Magnetic Tomography for Measurement of Dowel Bar and Tie Bar Position in Portland Cement Concrete Pa

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Magnetic Tomography for Measurement of Dowel Bar
and Tie Bar Position in Portland Cement Concrete
Pavements

• Todd Petersen, Masters Student KSU
• KTRAN Project Number KSU-03-1
• Quaji Jahan and Shilpa Vaze, PhD Students KSU
• Stan Young, KDOT-Advanced Technology Research
• Jim DeVault and Ruth Douglas Miller, Kansas State
  University

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Major Points

• Introduction
• Cover Meter as a measurement tool
• Validation testing setups
• Cover Meter Performance
• New Cover Meter and Test Platform
• Current and Future Work

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• Introduction
• Steel used for load transference and thermal
  expansion between concrete joints.

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Current Problems and Results of Misplaced Steel

• Problems
• Dowel Bars
• Movement of baskets
• Misplaced saw cuts
• Process control of automated inserters
• Tie Bars
• Vibrated out of place
• Too close to transverse joints

• Results of Misplaced Steel
• Weak Joints
• Poor load transfer
• Premature Cracking
• Reduced life of Pavement
• Expensive remedial work
• Cross-stitching and Dowel inserting

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Current Methods of Quality Control

• Plastic (Wet)
• Dig it out
• Poke it with a stick
• Set (Hard)
• Use a metal detector on your hands and knees
• Pay someone to do GPR
• Saw it up

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Objectives for Research

• Ultimate Objectives
• Real-time process monitoring
• Fully automated closed loop system for control of
  automatic paving machines.
• Fix problems as they develop (before the concrete
  hardens)

• Immediate Objectives for KSU Design Team
• Steel placement verification instrument
• Single user can rapidly and efficiently assess
  location and accuracy of steel placement
• Automated processing of data to assess the 3D
  location/orientation of steel accurately

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Cover Meter

• Measures depth to steel reinforcement
• Input bar diameter
• Measures up to 14 inch depth
• Manual observations and recording
• New meter has serial port output available

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Cover Meter Operation

• The current pulse in send coil 1 creates a
  magnetic field in the dowel bar.
• The magnetic field applied to the dowel bar
  induces a current in it.
• The induced current creates a (second) magnetic
  field.
• The second magnetic field induces a current in
  receive coil 2.
• The received current pulse is converted into a
  digital signal suitable for computer processing.

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Initial Test Platform

• X/Y Table with Quad-position encoders for
  position data.
• Accuracy inversely proportional to sweep speed
• Sensor puck restricted to Two Dimensional
  Movements

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Meter Interface

• Speaker tapped on old meter
• Intensity data measured by speaker frequency
• New meter outputs Hex number of scaled signal
  strength.

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1D Sensitivity to Depth
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2D Vertical Displacement
A
B
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6in Dowel Bar Depth
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2D Dowel Bar Array
Vertical Displacement
Horizontal Displacement
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Vertical Displacement
6.125 inch Array Depth
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Horizontal Displacement
6.125 inch Array Depth
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3D Plots
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Evaluation of Cover-Meter Performance for
Magnetic Tomography

• With the cover meter as our measuring instrument
  we can resolve the following spatial properties
  of the steel dowel bars in concrete
• Absolute depth to 0.125
• Vertical pitch to 2
• Horizontal yaw to 4
• Horizontal displacement normal to saw cut
• Up to 9 depth, resolution is inversely dependent
  on speed of sweep.

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New Test Platform

• Mobile Cart for use in on the road evaluation.
• Model Roadway
• LabView Controlled Data Gathering program
• MATLAB Evaluation program

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New Mobile Cart

• Quad-position encoder
• Clear template with 5 sensor positions
• Shelf for laptop and Cover Meter

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Model Test Roadway

• 5 bar position
• 2 end control bars
• 3 center adjustable cases
• Vertical
• Horizontal
• diagonal

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Measurement Concept

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Example Data

• All sweeps max signal strength ( S(x) ) equal and
  X position equal.
• All S(x) equal, X not equal.
• Gradient in S(x), X equal.
• Step in S(x), X equal.

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LabView Control Program
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Sample Matlab Outputs
3.5 inch depth all bars centered
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3.5 inch depth Bars 2 and 4 raised to 2.25
inch depth
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3.5 inch depth center bar horizontal yaw
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Future Work

• Refinement of LabView Data Collection software
• Refinement of MATLab Data Evaluation software
• Test trials on actual roadways

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Version 2.0

• Discrete design of our own sensor puck and
  associated hardware
• Minimize sweeps per saw cut
• Eliminate commercial Cover Meter
• Boost signal power to reach greater steel depth
• Motorized Cart
• Uniform traversal speed and path.

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Questions?