall be the repair or replacement of parts, without charge, which are defective in material or workmanship and which have not been misused, carelessly handled, or improperly repaired by persons other than Turf-Tec International. To make a claim under this Limited Warranty, you must return the complete tool, transportation prepaid, to Turf-Tec International after contacting Turf-Tec International and receiving a return authorization number. Please include a dated proof of purchase with your tool. ANY IMPLIED WARRANTIES SHALL BE LIMITED IN DURATION TO ONE YEAR FROM DATE OF PURCHASE. IN NO EVENT SHALL SELLER BE LIABLE FOR ANY INCIDENTAL OR CONSEQUENTIAL DAMAGES (INCLUDING BUT NOT LIMITED TO LIABILITY FOR LOSS OF PROFITS) ARISING FROM THE SALE OR USE OF THIS PRODUCT. THIS LIMITED WARRANTY GIVES YOU SPECIFIC LEGAL RIGHTS, AND YOU MAY ALSO HAVE OTHER RIGHTS WHICH VARY FROM STATE TO STATE IN THE U.S., PROVINCE TO PROVINCE IN CANADA AND FROM COUNTRY TO COUNTRY. Return Policy: Turf-Tec International has been in business since 1976 and we pride ourselves in producing quality tools that last for years and years. We offer a 100% satisfaction guarantee on all of our products and will gladly accept any return for a credit to be used at Turf-Tec International for future orders or a check refund may be issued. There is a 30% re-stocking fee for all returned merchandise whether an in house credit or a refund is requested and shipping charges will not be refunded. All returned merchandise must be new and in re-salable condition. Turf-Tec will only receive returns if a return authorization number is first obtained from Turf-Tec International. Again, all returned merchandise must be new and in re-salable condition and Turf-Tec does not pay return shipping fee's.
Impact Test Equipment UkNDTnet 1998 February, Vol.3 No.2The Impact-Echo Methodby Mary J. Sansalone and William B. Streett *
AbstractWhat Is An Impact Hammer
Impact-echo is an acoustic method for nondestructive evaluation of concrete and masonry, invented at the U.S. National Bureau of Standards (NBS) in the mid-1980's, and developed at Cornell University, in Ithaca, New York, from 1987-1997. This article provides a brief description of the method, information about test equipment manufactured by Impact-Echo Instruments, LLC of Ithaca, New York [1], a description of a new book about impact-echo, and a list of case studies describing a variety of applications. In December of 1997 the American Society of Testing Materials (ASTM) approved a new standard entitled, 'Standard Test Method for Measuring the P-Wave Speed and the Thickness of Concrete Plates Using the Impact-Echo Method.' This standard will appear in the 1998 Annual Book of ASTM Standards.
The Impact-Echo Method
Impact-echo is a method for nondestructive testing of concrete and masonry structures that is based on the use of impact-generated stress (sound) waves that propagate through concrete and masonry and are reflected by internal flaws and external surfaces. Impact-echo can be used to determine the location and extent of flaws such as cracks, delaminations, voids, honeycombing, and debonding in plain, reinforced, and post-tensioned concrete structures, including plates (slabs, pavements, walls, decks), layered plates (including concrete with asphalt overlays), columns and beams (round, square, rectangular and many I and T cross-sections), and hollow cylinders (pipes, tunnels, mine shaft liners, tanks). The method can be used to locate voids in the grouted tendon ducts of many types of post-tensioned structures. It can provide thickness measurements of concrete slabs with an accuracy better than three percent, and it can locate voids in the subgrade directly beneath slabs and pavements. The method can be used to determine thickness or to locate cracks, voids, and other defects in masonry structures where the brick or block units are bonded together with mortar.
When properly used the impact-echo method has achieved unparalleled success in locating flaws and defects in highway pavements, bridges, buildings, tunnels, dams, piers, sea walls, and many other types of structures. Its use has resulted in savings of millions of dollars in repair and retrofit costs on bridges, retaining walls and other large structures.
Impact-echo is not a 'black-box' system that can perform blind tests on concrete and masonry structures and always tell what is inside. The method is used most successfully to identify and quantify suspected problems within a structure, in quality control applications, such as measuring the thickness of new highway pavements, and in preventive maintenance programs, such as routine evaluation of bridge decks to detect delaminations. In all of these situations, impact-echo testing has a focused objective, such as locating cracks, voids or delaminations, determining the thickness of concrete slabs, or checking a post-tensioned structure for voids in the grouted tendon ducts. Experience has shown that a thorough understanding of the impact-echo method and knowledge about the structure being tested are both essential for successful field work.
The impact-echo method was invented and diverse applications were developed in a relatively short period of time, largely through the efforts of small research groups at the U.S. National Bureau of Standards (from 1983-86) and Cornell University (1987-present). Detailed information about the method and its applications has been available only through technical reports and journal articles of limited distribution. While the term 'impact-echo' has gained widespread use, it has been misapplied to other techniques to which it bears little relation. The purpose of this book is to provide a single, comprehensive, authoritative source of information for engineers, scientists, students and others who wish to understand the impact-echo method and make full use of its capabilities. Case studies illustrating the use of the method are presented throughout the book.
Destructive and Nondestructive Testing
The traditional, and still most widely used, test methods for concrete and masonry are destructive methods, such as coring, drilling or otherwise removing part of the structure to permit visual inspection of the interior. While these methods are highly reliable, they are also time consuming and expensive, and the defects they leave behind often become focal points for deterioration.
Over the past several decades, a range of nondestructive tests, including X-rays, gamma rays, radar, infra-red thermography, and acoustic methods, have become widely used, not only for concrete, but for other structural materials [Malhotra & Carino, 1991; Carino, 1994]. Acoustic methods are the oldest and most widely used form of nondestructive testing. They are based on the propagation, and in some cases reflection, of stress waves in solids. A well known example is striking an object with a hammer and listening to variations in the 'ringing' sound to detect the presence of internal voids, cracks or other defects. Three techniques based on stress wave propagation, and differentiated by the methods used to generate and receive stress waves, have been used for evaluation of concrete. They are [2-1]the through-transmission or pulse-velocity method, [2-2] resonance methods, and [2-3] echo methods [Sansalone and Carino, 1986]. We restrict our interest here to echo methods for flaw detection in concrete structures other than deep foundations 1.
1There are a variety of impact-based techniques for testing deep foundations [Malhotra and Carino, 1991].
Using the time base of the display, the travel time of the pulse is determined. If the wave velocity in the medium is known, the travel time can be used to determine the location of the defect or interface where the reflection occurs.
Since their introduction in the early 1940s, ultrasonic pulse-echo methods have been developed extensively, and have been become an efficient, versatile and reliable nondestructive test method for metals, plastics, and other homogeneous materials. Apart from limited use in detecting flaws in or measuring the thickness of thin concrete members, ultrasonic methods have previously had little success in the testing of concrete, because the high-frequency stress waves they employ (typically 100 kHz and above) are strongly attenuated by the heterogeneous nature of this material.
In the early 1970s, impact methods began to be used for integrity testing of deep foundations, such as piles. Hammers were used to generate very low frequency waves (less than 1 kHz) that could be used to determine the length of piles [Sansalone and Carino, 1986; Malhotra and Carino, 1991]. In the early 1980s research engineers at the U.S. National Bureau of Standards explored the use of short duration mechanical impacts, produced by small steel spheres, as a source of stress waves for testing concrete structural elements, such as slabs [Sansalone, 1986; Sansalone and Carino, 1986]. They found that by carefully choosing the diameter of the sphere, it is possible to generate stress waves with frequencies up to about 80 kHz that propagate through concrete as though it were a homogeneous elastic medium, but are reflected from internal flaws and interfaces. Researchers at National Bureau of Standards coined the term impact-echo to describe this method, and to set it apart from pulse-echo methods in which transducers are used to generate stress waves. In the mid-1990s this method was extended to masonry structures [Williams and Sansalone, 1996; Williams, et. al., 1997].
How Impact-Echo Works
It is the patterns present in the waveforms and spectra (especially the latter) that provide information about the existence and locations of flaws, or the dimensions of the cross-section of the structure where a test is performed, such as the thickness of a pavement. For each of the common geometrical forms encountered in concrete structures (plates; circular and rectangular columns; rectangular, I-, and T-beams; hollow cylinders; etc.), impact-echo tests on a solid structure produce distinctive waveforms and spectra, in which the dominant patterns-especially the number and distribution of peaks in the spectra-are easily recognized. If flaws are present (cracks, voids, delaminations, etc.) these patterns are disrupted and changed, in ways that provide qualitative and quantitative information about the existence and location of the flaws.
The Impact-Echo Test System
I. Basic impact-echo hardware and software, without a computer.
Systems Type A and Type B described here do not include a computer, and are designed for users who have suitable computer or wish to select their own. For information on selected complete systems, including a computer, scroll down this page. Click here for general information on computer requirements and recommendations.
Impact-Echo Test System, Type A
Impact-Echo Test System, Type B
II. Complete systems, with computer included.
These systems are shipped with the Imago software and the data acquisition card installed. They are ready for immediate use. Impact-Echo Test System (type A or B above) with Toshiba Tecra 510CDT notebook computer and Toshiba Desk Station V (docking station). (Only three remaining.)
Demo Program
A file named 'demozip.exe' (1.3MB) which contains two demo programs is available for download [3]: (1) an animated simulation of the propagation and reflection of impact-generated stress waves in a concrete slab, which explains the physical principles of impact-echo; and (2) an introduction to the organization and use of Imago software -- the software used with Impact-Echo Test Systems manufactured by Impact-Echo Instruments, LLC.
Applications
When properly used, the impact-echo method has achieved unparalleled success in locating flaws and defects in highway pavements, bridges, buildings, tunnels, dams, piers, sea walls and many other types of structures. It can also be used to measure the thickness of concrete slabs (pavements, floors, walls, etc.) with an accuracy of 3 percent or better.
Impact-echo is not a 'black-box' system that can perform blind tests on concrete and masonry structures and always tell what is inside. The method is used most successfully to identify and quantify suspected problems within a structure, in quality control applications (such as measuring the thickness of highway pavements) and in preventive maintenance programs (such as routine evaluation of bridge decks to detect delaminations). In each of these situations, impact-echo testing has a focused objective, such as locating cracks, voids or delaminations, determining the thickness of concrete slabs or checking a post-tensioned structure for voids in the grouted tendon ducts.
Experience has shown that an understanding of the physical principles of the impact-echo method and information about the structure being tested are both necessary for successful field work.
Case Studies
The following case studies illustrate how the impact-echo method and instrument can be used as a condition assessment tool for an engineer involved in evaluation of concrete structures. (One or both of the authors were involved in each of the investigations discussed, often working with the consultant or agency responsible for structural evaluation and repair.) Each of the cases presented includes a description of the structure and the problems to be diagnosed. The role of impact-echo is discussed, and the results of impact-echo testing are summarized. A statement about how the impactecho results were verified is given.
Impact-Echo: The Book
Impact-Echo: Nondestructive Evaluation of Concrete and Masonry
by
Mary J. Sansalone and William B. Streett (1997) 339 pp.[7] ReferencesAbout the Authors
Professor Mary J. Sansalone1 (PhD, Cornell) is the principal inventor of the impact-echo method, and a leading authority on the use of transient stress waves for nondestructive evaluation of heterogeneous materials. She has received numerous awards for research and teaching, including the Wason Medal for Materials Research from the American Concrete Institute, a Weiss Presidential Fellowship from Cornell University, and the U.S. Professor of the Year Award from the Council for Advancement and Support of Education (CASE) and the Carnegie Foundation. She shares a patent with one of her former graduate students for a portable, computer-operated system for impact-echo testing in the field. |Top |
Email: [email protected] Homepage: http://www.engr.cornell.edu/cee/Sansalone.html
William B. Streett (PhD, University of Michigan) is the President of Impact-Echo Instruments, LLC, a company that manufactures and markets impact-echo test equipment. He is a graduate of the U.S. Military Academy at West Point, New York, where he was a member of the faculty for 15 years. He was a member of the faculty of Cornell University from 1978-95, and was Dean of Engineering from 1984-93. In addition to his work on the impact-echo method, his expertise includes computer simulations of molecular liquids and experimental studies of fluids at extremes of pressure and temperature. He conducted research at Oxford University under a NATO Fellowship, and later under a Guggenheim Fellowship. He is the author of the software that is used with the impact-echo field unit manufactured by his company.
Email: [email protected] Homepage of Impact-Echo Instruments: http://www.impact-echo.com/
1 Mary J. Sansalone is a Professor of Civil Engineering at Cornell University in Ithaca, New York. She has no involvement with commercialization of impact-echo, or with the company, Impact-Echo Instruments, LLC, mentioned in this paper.
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