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The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity

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Presentation on 16th October 2018 by Isaak Tsalicoglou at the 3rd Japanese-Swiss workshop titled "Durability Testing of Concrete, on site and in the lab", at TFB in Wildegg, Switzerland.

The state of the art of non-destructive testing applied to civil engineering has in recent years achieved many significant milestones in the field of imaging technologies for the assessment of reinforced concrete structures. The constant improvement of the available electronic components and the increased computational power of consumer-grades mobile devices are among the key factors that drove mature technologies such as Ground Penetrating Radar (GPR) and Eddy Current Testing (ECT) into products delivering new levels of accuracy and usability. At the same time, recent developments of the pulse-echo-based Ultrasonic Tomography (UT) further broadened the range of applications potentially addressed. Still, there seems to be a general lack of awareness in the user community about the real potentials and main limitations of each of the three technologies. The current work focuses on the typical scenarios and the common challenges presented by tasks of embedded object detection (structural details, steel reinforcement, utility network) and flaw detection (voids, cracks, delaminations). The complementarity of the three technologies has been proven through measurements on test blocks and real-life cases. It is noted that the proper combination of technologies naturally results in more efficient workflows, increased positioning accuracy, and a less subjective, operator-dependent interpretation of the testing results.

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The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity

  1. 1. The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 3rd Japanese-Swiss Workshop - "Durability Testing of Concrete, on site and in the lab“ TFB, Wildegg, Switzerland – October 16, 2018 Isaak Tsalicoglou – Head of Product Management Proceq SA, Switzerland © Proceq 2018 1
  2. 2. © Proceq 2018 2 Image copyright: Disney
  3. 3. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 3 Three main technologies for concrete imaging Eddy Current Testing (ECT) Ultrasonic tomography (UT) / Ultrasonic Pulse Echo (UPE) Ground Penetrating Radar (GPR) rebars objects back wall rebars (limited) objects back wall defects rebars - cover - diameter defects (limited)
  4. 4. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 4 ECT relies on eddy currents and electromagnetic induction Transmitting coil Receiving coil Rebar . . . .
  5. 5. © Proceq 2018 5 GPR and UPE rely on the behavior of waves at interfaces Concrete 2nd material The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity Animation source: Wikipedia
  6. 6. © Proceq 2018 6 GPR detects “dielectric contrast” with electromagnetic waves Concrete 2nd material The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 𝜀1 𝜀2 Relative dielectric permittivity (“dielectric”) 𝑅 = 𝜀2 − 𝜀1 𝜀2 + 𝜀1 Reflection coefficient Animation source: Wikipedia
  7. 7. © Proceq 2018 7 UPE detects discontinuities of acoustic impedance with ultrasonic waves Concrete 2nd material The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 𝑧1 𝑧2 Acoustic impedance 𝑅 = (𝑧2−𝑧1)2 (𝑧2+𝑧1)2 Reflection coefficient Animation source: Wikipedia
  8. 8. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 8 Relative dielectric permittivity values typical in concrete GPR scanning ∞ Relative dielectric permittivity (“dielectric”)1 1473 SteelDry concrete Wet concreteAir Avg. concrete
  9. 9. © Proceq 2018 9 Metallic targets in concrete cause a full reflection of electromagnetic waves (GPR) The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity Reflection coefficient 𝑅 = −0.451 𝜀1 = 7 𝜀1 = 7 𝜀2 = 1 𝑅 = 1 (partial reflection) (full reflection) 𝜀2 = ∞ Animation source: Wikipedia
  10. 10. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 10 Acoustic impedance values typical in concrete UPE scanning Acoustic impedance [kg/m2×106] × 22377 × 4.84 0.000429 Air 9.6 Avg. concrete 46.5 Steel
  11. 11. 𝑧2 = 46.5 © Proceq 2018 11 Ultrasonic waves (UPE) demonstrate the opposite behavior of GPR waves The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity Reflection coefficient 𝑅 = 0.9998 𝑧1 = 9.6 𝑧1 = 9.6 𝑅 = 0.433 (practically full reflection) (partial reflection) (All z values expressed in 106 kg/m2) 𝑧2 = 0.000429 Animation source: Wikipedia
  12. 12. © Proceq 2018 12 In the imaging of concrete structures, GPR and UPE complement each other ideally • Total reflection • Better for detecting voids • Partial reflection • Detection below rebars is possible • Partial reflection • Detection below voids is possible • Total reflection • Better for detecting rebars GPR UT / UPE The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity
  13. 13. © Proceq 2018 13 Each of the three technologies offers a different set of advantages Single rebars very sharply delineated Can see beyond an air layer Insensitive to (non- metallic) surface coatings Extensive penetration, even in reinforced areas Very sensitive to voids and cracks Independent from concrete composition Concrete cover is very precise Determination of rebar diameter GPR UT/UPE ECT The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity
  14. 14. © Proceq 2018 14 Each of the three technologies also presents different disadvantages Only steel elements detected Limited to the upper reinforcement layer Cannot see past dense reinforcement or steel plate Cannot see small delaminations Limited penetration through fresh concrete Requires mechanical coupling to surface Cannot see beyond an air layer Poor resolution of single rebars Limited penetration through porous concrete The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity GPR UT/UPE ECT
  15. 15. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 15 Profometer 650 AI Recent implementations of the ECT, GPR and UPE in portable NDT instruments Proceq GPR Live Pundit Live Array Pro ECT instrument with Neighboring Rebar Correction Stepped-Frequency Continuous- Wave (SFCW) GPR UPE array transducer with 8 or 16 channels
  16. 16. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 16 Case 1: rebars, cavities, variable profile • Rebars Ø 20 mm in the upper half of the block • Two artificial voids 150x70 mm • Thickness variation from 400 to 550 mm (V-shaped back wall)
  17. 17. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 17 Case 1_A: no steel reinforcement
  18. 18. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 18 SFCW GPR can detect large enough voids, and even a deep backwall no steel reinforcement
  19. 19. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 19 UPE excels at concrete-to-air interfaces, i.e. the back wall and the void no steel reinforcement
  20. 20. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 20 GPR and UPE scans deliver similar information on the non-reinforced part of the block
  21. 21. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 21 Case 1_B: strong steel reinforcement
  22. 22. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 22 GPR sharply resolves the rebars – and they have a shielding effect on other features strong steel reinforcement
  23. 23. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 23 UPE does not image the rebars – but it does resolve the air pocket and the back wall strong steel reinforcement
  24. 24. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 24 Reinforcement makes the complementarity of GPR and UPE evident
  25. 25. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 25 ECT excels at 2D mapping of the cover of first- layer reinforcement mats
  26. 26. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 26 ECT delivers accurate estimates of rebar cover (±1 mm) / diameter (±2 mm), and spacing ±1 mm = 1/32nd of an inch
  27. 27. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 27 Case 2: detecting delaminations Scan direction 250mm/9.8in 800 mm / 31.5 in
  28. 28. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 28 GPR is blind to the delamination – but the back wall is clear, regardless
  29. 29. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 29 With UPE, the delamination is clear, and it masks the back wall
  30. 30. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 30 Case 3: embedded objects, cavities, back wall BA
  31. 31. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 31 Both GPR and UPE detect all highlighted concrete-air and concrete-steel transitions Rebar Metal pipe Back wall Plastic pipe Non-migrated GPR scan Migrated UPE scanMigrated GPR scan
  32. 32. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 32 Cracks are detectable with UPE, but only faintly so with GPR – and only beyond a critical size Crack Back wall Non-migrated GPR scan Migrated GPR scan Migrated UPE scan
  33. 33. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 33 Cracks are detectable with UPE, but only faintly so with GPR – and only beyond a critical size Migrated viewNon-migrated viewCrack geometry SFCW GPR UPE
  34. 34. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 34 Ground Penetrating Radar: versatile locator ECT and GPR combine for comprehensive reinforcement mapping to medium depth ranges Ultrasonic Pulse Echo: reliable flaw detector Eddy Current Testing: accurate cover meter
  35. 35. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 35 Ground Penetrating Radar: versatile locator GPR and UPE combine for comprehensive feature and flaw detection to large depth ranges Ultrasonic Pulse Echo: reliable flaw detector Eddy Current Testing: accurate cover meter
  36. 36. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 36 Ground Penetrating Radar: versatile locator Together, ECT, GPR and UCT are “The Three Musketeers” of structural concrete imaging Ultrasonic Pulse Echo: reliable flaw detector Eddy Current Testing: accurate cover meter
  37. 37. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 37 Data fusion of multi-technology GPR and UPE concrete measurements is within reach GPRUPE Migrated Isosurface Migrated Isosurface Multi-technology imaging Source: Taffe, Handbuch der Bauwerksprüfung - Mertens (Hrsg.)
  38. 38. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 38 • Complementary detection and insights • Comprehensive understanding • Increased objectivity of results • Reduced user- dependence Concrete imaging requires “the right tool for the job” and the right combinations thereof
  39. 39. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 39 Image copyright: Disney
  40. 40. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 40 Ishikawa (“fishbone”) diagram of concrete testing with Schmidt hammers for a holistic view Materials Methods / Processes Manpower / People Mother Nature / Environment Measurements Machines / Equipment ProblemCauses and effects The business case of concrete testing: 1. Cost-benefit ratio 2. Budget constraints
  41. 41. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 41 Variability of concrete, a bulk-produced material • Concrete will always be of variable quality • More tests are better than fewer tests • “Accurate enough” at low total effort makes business sense Materials Methods / Processes Manpower / People Mother Nature / Environment Measurements Machines / Equipment Image source: http://www.bbrnetwork.com/
  42. 42. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 42 Schmidt hammers continue to be an integral part of German and EU standards Equipment accuracy, quality, repeatability Total process productivity Holistic view of Schmidt hammer testing Materials Methods / Processes Manpower / People Mother Nature / Environment Measurements Machines / Equipment Image source: “Comparative investigations of rebound hammers related to R and Q values” since DIN 4240 since DIN EN 13791/A20
  43. 43. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 43 • Introduction of Q values as German-national appendix to DIN EN 13791/A20 • Q-value hammer (SilverSchmidt), compared to R-value hammer (Original Schmidt): ✓Lower dispersion of rebound values ✓High accuracy up to higher concrete strengths • Step-wise mapping of Q values to compressive strength classes is possible • “Even for high-strength concrete, it is possible to estimate the compressive strength through the Q value” Independent research in 2018 confirmed the accuracy benefits of R-value Schmidt hammers Source: “Comparative investigations of rebound hammers related to R and Q values”
  44. 44. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 44 Q value (SilverSchmidt) shows lower dispersion for higher-strength concrete Rebound value Compressive strength Image source: “Comparative investigations of rebound hammers related to R and Q values” ✓ Original Schmidt SilverSchmidt
  45. 45. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 45 Only destructive testing Real-world large-scale concrete testing… on a budget • 20x cores, destructive testing • Labor-intensive; no on-site insights possible • Data only every few meters • Weakened structure Multi-fidelity testing with multiple technologies Only high-effort NDT • Many efficient tests - e.g. Original Schmidt Live / SilverSchmidt Live • Added: few expensive tests (DT or NDT); correlate the efficient and expensive tests ✓ Large coverage at the right detail, within budget • Sophisticated NDT with non- hammer methods • Experienced people required; high cost • Low number of total tests “Japan: total length of expressways is 11,659 km” (!) Image source: https://www.japan- guide.com/e/e2354.html   ✓
  46. 46. © Proceq 2018 The Three (Four) Musketeers of multi-technology concrete NDT for accuracy and productivity 46 The Schmidt hammer(s) as a valuable fourth Musketeer of concrete NDT Original Schmidt Live R-value hammer SilverSchmidt Q-value hammer Image copyright: Disney
  47. 47. © Proceq 2018

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