Innovative technologies for condition assessment and monitoring of concrete

1. Innovative technologies for condition assessment and monitoring of concrete Richard Haskins ERDC - Vicksburg (601) 634-2931 Richard.W.Haskins@erdc.usace.army.mil

2. Overview: • Quick Summary of concrete Non-Destructive Testing • - Including Findings and Discoveries at ERDC • Partial plans of the Condition monitoring and assessment work unit

3. Concrete NDT is needed to: • To detect and/or characterize non-visible conditions • To gather data that is objective and quantitative • To facilitate improved destructive testing (such as determining coring locations)

4. What goes wrong with concrete and WhyCondition Potential Cause • Honeycombing and voids poor consolidation • Delaminations corroding rebar (road salt) • Ungrouted tendon ducts placement problems • Internal cracking Mechanical stress • Material deterioration Freeze Thaw damage • Alkali-silica reaction Chemical reaction NDT data generally alerts us that something is wrong but it does not always characterize the condition !

5. Sounding (resonance) and Visual inspection are the standard for most inspection programs Hollow sound (Tympanic Response) Applied energy Resonant energy 0 Frequency 0

6. Instrumentation components (digitizer, impactors, sensor) Free Plate Resonance = 2 * thickness = velocity frequency Easily applied to Simple Geometries

7. Solid Grout 20 14 8.3 26 Honeycomb #1 0 20 7.4 14 21 27 0 Empty Cell 5 13.6 0 20 Kilohertz Resonance Based SystemSpectral signature characterization

8. Strength-Velocity Correlation 6000 5000 4000 3000 2000 1000 Standard Deviation 20% Compressive Strength, psi 9.5 10.5 11.5 12.5 13.5 14.5 Ultrasonic Pulse Velocity, fps x 103 Ultrasonic Pulse Velocityuses high frequency stress waves L Travel path T Shortest time R T R Longer times T R T No arrival R T = Transmitter R = Receiver Velocity = distance / time

9. ERDC findings regarding ultrasonic through transmission Pulse Amplitude is better than Pulse Velocity for The detection of flaws such as honeycombing and parallel cracking (ERDC Test demonstrated two orders of magnitude) The oil filled transducer design used in the past Produce tremendous penetration gains when combined With modern PZT elements (>66 dB ) Signal processing techniques such as Tomography Can assist in localizing and characterizing damage (Diffraction based tomography is still needed)

10. 11 10 9 8 7 6 5 4 3 2 1 0 1 2 3 4 5 6 7 8 9 Tomographic imaging will likely advance future acoustical imaging for concrete (CAT-Scan) Tomogram From Blast Damaged Specimen Charge Hole Velocity ft/sec Sources Receivers

11. Eleven-axis Immersion scanning system being applied for through transmission imaging Disbond

12. Acoustics are very sensitive to mechanical properties Entrapped Air and microcracks Ultrasonic Reflection Image Photograph water Weak Aggregates detected This method is Applicable to Cores or Saw-cut specimens

13. 1 0.8 9 “ echo 0.6 0.4 Normalized Magnitude 0.2 0 -0.2 -0.4 -0.6 0 0.5 1 1.5 -4 Time (Seconds) x 10 Using specialized equipment it is Possible to make ultrasonic echo measurements and perform Scanning of concrete (non-commercialized technology)

14. Various thickness scans

15. Ultrasonic B-Scan of an 8-Inch Concrete Bridge Deck 0 -2 -4 -6 Depth (inches) -8 -10 -12 -14 0 5 10 15 20 25 30 Distance across surface (inches)

16. 200 180 160 140 ( K Hz ) FREQ 120 100 80 60 40 20 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 SPLIT SPECTRUM PROCESSING (Non-linear Filtering) Frequency time Recombined (minimum abs) Amplifies: Broadband phase Coherent data

17. UPE through 10-feet of Concrete By Spatial Averaging Technique (enhances compressional wave While averaging out surface waves) 15-feet 10 ft trans receiver Time of Arrival = 1.46 milliseconds

18. Common Difficulties with testing large concrete structures • a) Lack of Two sided access • Backwall Reflecting surface too deep • Large Aggregate (scattering ~ wavelength) • Surface Deterioration Conventional structural elements Mass Concrete

19. Partial Plan for the Condition monitoring • and assessment work unit • Develop or Examine better tools for site inspectors • -Low cost and practical to use • Evaluate performance of an Instrumented core rig • - for determining deteriorated concrete strength • as a function of depth • Perform better inspection of cores using NDT prior to DT • - Evaluate non-linear resonance spectroscopy • Scanned echo and through transmission on cores • Evaluate Tensile testing as damage indicator • Develop / Evaluate sensor package to be grouted into core hole • - measurement along key axis using proven technology PI: Dr. Stan Woodson

20. Need tools for improved Quantification of surface damage/deterioration Approx 4 inches Deep

21. Low Cost Topography Raw Video Frame System Setup and Preliminary Data Processing steps: Adjust camera settings to show only laser beam Collect video during target translation (fixed camera and light ) For each frame and Y position determine x position of beam edge Generate composite of x positions (below: y-axis is Frame count) Remove linear trends Y Composite data from Frame integration X Line Laser target USB cam Holes in Top of brick Fingers (moving target) Final Image plane

22. Global Minimum Laser camera High points detected

23. Alternate Visualizations -1/8 inch

24. Conceptualized System Reference Target To Calibrate Cross-range And depth cam laser Objectives: Determine material topography Referenced for chronological analysis Determine out of plane displacements usb

25. Pan Head (valve actuator) Fractured Concrete Surface (splitting Tensile)

26. Related plans include: Practical methods to mosaic detailed 2d and 3d images Imaging and processing methods to improve crack mapping - Show small cracks - Determine crack growth between inspections

27. Application of Standard Image Processing operations to better show damage

28. a b c Instrumented Core Rig (energy consumption ~ concrete strength) Existing core rigs can be retrofited in ½ hour Performance constantly improves via correlation on Destructive tests on the collected cores Low-cost, Simple, and robust concept Parts: a Weight b Real power Meter c string-pot

29. a b c Initial data from First Prototype System bad good Composite Is product (kWatt x seconds )/ inch Feed Rate .025 “/sec .018 “/sec Time Initial results show Excellent agreement With destructive test (linear fit) 900 W 700 W power 34.7 kWs/” 40.3 kWs/” Core energy Bad material Good material (F&T damage) strength

30. Non-linear resonance spectroscopy To detect and quantify microscopic damage AMP specimen Correlated to Destructive test data To determine Structural Significane

31. Instrumentation grouted intocore hole Candidate Sensor: Carlson Strain meter Core hole Sensor Package Notches Honed in side F&T cracks Objective: Get the sensor Oriented in the Right Dimension Final Realization (Recessed electrical terminals)

32. Questions