ASTM C1740-10

Standard Practice for Evaluating the Condition of Concrete Plates Using the Impulse-Response Method

SIGNIFICANCE AND USE
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.
This practice is not intended for integrity testing of piles. For such applications refer to Test Method D5882.
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.
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.
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.
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.
For highwa...
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.

General Information

• Status: Historical
• Publication Date: 14-Dec-2010
• ICS: 91.100.30 - Concrete and concrete products
• Technical Committee: C09 - Concrete and Concrete Aggregates
• Drafting Committee: C09.64 - Nondestructive and In-Place Testing

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: C1740 − 10
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 stress-wavetestingofconcreteandrefertoTerminologyE1316
for additional terms related to nondestructive ultrasonic exami-
1.1 This practice provides the procedure for using the
nation that are applicable to this practice.
impulse-response method to evaluate rapidly the condition of
concrete slabs, pavements, bridge decks, walls, or other plate- 3.2 Definitions of Terms Specific to This Standard:
like structures. 3.2.1 impulse-response method, n—a nondestructive test
method based on the use of mechanical impact to cause
1.2 The values stated in SI units are to be regarded as
transient vibration of a concrete test element, the use of a
standard. No other units of measurement are included in this
broadband velocity transducer placed on the test element
standard.
adjacent to the impact point to measure the response, and the
1.3 This standard does not purport to address all of the
use of signal processing to obtain the mobility spectrum of the
safety concerns, if any, associated with its use. It is the
test element.
responsibility of the user of this standard to establish appro-
3.2.1.1 Discussion—Fig. 1 shows the testing configuration
priate safety and health practices and determine the applica-
for the impulse-response method. The hammer contains a load
bility of regulatory limitations prior to use.
cell to measure the transient impact force and a velocity
1.4 The text of this standard references notes and footnotes transducer is used to measure the resulting motion of the test
object (see top plots in Fig. 2). In plate-like structures (as
that provide explanatory material. These notes and footnotes
(excluding those in tables and figures) shall not be considered defined in Test Method C1383), the impact results predomi-
nantly in flexural vibration of the tested element, although
as requirements of the standard.
other modes can be excited. Waveforms from the load cell and
2. Referenced Documents
velocity transducer are converted to the frequency domain and
used to calculate the mobility spectrum, which is analyzed to
2.1 ASTM Standards:
obtain parameters representing the element’s response to the
C125 Terminology Relating to Concrete and Concrete Ag-
impact. These parameters are used to identify anomalous
gregates
regions within the tested element.
C1383 Test Method for Measuring the P-Wave Speed and
the Thickness of Concrete Plates Using the Impact-Echo
3.2.2 mobility, n—ratio of the velocity amplitude at the test
Method
point to the force amplitude at a given frequency, expressed in
D5882 Test Method for Low Strain Impact Integrity Testing
units of (m/s)/N.
of Deep Foundations
3.2.2.1 Discussion—Foraplate-likestructure,mobilityisan
E1316 Terminology for Nondestructive Examinations
indicator of the relative flexibility of the tested element, which
is a function of plate thickness, concrete elastic modulus,
3. Terminology
support conditions, and presence of internal defects. A higher
3.1 Definitions:
mobilityindicatesthattheelementisrelativelymoreflexibleat
3.1.1 Refer to Terminology C125 for general terms related
that test point (1,2).
to concrete. Refer to Test Method C1383 for terms related to
3.2.3 mobility ratio, peak-mean, n—the ratio of the peak
mobility value between 0 to 100 Hz to the average mobility
This practice is under the jurisdiction of ASTM Committee C09 on Concrete
between 100 to 800 Hz
andConcreteAggregatesandisthedirectresponsibilityofSubcommitteeC09.64on
3.2.3.1 Discussion—Ahigh ratio of the peak mobility to the
Nondestructive and In-Place Testing.
average mobility has been found to correlate with poor support
Current edition approved Dec. 15, 2010. Published January 2011. DOI: 10.1520/
C1740-10.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on The boldface numbers in parentheses refer to a list of references at the end of
the ASTM website. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1740 − 10
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
conditions or voids that may exist beneath concrete slabs 3.2.4.1 Discussion—This parameter is used to compare
bearing on ground (1,2).
differences in overall mobility among test points in the tested
element (1,2).
3.2.4 mobility, average, n—average of the mobility values
from the mobility spectrum between 100 and 800 Hz, ex-
pressed in units of (m/s)/N.
C1740 − 10
3.2.5 slope, mobility, n—the slope of the mobility spectrum 3.2.7 stiffness, dynamic—inverse of the initial slope of the
obtained from the best-fit line to mobility values between 100 mobility spectrum from 0 to 40 Hz, expressed in units of N/m
Hz and 800 Hz. (See Fig. 3).
3.2.5.1 Discussion—A high mobility slope has been found
3.2.7.1 Discussion—The initial slope of the mobility spec-
to correlate with locations of poorly consolidated (or honey-
trum defines the dynamic compliance (or flexibility) at the test
combed) concrete in plate-like structures (1,2).
point. The inverse of the initial slope is the dynamic stiffness,
3.2.6 spectrum, mobility, n—the value of mobility as a which is an indicator of the relative quality of the concrete, of
the relative thickness of the member, of the relative quality of
function of frequency obtained from an impulse-response test
at one point on the surface of the tested element. the subgrade support for slabs-on-ground, and of the support
conditions for suspended structural slabs and walls (1,2).
3.2.6.1 Discussion—The mobility spectrum, also referred to
as the transfer function, is obtained by converting the recorded
4. Summary of Practice
waveforms of the hammer impact force and velocity response
into the frequency domain (3,4).The resulting spectra are used
4.1 Agrid is laid out on the surface of the concrete element
to compute the mobility spectrum as follows:
to be tested. Grid spacing normally ranges between 500 mm
*
V~ƒ! 3F ~ƒ!
and 2000 mm and is selected on the basis of the size and shape
M ƒ 5 (1)
~ !
*
F ƒ 3F ƒ
~ ! ~ !
of the element to be tested.Acloser spacing is used for smaller
elements and to locate smaller anomalous regions.
where:
M(ƒ) = mobility spectrum, 4.2 Ahand-held hammer with a force measuring load cell is
V(ƒ) = velocity spectrum,
used to impact the concrete surface and generate transient
F(ƒ) = impact force spectrum, and
stress waves in the concrete test element. These waves set up
*
F (ƒ) = complex conjugate of force spectrum.
flexural and other vibrational modes of the element in the
vicinity of the test point.
The numerator is the cross power spectrum of the force
and velocity and the denominator is the power spectrum of
4.3 The impact point is within 100 6 25 mm of the velocity
the force. Matrix multiplication by the complex conjugate of
transducer used to measure the response due to the hammer
the force spectrum is required because the velocity and
blow.
impact force spectra are matrices of complex numbers. By
the rule for division of complex numbers, the numerator and 4.4 The force and velocity waveforms are recorded and
subjected to digital signal processing to obtain the mobility
denominatorhavetobemultipliedbythecomplexconjugate
of the denominator, that is, the force spectrum. Fig. 3 is an spectrumateachtestpoint.Keyparametersarecomputedfrom
example of a mobility spectrum.The vertical axis represents the mobility spectra at the test points and displayed in the form
response velocity amplitude per unit of force and the of contour plots from which the likely locations of anomalous
horizontal axis is frequency. regions can be identified.
FIG. 3 Example of a Mobility Spectrum Obtained from an Impulse Response Test of a Plate-Like Concrete Element
C1740 − 10
5. Significance and Use 5.11 The practice is not applicable in the presence of
electrical noise, such as that produced by a generator or other
5.1 The impulse-response method is used to evaluate the
electrical sources, that is captured by the data-acquisition
condition of concrete slabs, pavements, bridge decks, walls, or
system.
other concrete plate structures. The method is also applicable
to plate structures with overlays, such as concrete bridge decks 4
6. Apparatus
with asphalt or portland cement concrete overlays. The
6.1 Fig. 1 is a schematic of the basic components of a
impulse-response method is intended for rapid screening of
suitable test system.
structures to identify potential locations of anomalous condi-
tions that require more detailed investigation.
6.2 Hammer—A nominal 1-kg hammer with a 50-mm
diametercylindricalrubbertipofsufficienthardnesstoproduce
5.2 Thispracticeisnotintendedforintegritytestingofpiles.
an impact force amplitude spectrum spanning at least 2 kHz.
For such applications refer to Test Method D5882.
The hammer shall have a built-in load cell, capable of
5.3 This practice can be used to locate delaminated or measuring dynamic forces up to 20 kN. The resonant fre-
poorly consolidated concrete. It can also be used to locate quency of the load cell shall exceed 10 kHz.
NOTE 2—Commercially available hammers equipped with load cells
regions of poor support or voids beneath slabs bearing on
have been found to produce the required force amplitude spectrum. Fig. 2
ground.
shows a typical force-time waveform and force amplitude spectrum for a
hammer with a hard rubber tip. The maximum frequency in the amplitude
5.4 Results are used on a comparative basis for comparing
spectrum of the waves generated by hammer impact is related inversely to
concrete quality or support conditions at one point in the tested
the duration of the impact.
structural element with conditions at other points in the same
6.3 Transducer—A broadband, induction coil, velocity
element, or for comparing a structural element with another
transducer (geophone) that responds to normal surface motion.
element of the same geometry. Invasive probing (drilling holes
The transducer shall have a natural frequency less than 15 Hz
or chipping away concrete) or drilling of cores is used to
and a constant sensitivity over the range 15 to 1000 Hz.
confirm interpretations of impulse-response results.
NOTE 3—Commercially available induction coil velocity transducers
with a base diameter of 50 mm have been found suitable. Such a
5.5 Becauseconcretepropertiescanvaryfrompointtopoint
transducer is housed in a case with three protruding screws or spikes
in the structure due to differences in concrete age, batch-to-
around its perimeter forming a tripod for stability during testing. No
batch variability, or placement and consolidation practices, the
coupling material such as gel or grease is needed to couple the transducer
measured mobility and dynamic stiffness can vary from point
to the concrete.
to point in a plate element of constant thickness.
6.4 Data-Acquisition and Analysis System—Hardware and
NOTE 1—The flexural stiffness of a plate is directly proportional to the
softwareforacquiring,recording,andprocessingtheoutputsof
elastic modulus of the material and directly proportional to the thickness
the hammer load cell and velocity transducer.The system shall
raised to the third power (5).As a result, variations in thickness will have
be capable of displaying test results immediately after impact
a greater effect on variations in mobility than variations in elastic
modulus. and storing test results.
5.6 The effective radius of influence of the hammer blow NOTE 4—Aportable computer with a two-channel data-acquisition card
or a portable two-channel waveform analyzer is acceptable. A computer
limits the maximum concrete element thickness that can be
data-acquisition card with a voltage range of 6 5 V and 8-bit resolution
tested. The apparatus defined in this practice is intended for
has been found to be suitable for the transducer described. Higher voltage
thicknesses less than 1 m.
ranges and resolutions are also suitable.
5.7 For highway applications, results may be influenced by 6.4.1 The sampling rate for each channel shall be 10 kHz or
traffic noise or low frequency structural vibrations set up by
higher (sampling interval of 100 µs or less). The recorded
normal movement of traffic across a structure. The intermittent waveforms from the load cell and velocity transducer shall
nature of these noises, however, may allow testing during
containatleast1024pointseach(seeNote5).Thesystemshall
traffic flow on adjacent portions of the structure. Engineering be capable of triggering on the signal from the hammer
judgment is required to determine whether the response has
channel.
been influenced by traffic-induced vibrations.
NOTE 5—The sampling frequency should be about 10 times the
maximum frequency of interest. For typical concrete structural elements,
5.8 Heavy loads on suspended slabs may affect test results
the maximum frequency of interest is about 1 kHz. For a sampling rate of
by altering the frequencies and shapes of different modes of
10 kHz and 1024 points, the frequency resolution is about 10 Hz. For
vibration. Debris on the test surface may interfere with
faster sampling rates, the number of points in the waveforms should be
obtaining a sharp impact and with measuring the response. increased to maintain a similar frequency resolution. Typical signal
processing software that is used to compute the velocity and force spectra
5.9 The practice is not applicable in the presence of vibra-
requires that the number of points in the waveforms be a power of 2 (for
tions created by mechanical equipment (jack hammers, sound- example, 512, 1024, 2048 and so forth).
ing with a hammer, mechanical sweepers, and the like)
6.4.2 The voltage range of the data-acquisition system shall
impacting the structure.
be matched with the sensitivity of the transducers so that the
5.10 Tests conducted next to or directly over structural
elements that stiffen the plate will result in reduced mobility
andnotberepresentativeoftheinternalc
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