Non Destructive Techniques

Non Destructive Techniques

1. Reasons

   • Quality Control
     • Qualitative
       • Comparing measurements in one part of structure to another (irregularity)
     • Quantitative
       • Comparing on-site measurements of sample with lab measurements
   • Forensic: Failure analysis
   • Residual properties: resiliance
     • Lifetime prediction
     • Strengthening requirement
   • Properties and/or artefacts
     • Properties it was supposed to have
     • Compressive strength
     • Chemical composition
     • Whats under the surface
       • Corrosion
       • Internal cracking
       • Rebars/tendons
         • Size
         • Placing
       • Voids
       • Honeycombing (insiufficient compaction)

2. Surveys

   • Systematic, grid based, time limited
   • Parallel visual/photo inspection
     • Cross correlate, 2 or more variables

3. Types

   • Visual
     • Observing surface manifestations of sub-surface problems
       • Cracking
       • Staining
       • Pop-outs
       • Poor finish
     • Persistent external factors
       • Water: run off, pooling, blocked drainage
       • Damage caused by vegetation
   • Percussive/acoustic
     • Tapping with steel rod/small hammer
       • Listen to sound & Vibration
     • Rebound/schmidt hammer
       • Concrete properties: Strength
       • Qualitative - OK, cheap way to show poor areas
       • Quantiative - Poor, correlation between strength should not be done
     • Ultra Sonic Pulse Velocity
       • Strength
       • Related to stiffness E, and density, P
       • PUNDIT
         • Piezoelectric Transducers
       • Not that sensitive to speed of sound
         • Correlation tricky
       • Qualitative - Good, easy to establish areas of poor quality
       • Quantitative - Reliable if good calibration established
   • Electromagnetic/chemical/static
     • E-magnetic Covermeter
       • Rebar location, cover & Distance
       • Bar size & depth
       • Pros
         • Does what it says
       • Cons
         • Closesly spaced bars cause problems
         • Max cover depth = 60mm
         • Other steel causes problems
     • E-Chem: 1/2 cell potentiometer
       • Rebar corrosion
       • Measures electrochemical potential of steel at surface
         • Potential maps plotted
           • Close controus -> high current flow -> corrosion
       • Cons
         • Fiddly
         • Need saturated concrete
         • Need to break out to expose steel
       • Pros
         • Only way to give liklihood of corrosion
     • E-static: Capacitance
       • Experimental
       • Contrast in dielectric properties
         • Viewing distortion of electric field
       • Shows voids & rebars

4. Last resorts

   • Sampling
     • Coring - samples for compression tests
     • Chemical analysis
   • Semi-destructive
     • Pull out bolts
       • Strength required to pull out