NDTnet 1998 February, Vol.3 No.2

• Concrete Impact Hammer Test
• Impact Hammer Test Equipment Review
• Impact Hammer Test Equipment Parts

The Impact-Echo Method

by Mary J. Sansalone and William B. Streett *

TABLE OF CONTENTS

Abstract

Abstract

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].

Figure 1. Schematic of pulse-echo technique applied to the testing of concrete.

In echo methods a stress pulse is introduced into the test medium at an accessible surface by a transducer or by mechanical impact. If a transmitter is used, the method is called pulse-echo; if mechanical impact is used, the method is called impact-echo. As shown in Figure 1, in pulse-echo techniques the pulse propagates through the medium and is reflected by material defects or by interfaces between regions of different densities and/or elastic moduli. These reflected waves, or echoes, are monitored by a second transducer coupled to the surface of the test object near the pulse source. The transducer output is displayed on an oscilloscope or similar device.
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

Figure 2. Simplified diagram of the impact-echo method.

Impact-echo is based on the use of transient stress waves generated by elastic impact. A diagram of the method is shown in Figure 2. A short-duration mechanical impact, produced by tapping a small steel sphere against a concrete or masonry surface, is used to generate low-frequency stress waves that propagate into the structure and are reflected by flaws and/or external surfaces. Surface displacements caused by reflections of these waves are recorded by a transducer, located adjacent to the impact. The resulting displacement versus time signals are transformed into the frequency domain, and plots of amplitude versus frequency (spectra) are obtained. Multiple reflections of stress waves between the impact surface, flaws, and/or other external surfaces give rise to transient resonances, which can be identified in the spectrum, and used to evaluate the integrity of the structure or to determine the location of flaws.
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

A typical impact-echo test system

A typical impact-echo test system is shown in the adjacent photograph. Its principal components are a cylindrical handheld transducer unit; a set of spherical impactors; a portable computer; a high-speed, analog-to-digital data acquisition system (on a full-sized ISA card installed in the computer); and a software program that controls and monitors the test and displays the results in numerical and graphical form. The entire system weighs less than 14 kilograms (about 30 pounds) and is powered by a 110/220-volt a.c. source or by a 12-volt car or truck battery. Two hand-held units, clamped in a spacer bar, are used to measure wave speed. A single hand-held unit, as shown here, is used for impact-echo testing.
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 A

The Type A impact-echo Test System includes the following items:
1. A Data Acquisition System (full size ISA card), 5 megasamples per second maximum speed;
2. One cylindrical hand-held transducer unit;
3. A box 0f 200 replacement lead disks for the transducer unit;
4. Ten spherical impactors, 1/8' (3mm) to 3/4' (19mm) diameter;
5. One 12-foot (3.7-meter) cable and one 25-foot (7.6-meter) cable for connecting the transducer unit to the data acquisition system;
6. One copy of the impact-echo operating software on 3.5-in floppy disks (the software is called 'Imago' - the Latin word for echo or image);
7. A software package labeled 'Demo-Tutorial' containing an animated, stress wave simulation program and a tutorial for Imago software (on floppy disks);
8. Two Sentinel Hardware Keys for software protection (a key must be attached to the computer to enable the software to run);
9. Printed materials:
• Book: 'Impact-Echo: Nondestructive Evaluation of Concrete and Masonry', by. M. J. Sansalone and W. B. Streett (1997), 339 pp., Bullbrier Press, R.R. 1, Box 332, Jersey Shore, PA 17740, USA.
• Instruction Manual for impact-echo test system.
• Software Manual for Imago software system.
Impact-Echo Test System, Type B

Impact-Echo Test System, Type B

The Impact-Echo Test System, Type B, is the same as Type A, above, with the following additional items:
• One additional hand-held transducer unit, cylindrical model, with two additional cables;
• Spacer bar for use with 2 transducers for independent measurements of wave speed.
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.

Case Study 1: Cracking in Deck of Reinforced Concrete Railway Bridge, Denmark.

Problem: Structural cracking due to alkali-aggregate reaction in 1-m thick reinforced deck of railway bridge. Results: Impact-Echo tests detected horizontal cracking at mid-depth over entire span. Verification: Cores (and mode of failure during demolition). Outcome: Bridge judged unsafe and demolished. When first hit with wrecking ball, lower half of deck separated almost as one piece, and fell to the ground.

Case Study 2: Testing the Integrity of Tunnel Walls in the Los Angeles County Subway System, California. [4]

Case Study 3: Measuring Thickness of Concrete Pavement in New Highway Test Section, Arizona.

Problem: Determine thickness of new highway pavements placed on different sub-bases, including aggregate, permeable asphalt, and lean concrete. Results: Independent measurements of wave speed were used with impact-echo tests to measure thickness at eight locations. Verification: Cores Outcome: Uncertainties in measured thickness were 1% for pavement on lean concrete sub-base, 2% for asphalt sub-base, and 3% for aggregate sub-base. Results contributed to preparation of new ASTM Standard entitled, 'Standard Test Method for Measuring the P-Wave Speed and the Thickness of Concrete Plates Using the Impact-Echo Method', approved by ASTM in December 1997.

Case Study 4: Locating Voids in Grouted Tendon Ducts of a Post-Tensioned Highway Bridge, Northeastern USA.

Problem: Identify areas where there are full or partial voids in the tendon ducts in post-tensioned bridge girders. Results: In a preliminary test, Impact-Echo identified areas of full or partial voids in three of fourteen girders tested Verification: Tendon ducts were opened and inspected. Photo (above right) shows duct identified by impact-echo as ungrouted. Outcome: Impact-Echo used to locate voids in grouted tendon ducts throughout the bridge. Empty and partial grouted ducts re-grouted.

Case Study 5: Identifying Weakened Panels in a 7.5-mile Concrete Seawall at Marina Del Rey, Los Angeles, California. [5]

Case Study 6: Impact-Echo Replaces Coring for Routine Testing and Evaluation of Concrete Pavements, South Dakota. [6]

Case Study 7: Delaminations in Concrete Bridge Deck with Asphalt Overlay, New York State, USA.

Problem: Delaminations due to corrosion of reinforcing steel in 200 mm thick concrete deck with 100 mm asphalt overlay. Results: Impact-Echo identified extensive areas of delamination at top layer of reinforcing steel. Verification: Cores Outcome: Concrete deck repaired and new asphalt overlay applied.

Case Study 8: Cracking in Beams and Columns of Parking Garage, New York State.

Problem: Cracking in columns and at flange-web intersections of T-beams, due to asymmetrical design and loading. Results: Impact-Echo identified cracks at flange-web intersections in certain T-beam configurations, determined extend of cracking in columns, and confirmed that solid cores existed in some cracked columns. Verification: Expansion joints in slabs removed to expose cracks in T-Beams. Outcome: Impact-Echo test results used to design and implement comprehensive repairs.

Case Study 9: Locating Hidden Headers Behind Masonry Facade of 13-Story Building, New York City.

Problem: How to locate hidden headers behind brick facing. No headers found where portions facing had fallen away from building, but invasive examination verified the presence of headers in other areas Results: Impact-Echo was used in exploratory tests to determine presence or absence of hidden headers. Verification: Brick facing removed in test areas to verify impact-echo results. Outcome: Impact-Echo tests were 100% accurate in locating headers. The method was recommended as part of testing and rehabilitation program for the building facade.

Some more examples of applications :

Contents: 1. Introduction 2. Development of the Method 3. Stress Waves 4. Waveforms 5. Frequency Analysis 6. Digital Signals 7. Wave Speed 8. Plate Thickness 9. Cracks and Voids in Plates 10. Shallow Delaminations 11. Unconsolidated Concrete 12. Surface-Opening Cracks 13. Plates in Contact With Soils 14. Plates Containing Two Layers 15. Bond Quality at Internal Interfaces 16. Plates With Asphalt Overlays 17. Steel Reinforcing Bars 18. Bonded Post-Tensioning Tendons 19. Hollow Cylinders 20. Mine Shaft and Tunnel Liners 21. Circular and Square Cross Sections 22. Rectangular Cross Sections 23. Masonry 24. Field Testing

Impact-Echo: The Book

Bullbrier Press announces the publication of the first book devoted entirely to the impact-echo method:
Impact-Echo: Nondestructive Evaluation of Concrete and Masonry
by
Mary J. Sansalone and William B. Streett (1997)
339 pp.[7]
This book draws together all available knowledge and information about the impact-echo method and presents it in a concise and logical format. This information has previously been available only in technical reports and journal articles published between 1986 and 1997. Following a brief introduction and review of the development of the method, five chapters are devoted to the physical and mathematical principles on which impact-echo is based, followed by seventeen chapters on applications and case studies. The case studies include photographs, drawings and impact-echo results from field tests on a wide variety of concrete and masonry structures.

References

About 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.
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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Charpy V Notch Test & Drop Weight Test

Impact Testing of metals is performed to determine the impact resistance or toughness of materials by calculating the amount of energy absorbed during fracture. The impact test is performed at various temperatures to uncover any effects on impact energy. These services provide test results that can be very useful in assessing the suitability of a material for a specific application and in predicting its expected service life.

Impact Test Methods Offered by LTI

Laboratory Testing Inc. in the Philadelphia, PA (USA) area offers metal impact testing using the drop weight test and charpy impact testing methods, including the charpy V-notch test and weld charpy test. The ASTM impact test methods are regularly performed. Testing can be accomplished at temperatures in the range of -452ºF to 500ºF with an impact energy up to 320 ft. lbs.

The Charpy Test method determines the toughness or impact strength of the material in the presence of a flaw or notch and fast loading conditions. This destructive test involves fracturing notched impact test specimens at a series of temperatures with a swinging pendulum. The amount of energy absorbed by the material during fracture is measured. Charpy V notch or U notch test specimens are used.

The Drop Weight Test determines the temperature at which the fracture mode of steel changes from ductile to brittle using a free-falling weight or striker.

Specimens for Impact Testing

LTI has extensive in-house machining capabilities enabling us to quickly prepare precision specimens for our impact testing lab. Our full-service Machine Shop prepares all types of metal impact specimens with the latest CNC equipment. LTI is on NIST’s (National Institute of Standards and Technology) Qualified Manufacturers List for Charpy V-notch Impact verification specimens.

Test Methods/Specifications

• ASTM A370
• ASTM E23
• ASTM E208
• ISO 148

Let us know your requirements for impact testing of metals, and we will provide a fast quote.

The Impact Test Processes

Iron and all other body-centered cubic metals undergo a transition from ductile behavior at higher temperatures to brittle behavior at lower temperatures. Impact Testing is required by many industries to evaluate the toughness of materials used in manufacturing products, including steel hull plate for ships, nuclear plant pressure vessels and forgings for electric power plant generator rotors.

Charpy Testing

The Charpy Impact Test entails striking a notched impact specimen with a swinging weight or a “tup” attached to a swinging pendulum. The specimen breaks at its notched cross-section upon impact, and the upward swing of the pendulum is used to determine the amount of energy absorbed (notch toughness) in the process. Energy absorption is directly related to the brittleness of the material. Since temperature can affect the toughness of a material, the charpy test is performed at a series of temperatures to show the relationship of ductile to brittle transition in absorbed energy.

Several machined bar specimens, sized at 1cm x 1cm x 5.5cm with a 2mm deep U-shaped notch at the middle of a specified flat surface, are required to perform some methods of charpy testing. The charpy V-notch impact test is also very common and requires a specimen with a V-shaped notch.

The impact specimens are tested at a series of specified temperatures (e.g. -20ºC, -10ºC, 0ºC, +10ºC, +20ºC) in the range of -452ºF to 500ºF. Low temperature charpy testing involves placing the charpy test specimen in a chamber bath of propylene glycol and dry ice until a calibrated thermocouple records the temperature required for the test.

Once a specimen reaches the precise temperature, it is quickly placed into a special holder in the test machine. The charpy test specimen is placed horizontally with the notch facing away from the pendulum or striker and is supported on two sides.

Watch the process in the Charpy Impact Test Video below.

Drop Weight Test

The drop weight impact test subjects a series of specimens at a progression of temperatures to a single impact load from a guided free-falling weight or striker dropped in a vertical direction. The drop weight test determines the maximum temperature at which a beam specimen breaks or the temperature at which the fracture mode of the steel changes from ductile to brittle, which is called nil-ductility transition (NDT). The initial test is conducted at a temperature estimated to be near the NDT temperature. The remaining specimens are then tested at a progression of temperature intervals to determine the break and no-break performance temperatures within 10°F or (5°C).

LTI Capabilities

• Types of Testing: charpy impact (including V notch, U notch and weld charpy test); drop weight impact test
• Temperatures: -452ºF to 500ºF
• Impact Energy: up to 320 ft. lbs.
• Materials Tested: metals
• Specimen Machining: in-house machine shop prepares drop weight, izod and charpy test specimens; NIST approved for charpy V-notch test specimens

Clegg Impact Tester / Clegg Decelerometer

The Clegg Impact Tester is a professional instrument to determine hardness on all types of areas - Readings in CIT's or Gravities (Gmax) 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.

Available in following models. 0.5 kg - Used for soft turf, sand areas and golf greens (0 to 1000 Gravities) 2.25 kg - Used for surfaces consisting of natural or synthetic turf (football, baseball, soccer fields, playgrounds, pitches, horse tracks, and golf greens). (0 to 1000 Gravities) (+/- 1% or 10 G Accuracy) 2.25 kg-A - New Used for surfaces consisting of natural or synthetic turf (football, baseball, soccer fields, playgrounds, pitches, horse tracks, and golf greens). (0 to 150 Gravities) New (+/- 1% or 1.5 G Accuracy) 4.5 kg - Used for surfaces such as preconstructed soils, trench reinstatement, bell holes, and foundations 10 kg - Used for flexible pavement, aggregate road beds, trench reinstatement, bell holes, and foundations. 20 kg - Used for surfaces such as flexible pavement, aggregate road beds, trench reinstatement, bell holes, and foundations.

Simple and quick test procedure The test procedure is very rapid and can easily be performed by site personnel with minimal training. Each test can be completed in less than 30 sec. The results are immediate. Select a level surface (If needed, lightly scuffing surface with a foot to level the strike area) The guide tube is set into position, secure by placing a foot on the tube's base flange and steadied with the lower leg and knee) The ON/RESET button on the control box is pressed and release to activate the circuitry. The hammer is raised to the drop height indicator mark The level is centered. The hammer is released allowing it to fall freely and cleanly Without moving the guide tube or pressing the ON/RESET button, the Hammer is raised to the mark and release The gravities value (Gmax) or CIT value is displayed after the fourth blow is recorded and the display automatically powers down 30 sec. after activation Move to the next test site.

Clegg shown with Turf-Tec optional hard case

The Clegg Impact Tester is a professional instrument to determine hardness on all types of areas from Baseball, Football, Soccer, Natural Grass, Artificial Turf, Infill, Horse Racing, Turf Racing and all types of sports where ever surface harness is important from turf care needs to playability.

Specifications: Clegg (either 0.5kg - OR - 2.25 kg) hammer with hardened strike face Guide tube is metal and will provide years of reliable, accurate service Tablet comes ready to use with Clegg Control Application pre-installed and calibrated to your Clegg Hammer (available in the Google Play store) Also see our infill depth gauges for accurate and consistent depths of infill materials Turf-Tec Professional Model Infill Depth Gauge Turf-Tec Economy Infill Depth Gauge for synthetic turf

Unit Comes with the following: Impact Hammer Guide Tube with foot Bubble Level Samsung Galaxy Tablet 'A' with Clegg Control App (available in the Google Play store and Apple App store) GPS integrated tablet Bluetooth sending unit BNC Coax Cable 12x12 inch foam Calibration Pad (0-150g 2.25 kg-A unit) Locking Pin to attach hammer to guide tube Handle and Hammer Release Spring Plunger with lockout Instruction Manual Charger Battery Life: 12 Hours 3.7V/1.75Ah Lithium Ion Battery Complete Charge in 3 hours Results displayed/stored on tablet-based application

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

Concrete Impact Hammer Test

'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)

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)