INFRASENSE, Inc.INFRASENSE, Inc.

Ground Penetrating Radar

(GPR) for Pavement

Condition Evaluation

by

Kenneth Maser

Infrasense, Inc.

Pavement Evaluation 2010

Roanoke, VA

INFRASENSE, Inc.INFRASENSE, Inc.

Presentation Outline

• Background

• GPR Equipment and Software

• Pavement Applications

• Future Prospects

INFRASENSE, Inc.INFRASENSE, Inc.

What is GPR?

• Transmits pulsed radio waves through

pavement materials

• Waves reflect at material boundaries

• Arrival time and strength of reflections

determine material depths, thicknesses, and

properties

INFRASENSE, Inc.INFRASENSE, Inc.

What does GPR Detect?

• Thickness of pavement layers

• Reinforcing steel

• Density variations

• Subsurface moisture

• Voids

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Evolution of GPR

• 1960’s,70’s - early development

– Military applications

– Tunnel and mine detection

• 1980’s - Initial adaptation to highways

• 1990’s - Practical development and

implementation for pavements

• 2000+ - Adaptation by highway agencies

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GPR Equipment

• Data acquisition and control systems

• GPR antennas

– Air Coupled

– Ground Coupled

INFRASENSE, Inc.INFRASENSE, Inc.

1 GHz Horn Antennas

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Current Horn Antennas

1 GHz Horns 2 GHz Horns

INFRASENSE, Inc.INFRASENSE, Inc.

Ground-Coupled Antennas

1.5 GHz 500 MHz

INFRASENSE, Inc.INFRASENSE, Inc.

Equipment Summary

• Antennas have become more compact

• Electronics have become more stable

• Range of frequencies has expanded

– Provides higher resolutions, greater depths of

penetration

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Software and Data

Interpretation

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Principles of GPR Application

Antenna

1 2 3

1

2

3

Air

base

Subgrade

Volts

Time Measurement Setup

GPR Record

Asphalt

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Sample of Data

Asphalt

Layers

Base

Layers

Ta

Tb

Pavement Structure

GPR Record

Time (ns)

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Sample Graphic GPR Data

Asphalt

Base

Pavement Surface

Time/depth

distance

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Sample Processed Graphic Data

on Asphalt Pavement

Asphalt

Base

Pavement Surface

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Linear Plot of Pavement Layer

Thickness

0.90 0.95 1.00 1.05 1.10 1.15 1.20 1.25 1.30 1.35 1.40

Mile Marker

0

5

10

15

20

Dep

th (

in)

Asphalt Layers

Base Layer

Cores

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GPR Data for PCC Pavement

Bottom of Base

Bottom of PCC Joints

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Typical Pavement Structure

Data Analysis

Bottom of Base

Bottom of AC

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GPR Data with Unclear

Interpretation

ACAC? Base?

AC

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Software/Interpretation

• Software developments have facilitated

quantitative analysis

• Some interpretation is still required to

distinguish layer types

• Fully automated processing is available for

limited applications (density, FWD)

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Pavement Applications

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Pavement Applications of GPR

• Pavement Management (Network)

• Rehabilitation Design (Project)

• Quality Assurance of New Pavement

Construction (thickness, density)

• Subsurface Moisture/Drainage

• Location of Dowels

• Detection of Asphalt Stripping

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GPR for Pavement Management

• Layer structure data for PMS

• Layer thickness for network FWD

• 100-200 lane miles per day coverage

• Results typically at 0.1 mile intervals

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Rehabilitation Design

• Existing thickness for overlay design

• Bound layer thickness for design of in place

recycling depths

• Thickness used with FWD data

• Locate areas of high moisture for drainage

design

• Locate subsurface damage

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Accelerated Rutting from

Clogged Drains

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View of Clogged Drain

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Detection of Drain with GPR

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Base Moisture Content from GPR

0%

2%

4%

6%

8%

10%

12%

14%

16%

133+00 143+00 153+00 163+00 173+00 183+00

Station

Est

imat

ed B

ase

%W

C

SB GPR

NB GPR

NB Cross Sections

SB Cross Sections

NB Lab Data

SB Lab Data

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Future Prospects for GPR• Equipment

– More compact, portable (wireless) equipment

– Implementation of antenna arrays

– Increased frequency range for depth/detail

• Software

– more automated, user friendly

• Applications

– Improved detection capability for expanded

applications