ASTM D6087-08(2015)e1
(Test Method)Standard Test Method for Evaluating Asphalt-Covered Concrete Bridge Decks Using Ground Penetrating Radar
Standard Test Method for Evaluating Asphalt-Covered Concrete Bridge Decks Using Ground Penetrating Radar
SIGNIFICANCE AND USE
3.1 This test method provides information on the condition of concrete bridge decks overlaid with asphaltic concrete without necessitating removal of the overlay, or other destructive procedures.
3.2 This test method also provides information on the condition of bridge decks without overlays and with portland cement concrete overlays.
3.3 A systematic approach to bridge deck rehabilitation requires considerable data on the condition of the decks. In the past, data has been collected using the traditional methods of visual inspection supplemented by physical testing and coring. Such methods have proven to be tedious, expensive, and of limited accuracy. Consequently, GPR provides a mechanism to rapidly survey bridges in an efficient, non-destructive manner.
3.4 Information on the condition of asphalt-covered concrete bridge decks is needed to estimate bridge deck condition for maintenance and rehabilitation, to provide cost-effective information necessary for rehabilitation contracts.
3.5 GPR is currently the only non-destructive method that can evaluate bridge deck condition on bridge decks containing an asphalt overlay.
SCOPE
1.1 This test method covers several ground penetrating radar (GPR) evaluation procedures that can be used to evaluate the condition of concrete bridge decks overlaid with asphaltic concrete wearing surfaces. These procedures can also be used for bridge decks overlaid with portland cement concrete and for bridge decks without an overlay. Specifically, this test method predicts the presence or absence of concrete or rebar deterioration at or above the level of the top layer of reinforcing bar.
1.2 Deterioration in concrete bridge decks is manifested by the corrosion of embedded reinforcement or the decomposition of concrete, or both. The most serious form of deterioration is that which is caused by corrosion of embedded reinforcement. Corrosion may be initiated by deicing salts, used for snow and ice control in the winter months, penetrating the concrete. In arid climates, the corrosion can be initiated by chloride ions contained in the mix ingredients. Deterioration may also be initiated by the intrusion of water and aggravated by subsequent freeze/thaw cycles causing damage to the concrete and subsequent debonding of the reinforcing steel with the surrounding compromised concrete.
1.2.1 As the reinforcing steel corrodes, it expands and creates a crack or subsurface fracture plane in the concrete at or just above the level of the reinforcement. The fracture plane, or delamination, may be localized or may extend over a substantial area, especially if the concrete cover to the reinforcement is small. It is not uncommon for more than one delamination to occur on different planes between the concrete surface and the reinforcing steel. Delaminations are not visible on the concrete surface. However, if repairs are not made, the delaminations progress to open spalls and, with continued corrosion, eventually affect the structural integrity of the deck.
1.2.2 The portion of concrete contaminated with excessive chlorides is generally structurally deficient compared with non-contaminated concrete. Additionally, the chloride-contaminated concrete provides a pathway for the chloride ions to initiate corrosion of the reinforcing steel. It is therefore of particular interest in bridge deck condition investigations to locate not only the areas of active reinforcement corrosion, but also areas of chloride-contaminated and otherwise deteriorated concrete.
1.3 This test method may not be suitable for evaluating bridges with delaminations that are localized over the diameter of the reinforcement, or for those bridges that have cathodic protection (coke breeze as cathode) installed on the bridge or for which a conductive aggregate has been used in the asphalt (that is, blast furnace slag). This is because metals are perfect reflectors of electromagnetic waves, since t...
General Information
Buy Standard
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
´1
Designation: D6087 − 08 (Reapproved 2015)
Standard Test Method for
Evaluating Asphalt-Covered Concrete Bridge Decks Using
Ground Penetrating Radar
This standard is issued under the fixed designation D6087; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Removed converted inch-pound units editorially in June 2015.
1. Scope 1.2.2 The portion of concrete contaminated with excessive
chlorides is generally structurally deficient compared with
1.1 This test method covers several ground penetrating
non-contaminated concrete. Additionally, the chloride-
radar(GPR)evaluationproceduresthatcanbeusedtoevaluate
contaminatedconcreteprovidesapathwayforthechlorideions
the condition of concrete bridge decks overlaid with asphaltic
to initiate corrosion of the reinforcing steel. It is therefore of
concrete wearing surfaces. These procedures can also be used
particular interest in bridge deck condition investigations to
for bridge decks overlaid with portland cement concrete and
locate not only the areas of active reinforcement corrosion, but
for bridge decks without an overlay. Specifically, this test
also areas of chloride-contaminated and otherwise deteriorated
method predicts the presence or absence of concrete or rebar
concrete.
deterioration at or above the level of the top layer of reinforc-
ing bar.
1.3 This test method may not be suitable for evaluating
bridgeswithdelaminationsthatarelocalizedoverthediameter
1.2 Deterioration in concrete bridge decks is manifested by
of the reinforcement, or for those bridges that have cathodic
thecorrosionofembeddedreinforcementorthedecomposition
protection (coke breeze as cathode) installed on the bridge or
of concrete, or both. The most serious form of deterioration is
for which a conductive aggregate has been used in the asphalt
that which is caused by corrosion of embedded reinforcement.
(that is, blast furnace slag). This is because metals are perfect
Corrosion may be initiated by deicing salts, used for snow and
reflectors of electromagnetic waves, since the wave imped-
ice control in the winter months, penetrating the concrete. In
arid climates, the corrosion can be initiated by chloride ions ances for metals are zero.
contained in the mix ingredients. Deterioration may also be
1.4 A precision and bias statement has not been developed
initiated by the intrusion of water and aggravated by subse-
at this time. Therefore, this standard should not be used for
quent freeze/thaw cycles causing damage to the concrete and
acceptance or rejection of a material for purchasing purposes.
subsequent debonding of the reinforcing steel with the sur-
rounding compromised concrete.
1.5 The values stated in SI units are to be regarded as
1.2.1 As the reinforcing steel corrodes, it expands and standard. No other units of measurement are included in this
creates a crack or subsurface fracture plane in the concrete at
standard.
orjustabovethelevelofthereinforcement.Thefractureplane,
1.6 This standard does not purport to address all of the
or delamination, may be localized or may extend over a
safety concerns, if any, associated with its use. It is the
substantial area, especially if the concrete cover to the rein-
responsibility of the user of this standard to establish appro-
forcement is small. It is not uncommon for more than one
priate safety and health practices and determine the applica-
delamination to occur on different planes between the concrete
bility of regulatory limitations prior to use. Specific precau-
surface and the reinforcing steel. Delaminations are not visible
tionary statements are given in Section 5.
on the concrete surface. However, if repairs are not made, the
delaminations progress to open spalls and, with continued
2. Summary of Test Method
corrosion, eventually affect the structural integrity of the deck.
2.1 The data collection equipment consists of a short-pulse
GPR device, data acquisition device, recording device, and
1 data processing and interpretation equipment. The user makes
This test method is under the jurisdiction of ASTM Committee D04 on Road
and Paving Materials and is the direct responsibility of Subcommittee D04.32 on
repeated passes with the data collection equipment in a
Bridges and Structures.
direction parallel or perpendicular to the centerline across a
CurrenteditionapprovedJune1,2015.PublishedJuly2015.Originallyapproved
bridge deck at specified locations. Bridge deck condition is
in 1997. Last previous edition approved in 2008 as D6087–08. DOI: 10.1520/
D6087-08R15E01. quantified based on the data obtained.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´1
D6087 − 08 (2015)
3. Significance and Use 4.2 Data Acquisition System—A data acquisition system,
consisting of equipment for gathering GPR data at the mini-
3.1 This test method provides information on the condition
mumdataratesspecifiedin4.1.1and4.1.2.Thesystemshallbe
of concrete bridge decks overlaid with asphaltic concrete
capable of accurately acquiring GPR data with a minimum of
without necessitating removal of the overlay, or other destruc-
60-dB dynamic range.
tive procedures.
4.3 Distance Measurement System—A distance measure-
3.2 This test method also provides information on the
mentsystemconsistingofafifth-wheelorappropriatedistance
condition of bridge decks without overlays and with portland
measurement instrument (DMI) with accuracy of 6100
cement concrete overlays.
mm/km and a resolution of 25 mm.
3.3 A systematic approach to bridge deck rehabilitation
NOTE 1—Fig. 1 shows a functional block diagram for multiple GPRs
requires considerable data on the condition of the decks. In the
and support equipment.
past, data has been collected using the traditional methods of
visual inspection supplemented by physical testing and coring.
5. Hazards
Such methods have proven to be tedious, expensive, and of
5.1 During operation of the GPR system, observe the
limitedaccuracy.Consequently,GPRprovidesamechanismto
manufacturer’s safety directions at all times.When conducting
rapidly survey bridges in an efficient, non-destructive manner.
inspections,ensurethatappropriatetrafficprotectionisutilized
3.4 Information on the condition of asphalt-covered con-
in accordance with accepted standards.
crete bridge decks is needed to estimate bridge deck condition
5.2 Electromagnetic emissions from the GPR apparatus, if
for maintenance and rehabilitation, to provide cost-effective
the system is improperly operated, could potentially interfere
information necessary for rehabilitation contracts.
with commercial communications, especially if the antenna is
3.5 GPR is currently the only non-destructive method that
not properly oriented toward the ground. Ensure that all such
can evaluate bridge deck condition on bridge decks containing
emissions from the system comply with Part 15 of the Federal
an asphalt overlay.
Communications Commission (FCC) Regulations.
4. Apparatus
6. Procedure
4.1 GPR System—TherearetwocategoriesofGPRsystems,
6.1 Conditions for Testing:
depending on the type of antenna utilized for data collection.
6.1.1 If soil, aggregate, or other particulate debris is present
4.1.1 GPR systems using air-launched horn antennas with
on the bridge deck surface, clean the bridge deck.
center frequencies 1 GHz and greater. The equipment may
6.1.2 Test the bridge deck in a surface dry condition.
consist of an air-coupled, short-pulse monostatic or bistatic
antenna(s) with sufficient center frequency to provide the 6.2 System Performance Compliance—The system should
accurate measurement ofa5cm thick asphalt pavement. be calibrated and performance verified in accordance with the
manufacturer’s recommendations and specifications. The fol-
4.1.2 GPR systems using ground-coupled antennas with
central frequencies greater than 1 GHz. lowinginformationisincludedforreferenceonlyanddescribes
FIG. 1 Block Diagram of GPR and Support Equipment
´1
D6087 − 08 (2015)
typical calibration procedures for different types of systems. factor Ci represents the speed between distance i and i+1. The
Compliance with the following procedures is not required and allowable variation in measured speed is shown as follows:
the manufacturer’s calibration procedure takes preference. For
C 2 C
1 2
,2%, (3)
air-launched antennas, this test shall consist of the following:
Meanof C and C
1 2
6.2.1 Signal-to-Noise Ratio:
where:
6.2.1.1 Signal-to-Noise Ratio Test—Position the antenna at
C =
its far field distance approximately equal to maximum dimen- 1
DistancefromPosition2 toPosition1
sion of antenna aperture above a square metal plate with a
T
width of 4× antenna aperture, minimum.Turn on the GPR unit
C =
and allow to operate for a 20-min warm-up period or the time
DistancefromPosition3 toPosition2
recommended by the manufacturer.After warming up the unit,
t
record 100 waveforms. Then evaluate the recorded waveform
6.2.3.2 The variation in time calibration factor should be
for signal-to-noise ratio. The signal-to-noise ratio is described
less than 2%.
by the following equation:
6.2.4 Long-Term Stability Test:
SignalLevel ~A !
mp
6.2.4.1 Long-Term Amplitude Variation—Use the same test
.20 26.0 dB (1)
~ !
NoiseLevel A
~ !
n
configuration as described in the signal-to-noise ratio test.
Switch on the GPR and allow to operate for 2 h continuously.
6.2.1.2 This will be performed on each of the 100 wave-
As a minimum, capture a single waveform every 1 min, 120
forms and the average signal-to-noise value of the 100 wave-
total. Calculate the amplitude of a metal plate reflection and
forms will be taken as the “signal-to-noise of the system.”
plotagainsttimeforeachwaveform.Forthesystemtoperform
Noise voltage (A ) is defined as the maximum amplitude
n
adequately, the amplitude of reflection should remain constant
occurringbetweenmetalplatereflectionandregionupto50%
after a short warm-up period. The stability criteria is as
of the time window after the metal plate reflection, normally
follows:
used with the antenna (that is, 1.0 GHz/20 ns: 10 ns.). The
signal level (A ) is defined as the amplitude of the echo from
mp A 2 A
max 20
,0.03 3% (4)
~ !
the metal plate.
A
6.2.1.3 Thesignal-to-noiseratiotestresultsfortheGPRunit
where:
should be greater than or equal to 20 (+26.0 dB).
A = the amplitude measured after 20 min, and
6.2.2 Signal Stability:
A = the largest amplitude measured between 20 min and
max
6.2.2.1 Signal Stability Test—Use the same test configura-
120 min.
tion as described in the signal-to-noise ratio test. Record 100
6.3 Pre-Operation Measurement:
traces at the maximum data acquisition rate. Evaluate the
signal stability using the following equation: 6.3.1 Free Space Signal (FSP)—The equipment manufac-
turer may require the GPR antenna to be mounted in an
A 2 A
max min
,0.01 1% (2)
~ ! operational configuration, and 100 waveforms gathered in the
A
avg
absenceofthematerialtobeinspected.Usetheaverageof100
where:
waveforms as a template for clutter removal.
6.3.2 Flat Metal Plate (FMP)—Position the GPR in an
A = the maximum amplitude of the metal plate reflection
max
for all 100 traces, operation configuration, and gather 100 waveforms while
A = the minimum amplitude of the metal plate reflection illuminating a flat plate with dimensions recommended by the
min
for all 100 traces, and
manufacturer. This is a measure of the emitted energy to be
A = the average trace amplitude of all 100 traces.
used in subsequent measurements, and as a template for
avg
decorrelation or background removal, or both.
6.2.2.2 The signal stability test results for the GPR system
should be less than or equal to 1%. 6.4 GPR Data Acquisition:
6.4.1 Air-Launched Antenna Systems:
6.2.3 Linearity in the Time Axis and Time Window Accu-
racy: 6.4.1.1 MakeGPRinspectionpassesinalongitudinaldirec-
tion parallel to the centerline of the bridge deck with the
6.2.3.1 Variations in Time Calibration Factor—Use the
antenna mounted to maintain a manufacturer-recommended
sametestconfigurationasdescribedinthesignal-to-noiseratio
distance from the bridge deck surface.
test, except that the metal plate can be replaced by any
6.4.1.2 Useatransversedistance(dt)betweenGPRinspec-
reflecting object. Collect a single waveform and measure the
tion passes <1 m is suggested.
distance from the antenna to the reflector. Perform this test at
6.4.1.3 Use a longitudinal distance (dl) between GPR scans
three different distances corresponding to approximately 15,
≤150 mm.
30, and 50% of the time window normally used with the
system. The time delay between the echo from the aperture of 6.4.1.4 Determine the starting location for passes, that is, at
abutments, joints, or a predetermined location.
the transmitting antenna and that from the reflecting object is
measured as time t (where subscript represents position 1, 6.4.1.5 Determine the optimum speed of operation for
1 1
and so forth). The difference between t and t and between t contiguous longitudinal coverage based on GPR range sweep
2 1 3
and t represents the travel time for a fixed distance in air. The rate and the scan-spacing.
´1
D6087 − 08 (2015)
6.4.2 Ground-Coupled Antenna Systems: where:
6.4.2.1 Make GPR inspection passes either parallel to the
X = percent delaminated in a GPR inspection pass, n,at
tn
direction of traffic, or perpendicular to the direction of traffic,
top steel,
depending on the direction of the top layer of reinforcing. The
n = GPR inspection pass identification number,
pass direction should be chosen so that the antenna crosses
W = concrete delaminated at top steel, m, and
dt
W = sound concrete at top steel, m.
over the top layer of reinforcing at an angle nearest to 90°.
st
6.4.2.2 Use a transverse distance (dt) between GPR inspec-
7.2.9 Calculate the estimated quantity of deck delaminated
tion passes <0.6 m.
at top steel for each GPR inspection pass using the following
6.4.2.3 Use a longitudinal distance (dl) between GPR scans
equation:
necessary to obtain sufficient data <150 mm is suggested.
Q 5 X L d (7)
~ !~ !~ !
6.4.2.4 Determine the starting location for passes, that is, at t tn n t
abutments, joints, or a predetermined location.
where:
Q = square metres of deck delaminated at top steel,
t
7. Data Processing
L = length of GPR inspection pass, n,m,and
n
7.1 There are two different accepted GPR data processing d = transverse distance between GPR inspection passes, m.
t
methodol
...
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.
´1
Designation: D6087 − 08 D6087 − 08 (Reapproved 2015)
Standard Test Method for
Evaluating Asphalt-Covered Concrete Bridge Decks Using
Ground Penetrating Radar
This standard is issued under the fixed designation D6087; 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.
ε NOTE—Removed converted inch-pound units editorially in June 2015.
1. Scope
1.1 This test method covers several ground penetrating radar (GPR) evaluation procedures that can be used to evaluate the
condition of concrete bridge decks overlaid with asphaltic concrete wearing surfaces. These procedures can also be used for bridge
decks overlaid with portland cement concrete and for bridge decks without an overlay. Specifically, this test method predicts the
presence or absence of concrete or rebar deterioration at or above the level of the top layer of reinforcing bar.
1.2 Deterioration in concrete bridge decks is manifested by the corrosion of embedded reinforcement or the decomposition of
concrete, or both. The most serious form of deterioration is that which is caused by corrosion of embedded reinforcement.
Corrosion may be initiated by deicing salts, used for snow and ice control in the winter months, penetrating the concrete. In arid
climates, the corrosion can be initiated by chloride ions contained in the mix ingredients. Deterioration may also be initiated by
the intrusion of water and aggravated by subsequent freeze/thaw cycles causing damage to the concrete and subsequent debonding
of the reinforcing steel with the surrounding compromised concrete.
1.2.1 As the reinforcing steel corrodes, it expands and creates a crack or subsurface fracture plane in the concrete at or just above
the level of the reinforcement. The fracture plane, or delamination, may be localized or may extend over a substantial area,
especially if the concrete cover to the reinforcement is small. It is not uncommon for more than one delamination to occur on
different planes between the concrete surface and the reinforcing steel. Delaminations are not visible on the concrete surface.
However, if repairs are not made, the delaminations progress to open spalls and, with continued corrosion, eventually affect the
structural integrity of the deck.
1.2.2 The portion of concrete contaminated with excessive chlorides is generally structurally deficient compared with
non-contaminated concrete. Additionally, the chloride-contaminated concrete provides a pathway for the chloride ions to initiate
corrosion of the reinforcing steel. It is therefore of particular interest in bridge deck condition investigations to locate not only the
areas of active reinforcement corrosion, but also areas of chloride-contaminated and otherwise deteriorated concrete.
1.3 This test method may not be suitable for evaluating bridges with delaminations that are localized over the diameter of the
reinforcement, or for those bridges that have cathodic protection (coke breeze as cathode) installed on the bridge or for which a
conductive aggregate has been used in the asphalt (that is, blast furnace slag). This is because metals are perfect reflectors of
electromagnetic waves, since the wave impedances for metals are zero.
1.4 A precision and bias statement has not been developed at this time. Therefore, this standard should not be used for
acceptance or rejection of a material for purchasing purposes.
1.5 The values stated in SI units are to be regarded as the standard. The inch-pound units given in parentheses are for
information only. No other units of measurement are included in this standard.
1.6 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. Specific precautionary statements are given in Section 5.
This test method is under the jurisdiction of ASTM Committee D04 on Road and Paving Materials and is the direct responsibility of Subcommittee D04.32 on Bridges
and Structures.
Current edition approved July 1, 2008June 1, 2015. Published July 2008July 2015. Originally approved in 1997. Last previous edition approved in 20072008 as
D6087 – 07.D6087 – 08. DOI: 10.1520/D6087-08.10.1520/D6087-08R15E01.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´1
D6087 − 08 (2015)
2. Summary of Test Method
2.1 The data collection equipment consists of a short-pulse GPR device, data acquisition device, recording device, and data
processing and interpretation equipment. The user makes repeated passes with the data collection equipment in a direction parallel
or perpendicular to the centerline across a bridge deck at specified locations. Bridge deck condition is quantified based on the data
obtained.
3. Significance and Use
3.1 This test method provides information on the condition of concrete bridge decks overlaid with asphaltic concrete without
necessitating removal of the overlay, or other destructive procedures.
3.2 This test method also provides information on the condition of bridge decks without overlays and with portland cement
concrete overlays.
3.3 A systematic approach to bridge deck rehabilitation requires considerable data on the condition of the decks. In the past,
data has been collected using the traditional methods of visual inspection supplemented by physical testing and coring. Such
methods have proven to be tedious, expensive, and of limited accuracy. Consequently, GPR provides a mechanism to rapidly
survey bridges in an efficient, non-destructive manner.
3.4 Information on the condition of asphalt-covered concrete bridge decks is needed to estimate bridge deck condition for
maintenance and rehabilitation, to provide cost-effective information necessary for rehabilitation contracts.
3.5 GPR is currently the only non-destructive method that can evaluate bridge deck condition on bridge decks containing an
asphalt overlay.
4. Apparatus
4.1 GPR System—There are two categories of GPR systems, depending on the type of antenna utilized for data collection.
4.1.1 GPR systems using air-launched horn antennas with center frequencies 1 GHz and greater. The equipment may consist
of an air-coupled, short-pulse monostatic or bistatic antenna(s) with sufficient center frequency to provide the accurate
measurement of a 5 cm (2 in.) thick asphalt pavement.
4.1.2 GPR systems using ground-coupled antennas with central frequencies greater than 1 GHz.
4.2 Data Acquisition System—A data acquisition system, consisting of equipment for gathering GPR data at the minimum data
rates specified in 4.1.1 and 4.1.2. The system shall be capable of accurately acquiring GPR data with a minimum of 60-dB dynamic
range.
4.3 Distance Measurement System—A distance measurement system consisting of a fifth-wheel or appropriate distance
measurement instrument (DMI) with accuracy of 6100 mm/km (66.5 in./mile) and a resolution of 25 mm (1 in.).mm.
NOTE 1—Fig. 1 shows a functional block diagram for multiple GPRs and support equipment.
5. Hazards
5.1 During operation of the GPR system, observe the manufacturer’s safety directions at all times. When conducting
inspections, ensure that appropriate traffic protection is utilized in accordance with accepted standards.
5.2 Electromagnetic emissions from the GPR apparatus, if the system is improperly operated, could potentially interfere with
commercial communications, especially if the antenna is not properly oriented toward the ground. Ensure that all such emissions
from the system comply with Part 15 of the Federal Communications Commission (FCC) Regulations.
6. Procedure
6.1 Conditions for Testing:
6.1.1 If soil, aggregate, or other particulate debris is present on the bridge deck surface, clean the bridge deck.
6.1.2 Test the bridge deck in a surface dry condition.
6.2 System Performance Compliance—The system should be calibrated and performance verified in accordance with the
manufacturer’s recommendations and specifications. The following information is included for reference only and describes typical
calibration procedures for different types of systems. Compliance with the following procedures is not required and the
manufacturer’s calibration procedure takes preference. For air-launched antennas, this test shall consist of the following:
6.2.1 Signal-to-Noise Ratio:
6.2.1.1 Signal-to-Noise Ratio Test—Position the antenna at its far field distance approximately equal to maximum dimension of
antenna aperture above a square metal plate with a width of 4× antenna aperture, minimum. Turn on the GPR unit and allow to
operate for a 20-min warm-up period or the time recommended by the manufacturer. After warming up the unit, record 100
waveforms. Then evaluate the recorded waveform for signal-to-noise ratio. The signal-to-noise ratio is described by the following
equation:
´1
D6087 − 08 (2015)
FIG. 1 Block Diagram of GPR and Support Equipment
Signal Level A
~ !
mp
.20 26.0 dB (1)
~ !
Noise Level A
~ !
n
6.2.1.2 This will be performed on each of the 100 waveforms and the average signal-to-noise value of the 100 waveforms will
be taken as the “signal-to-noise of the system.” Noise voltage (A ) is defined as the maximum amplitude occurring between metal
n
plate reflection and region up to 50 % of the time window after the metal plate reflection, normally used with the antenna (that
is, 1.0 GHz/20 ns: 10 ns.). The signal level (A ) is defined as the amplitude of the echo from the metal plate.
mp
6.2.1.3 The signal-to-noise ratio test results for the GPR unit should be greater than or equal to 20 (+26.0 dB).
6.2.2 Signal Stability:
6.2.2.1 Signal Stability Test—Use the same test configuration as described in the signal-to-noise ratio test. Record 100 traces
at the maximum data acquisition rate. Evaluate the signal stability using the following equation:
A 2 A
max min
,0.01 1% (2)
~ !
A
avg
where:
A = the maximum amplitude of the metal plate reflection for all 100 traces,
max
A = the minimum amplitude of the metal plate reflection for all 100 traces, and
min
A = the average trace amplitude of all 100 traces.
avg
6.2.2.2 The signal stability test results for the GPR system should be less than or equal to 1 %.
6.2.3 Linearity in the Time Axis and Time Window Accuracy:
6.2.3.1 Variations in Time Calibration Factor—Use the same test configuration as described in the signal-to-noise ratio test,
except that the metal plate can be replaced by any reflecting object. Collect a single waveform and measure the distance from the
antenna to the reflector. Perform this test at three different distances corresponding to approximately 15, 30, and 50 % of the time
window normally used with the system. The time delay between the echo from the aperture of the transmitting antenna and that
from the reflecting object is measured as time t (where subscript represents position 1, and so forth). The difference between t
1 1 2
and t and between t and t represents the travel time for a fixed distance in air. The factor Ci represents the speed between distance
1 3 2
i and i+1. The allowable variation in measured speed is shown as follows:
C 2 C
1 2
,2%, (3)
Mean of C and C
1 2
where:
C =
Distance from Position 2 to Position 1
T
´1
D6087 − 08 (2015)
C =
Distance from Position 3 to Position 2
t
6.2.3.2 The variation in time calibration factor should be less than 2 %.
6.2.4 Long-Term Stability Test:
6.2.4.1 Long-Term Amplitude Variation—Use the same test configuration as described in the signal-to-noise ratio test. Switch
on the GPR and allow to operate for 2 h continuously. As a minimum, capture a single waveform every 1 min, 120 total. Calculate
the amplitude of a metal plate reflection and plot against time for each waveform. For the system to perform adequately, the
amplitude of reflection should remain constant after a short warm-up period. The stability criteria is as follows:
A 2 A
max 20
,0.03 ~3%! (4)
A
where:
A = the amplitude measured after 20 min, and
A = the largest amplitude measured between 20 min and 120 min.
max
6.3 Pre-Operation Measurement:
6.3.1 Free Space Signal (FSP)—The equipment manufacturer may require the GPR antenna to be mounted in an operational
configuration, and 100 waveforms gathered in the absence of the material to be inspected. Use the average of 100 waveforms as
a template for clutter removal.
6.3.2 Flat Metal Plate (FMP)—Position the GPR in an operation configuration, and gather 100 waveforms while illuminating
a flat plate with dimensions recommended by the manufacturer. This is a measure of the emitted energy to be used in subsequent
measurements, and as a template for decorrelation or background removal, or both.
6.4 GPR Data Acquisition:
6.4.1 Air-Launched Antenna Systems:
6.4.1.1 Make GPR inspection passes in a longitudinal direction parallel to the centerline of the bridge deck with the antenna
mounted to maintain a manufacturer-recommended distance from the bridge deck surface.
6.4.1.2 Use a transverse distance (dt ) between GPR inspection passes <1 m (3 ft) is suggested.
6.4.1.3 Use a longitudinal distance (dl) between GPR scans ≤150 mm (6 in.).mm.
6.4.1.4 Determine the starting location for passes, that is, at abutments, joints, or a predetermined location.
6.4.1.5 Determine the optimum speed of operation for contiguous longitudinal coverage based on GPR range sweep rate and
the scan-spacing.
6.4.2 Ground-Coupled Antenna Systems:
6.4.2.1 Make GPR inspection passes either parallel to the direction of traffic, or perpendicular to the direction of traffic,
depending on the direction of the top layer of reinforcing. The pass direction should be chosen so that the antenna crosses over
the top layer of reinforcing at an angle nearest to 90°.
6.4.2.2 Use a transverse distance (dt) between GPR inspection passes <0.6 m (2 ft).m.
6.4.2.3 Use a longitudinal distance (dl) between GPR scans necessary to obtain sufficient data <150 mm (6 in.) is suggested.
6.4.2.4 Determine the starting location for passes, that is, at abutments, joints, or a predetermined location
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.