ground penetration radar as a tool for pavement condition diagnostics

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

mailto:[email protected]

mailto:[email protected]

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

=


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]:


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


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.