ASTM C1740-16

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C1740 − 10 C1740 − 16
Standard Practice for
Evaluating the Condition of Concrete Plates Using the
Impulse-Response Method
This standard is issued under the fixed designation C1740; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope Scope*
1.1 This practice provides the procedure for using the impulse-response method to evaluate rapidly the condition of concrete
slabs, pavements, bridge decks, walls, or other plate-like structures.
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 responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
1.4 The text of this standard references notes and footnotes that provide explanatory material. These notes and footnotes
(excluding those in tables and figures) shall not be considered as requirements of the standard.
2. Referenced Documents
2.1 ASTM Standards:
C125 Terminology Relating to Concrete and Concrete Aggregates
C1383 Test Method for Measuring the P-Wave Speed and the Thickness of Concrete Plates Using the Impact-Echo Method
D5882 Test Method for Low Strain Impact Integrity Testing of Deep Foundations
E1316 Terminology for Nondestructive Examinations
3. Terminology
3.1 Definitions:
3.1.1 Refer to Terminology C125 for general terms related to concrete. Refer to Test Method C1383 for terms related to
stress-wave testing of concrete and refer to Terminology E1316 for additional terms related to nondestructive ultrasonic
examination that are applicable to this practice.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 impulse-response method, n—a nondestructive test method based on the use of mechanical impact to cause transient
vibration of a concrete test element, the use of a broadband velocity transducer placed on the test element adjacent to the impact
point to measure the response, and the use of signal processing to obtain the mobility spectrum of the test element.
This practice is under the jurisdiction of ASTM Committee C09 on Concrete and Concrete Aggregates and is the direct responsibility of Subcommittee C09.64 on
Nondestructive and In-Place Testing.
Current edition approved Dec. 15, 2010Dec. 15, 2016. Published January 2011January 2017. Originally approved in 2010. Last previous edition approved in 2010 as
C1740–10. DOI: 10.1520/C1740-10.10.1520/C1740-16.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
3.2.1.1 Discussion—
Fig. 1 shows the testing configuration for the impulse-response method. The hammer contains a load cell to measure the transient
impact force and a velocity transducer is used to measure the resulting motion of the test object (see top plots in Fig. 2). In
plate-like structures (as defined in Test Method structures, C1383), the impact results predominantly in flexural vibration of the
tested element, although other modes can be excited. Waveforms from the load cell and velocity transducer are converted to the
frequency domain and used to calculate the mobility spectrum, which is analyzed to obtain parameters representing the element’s
response to the impact. These parameters are used to identify anomalous regions within the tested element.
*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
C1740 − 16
FIG. 1 Schematic of the Test Set-Up and Apparatus for Impulse-Response Test
FIG. 2 Typical Force-Time Waveform and Amplitude Spectrum Plots for Hammer with a Hard Rubber Tip
3.2.2 mobility, n—ratio of the velocity amplitude at the test point to the force amplitude at a given frequency, expressed in units
of (m/s)/N.
3.2.2.1 Discussion—
For a plate-like structure, mobility is an indicator of the relative flexibility of the tested element, which is a function of plate
C1740 − 16
thickness, concrete elastic modulus, support conditions, and presence of internal defects. A higher mobility indicates that the
element is relatively more flexible at that test point (1,2).
3.2.3 mobility ratio, peak-mean, n—the ratio of the peak mobility value between 0 to 100 Hz to the average mobility between
100 to 800 Hz
The boldface numbers in parentheses refer to a list of references at the end of this standard.
3.2.3.1 Discussion—
A high ratio of the peak mobility to the average mobility has been found to correlate with poor support conditions or voids that
may exist beneath concrete slabs bearing on ground (1,2).
3.2.4 mobility, average, n—average of the mobility values from the mobility spectrum between 100 and 800 Hz, expressed in
units of (m/s)/N.
3.2.4.1 Discussion—
This parameter is used to compare differences in overall mobility among test points in the tested element (1,2).
3.2.5 slope, mobility, n—the slope of the mobility spectrum obtained from the best-fit line to mobility values between 100 Hz
and 800 Hz.
3.2.5.1 Discussion—
A high mobility slope has been found to correlate with locations of poorly consolidated (or honeycombed) concrete in plate-like
structures (1,2).
3.2.6 spectrum, mobility, n—the value of mobility as a function of frequency obtained from an impulse-response test at one point
on the surface of the tested element.
3.2.6.1 Discussion—
The mobility spectrum, also referred to as the transfer function, is obtained by converting the recorded waveforms of the hammer
impact force and velocity response into the frequency domain (3,4). The resulting spectra are used to compute the mobility
spectrum as follows:
*
V ƒ 3F ƒ
~ ! ~ !
M~ƒ!5 (1)
*
F~ƒ!3F ~ƒ!
where:
M(ƒ) = mobility spectrum,
V(ƒ) = velocity spectrum,
F(ƒ) = impact force spectrum, and
*
F (ƒ) = complex conjugate of force spectrum.
The numerator is the cross power spectrum of the force and velocity and the denominator is the power spectrum of the force.
Matrix multiplication by the complex conjugate of the force spectrum is required because the velocity and impact force spectra
are matrices of complex numbers. By the rule for division of complex numbers, the numerator and denominator have to be
multiplied by the complex conjugate of the denominator, that is, the force spectrum. Fig. 3 is an example of a mobility spectrum.
The vertical axis represents response velocity amplitude per unit of force and the horizontal axis is frequency.
3.2.7 stiffness, dynamic—inverse of the initial slope of the mobility spectrum from 0 to 40 Hz, expressed in units of N/m (See
Fig. 3).
3.2.7.1 Discussion—
The initial slope of the mobility spectrum defines the dynamic compliance (or flexibility) at the test point. The inverse of the initial
slope is the dynamic stiffness, which is an indicator of the relative quality of the concrete, of the relative thickness of the member,
of the relative quality of the subgrade support for slabs-on-ground, and of the support conditions for suspended structural slabs and
walls (1,2).
C1740 − 16
FIG. 3 Example of a Mobility Spectrum Obtained from an Impulse Response Test of a Plate-Like Concrete Element
4. Summary of Practice
4.1 A grid is laid out on the surface of the concrete element to be tested. Grid spacing normally ranges between 500 mm and
2000 mm and is selected on the basis of the size and shape of the element to be tested. A closer spacing is used for smaller elements
and to locate smaller anomalous regions.
4.2 A hand-held hammer with a force measuring load cell is used to impact the concrete surface and generate transient stress
waves in the concrete test element. These waves set up flexural and other vibrational modes of the element in the vicinity of the
test point.
4.3 The impact point is within 100 6 25 mm of the velocity transducer used to measure the response due to the hammer blow.
4.4 The force and velocity waveforms are recorded and subjected to digital signal processing to obtain the mobility spectrum
at each test point. Key parameters are computed from the mobility spectra at the test points and displayed in the form of contour
plots from which the likely locations of anomalous regions can be identified.
5. Significance and Use
5.1 The impulse-response method is used to evaluate the condition of concrete slabs, pavements, bridge decks, walls, or other
concrete plate structures. The method is also applicable to plate structures with overlays, such as concrete bridge decks with asphalt
or portland cement concrete overlays. The impulse-response method is intended for rapid screening of structures to identify
potential locations of anomalous conditions 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 or poorly consolidated concrete. It can also be used to locate regions of poor
support or voids beneath slabs bearing on ground.
5.4 Results are used on a comparative basis for comparing concrete quality or support conditions at one point in the tested
structural element with conditions at other points in the same element, or for comparing a structural element with another element
of the same geometry. Invasive probing (drilling holes or chipping away concrete) or drilling of cores is used to confirm
interpretations of impulse-response results.
5.5 Because concrete properties can vary from point to point in the structure due to differences in concrete age, batch-to-batch
variability, or placement and consolidation practices, the measured mobility and dynamic stiffness can vary from point to point in
a plate element of constant thickness.
NOTE 1—The flexural stiffness of a plate is directly proportional to the elastic modulus of the material and directly proportional to the thickness raised
to the third power (5). As a result, variations in thickness will have a greater effect on variations in mobility than variations in elastic modulus.
C1740 − 16
5.6 The effective radius of influence of the hammer blow limits the maximum concrete element thickness that can be tested. The
apparatus defined in this practice is intended for thicknesses less than 1 m.
5.7 For highway applications, results may be influenced by traffic noise or low frequency structural vibrations set up by normal
movement of traffic across a structure. The intermittent nature of these noises, however, may allow testing during traffic flow on
adjacent portions of the structure. Engineering judgment is required to determine whether the response has been influenced by
traffic-induced vibrations.
5.8 Heavy loads on suspended slabs may affect test results by altering the frequencies and shapes of different modes of vibration.
Debris on the test surface may interfere with obtaining a sharp impact and with measuring the response.
5.9 The practice is not applicable in the presence of vibrations created by mechanical equipment (jack hammers, sounding with
a hammer, mechanical sweepers, and the like) impacting the structure.
5.10 Tests conducted next to or directly over structural elements that stiffen the plate will result in reduced mobility and not be
representative of the internal conditions of the plate.
5.11 The practice is not applicable in the presence of electrical noise, such as that produced by a generator or other electrical
sources, that is captured by the data-acquisition system.
6. Apparatus
6.1 Fig. 1 is a schematic of the basic components of a suitable test system.
6.2 Hammer—A nominal 1-kg hammer with a 50-mm diameter cylindrical rubber tip of sufficient hardness to produce an impact
force amplitude spectrum spanning at least 2 kHz. The hammer shall have a built-in load cell, capable of measuring dynamic forces
up to 20 kN. The resonant frequency of the load cell shall exceed 10 kHz.
NOTE 2—Commercially available hammers equipped with load cells have been found to produce the required force amplitude spectrum. Fig. 2 shows
a typical force-time waveform and force amplitude spectrum for a hammer with a hard rubber tip. The maximum frequency in the amplitude spectrum
of the waves generated by hammer impact is related inversely to the duration of the impact.
6.3 Transducer—A broadband, induction coil, velocity transducer (geophone) that responds to normal surface motion. The
transducer shall have a natural frequency less than 15 Hz and a constant sensitivity over the range 15 to 1000 Hz.
NOTE 3—Commercially available induction coil velocity transducers with a base diameter of 50 mm have been found suitable. Such a transducer is
housed in a case with three protruding screws or spikes around its perimeter forming a tripod for stability during testing. No coupling material such as
gel or grease is needed to couple the transducer to the concrete.
6.4 Data-Acquisition and Analysis System—Hardware and software for acquiring, recording, and processing the outputs of the
hammer load cell and velocity transducer. The system shall be capable of displaying test results immediately after impact and
storing test results.
NOTE 4—A portable computer with a two-channel data-acquisition card or a portable two-channel waveform analyzer is acceptable. A computer
data-acquisition card with a voltage range of 6 5 V and 8-bit resolution has been found to be suitable for the transducer described. Higher voltage ranges
and resolutions are also suitable.
6.4.1 The sampling rate for each channel shall be 10 kHz or higher (sampling interval of 100 μs or less). The recorded
waveforms from the load cell and velocity transducer shall contain at least 1024 points each (see Note 5). The system shall be
capable of triggering on the signal from the hammer channel.
NOTE 5—The sampling frequency should be about 10 times the maximum frequency of interest. For typical concrete structural elements, the maximum
frequency of interest is about 1 kHz. For a sampling rate of 10 kHz and 1024 points, the frequency resolution is about 10 Hz. For faster sampling rates,
the number of points in the waveforms should be increased to maintain a similar frequency resolution. Typical signal processing software that is used
to compute the velocity and force spectra requires that the number of points in the waveforms be a power of 2 (for example, 512, 1024, 2048 and so forth).
6.4.2 The voltage range of the data-acquisition system shall be matched with the sensitivity of the transducers so that the peak
hammer force and response velocity are measured without clipping of the signals.
6.4.3 Software shall be provided for acquiring, recording, displaying, analyzing, and storing data. The display shall include
voltage versus time waveforms for both the impact force and velocity measurements for each test. The software shall compute the
mobility spectrum from the recorded waveforms. The mobility spectrum shall be displayed immediately after the waveforms have
been captured.
NOTE 6—Fig. 4 is an example
...