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Ground Penetration Radar (GPR) is a reliable and high performance nondestructive testing tool for pavement management in a network level, which requires pavement condition assessment and deterioration modeling. GPR can determine the layer thickness, detect voids, and estimate moisture content of the in-situ soil underlying the pavement. Therefore, it is considered to be a promising tool for the assessment of pavement conditions. Pavement condition information obtained by GPR is very useful to predict the pavement structural capacity and performance. This will further help improve pavement maintenance and rehabilitation strategies and also provide rationalities in allocating available funds. However, the application of GPR in pavement is limited due to incomplete understanding of dielectric properties of pavement materials. This paper presents the state-of-the-art GPR applications in pavement condition assessment and its future development.
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Ground Penetration Radar as a Tool Ground Penetration Radar as a Tool for Pavement Condition Diagnosticsfor Pavement Condition Diagnostics
Desh R. SonyokDesh R. Sonyok11, S.M., S.M. ASCEASCE
Jie ZhangJie Zhang22, M. ASCE, Ph.D., P.E., M. ASCE, Ph.D., P.E.
20082008
11 Graduate Student, Civil Engineering Department, New Mexico State University, Graduate Student, Civil Engineering Department, New Mexico State University, Email: Email: [email protected]@nmsu.edu
22 Assist. Professor, Civil Engineering Department, New Mexico State University, Assist. Professor, Civil Engineering Department, New Mexico State University, Email: Email: [email protected]@nmsu.edu
Background and Objectives Background and Objectives
GPR TechnologyGPR Technology
GPR Wave and Material PropertiesGPR Wave and Material Properties
ApplicationsApplications
ConclusionsConclusions
Future ResearchFuture Research
What is GPRWhat is GPR??What is GPRWhat is GPR??ContentsContentsContentsContents
What is GPRWhat is GPR??What is GPRWhat is GPR??Background and PurposeBackground and PurposeBackground and PurposeBackground and Purpose
BackgroundBackground
GPR can determine the layer thickness, detect GPR can determine the layer thickness, detect voids, and estimate moisture contentvoids, and estimate moisture content
It can operate in highway speedIt can operate in highway speed
It provides continuous survey of pavementsIt provides continuous survey of pavements
ObjectivesObjectives To present the state-of-the-art GPR applications To present the state-of-the-art GPR applications
in pavement condition assessment and its future in pavement condition assessment and its future development development
GPR TechnologyGPR TechnologyGPR TechnologyGPR Technology
Electromagnetic frequency range: 10 MHz to a few GHz.
Air-Coupled (Horn Air-Coupled (Horn or Launched) or Launched) Antenna (Antenna (Al-Quadi Al-Quadi et al., 2006)et al., 2006)
Ground-Coupled Ground-Coupled Antenna (Antenna (Al-Quadi Al-Quadi et al., 2006)et al., 2006)
GPR Technology…GPR Technology…continuedcontinuedGPR Technology…GPR Technology…continuedcontinued
Types of GPR:
Penetration Capabilities and Resolutions
GPR Technology…GPR Technology…continuedcontinuedGPR Technology…GPR Technology…continuedcontinued
Types of GPR:Impulse GPR Step Frequency GPR
Dep
th o
f In
vest
igat
ion
High f Medium f Low f
High resolution
Low resolution
Medium resolution
GPR Wave and Material PropertiesGPR Wave and Material PropertiesGPR Wave and Material PropertiesGPR Wave and Material Properties
Velocity
Amplitude
Frequency
Dielectric constant
Dispersion
Depth
Thickness
Moisture content
Density
EM Wave Properties
Estimated Parameters
Material Properties
GPR ApplicationsGPR ApplicationsGPR ApplicationsGPR Applications
Pavement layers thickness measurementsPavement layers thickness measurements
Moisture detection and deteriorationMoisture detection and deterioration
Subsurface defects (e.g., stripping zones and Subsurface defects (e.g., stripping zones and trapped moisture)trapped moisture)
Input data to FWD measurement Input data to FWD measurement
Asphalt air void contentAsphalt air void content
Subsurface anomaliesSubsurface anomalies
Mapping underground utilities Mapping underground utilities
Layer Thickness CalculationLayer Thickness CalculationLayer Thickness CalculationLayer Thickness Calculation
ir
ii
ctd
,2 ε=
d = depth; c = speed of light in free space (m/s)t = two-way travel time; ε= dielectric constantA = amplitude; i = number of layers; a = attenuation (db/m); σ = electrical conductivity in mS/m
Al-Qadi et al. 2006 [1]:Al-Qadi et al. 2006 [1]:
( ) ( ), 1 , , 1 ,/i r i r i r i r iA ε ε ε ε+ += − +
GPR Applications: Layer ThicknessGPR Applications: Layer ThicknessGPR Applications: Layer ThicknessGPR Applications: Layer Thickness
1.69r
aσε
=
A0Surface
Base
Subgrade
t1
t2
A2
A3
Tim
e
,1rε
,3rε
,2rε
t3
Ao
GPR Applications: Layer ThicknessGPR Applications: Layer ThicknessGPR Applications: Layer ThicknessGPR Applications: Layer Thickness
(Source: http://www.cait.rutgers.edu)
Layer typeLayer type AccuracyAccuracy
New Asphalt ±3.0%
Old Asphalt ± 5.8%
Concrete (if dry) JPCPCRCP
± 2.3%± 3.0%
Granular base ± 12.0%
Layer Thickness CalculationLayer Thickness CalculationLayer Thickness CalculationLayer Thickness CalculationGPR Applications: Layer ThicknessGPR Applications: Layer ThicknessGPR Applications: Layer ThicknessGPR Applications: Layer Thickness
Material PropertiesMaterial PropertiesMaterial PropertiesMaterial Properties
Dielectric constant: Dielectric constant:
Air = 1.0; Aggregate ≈ 6.0; Asphalt 5 – 8 (dry) and 12 Air = 1.0; Aggregate ≈ 6.0; Asphalt 5 – 8 (dry) and 12 (wet); Water ≈ 80(wet); Water ≈ 80
Significant departure of Significant departure of ε from the mean valuefrom the mean value
indicates either high or low moisture contentindicates either high or low moisture content
In-situ material properties ( moisture content In-situ material properties ( moisture content and relative compactness)and relative compactness)
Changes in dielectric properties reflects Changes in dielectric properties reflects material deterioration material deterioration
GPR Applications: Material PropertiesGPR Applications: Material PropertiesGPR Applications: Material PropertiesGPR Applications: Material Properties
Estimating Material PropertiesEstimating Material PropertiesEstimating Material PropertiesEstimating Material Properties
1/2 1/2 1/2
1/2 1/2
(1 ) solid airv
water air
n nε ε εθε ε
− − −=−
Volumetric Water Content (θv)
Roth et al. (1990): ε = bulk dielectric constant of materialεair, εwater, εsolid are dielectric constant of the air, water, and solidε’ and ε” are real and imaginary parts
n = porosity
GPR Applications: Water ContentGPR Applications: Water ContentGPR Applications: Water ContentGPR Applications: Water Content
Topp et al. (1980): 2 2 4 2 6 3( 5.3 10 ) (2.92 10 ) (5.5 10 ) (4.3 10 )vθ ε ε ε− − − −= − × + × − × + ×
Assumption:
' '' '' 'whereε ε ε ε ε= + =
GPR Applications: DefectsGPR Applications: DefectsGPR Applications: DefectsGPR Applications: Defects
Asphalt with stripping defects
Subgrade
Asphalt layer
(Source: http://www.tpa-konferencia.hu)
(Source: http://training.ce.washington.edu
Voids are identified by large positive (high density or water) or negative reflection amplitude (low density or air)
GPR Applications: DefectsGPR Applications: DefectsGPR Applications: DefectsGPR Applications: Defects
Def
lect
ion
(m
m)
Weak places bellow surface sing FWD analysis in places with strong reflection amplitude (Source: http://www.tpa-konferencia.hu)
EM Velocity/ Frequency/ Amplitude
Dielectric constant
/Dispersion
DeteriorationDeterioration
Condition AssessmentCondition AssessmentCondition AssessmentCondition Assessment
Water content/Density
/Thickness
GPR Applications: GPR Applications: Condition AssessmentCondition AssessmentGPR Applications: GPR Applications: Condition AssessmentCondition Assessment
Application in M-E DesignApplication in M-E DesignApplication in M-E DesignApplication in M-E Design
Pavement thickness, water content, and relative Pavement thickness, water content, and relative compactnesscompactness
ImproveImprove accuracy of FWD/ RWD accuracy of FWD/ RWD measurementmeasurementss
Reduce Reduce required required number of coringnumber of coring
Continuous profile of pavement layersContinuous profile of pavement layers
Identify areas of poor pavement conditionIdentify areas of poor pavement conditionss
GPR Applications: M-E DesignGPR Applications: M-E DesignGPR Applications: M-E DesignGPR Applications: M-E Design
LimitationsLimitationsLimitationsLimitations
GPR signal attenuation and limitation in depth GPR signal attenuation and limitation in depth of penetrationof penetration
Requires fairly uniform soil for moisture Requires fairly uniform soil for moisture estimation estimation
Compromise between penetration depths and Compromise between penetration depths and target resolutions.target resolutions.
ConclusionsConclusionsConclusionsConclusions
Thickness accuracy from ±2.9% to ±12%Thickness accuracy from ±2.9% to ±12%
Reduces required number of coringReduces required number of coring
Volumetric water content and relative density of Volumetric water content and relative density of the in-situ materialthe in-situ material
Identify areas of poor pavement conditionIdentify areas of poor pavement conditionss
Thickness information can be used together Thickness information can be used together with FWD measurement to back-calculate the with FWD measurement to back-calculate the deflection and elastic modulideflection and elastic moduli
Future ResearchFuture ResearchFuture ResearchFuture Research
Study on interactions between EM signals and Study on interactions between EM signals and pavement materials mechanical characteristics:pavement materials mechanical characteristics:
− Wave frequencyWave frequency
− IImaginary part of dielectricmaginary part of dielectric constant (dispersion) constant (dispersion)
− Moisture contentMoisture content
− Pavement deteriorationPavement deterioration
ReferencesReferencesReferencesReferencesAl-Quadi, I.L., Kun, J., and S. Lahouar. Analysis Tool for Determining Flexible Pavement Layer Thickness at Highway Speed. In 85th Annual Meeting. CD-ROM. Transportation Research Board of the National Academics, Washington, D.C., 2006, pp. 1-13.
Al-Qadi, I.L., Lahouar, S., Jiang, K., MeGhee, K.K., and Mokarem, D. Validation of Ground Penetration Radar Accuray for Estimating Pavement Layer Thicknesses. In 84th Annual Meeting. CD-ROM. Transportation Research Board of the National Academics, Washington, D.C., 2005, pp. 1-25.
Liu, R., Li, J., Chen, X., Xing, H., Ekbote, A., and Y. Wang. Investigation of New Generation of FCC Compliant NDT Devices for Pavement Layer Information Collection. Publication FHWA/TX-05/0-4820. FHWA, U.S. Department of Transportation, 2006
Topp, G.C., Davis J.L., and A.P. Ann. Electromagnetic Determination of Soil Water Content: Measurements in Coaxial Transmission Lines. Water Resources Research, Vol. 16, No. 3, 1980, p.p. 574-582.
AcknowledgementAcknowledgementAcknowledgementAcknowledgement
Funding Sources:Funding Sources: Eisenhower Graduate Fellowship, FHWAEisenhower Graduate Fellowship, FHWA
Associated Students of New Mexico State University (ASNMSU)Associated Students of New Mexico State University (ASNMSU)
Civil Engineering Department, New Mexico State UniversityCivil Engineering Department, New Mexico State University
Graduate School, New Mexico State UniversityGraduate School, New Mexico State University
Research Team:Research Team: Dr. Jie Zhang, Prof., Civil EngineeringDr. Jie Zhang, Prof., Civil Engineering
Bin Zhang, CE Graduate StudentBin Zhang, CE Graduate Student
THANK YOU THANK YOU
FOR FOR
YOUR ATTENTIONYOUR ATTENTION
/ 2d v t= ×/ rv c ε=
C=3×108 m/s,
V = velocity in m/s,
εr = dielectric constant (dimensionless),
a = attenuation in decibels/m (db/m),
σ = electrical conductivity in mS/m
1.69r
aσε
=
Layer Thickness CalculationLayer Thickness CalculationLayer Thickness CalculationLayer Thickness Calculation
2
1,
1
1
−
+=
p
o
p
o
r
A
A
A
A
ε
2
12
1
2
12
1
2
1,,
1
1
−+
−
++
−
=−
−
=
−−
=
−
∑
∑
p
n
p
in
ii
p
o
p
n
p
in
ii
p
o
nrnr
A
A
A
A
A
A
A
A
A
A
A
A
γ
γεε
1,,
1,,
+
+
+
−=
irir
irir
iεε
εεγ
εr,1 = dielectric constant of the top layerAo = amplitude of the surface reflectionAp = amplitude of the reflected signal collected over flat metal plate
γi represents the reflection coefficients between the ith, and (i+1)th
(2)(2)
(3)(3)
(4)(4)
Al-Qadi et al. 2006 [1]:Al-Qadi et al. 2006 [1]:
Layer Thickness CalculationLayer Thickness CalculationLayer Thickness CalculationLayer Thickness Calculation
HMA dielectric constant could be estimatedusing:
εa: HMA dielectric constantAinc: Maximum amplitude of the incident wave. It is obtained by collecting data over a copper plate placed on the surface of the pavementAa: Maximum amplitude reflected from the HMA surface
Layer Thickness CalculationLayer Thickness CalculationLayer Thickness CalculationLayer Thickness Calculation
swg MMw /== θ
swv VV /=θ
=
===
w
bg
ws
bw
bs
ww
s
wv M
M
M
M
V
V
ρρθ
ρρ
ρρθ/
/
bρ bρ
t
sb V
M
volumeTotal
solidsoildryofMass == )(ρ
nSv =θ
Volumetric water content: volume of water per unit volume of soil.
Relationship between gravimetric to volumetric water content:
where, is bulk density. Soil bulk density
is used for density soil (solid).
The volumetric water content is also expressed in terms of the porosity, and the degree of saturation, S, (or saturation ratio), according to the following expression:
Gravimetric water content: mass of water per unit mass of dry soil
wt
drywet
t
wv
V
WW
V
V
ρθ
−==
Measurement Methodology:
Soil Water ContentSoil Water ContentSoil Water ContentSoil Water Content
Arrival time /amplitude Arrival time /amplitude Dielectric constantDielectric constant
Dielectric constant moisture content Dielectric constant moisture content /Relative compactness/Relative compactness
EM signal amplitude Voids/DelaminationEM signal amplitude Voids/Delamination
GPR Wave and Material Properties…GPR Wave and Material Properties…Cont.Cont.GPR Wave and Material Properties…GPR Wave and Material Properties…Cont.Cont.