1、Designation: C215 08C215 14Standard Test Method forFundamental Transverse, Longitudinal, andTorsional Resonant Frequencies of Concrete Specimens1This standard is issued under the fixed designation C215; the number immediately following the designation indicates the year oforiginal adoption or, in th
2、e case 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 U.S. Department of Defense.1. Scope*1.1
3、 This test method covers measurement of the fundamental transverse, longitudinal, and torsional resonant frequencies ofconcrete prisms and cylinders for the purpose of calculating dynamic Youngs modulus of elasticity, the dynamic modulus ofrigidity (sometimes designated as “the modulus of elasticity
4、 in shear”), and dynamic Poissons ratio.1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof
5、the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C31/C31M Practice for Making and Curing Concrete Test Specimens in the FieldC42/C42M Test Method for Obtaini
6、ng and Testing Drilled Cores and Sawed Beams of ConcreteC125 Terminology Relating to Concrete and Concrete AggregatesC192/C192M Practice for Making and Curing Concrete Test Specimens in the LaboratoryC469C469/C469M Test Method for Static Modulus of Elasticity and Poissons Ratio of Concrete in Compre
7、ssionC670 Practice for Preparing Precision and Bias Statements for Test Methods for Construction MaterialsE1316 Terminology for Nondestructive Examinations3. Terminology3.1 DefinitionsRefer to Terminology C125 and the section related to ultrasonic examination in Terminology E1316 fordefinitions of t
8、erms used in this test method.4. Summary of Test Method4.1 The fundamental resonant frequencies are determined using one of two alternative procedures: (1) the forced resonancemethod or (2) the impact resonance method. Regardless of which testing procedure is selected, the same procedure is to be us
9、edfor all specimens of an associated series.4.2 In the forced resonance method, a supported specimen is forced to vibrate by an electro-mechanical driving unit. Thespecimen response is monitored by a lightweight pickup unit on the specimen. The driving frequency is varied until the measuredspecimen
10、response reaches a maximum amplitude. The value of the frequency causing maximum response is the resonantfrequency of the specimen. The fundamental frequencies for the three different modes of vibration are obtained by proper locationof the driver and the pickup unit.4.3 In the impact resonance meth
11、od, a supported specimen is struck with a small impactor and the specimen response ismeasured by a lightweight accelerometer on the specimen. The output of the accelerometer is recorded. The fundamental frequency1 This test method is under the jurisdiction of ASTM Committee C09 on Concrete and Concr
12、ete Aggregatesand is the direct responsibility of Subcommittee C09.64 onNondestructive and In-Place Testing.Current edition approved Oct. 1, 2008Dec. 15, 2014. Published November 2008January 2015. Originally approved in 1947. Last previous edition approved in 20022008as C215 02.C215 08. DOI: 10.1520
13、/C0215-08.10.1520/C0215-14.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM stand
14、ard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases
15、 only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1of vibration is d
16、etermined by using digital signal processing methods or counting zero crossings in the recorded waveform. Thefundamental frequencies for the three different modes of vibration are obtained by proper location of the impact point and theaccelerometer.5. Significance and Use5.1 This test method is inte
17、nded primarily for detecting significant changes in the dynamic modulus of elasticity of laboratoryor field test specimens that are undergoing exposure to weathering or other types of potentially deteriorating influences. The testmethod may also be used to monitor the development of dynamic elastic
18、modulus with increasing maturity of test specimens.5.2 The value of the dynamic modulus of elasticity obtained by this test method will, in general, be greater than the staticmodulus of elasticity obtained by using Test Method C469C469/C469M. The difference depends, in part, on the strength level of
19、the concrete.5.3 The conditions of manufacture, the moisture content, and other characteristics of the test specimens (see section on TestSpecimens) materially influence the results obtained.5.4 Different computed values for the dynamic modulus of elasticity may result from widely different resonant
20、 frequencies ofmodes of vibration and from specimens of different sizes and shapes of the same concrete. Therefore, it is not advisable to compareresults from different modes of vibration or from specimens of different sizes or shapes.6. Apparatus6.1 Forced Resonance Apparatus (Fig. 1):6.1.1 Driving
21、 CircuitThe driving circuit shall consist of a variable frequency audio oscillator, an amplifier, and a driving unit.The oscillator shall be calibrated to read within 62 % of the true frequency over the range of use (about 100 to 10 00012 000 Hz).The combined oscillator and amplifier shall be capabl
22、e of delivering sufficient power output to induce vibrations in the testspecimen at frequencies other than the fundamental and shall be provided with a means for controlling the output. The driving unitfor creating the vibration in the specimen shall be capable of handling the full power output of t
23、he oscillator and amplifier. Thedriving unit is used in contact with the test specimen or separated from the specimen by an air gap. When the test specimen iscontact-driven, the vibrating parts of the driving unit shall be small in mass compared with that of the specimen. The oscillatorand amplifier
24、 shall be capable of producing a voltage that does not vary more than 620 % over the frequency range and, incombination with the driving unit, shall be free from spurious resonances that will be indicated in the output.NOTE 1It is recommended that the calibration of the variable frequency audio osci
25、llator be checked periodically against signals transmitted by theNational Institute of Standards and Technology radio station WWV, or against suitable electronic equipment such as a frequency counter, the calibrationof which has been previously checked previously and found to be adequate.6.1.2 Picku
26、p CircuitThe pickup circuit shall consist of a pickup unit, an amplifier, and an indicator. The pickup unit shallgenerate a voltage proportional to the displacement, velocity, or acceleration of the test specimen, and the vibrating parts shall besmall in mass compared with the mass so as to not affe
27、ct the vibrational frequency of the test specimen. specimen by more than1%. The pickup unit shall be free from spurious resonances in the normal operating range. range of 100 to 12 000 Hz. Either apiezoelectric or magnetic pickup unit meeting these requirements is acceptable. The amplifier shall hav
28、e a controllable output ofsufficient magnitude to actuate the indicator. The indicator shall consist of a voltmeter, milliammeter, or a voltmeter or amilliammeter that shows the relative amplitude of the signal from the pickup unit. The driver signal and the pickup signal shallbe connected to the ho
29、rizontal and vertical sweeps, respectively, of a real-time graphic display such as an oscilloscope or a dataFIG. 1 Schematic of Apparatus for Forced Resonance TestC215 142acquisition system with monitor (seemonitor. The Note 2). displayed pattern is used to confirm that the driver frequency atmaximu
30、m signal amplitude is the resonant frequency of the specimen.NOTE 2For routine testing of specimens whose fundamental frequency may be anticipated to be within reasonableknown limits, a meter-typeindicator is satisfactory and may be more convenient to use than an oscilloscope or computer monitor. fo
31、r determining the fundamental resonantfrequency. It is, however, strongly recommended that whenever feasible a the graphic display be provided for supplementary use or to replace themeter-type indicator. The use of a graphic display as an indicator may be necessary when specimens are to be tested us
32、ed. The graphic display will confirmthat the specimen is vibrating at its fundamental resonant frequency, and is necessary when testing specimens for which the fundamental frequency rangeis unpredictable. The graphic display isnot known beforehand. See Note 6 valuable also for checking the equipment
33、 for drift and for use in the event thatit should be desired to use the equipment for certain other purposes than those specifically contemplated by this test method.for additional guidance onusing the graphic display.6.1.3 Specimen SupportThe support shall permit the specimen to vibrate freely (Not
34、e 3). The locationlocations of the nodalpoints for the different modes of vibration are described in Notes 6-8Notes 4, 5, and 6. . The support system shall be dimensionedso that its resonant frequency falls outside the range of use (from 100 to 10 00012 000 Hz).NOTE 3This may be accomplished by plac
35、ing the specimen on soft rubber supports located near the nodal points or on a thick pad of spongerubber.sponge rubber pad.6.2 Impact Resonance Apparatus (Fig. 2):6.2.1 ImpactorThe impactor shall be made of metal or rigid plastic and shall produce an impact duration that is sufficientlyshort to exci
36、te the highest resonant frequency to be measured. The manufacturer shall indicate the maximum resonant frequencythat can be excited when the impactor strikes a concrete specimen with surfaces formed by a metal or plastic mold.NOTE 4A19 mmA19-mm diameter solid steel ball mounted on a thin rod to prod
37、uce a hammer is capable of exciting resonant frequencies up to about10 kHz when impacting a smooth concrete surface. A110A 110 g steel ball peen hammer may act similarly. Larger steel balls will reduce the maximumresonant frequencies that can be excited.As an approximate guide, the maximum frequency
38、 that can be excited by the impact is the inverse of the impactduration.6.2.2 SensorThe sensor shall be a piezoelectric accelerometer with a mass less than 30 g and having an operating frequencyrange from 100 to 10 00015 000 Hz. The resonant frequency of the accelerometer shall be at least two times
39、 the maximumoperating frequency.6.2.3 Frequency AnalyzerDetermine the frequency of the specimen vibration by using either a digital waveform analyzer ora frequency counter to analyze the signal measured by the sensor. The waveform analyzer shall have a sampling rate of at least20 kHz 2.5 times the m
40、aximum expected frequency to be measured and shall record at least 10242048 points of the waveform.The frequency counter shall have an accuracy of 61 % over the range of use.NOTE 5The maximum frequency that can be measured using a digital waveform analyzer and the fast Fourier transform method is on
41、e-half thesampling frequency; for example, a sampling frequency of 30 kHz will allow measuring resonant frequencies up to 15 kHz. A sampling frequency of2.5 times the expected frequency is called for in case the actual frequency exceeds the expected maximum frequency to be measured. The frequencyres
42、olution in the amplitude spectrum is the sampling frequency divided by the number of points in the waveform.6.2.4 Specimen SupportSupport shall be provided as specified in 6.1.3 for the forced resonance method.7. Test Specimens7.1 PreparationMake the cylindrical or prismatic test specimens in accord
43、ance with Practice C192/C192M, PracticeC31/C31M, Test Method C42/C42M, or other specified procedures.7.2 Measurement of Mass and DimensionsDetermine the mass and average length of the specimens within 60.5 %.Determine the average cross-sectional dimensions within 61 %.7.3 Limitations on Dimensional
44、RatioSpecimens having either small or large ratios of length to maximum transverse directionare frequently difficult to excite in the fundamental transverse mode of vibration. Best results are obtained when this ratio isbetween 3 and 5. For application of the formulas in this test method, the ratio
45、must be at least 2. For measurement of longitudinalresonant frequency, the specimen shall have a circular or square cross-section and the length shall be at least two times the diameterfor a cylinder or at least two times the side dimension for a prism.FIG. 2 Schematic of Apparatus for Impact Resona
46、nce TestC215 1438. Determination of Resonant FrequenciesForced Resonance Method8.1 Transverse Frequency:8.1.1 Support the specimen so that it is able to vibrate freely in the transverse mode (Note 56). Position the specimen and driverso that the driving force is perpendicular to the surface of the s
47、pecimen. Locate the driving unit driver at the approximate middleof the specimen. specimen as shown in Fig. 3a. Place the pickup unit on the specimen so that the direction of pickup sensitivitycoincides with the vibration direction, that is, the transverse direction (see direction. Fig. 3a). Positio
48、n the pickup near one end ofthe specimen. It is permissible to position the driver on the vertical face so that the specimen vibrates perpendicular to the directionshown in Fig. 3a.8.1.2 Force the test specimen to vibrate at varying frequencies.At the same time, observe the indication of the amplifi
49、ed outputof the pickup. If an oscilloscope or other graphic display is used, connect the driver signal to the horizontal sweep of the displayand connect the pickup signal to the vertical sweep. Record the fundamental transverse frequency of the specimen, which is thefrequency at which the indicator shows the maximum reading and observation of the graphic display or the nodal points indicatesfundamental transverse vibration (Note 56). Adjust the amplifiers in the driving and pickup circuits to provide a satisfactoryindication. To avoid distortion, maintain t
