Martin Schickert - Ultrasonic NDE of Concrete

7/22/2019 Martin Schickert - Ultrasonic NDE of Concrete

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Concrete accepts large compressive loads but issensitive to tensile traction. To improve its behavior

under tensile stress, steel bars are cast in. Two con-struction principles are used: reinforcement and post-

tensioned tendons.Reinforcement consists of single steel bars of 8 to

28 mm diameter. It is laid out in one or more layers ofparallel bars or meshes 20 to 60 mm below each sur-face of the concrete. The bars take part of the tensile

load.Pre-tensioned tendons are ropes of several steel

bars contained in a tendon duct of 30 to 100 mm di-

ameter (Fig. 2). The gaps are filled with injected mor-tar. After hardening of the concrete, stress is applied

to the tendons. As a result, the concrete is pre-loadedwith compressive strength, and more load can be

charged until a tensile state is reached. Pre-tensionedtendons are placed in the inner part of concrete ele-

ments.

Duct

Tendons

Injection

mortar

Concrete

Void

Fig. 2. Cross-section of a post-tensioned tendon

III. COMMON EVALUATION TASKS

A typical concrete slab, e.g. in a bridge deck, con-

sists of concrete with reinforcement close to the sur-faces and embedded tendon ducts (Fig. 3). Using this

example, a number of common inspection andevaluation tasks can be identified:

Thickness: Thickness measurements are a fre-quent demand in cases where the back-side of

concrete is buried in sand or rock, or is not eas-ily accessible.

Position: The exact lateral and depth position

of tendon ducts and reinforcement may differfrom the construction plan and needs to be de-

termined. Corrosion: Larger areas of corrosion of rein-

forcement and corrosion in tendons weaken the

construction.

Crack: The depth of surface-opening cracks isimportant to assess the structural condition.

Honeycombing: The appearance of voids as aresult of a lack of cement paste is named hon-

eycombing. It often occurs close to edges andbetween reinforcement. Of interest are position

and size. Voids in tendons: Voids in tendon ducts in-

volve the risk of rusting and eventual failure of

tendons (Fig. 2). Micro-cracking: Certain chemical processes

can cause areas of micro-cracking thus reduc-

ing concrete strength. Layers: If a concrete element is set-up of dif-

ferent layers or a repair layer is applied, thick-ness and boundary condition may need to be

determined. Compressive strength: The achieved strength is

among the most important concrete properties. Elastic moduli: For the development of con-

crete recipes, elastic moduli are frequently

evaluated. Hardening: Construction time can be shortened

if the hydration process can be monitored.

Thickness Crack

CorrosionCorrosion Micro-cracking

Position VoidThickness

Boundary condition

Layer

Honeycombing

Fig. 3. Common inspection tasks at a concrete slab

Any technique considered for the testing of con-crete structures has to fulfill requirements specific forapplications in civil engineering. Most important,

results need to be clear and unambiguous. Evaluationresults can cause far-reaching decisions, thus custom-ers require statements such as defect/no defect,

position or thickness in centimeters, concrete ele-ment is safe/ not safe. In order to achieve this

goal, it can be necessary to apply more than one non-destructive testing technique, possibly backed up bydestructive probing. Then, methods requiring one-sided access only are advantageous in cases where the

back-side is not easily accessible. Two-dimensional

maps or images of the results ease interpretation.

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2002 IEEE ULTRASONICS SYMPOSIUM-740


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Additionally, result interpretation should be made notonly from a non-destructive, but also from a civil

engineering point of view. Last not least, applicationof the techniques should be fast, with small effort, at

reasonable costs, and should not interfere with con-struction work or traffic.

In general an application-oriented approach, not amethod-oriented approach is demanded in NDE ofconcrete.

IV. ULTRASONIC PROPAGATION IN CONCRETE

The three components aggregate, cement matrix,

and pores constitute concrete as a heterogeneous ma-terial. In order to estimate consequences for the

propagation of ultrasonic waves, Table I contains

typical acoustic impedance values of the three com-ponents, and (plane wave) reflection factors relative

to the cement matrix. These values indicate that con-crete is a strongly scattering medium.

TABLE I

ACOUSTIC IMPEDANCES AND REFLECTION FACTORS RELA-

TIVE TO THE CEMENT MATRIX FOR LONGITUDINAL WAVES

Component ZL RL

Cement matrix 7 MRayl Aggregate 17 MRayl 0.4Air pores 0.4 MRayl 0.9

As a consequence, scattering is the most promi-nent cause for attenuation of an incident ultrasonic

pulse on its way through the concrete. Assuming theexponential attenuation model in (2), the attenuation

coefficient has been empirically determined to

= 5.6 dB/(MHz cm) (1)

(evaluating the results from [4], see below). Thisvalue is about five to 10 times larger than the one

characterizing biological soft tissues [5]. Incoherentscattering at the concrete structure of aggregate and

pores sums up to so called structural noise in thereceived signals.

The strong attenuation of ultrasound in concrete

has consequences for the ultrasonic testing procedure.Table II summarizes some test parameters in their

typical and maximum ranges. The values are givenfor longitudinal waves and may be exceeded in spe-cial cases.

TABLE II

TESTING PARAMETERS: MAXIMUM AND TYPICAL RANGES

FORLONGITUDINAL WAVES

Parameter Maximum Typical

Diagnosis range 0 1000 mm 50 500 mm

Frequency range 20 500 kHz 50 200 kHzSound velocity 3500 5000 m/s 4000 4500 m/s

Wave length 200 8 mm 90 20 mm

Divergence angle 20 180 40 100

Both the need to penetrate concrete to large depthsand strong attenuation restrict the frequency range to

the lower bound of ultrasonic testing. In combinationwith typical sound velocities, wavelengths of a coupleof centimeters follow, thus limiting resolution. Scat-

tering at pores occurs mainly in the Rayleigh regime,

scattering at the aggregate extends from the Rayleighto the Mie region. Since wavelengths and transducerdiameters are of the same order, broad divergenceangles result.

Concrete as a solid allows propagation of longitu-dinal, transversal, and Rayleigh waves. Mode conver-

sion occurs at all boundaries at objects as well as ataggregate and pores. Because of the low relation be-tween transducer diameter and wavelength, genera-

tion of Rayleigh waves can be prominent. As receivedsignals contain a superposition of excited, reflected,

and mode converted waves, signal identification es-pecially in single A-scans may be difficult.

Fig. 4 shows examples of received signals in

transmission and pulse-echo-mode. Please note thatthe plots have different time scales. In transmissionmode [Fig. 4(a)], the signal first received correspondsto the excited pulse, followed by structural noise(coda). Structural noise is also present in received

pulse-echo signals at all time instances [Fig. 4(b)]. Asin this example, indications of object reflections areoften hard to detect from single time signals.

In Fig. 4(b), noise shape smoothens in the course

of the signal. This effect is due to the behavior ofconcrete as an acoustic low-pass filter, based on fre-quency-dependent sound attenuation [4], and, to aminor extend, on dispersion [6].

Fig. 5 depicts the filtering effect for transmission

signals in both the time and the frequency domain. Ineither case, a reference signal measured at a homoge-nous material is compared to signals received aftersound paths of 100 and 500 mm, respectively, in con-crete. The coherent parts were extracted by time-




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windowing. With increasing sound path, signalsbroaden in the time domain, and their spectra are

shifted to lower frequencies in the frequency domain.As a consequence, broadband transducers are em-

ployed to balance between resolution and penetrationdepth. These graphs also show that in ultrasonic con-

crete testing all signal parameters become dependentof depth and, therefore, time.

Fig. 4. Examples of received signals: (a) trans-mission mode, (b) pulse-echo mode

V. UNDERSTANDING PROPAGATION

Understanding the propagation of ultrasonicwaves in concrete is essential for the successful de-velopment of measurement systems and signal proc-essing techniques. Important aspects of this task are

first to investigate the propagation of ultrasonicwaves depending on concrete parameters such as

aggregate size, porosity distribution, and strength.

Then, the interaction of ultrasonic waves with flawsand objects such as reinforcement and tendon ducts

needs to be clarified. Keeping the number of influen-tial material parameters in mind, this turns out to be

an extensive task.Analytical modelingis usually best suited to make

dependencies obvious. But considering the large

number of densely packed, strong scatterers, present

models do not seem to be able to handle such ar-rangements.

Fig. 5. Effect of frequency-dependent sound at-

tenuation: (a) time domain, (b) frequency domain

Numerical models exist in a wide variety of, e.g.,ray and grid-based models. During the past years,

particular progress has been achieved using the Elas-todynamic Finite Integration Technique (EFIT) [7],

[8], [9]. Fig. 6 shows a certain time instant of thepropagation of longitudinal waves, transversal waves,and structural noise, excited by the transducer at the

bottom.

Fig. 6. Numerical modeling of wave propagation

using the Elastodynamic Finite Integration Tech-

nique (EFIT) [10]




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Measurements at test specimen have the advantagethat true conditions are treated without restrictions.

On the other hand, every situation has to be builtseparately. This is a problem for concrete, which is

hardly reproducible even for identical recipes, andwhich takes weeks to harden. Also, size and weight of

the specimen grow easily to values that are hard tohandle if boundary reflections are to be avoided.Fig. 7 shows three concrete blocks as an example for

small test specimens. Their dimensions are 300 x 300x 300 mm, and their masses are about 60 kg.

Fig. 7. Concrete test specimens with varied

maximum aggregate size and lateral drillings

Larger specimens containing tendons and rein-

forcement can exceed a volume of 2 m and a weightof 4.5 t [11]. For field trials, structures to be demol-ished are particularly attractive. As an example, com-

parative studies of different non-destructive tech-

niques were carried out at a bridge girder [12]. Insuch cases results can be compared to destructiveexaminations. A two-dimensional model concretewith dimensions of 300 x 100 x 400 mm uses glass

bars of 3 to 14 mm diameter as a substitute for aggre-gate. Fig. 8 shows the specimen prior to filling with

mortar [13].

Fig. 8. Two-dimensional model concrete

specimen using glass bars as aggregate [13]

Measurements at concrete specimens whose prop-erties are varied systematically may lead to models of

ultrasonic propagation that can be classified as em-pirical modeling. A model for the frequency-

dependent sound attenuation of the coherent signal inconcrete was proposed in [4]. It uses an exponential

approach for the magnitude of the acoustical transferfunction |H| of the form

|H| = exp[(s, g, p) f] , (2)

wherefis the frequency and the attenuation coeffi-

cient dependent on sound paths, maximum aggregatesize g, and porosity p. Employing linear correlationwith measurements and setting some correlationcoefficients constant, the final model reads

|H| = exp[(As + Bg + C) f] . (3)

The values of the coefficients are determined to

A = 0.065 s/mm, B = 0.17 s/mm, and C = 4.5 s.Model and measurements are compared in Fig. 9 for aconcrete of 16 mm maximum aggregate size. Thismodel is preliminary in that porosity is not included(see also [6]), and geometric dispersion is neglected.

Fig. 9. Empirical propagation model: comparison of

model (solid lines) and measurements (dotted),

parameter is the sound paths

VI. MEASUREMENT SYSTEMS

Ultrasonic measurement systems for concrete ap-

plications can be divided in two groups: Transmissionand pulse-echo systems.

Transmission systems are used for determination

of ultrasonic pulse velocity and attenuation. Duringthe last decades, a variety of such systems have been

developed. Two transducers, sender and receiver, are




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to be connected to the main unit (Fig. 10). Usuallylow frequency (20 to 100 kHz) transducers with low

damping are employed offering high-energy pulses.Pulse velocity results of different systems should be

compared with caution since measured values dependon the trigger principle [14].

Fig. 10. Transmission system for pulse velocityand attenuation measurements. Membrane shoes

are developed for easier coupling [15]

In contrast, few commercial pulse-echo systemsexist to date. One unit contained in a 19-box is de-

picted in Fig. 11. It enables digital A-scan and B-scan

measurements as well as transmission experiments.Featuring a rectangular pulser with adjustable width,high gain/low noise amplifier, filtering, and time-gaincontrol, this device is particularly suited for concrete

testing.

Fig. 11. Pulse-echo system for A-scan and B-scan

measurements

Meanwhile, a hand-held A-/B-scan unit is avail-able from another vendor (Fig. 12). This system oper-

ates in pitch-catch mode and is intended for thicknessmeasurements and the detection of larger objects.

Fig. 12. Pulse-echo system for A-scan and B-scan

measurements [16]

To achieve high axial resolution, usually large-bandwidth transducers from 50 to 400 kHz center

frequency are used for pulse-echo systems, most ofthem having bandwidths from 100 to 200 %.

Acoustical coupling of transducers to the con-

cretes surface is a major concern. The process of ap-plying coupling agents such as honey or vaseline istime-consuming, and coupling fluctuations may ex-ceed 6 dB. Rough surfaces need to be grinded, butstill concave portions of the surface pose a problem to

transducers with large diameter.Dry Point Contact (DPC) transducers avoid this

problem by establishing a direct, point-like contact tothe concrete without the need of a coupling agent[16]. Two versions with conical and flat tips have

been developed. Fig. 12 shows a transducer arraywith 24 conical tip DPC-transducers, each 12 of them

being interconnected as the sending and the receivingportion. The array, belonging to the pitch-catch echosystem mentioned above, allows for fast coupling and

scanning but seems to produce increased couplingfluctuations.

Other detection approaches include a scanningDoppler vibrometer which enables scanning on a two-

dimensional grid [17]. Besides being an attractivemeans the signal-to-noise ratio needs to be improved.

VII. APPLICATIONS

To illustrate the range of ultrasonic concreteevaluation, a number of research topics and exampleapplications are described in the following without




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striving for completeness. The list includes well-triedmethods as well as results of current research.

Compressive Strength

The correlation of pulse velocity to compressivestrength is among the earliest applications of ultra-

sound to concrete testing [1], [18]. This method relieson empirical correlation curves found in transmission

experiments [Fig. 13(a)], which are subsequentlyused to estimate the compressive strength of concretesamples and elements. Unfortunately, there is no sin-gle relationship between these two quantities. Instead,a number of parameters have influence on the correla-

tion. In Fig. 13(b), concrete age and curing conditionsare added to the effects considered, thus making theestimation of compressive strength much more diffi-

cult. These problems were discovered soon [1], andthe method should be applied only under conditions

where most influential parameters are controlled.

Fig. 13. Correlation of pulse velocity to compressive

strength, (a) early-age concrete [19], (b) influence of

concrete age and curing condition [20]

Concrete Hardening

Monitoring the hydration process of concrete canhelp to determine the time instant at which the con-crete is able to take strain [21]. It is also used for rec-

ipe development. Often the pulse velocity measuredin transmission is evaluated. Fig. 14 shows graphs of

concrete with different admixtures. In another ap-proach, the reflection coefficient of transversal waves

is used, which is particularly sensitive since transver-sal wave cannot propagate in the fluid phase [22].

Fig. 14. Concrete hardening monitored with different

admixtures [21]

Crack Detection

Macroscopic cracks in concrete can be caused,

e.g., by deterioration, overload, or earthquake. Depthmeasurement of surface-opening cracks is thus im-

portant for determination of the concrete condition. Inorder to do this, transducers are placed on either sideof the crack, and the crack depth is estimated from

pulse transit time. Because of the larger pulse velocityin steel than in concrete, reinforcement can causeinterfering indications (Fig. 15). A number of meth-ods have been proposed to handle this problem.

Fig. 15. Evaluation of crack depth: problems

caused by reinforcement [23]




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Another task is the detection of cracks in post-tensioned tendons. Calculations of guided ultrasonic

propagation in a steel bar embedded in concrete haverevealed that low attenuation can only be achieved for

certain modes at narrow frequency bands (Fig. 16).Applying this result, it was possible to localize artifi-

cial tendon cracks in pulse-echo mode [24].

Fig. 16. Attenuation dispersion curve of a steelbar in concrete [24]

SAFT-Imaging

To overcome masking of object reflections bystructural noise in single A-scans, SAFT (SyntheticAperture Focusing Technique) reconstruction can beemployed. The SAFT algorithm focuses A-scan

measurements recorded along an aperture to eachelement of an image by coherent superposition, thussynthesizing a transducer of the size of the aperturewith variable focusing [25], [26]. Linear apertures

lead to two-dimensional images, planar apertures tothree-dimensional images. Indications in SAFT-images are reconstructions of object boundaries andneed to be interpreted using additional information.As an example, Fig. 17 shows the SAFT-reconstruc-tion of a cross section through the bottom of a pre-

stressed concrete bridge (see also Fig. 18, with indi-cations explained). SAFT-reconstructions provide

detailed information about the imaged concrete sec-tion and can therefore be used for detection and local-ization tasks. A present disadvantage is the tedious

transducer coupling necessary at all aperture posi-

tions.

Noise Modeling and Thresholding

As has been pointed out before, structural noise iscomplicating the interpretation of ultrasonic A-scansand images of concrete. The recognition of indica-tions within noise can be considered a detection prob-lem. In an analogy to Radar detection methods, am-

plitude detection can be used based on a thresholdcalculated from statistical noise distribution [27].

Fig. 17. SAFT-reconstruction of a pre-stressed

concrete slab

For implementation, first a noise region is se-

lected. Then the amplitude distribution of the noise ismodeled by a parametric model using Weibull or

LogNormal probability density functions. Given thisdistribution and a chosen false alarm probability, thethreshold can be computed. Finally, all A-scan or

image points with amplitudes below the threshold arediscarded. Fig. 18 shows the SAFT-image of Fig. 17

after the thresholding operation. A Weibull distribu-tion and a false alarm probability of 1 % were used.The result of investigations carried out so far is that

noticeable noise reduction can be achieved withoutsignificantly changing the shape of indications. This

method is also intended as a step toward quality con-trol in image examination.

Fig. 18. SAFT-reconstruction of Fig. 17 after thre-

sholding based on parametric noise modeling [28]




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Split Spectrum Processing

Split Spectrum Processing is a signal processingtechniques that exploits the different behavior of ob-

jects and concrete to frequency changes. The proce-

dure consists of two steps. First, the measured signalis split in a filter bank. Then, all partial signals are

exposed to a nonlinear operation such as polaritythresholding, and are superimposed to yield the proc-

essed output [30]. Fig. 19 shows examples of a meas-ured and a processed signal. While being a promisingapproach, sensitivity against frequency-dependentsound attenuation remains a currently unresolved

problem.

Fig. 19. Split Spectrum Processing: examples of

(a) a measured and (b) a processed signal [30]

VIII. CONCLUSION

Due to its inhomogeneous composition, concrete

is an interesting and demanding material for ultra-sonic evaluation. Advanced methods are required for

testing as well as understanding propagation charac-teristics. The described research results and applica-tions show that ultrasonic testing can provide high

potential solutions for the NDE of concrete.To promote regular use of ultrasonic NDE of con-

crete, more standards should be compiled and intro-duced. Up to date only standards on pulse velocitymethods exist with the exception of [29].

Being fundamental for the development of testingmethods, a better understanding of ultrasonic propa-

gation in concrete and scattering from objects is re-quired. To achieve this goal, both measurements and

modeling need to be performed.Additional progress is demanded in a number of

fields. Most important are means for faster and morereliable transducer coupling. Robust measurementsystems employing elaborated methods are needed,

which offer unambiguous results to the user. Here awide field for fundamental and applied researchopens.

IX. ACKNOWLEDGEMENTS

The author is greatly indebted to all colleagues

who have contributed information and figures, espe-cially to S. Bussat, C. Groe, R. Jansohn, M. Krause,

O. Kroggel, M. Lowe, K. Mayer, R. Marklein,J.S. Popovics, F. Schubert, S.P. Shah, V. Shevaldy-kin, T. Voigt, T. Yamaguchi, and D. Yuhas.

Part of this work was supported by the DeutscheForschungsgemeinschaft (German Research Council).

Cooperation within the framework of the researchinitiative FOR 384 is particularly acknowledged(www.for384.uni-stuttgart.de).

X. REFERENCES

[1] E. Pohl, Prfung von Beton mit Ultraschall, Schrif-

tenreihe der Bauforschung, Reihe Stahlbeton, Heft 4,Berlin: Deutsche Bauinformation, 1966, pp. 5-17.

[2] J. S. Popovics and J. L. Rose, A Survey of Devel-

opments in Ultrasonic NDE of Concrete, IEEE

Trans. Ultrason. Ferroelec. Freq. Control, vol. 41,

pp. 140-143, 1994.

[3] N. G. Zoldners and J. A. Soles, An Annotated Bib-

liography on Nondestructive Testing of Concrete,

1975-1983, in Proceedings, In Situ/Nondestructive

Testing of Concrete, Detroit: American Concrete

Institute, SP-82, 1984, pp. 745-825.

[4] M. Schickert, Ein empirisches Modell der frequenz-

abhngigen Schallschwchung von Beton," in Pro-

ceedings, DGZfP-Jahrestagung 1998, Berlin,DGZfP, 1999, pp. 233-240.

[5] P. Atkinson and J. P. Woodcock, Doppler Ultra-

sound and Its Use in Clinical Measurement, London,

Academic Press, 1982.

[6] M. Schickert, Ein empirisches Modell der Disper-

sion von Ultraschall in Beton," in Proceedings,

DGZfP-Jahrestagung 1999, Berlin, DGZfP, 1999,

pp. 559-566.




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[7] F. Schubert and R. Marklein, Numerical Compu-

tation of Ultrasonic Wave Propagation in Concrete

Using the Elastodynamic Finite Integration Tech-

nique (EFIT), (these Proceedings).

[8] R. Marklein, K. J. Langenberg, R. Brmann, K.

Mayer, and S. Klaholz, Nondestructive Testing with

Ultrasound: Numerical Modeling and Imaging,

Acoustical Imaging, vol. 22, 1996, pp. 757-764.

[9] F. Schubert and B. Khler, Numerical Modeling of

Ultrasonic Attenuation and Dispersion in Concrete.

The Effect of Aggregates and Porosity, in Proceed-

ings, Nondestructive Testing in Civil Engineering

(NDT-CE), Northampton: The British Institute of

NDT, 1997, vol. 1, pp. 143-157.

[10] F. Schubert (Fraunhofer-Institute for Non-Destruc-

tive Testing, Branch Lab EADQ), private communi-

cation.

[11] J. Krieger, M. Krause, and H. Wiggenhauser, Tests

and Assessments of NDT Methods for Concrete

Bridges, in Proceedings, Structural Materials Tech-

nology III, Proceedings of SPIE, vol. 3400, 1998, pp.258-269.

[12] M. Krause, H. Wiggenhauser, and J. Krieger, NDE

of a Post Tensioned Concrete Bridge Girder Using

Ultrasonic Pulse Echo and Impact Echo, Proceed-

ings, Structural Materials Technology (SMT): NDE/

NDT Highways and Bridges, 2002 (to be published).

[13] S. Bussat, J. Neisecke (University of Dortmund,

Germany), private communication.

[14] M. Schickert, Einflu der frequenzabhngigen

Schallschwchung auf die Ultraschall-Laufzeitmes-

sung an mineralischen Stoffen, in Proceedings,

DGZfP-Jahrestagung 1994, Berlin: DGZfP, 1995,

pp. 479-485.[15] R. Long, M. Lowe, and P. Cawley, Investigation

into Convenient Coupling for Ultrasonic Transducers

when Inspecting Concrete Structures, Review of

Progress in Quantitative NDE, vol. 19, New York:

American Institute of Physics, 2000, pp. 1677-1684.

[16] A. A. Samokrutov, V. N. Kozlov, and V. G. She-

valdykin, Ultrasonic Defectoscopy of Concrete by

Means of Pulse-Echo Technique, in Proceedings,

8th ECNDT 2002, Madrid: Spanish Society for NDT

(AEND), CD-ROM, 2002, pp. 1-9.

[17] M. Krause and H. Wiggenhauser, Ultrasonic Pulse

Echo Technique for Concrete Elements Using Syn-

thetic Aperture, in Proceedings, NondestructiveTesting in Civil Engineering (NDT-CE) 1997,

Northampton: The British Institute of NDT, 1997,

vol. 1, pp. 135-142.

[18] RILEM NDT 1, Testing of Concrete by the Ultra-

sonic Pulse Method, RILEM, 1972.

[19] G. G. Carette and V. M. Malhotra, In Situ Tests:

Variability and Strength Prediction of Concrete at

Early Ages, in Proceedings, In Situ/Nondestructive

Testing of Concrete, Detroit: American Concrete

Institute, SP-82, 1984, pp. 111-141.

[20] Y. Tanigawa, K. Baba, and H. Mori, Estimation of

Concrete Strength by Combined Nondestructive

Testing Method, in Proceedings, In Situ/Non-

destructive Testing of Concrete, Detroit: American

Concrete Institute, SP-82, 1984, pp. 57-76.

[21] C. U. Grosse and H.-W. Reinhardt, Ultrasound

Technique for Quality Control of Cementitious Ma-

terials, in Proceedings, 15th World Conference on

NDT, Rome, CD-ROM, 2000.

[22] T. Voigt, Y. Akkaya, and S. P. Shah, Determination

of Early Age Concrete Strength by a Reflective Ul-

trasonic Technique, in Proceedings, 6th Int. Symp.

High Strength/High Performance Concrete, Leipzig,

2002, pp. 1489-1501.

[23] T. Yamaguchi and T. Yamaguchi, Measurement of

Thickness and Crack Depth in Concrete by Ultra-

sonic Methods, in Proceedings, NDT-CE Sympo-

sium 2000 and Seiken Symposium 26, Oxford: El-

sevier, 2000, pp. 331-340.[24] B. Pavlakovic, M. Lowe, and P. Cawley, Guided

Ultrasonic Waves for the Inspection of Post-

Tensioned Bridges, Review of Progress in Quantita-

tive Nondestructive Evaluation, vol. 17, New York:

Plenum Press, 1998, pp. 1557-1564.

[25] M. Schickert, M. Krause, and W. Mller, Ultrasonic

Imaging of Concrete Elements Using SAFT-

Reconstruction, J. of Materials in Civil Engineering

(accepted for publication).

[26] M. Schickert, Towards SAFT-Imaging in Ultra-

sonic Inspection of Concrete, in Proceedings, Int.

Symp. Non-Destructive Testing in Civil Engineering

(NDT-CE), Berlin: DGZfP, 1995, pp. 411-418.[27] R. Jansohn and M. Schickert, Objective Interpreta-

tion of Ultrasonic Concrete Images," in Proceedings,

7th European Conference on Non-Destructive Test-

ing (ECNDT), Broendby, 7th ECNDT, 1998, vol. 1,

pp. 808-815.

[28] M. Schickert, Hochauflsende Schnittbilder von

Beton mit Ultraschall-Abbildungsverfahren, in

Proceedings, Bauwerksdiagnose Praktische An-

wendungen Zerstrungsfreier Prfungen, Berlin:

DGZfP, CD-ROM, 2001, pp. 16.

[29] RI-ZFP-TU, Richtlinie fr die Anwendung der zer-

strungsfreien Prfung von Tunnelinnenschalen,

Bergisch-Gladbach, Germany: Bundesanstalt frStraenwesen, 2001.

[30] N. Bilgtay, J. Popovics, S. Popovics, and M.

Karaoguz, Recent Developments in Concrete Non-

destructive Evaluation, in Proceedings, Int. Conf.

Acoustics, Speech, and Signal Processing, 2001.

*Martin Schickert e-mail: [email protected]


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Martin Schickert - Ultrasonic NDE of Concrete