GPR ImplementationTaking the Show on the Road

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GPR ImplementationTaking the Show on the Road

• by
• Marc Loken
• Senior Research Engineer
• Minnesota Department of Transportation
• Presented to
• City Engineers Association of Minnesota
• January 27, 2006

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MnDOT Web Page Links
http//www.mnroad.dot.state.mn.us/research/MnROAD_
Project/persons/loken.asp
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GPR Implementation Objectives

• Through demonstration of GPR, to inform and
  educate district material engineers and local
  engineers on GPR applications and potential cost
  savings
• Encourage districts and local engineers to use
  this new technology along with other field-test
  methods (FWD, coring, and/or pavement surface
  condition surveys) for more complete pavement
  analysis

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MnDOT Field Testing GPR FWD Coring
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GPR Implementation -- Outline

• Task 1 Summarize LRRB 771 Results
• Task 2 Produce brochure and CD
• Task 3 Survey to identify demonstration
  projects
• Task 4 Perform GPR surveys
• Task 5 Statewide presentations
• Task 6 Final Report

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Task 1 GPR Summary Report

•  
• 1.      Introduction
• 2.      Mathematical Principles
• 3.      Equipment
• 4.      Potential GPR Applications
• 5.      GPR Experience in Minnesota
• 6.      Summary
• References

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Potential GPR Applications

• Determine Pavement Layer Thickness
•      Estimate Material Properties
•       Identify Stripping Zones within Asphalt
•       Detect Subsurface Voids
•       Analyze Rutting Mechanisms
•       Detect Subsurface Anomalies
•       Bridge Deck Delamination
•       Rebar and Dowel Bar Locates

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GPR Experience in Minnesota

• MnROAD -- Calibration/Layer Thickness
• TH59, Worthington Interface Separation
• TH10, Big Lake Void Detection
• CSAH3, Cokato -- RAP
• Gervais Ave. Density/Moisture Content
• TH212, Dawson -- Stripping

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MnROAD -- Objectives

• Field Calibration (Cell 33)
• 2 Metal Plates _at_ 10 Depth _at_ 100 spacing
• 2 Metal Plates _at_ 16 Depth _at_ 100 spacing
• Calculate Layer Thickness (Cells 33, 34)
• Asphalt 4
• Class 5 Base 12

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MnROAD Field Calibration
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MnROAD Layer Thickness
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TH59 -- Objectives

• Determine magnitude and extent of subsurface
  voids beneath concrete slab on 15 mile stretch of
  TH 59 between Worthington and Fulda

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TH59 -- Interface Separation
Surface
Interface
Mid-Panel
Joint
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TH 59 --Air Gap Thickness

• Calibrate GPR results with Lab results

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CSAH 3 -- Objectives

• CSAH 3 Cokato to French Lake (15 mi)
• Determine asphalt and base layer thicknesses
  using GPR and compare to coring results
• Before
• After

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CSAH 3GPR Images
Base
Surface
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CSAH 3--Results (EXCEL)
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TH 10 Big Lake -- Objectives

• Problem Dip in Road
• Why Possible Voids
• Solution Video Images and GPR

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TH 10 GPR Images
70
Void
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Gervais Ave -- Objective

• Simultaneously calculate layer thickness and
  dielectric constant (density) using two antennas

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Gervais Ave 2 Antennas
2x
Concrete
Base
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Gervais Ave System of Eqs.
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Gervais Ave. -- Density
Solid Dielectric
Solid Volume
Bitumen Dielectric
Measured Dielectric
Porosity
Density
Air Dielectric
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Gervais Ave GPR Images AC
GC
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Gervais Ave Results
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TH212 -- Objectives

• TH212 Dawson to TH75 (15 mi) Full Depth Asphalt
• Determine locations of stripping and corrlelate
  with field cores

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TH 212 - Stripping
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Potential New Applications

• Bridge Deck Delamination
• Rebar and Dowel Bar Locates
• Asphalt Sub layer identification
• Simultaneous calculation of asphalt
  density-thickness
• Layer separation at interfaces

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Task 2 GPR Brochure
http//www.mnroad.dot.state.mn.us/research/MnROAD_
Project/persons/loken.asp
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Task 3 GPR Questionaire
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Task 4 -- Database
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Task 4 -- Government Levels

• State (2)
• County (14)
• City (6)

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Task 4 --- MnDOT DIstricts

• District 1 (3)
• District 2 (2)
• District 3 (1)
• District 4 (2)
• Metro (3)
• District 6 (3)
• District 7 (2)
• District 8 (3)

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Task 4 -- GPR Project Type
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GPR Conclusions

• GPR is nondestructive field test used to
  determine road structure
• GPR utilizes high-speed data collection at speeds
  up to 70 mph
• GPR gives a continuous subsurface description
• GPR has potential to calculate density and
  moisture content simultaneously