CIVE1173 Non Destructive Test (NDT) Methods

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higgsboson
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CIVE1173 Non Destructive Test (NDT) Methods
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2013-06-22 23:46:36
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Survey Testing Site
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Week 4 lecture notes summary. Exam
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  1. SiteTests
    • – Visual Inspection
    • – Delamination Survey
    • – Cover Survey
    • – Half Cell Survey
    • – Resistivity
    • – UPV
    • – Schmidt Hammer
    • – Sampling
  2. Visual Survey/Inspection
    • – Photographs
    • • Keep a log
    • – Detailed Notes and sketches
    • • May be expensive and difficult to go back!
    • – Type of defect
    • – Frequency and distribution of defects
    • – Size of defects
    • – Evidence of deterioration mechanism
  3. Delamination Survey
    • • Use Hammer to tap surface
    • – Dragging chains
    • – Rubbing coin
    • • Hollow sounds denote delamination of concrete
    • – Ensure no other noise
    • • Record delaminated area
    • – No notes
    • – Spray/chalk area if possible
  4. Cover Survey
    • Magnetic Reluctance Method & Pulse Current Method (similar to magnetic but with an eddy current)
    • Improve accuracy by setting bar DN
    • • Check cover meter operation and calibration (break out to steel)• Record location and depth of bars• At least TWO sweeps per grid to determine orientation of bars• Record on surface and sketch and photograph
  5. Cores
    • • Select Location•
    • Avoid Steel unless a steel sample is required. If so ALWAYS check structural implications
    • • Uses; Chlorides, Carbonation, Strength, Cement Content, Mix Design, Steel Connections (Half Cell, LPR), Continuity, Steel Type
  6. Half Cell Survey
    • • Plot Contour Map (Surfer) • Analyse Contour Map (Van Der Veer criteria, Shape of contour plots, Environmental conditions) • Dry, no corrosion, but may corrode when wet • Saturated, very low potentials, no corrosion
  7. Corrosion Rate - Linear Polarisation Resistance (LPR) Measurement or Zero Resistance Ammeter
    • Week 4 pp22-35
    • LPR
    • ca
  8. LPR – Corrosion Rate
    • Polarisation resistance, Rp
    • Rp = ΔE/ ΔI
    • Instantaneous Corrosion Rate, Icorr
    • Icorr = B/(Rp – Rs)
    • Corrosion Current Density, icorr
    • icorr = Icorr/A



  9. LPR – Corrosion Rate;
    Average section loss (penetration), P
    • P = Μ icorr t/ρi z F
    • Μ – Atomic weight iron (55.85g/mol)
    • ρi – density steel (7.85g/cm3)
    • t - time
    • z – No of electrons (2)
    • F – Faraday constant (96 500 C/mol)
  10. LPR – Corrosion Rate;
    Results
  11. Resistivity Measurements
    • • Measures resistance of concrete
    • • Indication of likely corrosion rate IF corrosion is occurring
    • • Does NOT show if corrosion is occurring
    • • Measurement taken on concrete surface
    • Method: Avoid steel, Drill 4 holes to depth of 2-5mm to eliminate surface effects, Avoid moisture
  12. Resistivity Technique
  13. Resistivity Continuity
    • • Check all steel is continuous
    • • Make connections to two locations
    • • Measure resistance (must be less than 2Ohms)
    • • Continuity required for cathodic protection systems
  14. Resistivity Measurements
    • Resistivity ( r )
    • = 2(Pi)Ra
    • = 4(Pi)Ra (embedded probes)
    • R – Resistance measured
    • A = spacing (cm)
  15. Resistivity Result Parameters
    • Probability of rate of corrosion, not whether corrosion occurring
  16. Schmidt Hammer
    • • Schmidt Hammer
    • – Strength of Concrete
    • – Hits surface with defined energy
    • – Rebound measures hardness
    • – Hardness relates to compressive strength
    • – Questionable accuracy and reproducibility
  17. Ultrasonic Pulse Velocity (UPV)
    • • Measures time for pulse to travel through concrete
    • • Place transducer at two locations on surface
    • • Measure distance between transducers
    • • Use conductive gel to ensure good contact
    • • Calibrate on known material
    • • Apply to opposite sides if possible.  Or, if not, then adjacent sides
    • • Can be same sides at fixed distance
  18. UPV - how it works:
    • Investigate cracks, Pulse must go around crack, Time will indicate depth of crack, Moving transducer will also provide information on shape of crack, Proximity of rebar will affect results, Maximise distance from rebar, Undertake cover survey prior to test
    • • Temperature will affect result: Higher temperature = higher velocity, Test range 0 – 30oC

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