Development of APE System using Step-Frequency GPR

Nicolas Gagarin

Starodub, Inc.

A. Advanced Pavement Evaluation

� APE Developed for the Office of Pavement

Technology (HIPT) to:

� Demonstrate Sub-Surface Imaging and

Continuous Material Calibration using SF-GPR

� Develop Analysis Algorithms

� Test and Evaluate Performance

� Pavement rehabilitation is a key focus area

� Pavement evaluation

� Rehabilitation selection

B. SF-GPR & APE System

STARODUB, INC.

July 2006-October 2010

Task Order 13 DTFH61-06-D-00021

B.1. Impulse vs. Step-Frequency GPR

B.1. Impulse vs. Step-Frequency GPR

Impulse radar frequency response

B.1. Impulse vs. Step-Frequency GPR

B.2. SF-GPR antenna array

B.3. SF-GPR – scan images

Surface – no distress Layer interface showing

inconsistent condition and

presence of water

B.4. Voids under composite pavement

135+40 144+00

B.5. Dielectric PropertiesTable of Relative Dielectric Permittivity for A Selection of Materials

Losses

Low High

B.6. Continuous calibrationContinuous calibration by common midpoint (CMP) method without coring

B.6. Example Semblance PlotSemblance Plot Used for Estimation of Dielectric Properties and Layer Tracking

Layer Interface

Layer Interface

B.7. APE Analysis DomainsSF-GPR Data in Frequency Domain

B.8. APE Software ModulesVersion 0.2 – Analysis Pipeline

B.9. Direct Comparison of APE

and GSSI Systems

1 GHz GSSI

B.9. Performance Comparison

APE System (Single Antenna)

Cell 84

Asphalt Base Interface

Base Subgrade Interface

Surface

B.9. Performance Comparison

2 GHz GSSI

Cell 84

APE System (Single Antenna)

Asphalt Base Interface

Base Subgrade Interface

Surface

C. Measurement of Layer ThicknessUsing APE System

STARODUB, INC.

October 2010

Task Order 16DTFH61-06-D-00021

C.1. Sample from Minnesota Project

� Cell 33

� B1847

� 150MHz to 3GHz

� 47 antenna pairs

Cell 33

Asphalt

Base – Class 6

Length = 500 feet

4 inches

12 inches

Source: Design Criteria

Cores 33-5 @ 5.0 inches and 33-6 @ 4.5 inches

C.1.1. Reference thicknesses – cell 33

C.1.1. APE Layer Detection and Tracking

Cell 84

Cell 33

C.1.1. Layer Measurement

Orthotropic View

Reference Surface

Asphalt/Base

Interface

Base/Sub-grade

Interface

Cell 33 Cross-Sectional View

C.1.1. Layer Measurement

Reference Surface

Asphalt

Base

4.1”

12.6”

47 Antenna Pairs

C.2. Evaluation of APE System for

Pavement Thickness Measurements

Using Metal Plate Experiment

C.2.1. Ground TruthMIT-SCAN T2

� NDT device for pavement layer

thickness measurements

� Pulse-induction technology

� Measures vertical distance to pre-positioned metal targets

� Measurement range: 0 to 20 in

� Specified accuracy

� 0.5% of the measured depth +1 mm

� Translates to 0.1 in (less than 3 mm) for 13 in pavement

� Consistently less than 2-mm (0.08 in)

error were observed in the field

C.2.1. Ground Truth

C.2.2. Comparing Thicknesses

MIT-SCAN T2 vs. APE

Mean Pavement Thickness Based on Large Plate Measurements

(First and Second Lift)

±3σ Intervals (99.74% Certainty) Shown for APE Thickness (Red Bars)

3.5

4.5

5.5

6.5

7.5

8.5

9.5

10.5

11.5

12.5

0 5 10 15 20 25 30 35 40

Asp

ha

lt T

hic

kn

ess

(in

che

s)

Metal Plate Test Location

MIT Scan Thickness (1st Lift)

MIT Scan Thickness (2nd Lift)

APE Thickness (1st Lift)

APE Thickness (2nd Lift)

APE Mean Thickness – MIT Scan Mean Thickness

(for Large Plate Measurements, 1st Lift)

(Including 99% Confidence Interval Estimate of

the Difference Between Two Independent Means)

*Analysis based on Kachigan, pp. 151-153, 1986

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

0 5 10 15 20 25 30 35 40

Dif

fere

nce

in M

ea

n T

hic

kn

ess

(in

che

s)

Metal Plate Test Location

Mean Thickness Difference (APE-MIT Scan)

Plot of MIT Scan Thickness Measurement vs. APE Thickness Measurement

(Large Plates)

(Including Regression Line and Corresponding Correlation Coefficient)

Trend line equation: y = 0.9969x + 0.0073

R² = 0.9998

3.5

4.5

5.5

6.5

7.5

8.5

9.5

10.5

11.5

12.5

0 2 4 6 8 10 12

AP

E T

hic

kn

ess

Me

asu

rem

en

t (I

nch

es)

MIT Scan Thickness Measurement (Inches)

C.2.3. Estimating Accuracy and Precision

MIT-SCAN vs. APE

Error Histogram (APE Measurement – MIT Mean)Day 1, First Lift, APE Test Run 1

σ = 0.04 inch

2σ = 0.07 inch

3σ = 0.11 inch

Meanerror = 0.02 inch

1σ-1σ-2σ

-3σ2σ

3σ

0

1

2

3

4

5

6

7

8

9

10

-0.15 -0.1 -0.05 0 0.05 0.1 0.15

Measurement Error (inches)

Error Histogram (APE Measurement – MIT Mean)Day 1, First Lift, APE Test Run 2

σ = 0.03 inch

2σ = 0.06 inch

3σ = 0.09 inch

Meanerror = 0.02 inch

1σ-1σ-2σ

-3σ2σ

3σ

0

2

4

6

8

10

12

-0.15 -0.1 -0.05 0 0.05 0.1 0.15

Measurement Error (inches)

Error Histogram (APE Measurement – MIT Mean)Day 1, First Lift, APE Test Run 3

σ = 0.05 inch

2σ = 0.09 inch

3σ = 0.14 inch

Meanerror = 0.00 inch1σ-1σ

-2σ

-3σ

2σ3σ

0

1

2

3

4

5

6

7

8

9

-0.15 -0.05 0.05 0.15

Measurement Error (inches)

C.2.5. Summary of ResultsGround truth and APE measurement are virtually

equivalent.

Metal plate experiment establishes value of

continuous calibration using Common Mid-Point

implementation in APE

Repeated Accuracy of 0.11 to 0.14 inches (Mean+3

sigma)

Repeated Precision of 0.09 to 0.14 inches (3 sigma)

STARODUB, INC.

October 2010

Task Order 16DTFH61-06-D-00021

D. Measurement of Material DensityUsing APE System

D.2. Density Indicators

D.3. Density Indicators

E. Current status of APE� Current applications – pilot implementation in FY10/11

� Pavement layer thickness

� Moisture detection

� Void detection

� Rutting evaluation (2-D & 3-D imaging)

� Future applications

� Variations in material properties (AC density) [4]

� AC stripping [3]

� Layer debonding [5]

� Detection and quantification of cracking [4]

� Depth of dowel bars, tie bars, and reinforcing steel [2-3]