1、Designation: C1740 10Standard Practice forEvaluating the Condition of Concrete Plates Using theImpulse-Response Method1This standard is issued under the fixed designation C1740; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the y
2、ear 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.1. Scope1.1 This practice provides the procedure for using theimpulse-response method to evaluate rapidly the condition ofc
3、oncrete slabs, pavements, bridge decks, walls, or other plate-like structures.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 i
4、ts use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.1.4 The text of this standard references notes and footnotesthat provide explanatory material. These notes and fo
5、otnotes(excluding those in tables and figures) shall not be consideredas requirements of the standard.2. Referenced Documents2.1 ASTM Standards:2C125 Terminology Relating to Concrete and Concrete Ag-gregatesC1383 Test Method for Measuring the P-Wave Speed andthe Thickness of Concrete Plates Using th
6、e Impact-EchoMethodD5882 Test Method for Low Strain Impact Integrity Testingof Deep FoundationsE1316 Terminology for Nondestructive Examinations3. Terminology3.1 Definitions:3.1.1 Refer to Terminology C125 for general terms relatedto concrete. Refer to Test Method C1383 for terms related tostress-wa
7、ve testing of concrete and refer to Terminology E1316for additional terms related to nondestructive ultrasonic exami-nation that are applicable to this practice.3.2 Definitions of Terms Specific to This Standard:3.2.1 impulse-response method, na nondestructive testmethod based on the use of mechanic
8、al impact to causetransient vibration of a concrete test element, the use of abroadband velocity transducer placed on the test elementadjacent to the impact point to measure the response, and theuse of signal processing to obtain the mobility spectrum of thetest element.3.2.1.1 DiscussionFig. 1 show
9、s the testing configurationfor the impulse-response method. The hammer contains a loadcell to measure the transient impact force and a velocitytransducer is used to measure the resulting motion of the testobject (see top plots in Fig. 2). In plate-like structures (asdefined in Test Method C1383), th
10、e impact results predomi-nantly in flexural vibration of the tested element, althoughother modes can be excited. Waveforms from the load cell andvelocity transducer are converted to the frequency domain andused to calculate the mobility spectrum, which is analyzed toobtain parameters representing th
11、e elements response to theimpact. These parameters are used to identify anomalousregions within the tested element.3.2.2 mobility, nratio of the velocity amplitude at the testpoint to the force amplitude at a given frequency, expressed inunits of (m/s)/N.3.2.2.1 DiscussionFor a plate-like structure,
12、 mobility isan indicator of the relative flexibility of the tested element,which is a function of plate thickness, concrete elastic modu-lus, support conditions, and presence of internal defects. Ahigher mobility indicates that the element is relatively moreflexible at that test point (1,2).33.2.3 m
13、obility ratio, peak-mean, nthe ratio of the peakmobility value between 0 to 100 Hz to the average mobilitybetween 100 to 800 Hz3.2.3.1 DiscussionA high ratio of the peak mobility to theaverage mobility has been found to correlate with poor support1This practice is under the jurisdiction of ASTM Comm
14、ittee C09 on Concreteand ConcreteAggregates and is the direct responsibility of Subcommittee C09.64 onNondestructive and In-Place Testing.Current edition approved Dec. 15, 2010. Published January 2011. DOI: 10.1520/C1740-10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcont
15、act ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The boldface numbers in parentheses refer to a list of references at the end ofthis standard.1Copyright ASTM International, 100 Barr Har
16、bor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.conditions or voids that may exist beneath concrete slabsbearing on ground (1,2).3.2.4 mobility, average, naverage of the mobility valuesfrom the mobility spectrum between 100 and 800 Hz, ex-pressed in units of (m/s)/N.3.2.4.1 D
17、iscussionThis parameter is used to comparedifferences in overall mobility among test points in the testedelement (1,2).3.2.5 slope, mobility, nthe slope of the mobility spectrumobtained from the best-fit line to mobility values between 100Hz and 800 Hz.3.2.5.1 DiscussionA high mobility slope has bee
18、n foundto correlate with locations of poorly consolidated (or honey-combed) concrete in plate-like structures (1,2).FIG. 1 Schematic of the Test Set-Up and Apparatus for Impulse-Response TestFIG. 2 Typical Force-Time Waveform and Amplitude Spectrum Plots for Hammer with a Hard Rubber TipC1740 1023.2
19、.6 spectrum, mobility, nthe value of mobility as afunction of frequency obtained from an impulse-response testat one point on the surface of the tested element.3.2.6.1 DiscussionThe mobility spectrum, also referred toas the transfer function, is obtained by converting the recordedwaveforms of the ha
20、mmer impact force and velocity responseinto the frequency domain (3,4). The resulting spectra are usedto compute the mobility spectrum as follows:M! 5V! 3 F*!F! 3 F*!(1)where:M() = mobility spectrum,V() = velocity spectrum,F() = impact force spectrum, andF*() = complex conjugate of force spectrum.Th
21、e numerator is the cross power spectrum of the force andvelocity and the denominator is the power spectrum of theforce. Matrix multiplication by the complex conjugate of theforce spectrum is required because the velocity and impactforce spectra are matrices of complex numbers. By the rule fordivisio
22、n of complex numbers, the numerator and denominatorhave to be multiplied by the complex conjugate of thedenominator, that is, the force spectrum. Fig. 3 is an exampleof a mobility spectrum. The vertical axis represents responsevelocity amplitude per unit of force and the horizontal axis isfrequency.
23、3.2.7 stiffness, dynamicinverse of the initial slope of themobility spectrum from 0 to 40 Hz, expressed in units of N/m(See Fig. 3).3.2.7.1 DiscussionThe initial slope of the mobility spec-trum defines the dynamic compliance (or flexibility) at the testpoint. The inverse of the initial slope is the
24、dynamic stiffness,which is an indicator of the relative quality of the concrete, ofthe relative thickness of the member, of the relative quality ofthe subgrade support for slabs-on-ground, and of the supportconditions for suspended structural slabs and walls (1,2).4. Summary of Practice4.1 A grid is
25、 laid out on the surface of the concrete elementto be tested. Grid spacing normally ranges between 500 mmand 2000 mm and is selected on the basis of the size and shapeof the element to be tested. A closer spacing is used for smallerelements and to locate smaller anomalous regions.4.2 A hand-held ham
26、mer with a force measuring load cell isused to impact the concrete surface and generate transientstress waves in the concrete test element. These waves set upflexural and other vibrational modes of the element in thevicinity of the test point.4.3 The impact point is within 100 6 25 mm of the velocit
27、ytransducer used to measure the response due to the hammerblow.4.4 The force and velocity waveforms are recorded andsubjected to digital signal processing to obtain the mobilityspectrum at each test point. Key parameters are computed fromthe mobility spectra at the test points and displayed in the f
28、ormof contour plots from which the likely locations of anomalousregions can be identified.5. Significance and Use5.1 The impulse-response method is used to evaluate thecondition of concrete slabs, pavements, bridge decks, walls, orFIG. 3 Example of a Mobility Spectrum Obtained from an Impulse Respon
29、se Test of a Plate-Like Concrete ElementC1740 103other concrete plate structures. The method is also applicableto plate structures with overlays, such as concrete bridge deckswith asphalt or portland cement concrete overlays. Theimpulse-response method is intended for rapid screening ofstructures to
30、 identify potential locations of anomalous condi-tions that require more detailed investigation.5.2 This practice is not intended for integrity testing of piles.For such applications refer to Test Method D5882.5.3 This practice can be used to locate delaminated orpoorly consolidated concrete. It can
31、 also be used to locateregions of poor support or voids beneath slabs bearing onground.5.4 Results are used on a comparative basis for comparingconcrete quality or support conditions at one point in the testedstructural element with conditions at other points in the sameelement, or for comparing a s
32、tructural element with anotherelement of the same geometry. Invasive probing (drilling holesor chipping away concrete) or drilling of cores is used toconfirm interpretations of impulse-response results.5.5 Because concrete properties can vary from point to pointin the structure due to differences in
33、 concrete age, batch-to-batch variability, or placement and consolidation practices, themeasured mobility and dynamic stiffness can vary from pointto point in a plate element of constant thickness.NOTE 1The flexural stiffness of a plate is directly proportional to theelastic modulus of the material
34、and directly proportional to the thicknessraised to the third power (5). As a result, variations in thickness will havea greater effect on variations in mobility than variations in elasticmodulus.5.6 The effective radius of influence of the hammer blowlimits the maximum concrete element thickness th
35、at can betested. The apparatus defined in this practice is intended forthicknesses less than 1 m.5.7 For highway applications, results may be influenced bytraffic noise or low frequency structural vibrations set up bynormal movement of traffic across a structure. The intermittentnature of these nois
36、es, however, may allow testing duringtraffic flow on adjacent portions of the structure. Engineeringjudgment is required to determine whether the response hasbeen influenced by traffic-induced vibrations.5.8 Heavy loads on suspended slabs may affect test resultsby altering the frequencies and shapes
37、 of different modes ofvibration. Debris on the test surface may interfere withobtaining a sharp impact and with measuring the response.5.9 The practice is not applicable in the presence of vibra-tions created by mechanical equipment (jack hammers, sound-ing with a hammer, mechanical sweepers, and th
38、e like)impacting the structure.5.10 Tests conducted next to or directly over structuralelements that stiffen the plate will result in reduced mobilityand not be representative of the internal conditions of the plate.5.11 The practice is not applicable in the presence ofelectrical noise, such as that
39、 produced by a generator or otherelectrical sources, that is captured by the data-acquisitionsystem.6. Apparatus46.1 Fig. 1 is a schematic of the basic components of asuitable test system.6.2 HammerA nominal 1-kg hammer with a 50-mmdiameter cylindrical rubber tip of sufficient hardness to producean
40、impact force amplitude spectrum spanning at least 2 kHz.The hammer shall have a built-in load cell, capable ofmeasuring dynamic forces up to 20 kN. The resonant fre-quency of the load cell shall exceed 10 kHz.NOTE 2Commercially available hammers equipped with load cellshave been found to produce the
41、 required force amplitude spectrum. Fig. 2shows a typical force-time waveform and force amplitude spectrum for ahammer with a hard rubber tip. The maximum frequency in the amplitudespectrum of the waves generated by hammer impact is related inversely tothe duration of the impact.6.3 TransducerA broa
42、dband, induction coil, velocitytransducer (geophone) that responds to normal surface motion.The transducer shall have a natural frequency less than 15 Hzand a constant sensitivity over the range 15 to 1000 Hz.NOTE 3Commercially available induction coil velocity transducerswith a base diameter of 50
43、mm have been found suitable. Such atransducer is housed in a case with three protruding screws or spikesaround its perimeter forming a tripod for stability during testing. Nocoupling material such as gel or grease is needed to couple the transducerto the concrete.6.4 Data-Acquisition and Analysis Sy
44、stemHardware andsoftware for acquiring, recording, and processing the outputs ofthe hammer load cell and velocity transducer. The system shallbe capable of displaying test results immediately after impactand storing test results.NOTE 4Aportable computer with a two-channel data-acquisition cardor a p
45、ortable two-channel waveform analyzer is acceptable. A computerdata-acquisition card with a voltage range of 6 5 V and 8-bit resolutionhas been found to be suitable for the transducer described. Higher voltageranges and resolutions are also suitable.6.4.1 The sampling rate for each channel shall be
46、10 kHz orhigher (sampling interval of 100 s or less). The recordedwaveforms from the load cell and velocity transducer shallcontain at least 1024 points each (see Note 5). The system shallbe capable of triggering on the signal from the hammerchannel.NOTE 5The sampling frequency should be about 10 ti
47、mes themaximum frequency of interest. For typical concrete structural elements,the maximum frequency of interest is about 1 kHz. For a sampling rate of10 kHz and 1024 points, the frequency resolution is about 10 Hz. Forfaster sampling rates, the number of points in the waveforms should beincreased t
48、o maintain a similar frequency resolution. Typical signalprocessing software that is used to compute the velocity and force spectrarequires that the number of points in the waveforms be a power of 2 (forexample, 512, 1024, 2048 and so forth).6.4.2 The voltage range of the data-acquisition system sha
49、llbe matched with the sensitivity of the transducers so that thepeak hammer force and response velocity are measured with-out clipping of the signals.6.4.3 Software shall be provided for acquiring, recording,displaying, analyzing, and storing data. The display shall4Suitable apparatus is available commercially.C1740 104include voltage versus time waveforms for both the impactforce and velocity measurements for each test. The softwareshall compute the mobility spectrum from the recorded wave-forms. The mobility spectrum shall be displayed immed
