1、Designation: C 215 08Standard Test Method forFundamental Transverse, Longitudinal, andTorsional Resonant Frequencies of Concrete Specimens1This standard is issued under the fixed designation C 215; the number immediately following the designation indicates the year oforiginal adoption or, in the cas
2、e of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope*1.1 This test
3、 method covers measurement of the fundamen-tal transverse, longitudinal, and torsional resonant frequenciesof concrete prisms and cylinders for the purpose of calculatingdynamic Youngs modulus of elasticity, the dynamic modulusof rigidity (sometimes designated as “the modulus of elasticityin shear”)
4、, and dynamic Poissons ratio.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of th
5、is standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C 31/C 31M Practice for Making and Curing Concrete TestSpecimens in the FieldC 42/C 42M Test Method for Obtaining and T
6、esting DrilledCores and Sawed Beams of ConcreteC 125 Terminology Relating to Concrete and ConcreteAggregatesC 192/C 192M Practice for Making and Curing ConcreteTest Specimens in the LaboratoryC 469 Test Method for Static Modulus of Elasticity andPoissons Ratio of Concrete in CompressionC 670 Practic
7、e for Preparing Precision and Bias Statementsfor Test Methods for Construction MaterialsE 1316 Terminology for Nondestructive Examinations3. Terminology3.1 DefinitionsRefer to Terminology C 125 and the sec-tion related to ultrasonic examination in Terminology E 1316for definitions of terms used in t
8、his test method.4. Summary of Test Method4.1 The fundamental resonant frequencies are determinedusing one of two alternative procedures: (1) the forced reso-nance method or (2) the impact resonance method. Regardlessof which testing procedure is selected, the same procedure is tobe used for all spec
9、imens of an associated series.4.2 In the forced resonance method, a supported specimen isforced to vibrate by an electro-mechanical driving unit. Thespecimen response is monitored by a lightweight pickup uniton the specimen. The driving frequency is varied until themeasured specimen response reaches
10、 a maximum amplitude.The value of the frequency causing maximum response is theresonant frequency of the specimen. The fundamental frequen-cies for the three different modes of vibration are obtained byproper location of the driver and the pickup unit.4.3 In the impact resonance method, a supported
11、specimenis struck with a small impactor and the specimen response ismeasured by a lightweight accelerometer on the specimen. Theoutput of the accelerometer is recorded. The fundamentalfrequency of vibration is determined by using digital signalprocessing methods or counting zero crossings in the rec
12、ordedwaveform. The fundamental frequencies for the three differentmodes of vibration are obtained by proper location of theimpact point and the accelerometer.5. Significance and Use5.1 This test method is intended primarily for detectingsignificant changes in the dynamic modulus of elasticity oflabo
13、ratory or field test specimens that are undergoing exposure1This test method is under the jurisdiction of ASTM Committee C09 onConcrete and Concrete Aggregates and is the direct responsibility of SubcommitteeC09.64 on Nondestructive and In-Place Testing.Current edition approved Oct. 1, 2008. Publish
14、ed November 2008. Originallyapproved in 1947. Last previous edition approved in 2002 as C 215 02.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Docum
15、ent Summary page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.to weathering or other types of potentially deteriorating influ-ences. The test met
16、hod may also be used to monitor thedevelopment of dynamic elastic modulus with increasingmaturity of test specimens.5.2 The value of the dynamic modulus of elasticity obtainedby this test method will, in general, be greater than the staticmodulus of elasticity obtained by using Test Method C 469.The
17、 difference depends, in part, on the strength level of theconcrete.5.3 The conditions of manufacture, the moisture content,and other characteristics of the test specimens (see section onTest Specimens) materially influence the results obtained.5.4 Different computed values for the dynamic modulus of
18、elasticity may result from widely different resonant frequenciesof specimens of different sizes and shapes of the sameconcrete. Therefore, it is not advisable to compare results fromspecimens of different sizes or shapes.6. Apparatus6.1 Forced Resonance Apparatus (Fig. 1):6.1.1 Driving CircuitThe dr
19、iving circuit shall consist of avariable frequency audio oscillator, an amplifier, and a drivingunit. The oscillator shall be calibrated to read within 62%ofthe true frequency over the range of use (about 100 to 10 000Hz). The combined oscillator and amplifier shall be capable ofdelivering sufficien
20、t power output to induce vibrations in thetest specimen at frequencies other than the fundamental andshall be provided with a means for controlling the output. Thedriving unit for creating the vibration in the specimen shall becapable of handling the full power output of the oscillator andamplifier.
21、 The driving unit is used in contact with the testspecimen or separated from the specimen by an air gap. Whenthe test specimen is contact-driven, the vibrating parts of thedriving unit shall be small in mass compared with that of thespecimen. The oscillator and amplifier shall be capable ofproducing
22、 a voltage that does not vary more than 620 % overthe frequency range and, in combination with the driving unit,shall be free from spurious resonances that will be indicated inthe output.NOTE 1It is recommended that the calibration of the variable fre-quency audio oscillator be checked periodically
23、against signals transmit-ted by the National Institute of Standards and Technology radio stationWWV, or against suitable electronic equipment such as a frequencycounter, the calibration of which has been previously checked and foundto be adequate.6.1.2 Pickup CircuitThe pickup circuit shall consist
24、of apickup unit, an amplifier, and an indicator. The pickup unitshall generate a voltage proportional to the displacement,velocity, or acceleration of the test specimen, and the vibratingparts shall be small in mass compared with the mass of the testspecimen. The pickup unit shall be free from spuri
25、ous reso-nances in the normal operating range. Either a piezoelectric ormagnetic pickup unit meeting these requirements is acceptable.The amplifier shall have a controllable output of sufficientmagnitude to actuate the indicator. The indicator shall consistof a voltmeter, milliammeter, or a real-tim
26、e graphic displaysuch as an oscilloscope or a data acquisition system withmonitor (see Note 2).NOTE 2For routine testing of specimens whose fundamental fre-quency may be anticipated within reasonable limits, a meter-type indicatoris satisfactory and may be more convenient to use than an oscilloscope
27、 orcomputer monitor. It is, however, strongly recommended that wheneverfeasible a graphic display be provided for supplementary use or to replacethe meter-type indicator. The use of a graphic display as an indicator maybe necessary when specimens are to be tested for which the fundamentalfrequency r
28、ange is unpredictable. The graphic display is valuable also forchecking the equipment for drift and for use in the event that it should bedesired to use the equipment for certain other purposes than thosespecifically contemplated by this test method.6.1.3 Specimen SupportThe support shall permit the
29、specimen to vibrate freely (Note 3). The location of the nodalpoints for the different modes of vibration are described inNotes 4, 5, and 6. The support system shall be dimensioned sothat its resonant frequency falls outside the range of use (from100 to 10 000 Hz).NOTE 3This may be accomplished by p
30、lacing the specimen on softrubber supports located near the nodal points or on a thick pad of spongerubber.6.2 Impact Resonance Apparatus (Fig. 2):6.2.1 ImpactorThe impactor shall be made of metal orrigid plastic and shall produce an impact duration that issufficiently short to excite the highest re
31、sonant frequency to bemeasured. The manufacturer shall indicate the maximumresonant frequency that can be excited when the impactorstrikes a concrete specimen with surfaces formed by a metal orplastic mold.NOTE 4A 19 mm diameter solid steel ball mounted on a thin rod toproduce a hammer is capable of
32、 exciting resonant frequencies up to about10 kHz when impacting a smooth concrete surface.A110 g steel ball peenhammer may act similarly. Larger steel balls will reduce the maximumFIG. 1 Schematic of Apparatus for Forced Resonance Test FIG. 2 Schematic of Apparatus for Impact Resonance TestC215082re
33、sonant frequencies that can be excited.6.2.2 SensorThe sensor shall be a piezoelectric acceler-ometer with a mass less than 30 g and having an operatingfrequency range from 100 to 10 000 Hz. The resonant fre-quency of the accelerometer shall be at least two times themaximum operating frequency.6.2.3
34、 Frequency AnalyzerDetermine the frequency of thespecimen vibration by using either a digital waveform analyzeror a frequency counter to analyze the signal measured by thesensor. The waveform analyzer shall have a sampling rate of atleast 20 kHz and shall record at least 1024 points of thewaveform.
35、The frequency counter shall have an accuracy of61 % over the range of use.6.2.4 Specimen SupportSupport shall be provided asspecified in 6.1.3 for the forced resonance method.7. Test Specimens7.1 PreparationMake the cylindrical or prismatic testspecimens in accordance with Practice C 192/C 192M, Pra
36、c-tice C 31/C 31M, Test Method C 42/C 42M, or other specifiedprocedures.7.2 Measurement of Mass and DimensionsDetermine themass and average length of the specimens within 60.5 %.Determine the average cross-sectional dimensions within61%.7.3 Limitations on Dimensional RatioSpecimens havingeither smal
37、l or large ratios of length to maximum transversedirection are frequently difficult to excite in the fundamentalmode of vibration. Best results are obtained when this ratio isbetween 3 and 5. For application of the formulas in this testmethod, the ratio must be at least 2.8. Determination of Resonan
38、t FrequenciesForcedResonance Method8.1 Transverse Frequency:8.1.1 Support the specimen so that it is able to vibrate freelyin the transverse mode (Note 5). Position the specimen anddriver so that the driving force is perpendicular to the surfaceof the specimen. Locate the driving unit at the approxi
39、matemiddle of the specimen. Place the pickup unit on the specimenso that the direction of pickup sensitivity coincides with thevibration direction, that is, the transverse direction (see Fig.3a). Position the pickup near one end of the specimen. It ispermissible to position the driver on the vertica
40、l face so that thespecimen vibrates perpendicular to the direction shown in Fig.3a.8.1.2 Force the test specimen to vibrate at varying frequen-cies. At the same time, observe the indication of the amplifiedoutput of the pickup. Record the fundamental transversefrequency of the specimen, which is the
41、 frequency at which theindicator shows the maximum reading and observation ofnodal points indicates fundamental transverse vibration (Note5). Adjust the amplifiers in the driving and pickup circuits toFIG. 3 Locations of Driver (or Impact) and Needle Pickup (or Accelerometer)C215083provide a satisfa
42、ctory indication. To avoid distortion, maintainthe driving force as low as is feasible for good response atresonance.NOTE 5For fundamental transverse vibration, the nodal points arelocated 0.224 of the length of the specimen from each end (approximatelythe quarter points). Vibrations are a maximum a
43、t the ends, approximatelythree fifths of the maximum at the center, and zero at the nodal points;therefore, movement of the pickup along the length of the specimen willinform the operator whether the vibrations observed in the indicator arefrom the specimen vibrating in its fundamental transverse mo
44、de. Anoscilloscope may also be used to determine whether the specimen isvibrating in its fundamental transverse mode. The driver signal isconnected to the horizontal sweep and the pickup signal is connected tothe vertical sweep of the oscilloscope. When the pickup is located at theend of the specime
45、n, which is vibrating in its fundamental transversemode, the oscilloscope will display an inclined elliptical pattern. When thepickup is placed at a node, the oscilloscope displays a horizontal line.When the pickup is placed at the center of the specimen, the display willbe an elliptical pattern but
46、 inclined in the opposite direction to when thepickup was placed at the end of the specimen. The oscilloscope can alsobe used to verify that the driving frequency is the fundamental resonantfrequency. Resonance can occur when the driving frequency is a fractionof the fundamental frequency. In this c
47、ase, however, the oscilloscopepattern will not be an ellipse.8.2 Longitudinal Frequency:8.2.1 Support the specimen so that it is able to vibrate freelyin the longitudinal mode (Note 6). Position the specimen anddriver so that the driving force is perpendicular to andapproximately at the center of on
48、e end surface of the specimen.Place the pickup unit on the specimen so that the direction ofpickup sensitivity coincides with the vibration direction, that is,the longitudinal axis of the specimen (see Fig. 3b).8.2.2 Force the test specimen to vibrate at varying frequen-cies. At the same time, obser
49、ve the indication of the amplifiedoutput of the pickup. Record the fundamental longitudinalfrequency of the specimen, which is the frequency at which theindicator shows the maximum reading and observation of thenodal point indicates fundamental longitudinal vibration (Note6).NOTE 6For the fundamental longitudinal mode, there is one node atthe center of length of the specimen. Vibrations are a maximum at theends.8.3 Torsional Frequency:8.3.1 Support the specimen so that it is able to vibrate freelyin the torsional mode (Note 7). Position the specimen anddriver so
