Evaluation of NDTE Technologies for Airport Pavement Maintenance

and Acceptance Activities

Imad L. Al-QadiJohn S. Popovics

Wei XieSara Alzate

University of Illinois at Urbana-Champaign

Outline

• Project Scope and Objectives

• NDTE State-of-art report: Promising NDTE technologies to assess existing and new airport pavements

• Future Work

Objectives

• To determine the effectiveness and practicality of new and existing NDTE technologies for maintenance, evaluation, quality control and acceptance of flexible airport pavements

• To evaluate and recommend appropriate NDTE technologies to the FAA based on field evaluation results

Scope of workReview and summarizeexisting and new NDTE

technologies

Identify promising NDTE technology

(technical and practical suitability)

Identify current NDTE needs for airport pavements

and facilities

Field testing andanalysis of promising

NDTE technology

State-of-the-artreport

Finalreport

New research

NDTE State-of-the-art Report• Existing NDTE methods are summarized in a

draft report, for FAA review and comment• Each method is presented in a chapter:

– 1) Impact-echo – 2) Surface waves – 3) Sonic/ultrasonic – 4) Nuclear radiometry – 5) Infrared thermography – 6) GPR – 7) Laser profiling – 8) Digital imaging

NDTE State-of-the-art Report

• Each chapter discusses the following:– Theory– Equipment– Benefits and applications– Limitations – Recent developments

Nuclear Density Gauge

• The radiation intensity of gamma rays that passes through a medium, or is scattered back from a medium, is used to measure density.

• Nuclear density gauges are compact and provide direct and rapid measurements

Application of Nuclear Density Gauge

• Measuring in-situ HMA, concrete and solid densities

• Suitable for both thin and thick layers; better for thick layers.

Limitations of Nuclear Density Gauge

• Need for calibration

• Affected by lift thickness and variability of supporting layer

• Difficulties in identifying levels of segregation

• High initial cost, certification requirement, periodic inspection, and difficulties in shipping and transport and disposal.

Impact Echo

Resonant frequency interpreted for thickness information

Application of Impact-echo

• Measuring concrete slab thickness

• Identifying location and depth of delamination defects in concrete

Limitations of Impact-echo

• Local, point contact measurement

• Not effective for HMA pavements

• Only effective for top layer in pavement system

• Difficulties in locating small defects

Surface Waves (Spectral/Multiple Analysis of Surface Waves

(SASW/ MASW)

Measure dispersion of surface waves in layered media

Application of surface waves

• Estimate pavement layer properties (thickness and modulus)

Portable Seismic Pavement Analyzer (PSPA) for SASW

Estimated

stiffness

profile

Interpretation of MASW

Time(s)

dist

ance

(cm

)

0 0.5 1 1.5 2 2.5 3 3.5

x 10-3

50

100

150

200

250P

hase

vel

ocity

(m/s

)

Frequency (kHz)2 4 6 8 10 12 14 16 18 20

1000

2000

3000

4000

5000

6000

Impact-echo mode

Stacked multiple signal data MASW mapping of signal data

Lamb wave curve best fit to data to give layered structure

Limitations of surface wave• Local, point contact measurement

• Data inversion is complicated (MASW approach has sounder technical basis than SASW)

• Not reliable for accurate thickness measurements of a specific layer

Sonic/ Ultrasonic

http://www.cflhd.gov/agm/engApplications/Pavements/413SpecAnalySurfWaveandUltrSonicSurfWaveMethods.htm

1 105

2 105

3 105

4 105

5 105

6 105

7 105

0.04

0.03

0.02

0.01

0

0.01

0.02

0.03

0.04

Near sensorFar sensor

Time (s)

Am

plitu

de

ΔtΔt

Measure velocity of various wave modes propagating in pavementand relate to mechanical properties

Application of sonic/ ultrasonic• Estimate mechanical properties of

pavement (Modulus, strength, damage level, etc.)

• Locate voids/ interfaces

Limitations of sonic/ ultrasonic

• Local, point contact measurement

• Estimation of absolute values of modulus and strength of concrete is not accurate

Digital Imaging Technology• Automated digital imaging system consists of

image acquisition and distress image processing

After Huang et al. 2006

Equipment and Data Collection• DMI is used to control the acquisition of

digital image• Distress detection, isolation, classification,

segmentation, and compress• Fast wavelet transform for the wavelet-based

distress detection, isolation, and evaluationVideoVideo

Application of Video Imaging• Segregation measurement:

– Identify texture variation related to HMA segregation– Use GLCM technique to identify segregation

• Crack Detection/ Surface Distress– Individual crack information can be vectorizing– WiseCrax is used to automatically detect cracks,

classify and generate crack map– Recent development uses processing algorithm for

high-speed, real-time inspection of pavement cracking

Limitations of Imaging Technique

• Video image can only detect surface distress

• There is environmental requirement during data collection

• The system is vulnerable to vehicle vibration

• Video image can measure gradation segregation level; but not temperature segregation

Laser Technique• Pavement surface information can be determined by the

movement of reflected beam spot on the detector• It can supply rapid, continuous, and high accurate

measurement

Laser Beam

Pavement Surface

Lens

Detector

Laser Beam

Pavement Surface

Lens

Detector

Laser Beam

Pavement Surface

Lens

Detector

Equipment and Data Collection

Line scan and area scan laser systems (Xu et al. 2006)

Two types of laser camera are available to digitally image pavement surface: area scan and line scan

Friction and Roughness Measurements

Texture Classification Relative Wavelength

Microtexture λ<0.5 mm

Macrotexture 0.5mm < λ < 50mm

Megatexture 50mm < λ < 500mm

Roughness 0.5m < λ < 50m

• For friction use high-pass filter with 50mm wavelength cutoff

• For roughness use low-pass filter with 0.5m wavelength cutoff

Applications• Detect segregation:

– texture ratio of segregated to non-segregated area to measure segregation level

• Rutting measurements:– Automatic, rapid and continuous

• Crack measurements:– Valley detection of candidate cracks– Validation algorithm– Characterize crack types and pattern– 3D laser imaging has been introduced

Limitations• It provides pavement surface condition

only• Difficult to distinguish between texture

and crack • Transversal cracks are likely to be

detected, while longitudinal cracks are easily missed

• Narrow and shallow cracks may be filtered out during data processing

Infrared Thermography• Infrared thermography is standardized by ASTM

D4788. It includes passive and active methods• Subsurface changes in pavements generate surface

temperature variations

Equipment and Data Collection

Infrared sensors bar

Applications• QC/QA

• Segregation measurement

• Crack and defect measurement detection

Defect

Limitations

• It is applied for near-surface surveys

• It cannot distinguish between gradation and temperature segregation

• For existing pavements, it depends on solar energy

Ground Penetrating Radar• Ground Penetrating Radar (GPR) is a

special kind of RADAR• Purpose of using GPR:

– Detect targets buried in a dielectric medium

– Estimate their depths• GPR applications: geophysics,

archeology, law enforcement, evaluation of civil structures (buildings, bridges, pavements)

Principle of GPR

Layer 1

Layer 2

Control Unit

Transceiver

Antenna DMI

GPR Antennae• Ground-coupled antenna: in contact with ground

surface• Air-coupled antenna: 1 to 2 ft above surface

Ground Coupled Antenna Horn Antennae

Typical GPR Response (scan)

HMA

Base

Subgrade

t1

t2

A1

A2

-80

00

-60

00

-40

00

-20

00 0

20

00

40

00

60

00

80

00

10

00

0

12

00

0

02

46

81

01

21

41

6

Tim

e (n

s)

Amplitude

HM

AB

aseS

ub

grad

e

A0

GPR Data Collection

HMA

Base

Subgrade

HMA

Base

Subgrade

Layer Thickness Estimation

2

12

1

2

0

12

1

2

0

1,,

1

1

p

nn

i p

ii

p

p

nn

i p

ii

p

n-rnr

A

A

A

Aγ

A

A

A

A

A

Aγ

A

A

εε

Thickness of i th layer:HMA

Base

Subgrade

t1, d1

t2, d2

A0

A1

A2

r,1

r,2

r,3

1,,

1,,

irir

iriri

ir

ii

ctd

,2

2

1,

op

opr AA

AAε

New Pavements (QC/QA )Classic GPR thickness estimation gives accurate results:

0

50

100

150

200

250

300

350

400

450

500

40 42.5 45 47.5 50 52.5 55 57.5 60Distance (m)

De

pth

(m

m)

HMA Base

HMA Design Base Design

GPR Accuracy: New Pavements

Dielectric Constant Using CMP

Common midpoint (CMP) technique (or common-depth point, CDP) is used as follows:

T/RT R

x

t1

t2

P

HMAr1

h

: EM velocity in the layer 2

21

22

2

21

22

222

1

22

2

x

ttc

tt

xcv

xhvt

hvt

r

r

)(

)/(

Modified CMP Technique Modified common midpoint technique:

h1

T/R

x0

t1

t2

P

PCCr1

h0

airr0=1

x1

T R

i

t

Snell’s law of refraction:

Using the figure:

(1)

(2)

(3)

(4)

Modified CMP Technique Modified common midpoint algorithm:1. Measure the reflection times t1 and t2

2. Calculate the transmission angle t using:

3. Find the angle i by solving numerically

4. Solve for r1 using:

5. Compute HMA thickness using t1 and r1

2

t

i1 θsin

θsin

r

111 2 rcth Modified CMP Setup

-6000

-4000

-2000

0

2000

4000

6000

8000

10000

12000

0 5 10 15

Time (ns)

Am

pli

tud

e

Surface Reflection

OGDL/Base Reflection

WS/BM-25.0 Reflection

BM-25.0/OGDL Reflection

Base/Subgrade Reflection

Depth Resolution Enhancement

Measured Signal from:

Thin layer interfaces not visible because of

reflection overlap

Synthesized Signal

-8000

-6000

-4000

-2000

0

2000

4000

6000

8000

10000

12000

0 5 10 15

Time (ns)

Am

pli

tud

e

Reflection Overlap

Surface Reflection HMA/Base

Reflection

Base/Subgrade Reflection

Base

OGDL

WS

BM-25.0

Measured vs. Simulated Signal

Layer Thickness Estimation by Iteration

Raw GPR Data

Layer Interface Detection

Dielectric Properties Estimation

Layer Thicknesses

Preprocessing

Detection Results

0

2

4

6

8

10

12

14

16

20 30 40 50 60

Distance (m)

Tim

e D

elay

(n

s)

Detected Layer Interfaces

WS

BM-25.0

OGDL

Base

Copper plates

GPR Data Analysis Software

Channel 1

Channel 2

Channel 1

Channel 2

Density Measurement with GPR• According to volumetric mixture theory, HMA dielectric

constant depends on aggregate, binder and air volumes

abeavoid (%)

Note: calibration coefficients (a and b) are determined from field cores.

• A drop in dielectric value may indicate a density change

• 2GHz antenna is preferred• It has potential….it requires more investigation

Defects Detection with GPR• Segregation: locations of course-graded and

dense-graded mixes has been reported

• Stripping: additional reflections appear between surface and layer interface

• Moisture content: relationship between dielectric constant and moisture content

bDCmoisture (%)

Ground-Coupled Data, CRCP, VA. Smart Road

Locating Reinforcement (CRCP)

Copper Plate under Slab

Transversal Reinforcement

Concrete

Asphalt OGDL Longitudinal Reinforcement

GPR Application on Composite Pavement

100 ft Joint Spacing

Rebar

Interface of HMA and PCC

Surface

8 in

Overlay

Measure overlay thickness and detect overlaid joints:

3 ft 3 ft

ISAC

Limitations of GPR Technique• Air-coupled antenna has limited penetration

depth • GPR survey requires dry pavement condition• Errors may result from dielectric constant

estimates from surface reflection • Cores may be needed to determine

calibration coefficients • Strong reflection may mask weak signals• Accuracy of GPR results depends on

adopted data analysis technique

Future Work

• During this project year, we aim to

– Identify current NDTE needs for airport flexible pavements

– Identify promising NDTE technology, and carry out new research efforts to meet those needs