THE I-HSTORY AND DEVELOPMENT OF ACOUSTIC EMISSION IN CONCRETE ENGINEERING
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(2) 1.. INTROI)UCTION. In the 1960sAE (acousticemission)techniquesdrewa great deal of attention for the inspection of pressurevessels in the U. S.. The level of researchactivitybecameso high that International AE Symposiawere held all over the world. Amongthese, the InternationalSymposiumorganized by the Japanese Societyfor NondestructiveInspection(JSNDI)has been held every other year slnCe1972 [1]. In the field of civil engineering, it is only in Japan that AE conferences have been held continuously,and the 5th Domestic Conferencewas held in 1993 [2]. In response to this high level of researchactivity, AE has been investigatedincreasingly as a diagnostic tool for existing concrete structures. Further, the application of AE to construction monitoringhas also attracteda good deal of attention recently. Thus, an updatedreview of the applicationof AE to concreteengineeringis givenhere. In addition,historicaldevelopmentof AE in concreteengineeringare brieflysummarized.. l-•`. 2. HSTORY. - - •`. OF AE RESEARCH. Earlier in AE history,ma)'oreffortswere directedat probingthe fundamentalsof AE phenomena and studyingAE behavior duringthe deformationandfracture of various materials. In the literature [3], it began in Germanyin 1950 with the research work on metal carried out by J. Kaiser, althoughAE on rock was known in miningtechnology. Terminology-wise,the use of.,AE.. was initiated by B. H. Schofield in the U. S. in 1954. He published the pioneering report entitled TTAcoustic Emission under Applied Stress''. Quite recently,T. F. Drouillardfound that the first report on a scientificallyplanned AE experimentwas publishedin Japan [4]. In order to study fracture of earthTscrust, F. Kishinouye of the EarthquakeResearch Institute at Tokyo lmperial University,conducteda series of experiments to record jW signals from fracturesof wood [5]. To date, this is recognizedas the oldest AE report anywhere.. A E. s ig n a l. I I I I I :. D. (. etection of AE. /. ) l l I l. wave velocity Crack generation Poisson's. llSi.n.f a. Waves. ratio tt. •`. •`-----. tL. /. / /. tt... /. •`-•`_"_-•`. / /. /. ---____--/. axial. Propagationof fracture sound !A. ----. T(. T]?. Fig. 2 Generation,propagationanddetection of AE signals. Load. Fig.1 Mechanicalparametersof concrete undercompression[7]. -122-.
(3) with regard to AE research in concrete, three early paperswere published [6,7,8]. These discussed the relation between the fracture process and volumetric change in the concrete under uniaxial compression. With the crudeequipmentof the day,it was reportedthat AE events were recorded above 75 % failureload, with occurrenceincreasingmore andmore as the final failure was approached. As can be seen in Fig. 1' this AE activity over 75% failure load is closely correlatedwith the decrease inwave velocityand volumetricchange(increasesin Poisson.sratio and axial displacement). This fact led to one well-known episode of misunderstanding in. !tarpeanng.th :faSceodncornetten.ewhiF;rep.ascetivityyHaf ir.ekai=i Thy.f75HO'.o&ailiudr.e don3vd;rtshi?yCF9n]?ePAlOtEiTug was only a commenton the fact that the stress level at the onset of active AE generation was closely related to the fatiguelimit and creep strengthof concrete,a newswritertragicallymisinterpreted this concept and erroneously reported that accidental failure of concrete structures might occur dueto faultydesignbasedon conventionalnon-genuine strength.. Recent applicationof AEto concreteengineeringstartedin the late 1970s[10,ll,12,13]. Originally, technologydevelopedfor use with metalswas modifiedto suit concrete. IJater,research interestgrewstronger. In 1986,T. F. Drouillardlisted 76 papersin the bibliography:AE literature-concrete [14]. A committeereport on nondestructivetestingby the Japan ConcreteInstitute (JCI) collected116 paperspublishedinJapanand 8 overseasduringthe period 1980to 1991 [15]. Theseoutcomesare updatedin the followingsections.. _•` - -•`. 3. BASICS OF AE MEASUREMENT. il i 4f pb9Pi2Bgg cracking takes placewith the release of stored strainenergy at the time of fracture. As a result of microcracking)someof the storedenergyis releasedas elasticwaves, which are calledacoustic emission(and abbreviatedas AE). As shownin Fig. 2, AE waves propagatesthrough concrete andcan be detectedon the surfaceby an AE sensor, whichturns the vibrationsinto electrical signals. The propagationof fracturesoundwas originallyreferredto as AE, since it is acoustic and audible. on the basis of elastodymanics,it has been clarifiedthat AE waves couldbe synthesizedas elastic waves dueto dislocationmotion [16]. Physically,AE wavesconsistof P waves (longitudinal waves) and S waves (shear waves), and further might include surface waves (Rayleighwaves), reflectedwaves, diffractedwaves, and othercomponents. In particular,the latter portion of AE waveform normally results from resonance vibration of AE sensor. A detected AE waveform should theoreticallystart with the P wave portion. If the noise level is high and the P wave is interfered with, the first motion may not be discriminated and either the S wave or Rayleigh wave maybe observed. It should be notedthat the first motions detectedare thus not necessarily P waves at the source (flaw)location. In metals, two types of AE waveform are conventionallyknown. One is of a burst type and the other is continuous. It is, however,understoodthat they are basicallyidentical; their durations become differentdependingon attenuation. In a materialwith high attenuation,AE waveamplitude decreases immediately, while the amplitude is maintained in low-attenuation materials. ne former leads toAE wavesof burst type, andthe latter givesrise to continuousAE waves. 3: 2 A49ASg&5ygSg a. signalsare usually amplifiedfirst by a pre-amplifier and then by a main amplifier,as shown. 5:bF,jsi.3; s.Tfhle.y-9armeii lat=peldi tuuSdlenfn?.bealnedcf,aiScSalf1:itgeL.a isA.ftylP.1-C6aieEm a?iTS odre.t raSneSf:tTssneeleas ttis have high signal-to-noise (Sm) ratio and a flat frequencyresponseover a broad range. The. -123-.
(4) AE sensor. 1500. n. J^. 1a m > -. (a). 1 000. -A. p. re-amp.. >. mainamp.. bandpassfilter. Iy). 5. U]. Fig. 3 AE measuring system. 50O. 105. ,•`. (b). a, O. -S. E5 101. > .g. LOB. U). 2000. '-. 103. 4). 3000 17 y). > I. m e as u ra b le d ista n c e v .s . fre q u e n c y. 104. loo. 1.000. 4). U). 10-1. I. lot 1.0. I. 103. I. 105. I. 107. FrequencyPz). FrequencyPIttz). Fig. 4 Frequencyresponse Ofa. I. 2.0. Fig. 5 Relation between distance and &equencyrange. sensors. frequencyresponse of commerciallyavailableAE sensorsare given in Fig. 4; the top figure is for a broad-band transducerand thebottomfor a resonanttype. WhenAEwaves are generated in concrete,thedetectedsignalsaremaskedby theseresponses. As can be seen, both transducers respond so irregularly that the frequencycontentof an AE signalwould be smearedby the sensorresponse. It shouldbe noted thatthe use of waveguideintroducesfurther complexityto frequencycontentof a waves. The gain of the amplifieris given in dB (decibels), whichrepresents the ratio between input voltageEi andoutputvoltageEo, as follows; dB = 20 log10(EoPi).. (1). In concrete, it is found that AE events can be detected using amplifier with 60 to 100 dB of gain. The optimalfrequencyrange in concreteis knownto be h.omseveral kHz to a few hundred kHz. The range analyzedhas been increases as equipmenthas improved. In the past, any frequencies below a few kHz could be utilized. Attenuation properties depend on the frequency range: higher frequencycomponentspropagatein concretewith greater attenuation. The attenuationis quantitativelyrepresentedby Q value. When AE waves with an energy level E are attenuated by AE over a one-wavelengthpropagationdistance,Q is definedas, Q = 2 3TE/AE. (2). In the case of a genuineelastic material,AE= 0 and thus Q is infinite. In typical metals, Q is greater than 1,000,whereas it is known that Q values are lower than 100 in rock and concrete. Whena wavespropagatefor a distanceD, the amplitudeU(f) decreasesaS, U(O = exp(-3TfD/vQ),. (3). -124-.
(5) wherev is the wave velocity. In concrete,typical values are Q = 10,-v= 4000 m/s, and D = 1 m. Substituting these values into Eq. 3 for a h.equencycomponent f = 100 kHz gives exp(-0.65) = 0.522. This lmplies that the amplitude of a 100 kHz components attenuates to approximately half after propagating lm. Based on this result, the empirical relation indicated in Fig. 5 [17] is proposed. This gives base-line informationfor the determinationof sensor array. For a measuring area at 10 m distance, AE waves with frequencycomponentslower than 100 kHz only are detectable. The fundamental requirements for AE measuring equipment are prescribed in the JSNDI standards[18]. ^ ^ ^ ^ ^^ ^ ^ ^ ^ ^ ^ ^ ^. 3: 3 4B SiBg* AP44Paiy*. v u y v ‑A E w av efo rm. AE signalsare analyzedusing both analog and digital methods. Analog processingallows several AE parametersto be extracted,while " ,T,,T A.A. +,":_?_.:;?..o:?. _l_7_I e_I quantitativewaveform analysisis possibleby I digital processing. (a) Ringdown. # I. tl t[ I. I. (a) Analog parameters. I. I IL ll. ringdowncounting 1. 2. 3. 4. 5. 6. event counting. I. L. 1) AE counts:the occurrenceofAE events in the fractureprocess is counted. The counting methods commerciallyavailableare summarized in Fig. 6. All cyclesaboveathreshold level are countedby ringdowncounting. This methodis useful in metal, becausecontinuous AE signals are often observed. In concrete,. y I;JLt).J' (b). dT6ia6F Pulse. I II. -7.?TIAJ'iiLt,T ll 1l. TT ;.:,-.J.. ,._ _. tT. •`..fLt!:(c). Envelope. ll (L II J1 I I I I ll II. Z:Z3;iEoeun.t,i;egc1;;i;;nUgietdheOatabvyefe.ifEerinste.ttinng a Fig.6 Counting -ethodsforAEevents envelope. The number of event counts should then correspond closely to AE occurrence. However,this is not the case in typicalobservations. AE eventsof small amplitudemay not be discriminatedfrom the noise,and AEwaves mayattenuatequickly en route to the sensor &oma distance. Accordingly,the numberof AE events is consideredto be correlatedwith AE generating behaviorin the fractureprocess. 2) Amplitudedistribution:the maximumamplitudemarkedin Fig. 7 correlateswith the relative size of AE events, althoughit is usually smearedby propagationeffects betweenthe sensor and the source (microcrack). In seismology,the Gutenberg-Richter relation between maximum amplitudesof seismicwaves and the frequencyof occurrenceis known. It has been modified for AE events, and a statistical relationshipbetweenthe number of AE events N and the maximum amplitudea is obtainedas follows: log10N - a - b log10a.. (4). I lP w av e /I/ttt t t tt m ax im u m am p litude threshold i71v̲:Iid ,i ' I ̲A̲i 1:2i‑̲‑i‑̲‑A ‑A ‑̲̲b 〜̲i I. V y. V v : u,:ti: n. i. arrival time Fig. 7 AE waveform parameters. -125-.
(6) In this logarithmicequation,the gradientb is negative,implyingthat AE events of large amplitude are observedless often than those of small amplitude. It has also been reported that the value b decreasesas the materialapproachesimpendingfailure [12]. 3) RMSvoltage: the root mean square (RMS)voltage of the waveform in Fig. 7 is readily obtained using analogcircuitry. It approximatelycorrespondsto the area below the envelopeof the waveform in Fig. 7, and is occasionallyreferredto as equivalentto AE energy.. (b)Digitalprocessing. c•`. 1) Source (flaw) location:the arrival time of the AE waveform at a sensor is dependenton the distance between the AE sourceand the sensor. Therefore,differencesin arrival times at varioussensorsleadsto a systemof algebraic equationsgivingsource location[19,20]. As an example,AE sourcelocationsdetermined in bending tests of reinforcedconcrete beams are shownin Fig. 8. Twofailure modes, bending failureand diagonalshear failure, are clearly identifiedfromthe 3-D maps of sourcelocation [3]. 2) Spectral analysis: the frequency components of AE waves are readilyanalyzedby a FFT (fast Fouriertransform)procedure. The frequency componentsof detectedAE waves in concrete depend considerably on the geometricalrelationship between crack location and observationpoint becauseof inhomogeneity in the concretematerial [21]. In addition, frequencycomponentsare influenced greatlyby the sensor characteristics,as indi-. a"---O. 1500-2700. ¥-.-.-.. 2700-3i50(kg). 0-i 500. 9. J. ....!,... {1. 4. I. T I I I L l ._I I. +.'. -. I. _q_c.__i_. -. __. "._. ------, II_. __. I. J. I. f I I. ,_. .. s:,o93 __. JL, _. _. _. _. _. _. _. -. -A-. -. I 4tlfo-.o 4. oo. _ -. -1-cl-0.AL-. .... ol. -/. - -.3.i-7.----'-. rI. 4 I. -. l1. -. (a) AE locationssub)'ectedto bending failure. c•`. 0 ;‑ i : J.‑ ‑. v 1 . 't / c { ' .I.. '. '. ". ̲ ̲ ̲ ". o/. i <. 2 000-i. ¥-.-.-.. 4200-5700(kg). -200 > o ‑7. I I.Tt . a. ,.. 0-2 000. o----c'. / 3+ L J .̲ ". " ‑ ‑‑‑o. Q c〜 S ?o + t tq ". , .. ̲ . ,i { l ̲ ". ̲ ". ̲ ). .. lA e . . .. o. : 8' ,I ̲ L o ‑ & b. 3 LI. c. cated in Fig. 4.. . .. .. .. ･‑I‑ "‑ ‑ ̲ ‑ ̲ ̲ ‑ " ‑ ‑̲ ‑̲ ‑ ̲ ‑ ̲ ‑̲ ‑.t it ̲‑i .‑" g ‑ ̲‑ .0 ̲‑ ̲‑. Li. n Q ̲I '̲ ‑ ̲‑ ̲F‑ i ̲ ‑ ̲‑ ̲ ‑ ̲ ̲‑ ̲‑ ̲ ̲‑ Jl. 3) Moment tensoranalysis: the source location procedure has beenfurtherinvestigated and coupledwiththe outcome&oma theoret(b) AElocationssut))'ectedto diagonalshear failure ical treatmentof AE wavesbasedon elastodynamics[22]. As a result,a momenttensor Fig. 8 Source locations in RC beams analysiswas proposedas the sourceinversion procedure [23]. In orderto classifycrackmodesinto tensileand sheartypes and to determine .. /. ,.s. ,o o oQ. Q. y. •`./. x. tt. .___--I I. I-. 7L. + +. +. )". 3#):-i-I/. +. 7L. Flo. -20. -10. i. X. 10. + shear crack + mixedmode crack - tensile crack 20. Fig. 9 Moment tensor analysisin a pull-out test.. -126-. a. X.
(7) crackorientation,this procedurehas been developedinto the SiGMAcode (simplifiedGreenTs functionfor momenttensoranalysis)[24]. Successfulapplicationto a pull-out test of an anchor-bolt is shown in Fig. 9 [25]. In SiGMA analysis, a 6-channel system of digital waveform memory is necessary for a 3-D problem, and a 4-channel system is good enough for a 2-D problem [26]. 4. APPLICATION TO CONCRETE ENGINEERING. AE measurementsare used in a variety of fieldsin concrete engineering. With the demandfor nondestructiveevaluationsof in-service structures,AE techniquesoffer greatpromiseas means to estimatestructuralintegrity. Constructionmonitoring,in addition,has received a great deal of attention. These new applicationsof AE in concreteengineeringare summarizedhere, since the state of the arthas beenpublishedpreviously[15]. 41i Q. gBSkipg9P49tgag g2P9* g9PgBtgi9A. In the placement of ready-mixed concrete, thermal cracking often occurs due to the uneven temperature distribution when the structure is of large mass. To detect cracks promptly and implementproper treatment,AE monitoringis beingconsidered[27]. A major concernis noise elimination, since a variety of construction noise is always present. TypicalAE signals observed on site are given in Fig. 10. AE waveforms and their frequencyspectra are recorded duringconcrete casting. AE sensorsare attachedto reinforcingbars in formwork. In the figure, AE waveforms. Frequency spectra. +0.05 A. > -. 23!fgo ]. O. 1 -j I-. CL. E. <. -0.. .;i. 2000 a. Time (LISeC). Frequency O'Hz). loo. (a) Cracking +0.. 05r. 5XlOI. A. > 4) ITS j. oLJ*. -. I-. l li?A. a E. <. 0.056. 2000 a. Time ( LISeC). Frequency (kftz). 50. (b) Green-cutting i)<106. +0.05. J^. O. >. V. O. '9 -. o. W. 1. NvW. j. -. t-. CL. E: a. P<. O >. E. a. <. +I<. Time ( LISee). 2000. O. F<. 50 F. requency (kHz). (c) Chipping. Fig. 10 AE signalsduringmass concreteconstruction. -127-.
(8) g reen-cutting meansthe removal of dirt from the concretesurfaceusingwater. The AE waveforms of thermalcracksare differenth.omthose of such AE sourcesas green-cutting andchipping. So, thermalcrackingshouldbe easily identifiedby measuringAE eventswith a properly filteredsystem.. 4L2 99y9bpg9Pi 9f:g?P9ggd g* In developingcement-based materialssuch as aluminacement [28] and asbestoscement [29], AE monitoring has been applied. An application to the concretehardening process has also beenreportedin thedevelopmentof autoclaveaeratedconcrete[30]. A. 4!3ft99Zigg ap44*. 9ff9ga. F;. One significantdeteriorationof concrete in a E3=10 severeenviroTmentis causedby freezeand 3LoS: g2e 4 thaw. Becauseconcreteusuallycontains 2u 20 moisture, &eezing resultsin microcracking around water voids due to the volumetric E:4 increase. After thawing, the volumetric 3L changeis repeated dueto refreezing. The gB 2 resulting microcracks are accumulatedin the 010 20 30 40 50 concrete. AE measurementsduring freezing and thawing [31] are showninFig. ll. The Freeze-thawcycles ratio of releasedenergyto elasticenergy inthe p rocessstartsto increaseat the30thfreezethawcycle, whenhighAE activityis observed. Fig. ll AE generationduringfreeze-thawaction This implies that continuousAE monitoringof the freezing and thawing process could give waning of degradation. Anotherapplicationof AE sourcelocationduringcyclic freezingand thawingprocesshas also beenreported[32].. ago. 4=4 4ppii9a*. @h4g*. 99Bg9@. eL O 90Oi. 8 000. j3. + newly cast 0. OOD. 2: )i;. e gU. 7000. A. 6000. D. 'J. (. a. -. E. JJ. 5000. / /. r-. E: U. 4000. u i 3. 2000. E=. 1000. j]. Iv A. ,J). C). L7/. >'. d _q}. 3000. A. LI. I3. -. 5>. A. alkali-silica reacdon freezing-thawing. I_D. __D-. -J}-. -S. ji'. JL}-. C9 0. /. 9u. 0. O. q>. q. o 10. 20. 30. 40. 50. 60. 70. 80. 90. loo. stress level : V (%). oetP. Fig.13 TotalAE eventcountversusstress levelin concretesample 12 Identificationof the h.actureprocess gFig. zone by AE source location. -128-.
(9) AE behavior during the fracture process has been investigated in relation to the Kaiser effect [33]. Under cyclic loading,AE activity is quite low as sequentialloading takes place up to the preloadlevel. Based on this knowledge,the estimationof previousstress level is under investigation[34,35],althoughresultsare still marginal. In otherareas,AE behaviorat failure of jointedconcrete [36] andduring fatigueinwater [37]is beinginvestigated. An applicationto fracturemechanicswas recentlyreported[38,39]. To determinethe parameters of fracture mechanicsand determine the &actureprocess zone, JW generationwas monitored. The source locationprocedurecan be successfullyappliedto identifythe h-actureprocess zone, as shown in Fig. 12 [40]. Nucleationin the processzone might be correlatedwith the intense zone of AE cluster. It is foundthat AE clustersspreadout as the gravelsize increases. As a diagnosticmethod for evaluatingstructural integrity,the application of AE to coretests is being studied. One procedurehas been proposedfor uniaxialcompressiontests of core samples [41, 42]. The different type of AE activity under compression.are compared in Fig. 13 for a sound concrete sample and deterioratedsamples affected by alkali-aggregate reaction and the freezing-thawingeffect [41]. It is clear that AE activity is high even at low stress levels when concrete containsmany microcracksdue to deterioration. A quantitativemethod of evaluating deteriorationfrom the AE activitymeasuredundercompressionis proposed[42]. 4. 5 Reinforcedconcrete AE studies of actualconcretestructureshave generateda lot of interest,becausediagnostictechniques are of great concern to concrete engineers [25]. With respect to the inspection of inservice concrete structures, a relationship between crack width in reinforced concrete (RC) members and the occurrence of the Kaiser effect was been reported [43]. As summarized in Table 1, the disappearanceof the Kaisereffectcoincideswith the crackwidth expandingbeyond the criticallimit in the designcode or with the initiationof diagonalshear failure. Thus, if the Kaisereffect is present,minor deteriorationof an in-service RC structuresis suggested. On the disappearanceof Kaisereffect, the momenttensor analysiswas appliedto cyclicbendingtests of RC beams. One of the results is shown in Table2 [44]. It is observedthat the numberof shear cracks increaseswith the more loading cycles. The result of Table 1 is confirmedfrom the fact that the Kaiser effectwas not observedfromthe firstcycle inthis experiment. Table 1 Relation betweencrack width and Kaisereffect crack nucleation. observ ed. tensile cracks of w idth m ore than 0 .15 ‑0.2 0 m. not observed. sh ear cracks. not observed. ProCeSS. L L)ad in g cy cles ten sile m ix ed sh ear to tal crack s crack s crack s. K aiser effect. tensile crack s of w idth less than 0.15‑ 0.2 m. Table 2 Numberof cracksand the loading. 1 st lo ad in g u n lo a d in g 2n d lo ad in g ‑ 1 h old in g lo ad in g ‑ 2. 3 8. 5 5. 7 10. 15 23. 15 3 13. 8 4 6. 14 4 23. 37 ll 42. Another important aspectof the maintenanceof RC structures is reinforcementcorrosion. AE activityrelatedto the corrosionprocesshas alsobeen studied[45]. 4. 6 Concretestructures So far, the measurementofAE in existingstructureshas rarelybeen attempted. Photos 1 and 2 show a mobileAE measuringfacilityand in-situ AE observationsconducted in Australia. A. -129-.
(10) Photo i A mobilefacilityforAE measurement. Photo 2 h-situ AE measurement result of an in-situ observationattemptedin Japan is given in Fig. 14 [46]. Theseare AE waveforms detectedin a compositebridge of steel and prestressedconcrete(PC) bridge. Measurementwere conductedwith traffic load, althoughAE events wereseldomrecorded. In existing structures,detailed observationmight be requiredfor the prediction of service life. For this purpose,practicalapplicationof momenttensor analysisis under investigation. Results of a tensiletest on a reinforcedconcrete(RC)frame model are shownin Fig. 15 [47]. Moment tensor analysis was performed. The observedAE sourcesare located close to the final surface cracks. Tensile cracks open up vertical to the surface cracks, while shear cracks are almost parallel to the surface cracks. These results confirm the applicability of moment tensor (SiGMA)analysisto the elucidationof crackingmechanismsin concretestructures. To identify the crack distributionin an existingconcretestructure, a useful technique is source location. In-situ ju observationshave been performedin a crackedretainingwall [48]. As the temperatureand ground waterlevel changed,AE events were observed. Two-dimensionalAE source locations are shown at the top of Fig. 16. BecauseAE sources were distributed away &omthe existingsurfacecracks, calibrationwas carriedout by a pencilJead break test. Based on the location errors observedin the calibrationtest, the locationswere corrected. Resultsare given in the bottom figure. AE sources are locatedclose to the surface cracks. This suggests that most AE events are nucleatedby rubbingmotion of the cracked surfacesdue to temperature changes.. -130-.
(11) O. traffic load. -A_. ¥--- sensor location. oO. _C_ c!. osn!.E. 1t•`. _/ o Oo. CT. -cq-. o c ooo. --eq.. Oo. steel bridge. Prestressedconcrete (PC) bridge. [ :o. O. o. -•`--. i ij:. ' ^EScn)of(6O. 0. G. Llt1_ 60 }nd 9O cm D1,tt3rN=CAmrnF Lh{ Scn1. Noise generatedby rain and snow. 1.024msec. AE waveform detected in the steel bridge. Electric. T. gfj. Eliminated. F,1iminntcd. Resultsorpencil-leadbreak tests. 0. 1.024msec. DcteTTnine^E scMlrCC locations in the pencil-)cad break test rTOmarrivahin=s. AE waveform detectedin the PC bridge. C21culaLedistance txtwecn pohLs o[ rcnCil-lead break a.nd obseTVCdpoints. Fig. 14 AE waveforms detected in a compositebridge. Observed AE source lKations from ule StmCnlre htetnhe ^E SCRITCC locations (Tornarrival Lin3S. +. y. i. f3;. +b># ;; *. J. A. i. / tensile crack. (J. + shear crack. ^t:StJ1101. (60 i)[T.. a. InJ. 90 cm l>iSL>MC }l]y)n& tllC Scr)solJ. Fig. 15 Moment tenSOranalysisin a tensiletest of an RC frame Fig. 16 Two-dimensional source location. in a concreteretainingwall. 4l i gg2g& Otherfield applicationsof ABhavebeendevelopedin a varietyconstructions.An applicationto the grouting process is under investigation[49]. By employingan ju mOnitoringsystemas shownin Fig. 17, a procedurefor consistentgroutingisbeingstudied.. -131-.
(12) AB analyzer. .(fT7 g:T.L. ‑ r Tm :" .iH.I,i" ..jl:.". P. ump. roc k s u rf a c e. .@! rTl /.. grout mixer. I. P. AE sensor. reSSuremeter. bore hole U. Fig. 17 AE monitoring system for grouting. 5. . CONCLUDING REMARKS. AE research activity is increasing in the field of concrete technology because of the urgent demandfor repair, restoration,and rehabilitationof concretestructures. In addition,the application of AE to constructionmonitoringis in progress. This activity demonstratesthat AE research in civil engineeringhas shifted &omthe developmentstage to the applicationstage. The latestresults in relation to concretetechnologyhavebeen summarized. Becausecivil engineering covers a variety of fields and consists of many on-site practices, AE has not always been successful when applied to practical problems. Further studies are, therefore, still needed to meet the demandsof particulartargets. References [1] T. Kishi, K. Takahashi, and M. Ohtsu eds., Progress in Acoustic Emission VI, JSNDI, 1992 [2] Proc. of 5th Domestic Conf. on Subsurface and Civil Engineering AE, MMIJ, 1993 [3] M. Ohtsu, Theory and Characteristics of Acoustic Emission, Morikita Pub., 1988 [4] T. F. Drouillard, "Acoustic Emission-A Bibliography for 1970-1972,'' Monitoring Structural htegrity by Acoustic Emission, ASTM, STP-571, pp. 241-271, 1975 [5] F. Kishinouye, 'rAn Experiment on the Progress of Fracture (A Preliminary Report)," Jishin, Vol. 6, pp. 25-31,. 1934. [6] H. Rusch, "Physical Problems in the Testing of Concrete,'TZement-Kalk-Gips (Wiesbaden), 12(1),. pp. 1-9,. 1959. [7] R. G. LTHermite, "Volume Change of Concrete," Proc. 4th Intl. Symp. Chemistry of Cement, V-3, NBS, Washington D. C., NBS Monograph, 43, pp. 659-694, 1960. [8] G. S. Robinson, ''Methods of Detecting the Formation and Propagation of Microcracks in Concrete," Proc. Int. Conf. on the Structure of Concrete and It's Behavior Under Load, Cement and Concrete Association, pp. 131-145, 1965 [9] H. Yokomichi, I. Ikeda, and K. Matsuoka, "Elastic Wave Propagation due to Cracking of Concrete,TTCement Concrete, 212, pp. 2-6, 1964 (in Japanese) [10] W. M. McCabe, R. M. Koerner, and A. E. IJOad,Jr.,''Acoustic Emission Behavior of. -132-.
(13) Concrete hboratory Specimens, ACI Joumal, Vol. 13, No. 3, pp. 367-71, 1976 [11] D. G. Fetis, ''Concrete Material Response by Acoustic Spectral Analysis, J. Struc. Div., Proc. ASCE, No. 102 (ST2), pp. 387-400, 1976 [12] Y. Niwa, S. Kobayashi, and M. Ohtsu, ''Studies of AE in Concrete Structures," Proc. of JSCE, No. 276, pp. 135-147, 1978 (in Japanese) [13] Y. Tanigawa, K. Yamada, and S. hiyama,"Frequency Characteristics of AE in Concrete," Proc. of JCI, Vo1. 2, pp. 129-132, 1977 [14] T. F. Drouillard, HAE Literature - Concrete," J. Acoustic Emission, Vo1. 5, No. 2, pp. 103109,1986. [15] CommitteeReporton NondestructiveTestingin Concrete,JCI, 1992 [16] Y. Niwa, S. Kobayashi, and M. Ohtsu, T'SourceMechanisms of AE,HProc. of JSCE, No. 314, pp. 125-136, 1981 (in Japanese) [17] T. Uomoto, K. Kato, and S. Hirono, Nondestructive Inspection of Concrete Structures, Morikita Pub., 1990. [18] JSNDI Standards, ''System Requirements of AE Measuring Equipment, NDIS 21109-79, 1979. [19] Y. Niwa, S. Kobayashi, and M. Ohtsu, "Studies of Source Location by Acoustic Emission;. Proc. of JSCE, No. 276, pp. 135-147, 1978 (in Japanese). [20] T. Kawakami and T. Uomoto, 'TApplicationof AE Monitoringand Planar Source Location in Split-Tensile Tests of Concrete,7' Proc. of JCI, Vol. 10, No. 2, pp. 385-390, 1988 [21] J. M. Berthelot, M. B. Souda, and J. L. Robert, T'Frequency Analysis of Acoustic Emission Signals in Concrete, J. Acoustic Emission, Vol. ll, No. 1, pp. ll-18, 1993 [22] M. Ohtsu, ''Radiation Pattern of Acoustic Emission,T' J. Soc. Mat. Sci. Japan, Vol. 32, No. 356, pp. 577-583,. 1983. [23] M. Ohtsu, "Mathematical Theory of Acoustic Emission and Moment Tensor Solution,'7J. Soc. Mat. Sci. Japan, Vol. 36, No. 408, pp. 1025-1031,. 1987. [24] M. Ohtsu, T'Source Inversion of Acoustic Emission Wave form," Proc. of JSCE, 398P-10, pp. 71-79, 1988 [25] M. Ohtsu, M. Shigeishi, and H. Iwase, ''AE Observation in the Pull-Out Process of Shallow Hook Anchors,7' Proc. of JSCE, No. 408N-ll, pp. 177186, 1989 [26] M. Ohtsu, M. Shigeishi, S. Yuyama, and T. Okamoto, '7SiGMA Procedure for AE Moment Tensor Analysis,'T J. ofNDI, Vol. 42, No. 10, pp. 570-575, 1991. [27] Y. Hironaka et al., "Thermal Crack Detection during Mass Concrete Construction by AE," Report of Central Research Institute, Sato Kogyo Inc., 1991 [28] M. Anington and B. Evans, 'TAETesting of High Alumina Cement Concrete, NDT International, Vol. 10, No. 2, pp. 81-87,. 1977. [29] S. A. A. Akers and G. G. Garrett, "AE Monitoring of Flexual Failure in Asbestos Cement Composite, Int. J. Cement Composite and Lightweight Concrete, Vol. 5, No. 2, pp. 97-103, 1983 [30] S. Teramura, K. Tsukiyama, and H. Takahashi, ''The Detection of The Fracture of Autoclaved Aerated Concrete during Autoclave Curing Process by Acoustic Emission," J. Acoustic Emission,. Vol. 6, No. 4, pp. 261-266,. 1987. [31] Y. Murakami, H. Yamashita, T. Kita, and H. Yoshikawa, HRelationbetween Deformation Behavior and Acoustic Emission of Concrete subjected Freezing and Thawing," Proc. 4th Domestic Conf. on Subsurface and Civil Engineering AE, pp. 47-51, 1991 [32] H. Shimada and K. Sakai, '7AcousticEmission Teclmiquefor the Evaluation of Frost Damage in Mortar," Proc. ofJCI, Vol. 13, No. 1, pp. 467-472,. 1991. [33] T. Kanagawa, M. Hayashi, and H. Nakasa,"Estimation of Spatial Geostress Components in Rock Samples using Kaiser Effect of Acoustic Emission,'' Proc. of JSCE, No. 258, pp. 63-76, 1977 (in Japanese) [34] S. Sato and T. Uomoto, "Evaluation of Maximum Loaded Stress of Concrete by AE technique," Proc. ofJCI, Vol. 8, pp. 397-400, 1986 [35] S. Nakasone and K. Kodama, ''Flexual Fatigue of Concrete,T' Proc. of JCI, Vol. 8, pp. 565568,1986. [36] T. Kyogoku, Y. Murakami, K. Miyano, and T. Kita, '7Evaluationof Joint Properties of Concrete by Acoustic Emission,HProc. 4th Domestic Conf. on Subsurface and Civil Engineering. -133-.
(14) jW, pp. 70-74,. 1991. [37] H. Muguruma and F. Watanabe, ''Compressive Fatigue of Concrete in Water and AE," Amual Report of CAJ, Vol. 39, pp. 332-335, 1985 [38] S. Mindes, "Acoustic Emission and Ultrasonic Pulse Velocity of Concrete,T'Int.J. Cement Composites and Lightweight Concrete, Vol. 4, No. 3, pp. 173-179, 1982 [39] S. Teramura and H. Takahashi, "Evaluation of Fracture Toughness on Autoclaved Calcium SilicatePoodfiber I-aminates," Progress in Acoustic Emission IV, pp. 748-756, 1988 [40] N. Nomura, H. Mihashi, and S. Niiseki, HInnuenceof Coarse Aggregate Size on Fractu1.e Energy and Tension Softening of Concrete,'' Concrete Research and Technology, JCI, Vol. 2, No. 1, pp. 57-66,. 1991. [41] K. Yuno, Y. Inoue, and M. Ohtsu, "Evaluationof Deteriorated Concrete Test Specimens by Stochastic Analysis ofjW Activity,'' Proc. 9th National Conf. on AE, pp. 115-120, 1993 [42] M. Ohtsu, "Rate Process Analysis of Acoustic Emission Activity in Core Test of Concrete,I Concrete Library of JSCE, No. 20, pp. 143-153, 1992 [43] S. Nagataki, T. Okamoto, T. Ayata, and S. Yuyama, HClassification of Crack Pattern developed in Reinforced Concrete Members by Acoustic Emission," Proc. Sym. NDE in Civil Engineering, JSCE, pp. 139-144, 1991 [44] S. Yuyama, T. Okamoto, M. Shigeishi, and M. Ohtsu, 'TSomeApplication of Moment Tensor Analysis for Concrete Specimen," Proc. 9th National Conf. on AE, JSNDI, pp. 121-129, 1993. [45] Y. Murakami, H. Yamashita, T. Kita, and M. Ohtsu, 'TRelationbetween the Mechanical Behavior and Acoustic Emission of the Member subjected to Steel Corrosion," Proc. 8th National Conf. on ju, JSNDI, pp. 183-188, 1991 [46] T. Sakuta, Y. Tachibana, and K. Maeda, ''Test for the Use of Acoustic Emission on RC Slab Inspection Methods," JSNDI, Committee 006 on AEWG-Report, No. 87, pp. 68-73, 1988 [47] Y. Murakami, S. Yuyama, T. Shimizu, H. Kouyama, and M. Matsushima, T'Studyof the. DeformationBehaviorand AE Propertieson Pull OutTestingof FoundationAnchorof Steel Tower, Proc. 9th National Conf. on AE, JSNDI, pp. 137-150, 1993 [48] A. Ishibashi, T. Fujiwara, T. Matsuyama, and M. Ohtsu, HAEField Application for Diagnosing Deterioration of Retaining Wall,HProc. 9th National Conf. on AE, JSNDI, pp. 131139,1993. [49] T. Ueda, M. Ohtsu, and S. Yuyama, 'TAEWaveform Analysis for Rock Mass in Grout InJ'eCtionof Dam," 4th World Meeting on AE, ASNT, pp. 223-229, 1991. -134-.
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