1、Designation: C1740 16Standard 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. Scope*1.1 This practice provides the procedure for using theimpulse-response method to evaluate rapidly the condition of
3、concrete 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
4、its 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 f
5、ootnotes(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 t
6、he 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 Terminology E1316 for terms related tonondestr
7、uctive ultrasonic examination that are applicable tothis practice.3.2 Definitions of Terms Specific to This Standard:3.2.1 impulse-response method, na nondestructive testmethod based on the use of mechanical impact to causetransient vibration of a concrete test element, the use of abroadband velocit
8、y 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 shows the testing configurationfor the impulse-response method. The hammer contains a loadcell to m
9、easure 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, theimpact results predominantly in flexural vibration of the testedelement, although other modes can be excited. Waveformsfrom the
10、 load cell and velocity transducer are converted to thefrequency domain and used to calculate the mobility spectrum,which is analyzed to obtain parameters representing the el-ements response to the impact. These parameters are used toidentify anomalous regions within the tested element.3.2.2 mobilit
11、y, 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, mobility is anindicator of the relative flexibility of the tested element, whichis a function of plate thickness, concrete elas
12、tic modulus,support conditions, and presence of internal defects. A highermobility indicates that the element is relatively more flexible atthat test point (1,2).33.2.3 mobility ratio, peak-mean, nthe ratio of the peakmobility value between 0 to 100 Hz to the average mobilitybetween 100 to 800 Hz3.2
13、.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 Committee C09 on Concreteand ConcreteAggregates and is the direct responsibility of Subcommittee C09.64 onNondestructive and In-Place
14、Testing.Current edition approved Dec. 15, 2016. Published January 2017. Originallyapproved in 2010. Last previous edition approved in 2010 as C174010. DOI:10.1520/C1740-16.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For An
15、nual 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.*A Summary of Changes section appears at the end of this standardCopyright ASTM International,
16、100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and
17、 Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1conditions 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
18、in units of (m/s)/N.3.2.4.1 DiscussionThis parameter is used to comparedifferences in overall mobility among test points in the testedelement (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 wi
19、th a Hard Rubber TipC1740 1623.2.5 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 been foundto correlate with locations of poorly consolidated (or honey-combed) concrete in pl
20、ate-like structures (1,2).3.2.6 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 th
21、e recordedwaveforms of the hammer 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 c
22、onjugate of force spectrum.The numerator is the cross power spectrum of the forceand velocity and the denominator is the power spectrum ofthe force. Matrix multiplication by the complex conjugate ofthe force spectrum is required because the velocity andimpact force spectra are matrices of complex nu
23、mbers. Bythe rule for division of complex numbers, the numerator anddenominator have to be multiplied by the complex conjugateof the denominator, that is, the force spectrum. Fig. 3 is anexample of a mobility spectrum. The vertical axis representsresponse velocity amplitude per unit of force and the
24、horizontal axis is frequency.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
25、 of the initial slope is the 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. Sum
26、mary of Practice4.1 A grid is 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 anomalou
27、s regions.4.2 A hand-held hammer 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 with
28、in 100 6 25 mm of the velocitytransducer 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
29、points and displayed in the formof contour plots from which the likely locations of anomalousregions can be identified.FIG. 3 Example of a Mobility Spectrum Obtained from an Impulse Response Test of a Plate-Like Concrete ElementC1740 1635. Significance and Use5.1 The impulse-response method is used
30、to evaluate thecondition of concrete slabs, pavements, bridge decks, walls, orother 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 ra
31、pid screening ofstructures to 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
32、consolidated concrete. It can 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 same
33、element, or for comparing a structural 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 st
34、ructure due to differences in 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 theela
35、stic modulus of the material 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
36、concrete element thickness that 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 int
37、ermittentnature of these noises, 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 alteri
38、ng the frequencies and shapes 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
39、, mechanical sweepers, and the 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 ofe
40、lectrical noise, such as that 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 suff
41、icient hardness to producean 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 cellsh
42、ave been found to produce the 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 th
43、e impact.6.3 TransducerA broadband, 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 transduce
44、rswith a base diameter of 50 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 Dat
45、a-Acquisition and Analysis SystemHardware 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 4A portable computer with a two-chann
46、el data-acquisition cardor a portable 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 r
47、ate for each channel shall be 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 f
48、requency should be about 10 times 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
49、waveforms should beincreased to 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 shallbe matched with the sensitivity of the transducers so that the4Suitable apparatus is available commercially.C1740 164peak hammer force and response velocity are measured with-out clipping of the signals.6.4.3 Softwar
