Thermocouple Applications in Pavement Systems
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Thermocouple Applications in Pavement Systems. Jake Hiller Graduate Research Assistant. Presentation for CEE 398 KUC – Experiments in Structures and Materials March 6, 2002. Outline of Presentation. Background on Thermocouples Rigid Pavement Applications Flexible Pavement Applications

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Thermocouple applications in pavement systems

Thermocouple Applications in Pavement Systems

Jake Hiller

Graduate Research Assistant

Presentation for CEE 398 KUC – Experiments in Structures and Materials

March 6, 2002

Outline of presentation
Outline of Presentation

  • Background on Thermocouples

  • Rigid Pavement Applications

  • Flexible Pavement Applications

  • Summary

Background on thermocouples
Background on Thermocouples

  • Two conductor cables

  • Composed of metal alloys

  • Ends of wires are soldered to form a couple

  • Resistance of couple changes with temperature

    • Seebeck Effect – 1822

  • Resistance is then correlated with temperature

    • Standardized correlations

    • Correlations can change over time (deformation, corrosion)

Seebeck effect
Seebeck Effect

  • Discovered by Thomas Seebeck, 1822

  • Electrons flow from one wire to other

    • Due to different energy potentials of alloys

  • As temperature changes, current flows

  • Voltage is measured between the two alloys

    • Small voltage (less than 10 mV)

Many types of thermocouples
Many types of Thermocouples

  • Type K – cheap, general purpose

    • Positive 90% Ni, 10% Cr Negative 95% Ni…Al, Mn, Si

  • Type T – Good accuracy in pav’t temp range

    • Positive 100% Cu Negative 55% Cu, 45% Ni (constantan)

    • Low corrosion potential

  • Type J

    • Positive 100% Fe Negative 55% Cu, 45% Ni (constantan)

  • Type N

    • Positive 85% Ni…Cr, Si Negative 96% Ni… Si, etc.

Thermocouples options
Thermocouples Options

  • Insulation/sheathing to protect from outside factors

  • Gage of wire is related to performance

  • Pre-assembled with connectors to fit thermometer

    • Multiple TC’s pre-assembled

  • Unassembled wire

    • Color code by type

    • Differs between some countries

Problems with thermocouples
Problems with Thermocouples

  • Accuracy

    • Often between 0.5 and 2.2ºC, depending on TC type

  • Noise

    • Long leads can attract electrical signals

    • Already low signal from thermocouple

  • Thermal shunting

    • Heating of wire mass can affect measurements by absorbing energy

  • Corrosion

    • High alkali or water environments can modify calibration

Rigid pavement applications



Rigid Pavement Applications

  • Three types of thermal movements in rigid pav’ts

    • Curling

      • Thermal gradient in slab

    • Expansion/Contraction

      • Uniform temperature change

    • Soil frost heave

      • Lifting of slab due to increasing volume of underlying layers

Upward curling: Top contracts relative to bottom

Downward curling: Bottom contracts relative to top

Calibration instrumentation of thermocouples
Calibration/Instrumentation of Thermocouples

  • Typically tested in hot and cold baths

    • Confirmation and sway in readings

  • Placed in two ways

    • Set at different depths along wooden dowel or bracket

    • Placed in by hand as paving is occurring (less reliable)

  • Minimum of 0.5” of cover needed

Rigid pavement testing
Rigid Pavement Testing

  • Used in conjunction with other sensors to evaluate pavement performance

  • Include vibrating wire, moisture resistance sensors, psychrometers, etc.

  • Typically placed at either corner, edge, or middle of slabs

Flexible pavement applications
Flexible Pavement Applications

  • Determination of Viscoelastic Properties

    • Rutting potential increases with temperature

    • Lower modulus - Higher deflections

  • Thermal Cracking

    • Low temperatures – thermal stresses increase

    • Stress can surpass tensile strength of material

    • Fatigue of material can also occur

  • Soil frost heave

Flexible pavement applications1
Flexible Pavement Applications

  • TC’s placed near: pressure cells, strain gages, or FWD test locations to correlate with temperature


  • TC’s based on energy potential differences of alloys

  • Each TC type has distinct advantages

    • Type T and K most used in pav’t field testing

    • Accuracy is sometimes questionable

    • Corrosion can be a potential problem

  • Used in rigid pav’t to assess curling and expansion

    • Installed before paving typically

  • Used in flexible pav’t to determine seasonal variability and frost action