Outline

1. Evaluation of NDTE Technologies for Airport Pavement Maintenance and Acceptance ActivitiesImad L. Al-QadiJohn S. PopovicsWei XieSara AlzateUniversity of Illinois at Urbana-Champaign

2. Outline • Project Scope and Objectives • NDTE State-of-art report: Promising NDTE technologies to assess existing and new airport pavements • Future Work

3. Objectives • To determine the effectiveness and practicality of new and existing NDTE technologies for maintenance, evaluation, quality control and acceptance of flexible airport pavements • To evaluate and recommend appropriate NDTE technologies to the FAA based on field evaluation results

4. Scope of work Review and summarize existing and new NDTE technologies State-of-the-art report New research Identify promising NDTE technology (technical and practical suitability) Identify current NDTE needs for airport pavements and facilities Field testing and analysis of promising NDTE technology Final report

5. NDTE State-of-the-art Report • Existing NDTE methods are summarized in a draft report, for FAA review and comment • Each method is presented in a chapter: • 1) Impact-echo • 2) Surface waves • 3) Sonic/ultrasonic • 4) Nuclear radiometry • 5) Infrared thermography • 6) GPR • 7) Laser profiling • 8) Digital imaging

6. NDTE State-of-the-art Report • Each chapter discusses the following: • Theory • Equipment • Benefits and applications • Limitations • Recent developments

7. Nuclear Density Gauge • The radiation intensity of gamma rays that passes through a medium, or is scattered back from a medium, is used to measure density. • Nuclear density gauges are compact and provide direct and rapid measurements

8. Application of Nuclear Density Gauge • Measuring in-situ HMA, concrete and solid densities • Suitable for both thin and thick layers; better for thick layers.

9. Limitations of Nuclear Density Gauge • Need for calibration • Affected by lift thickness and variability of supporting layer • Difficulties in identifying levels of segregation • High initial cost, certification requirement, periodic inspection, and difficulties in shipping and transport and disposal.

10. Impact Echo Resonant frequency interpreted for thickness information

11. Application of Impact-echo • Measuring concrete slab thickness • Identifying location and depth of delamination defects in concrete

12. Limitations of Impact-echo • Local, point contact measurement • Not effective for HMA pavements • Only effective for top layer in pavement system • Difficulties in locating small defects

13. Surface Waves (Spectral/Multiple Analysis of Surface Waves (SASW/ MASW) Measure dispersion of surface waves in layered media

14. Application of surface waves • Estimate pavement layer properties (thickness and modulus) Estimated stiffness profile Portable Seismic Pavement Analyzer (PSPA) for SASW

15. Interpretation of MASW Lamb wave curve best fit to data to give layered structure Stacked multiple signal data MASW mapping of signal data

16. Limitations of surface wave • Local, point contact measurement • Data inversion is complicated (MASW approach has sounder technical basis than SASW) • Not reliable for accurate thickness measurements of a specific layer

17. Δt Δt Sonic/ Ultrasonic Measure velocity of various wave modes propagating in pavement and relate to mechanical properties http://www.cflhd.gov/agm/engApplications/Pavements/413SpecAnalySurfWaveandUltrSonicSurfWaveMethods.htm

18. Application of sonic/ ultrasonic • Estimate mechanical properties of pavement (Modulus, strength, damage level, etc.) • Locate voids/ interfaces

19. Limitations of sonic/ ultrasonic • Local, point contact measurement • Estimation of absolute values of modulus and strength of concrete is not accurate

20. Digital Imaging Technology • Automated digital imaging system consists of image acquisition and distress image processing After Huang et al. 2006

21. Equipment and Data Collection • DMI is used to control the acquisition of digital image • Distress detection, isolation, classification, segmentation, and compress • Fast wavelet transform for the wavelet-based distress detection, isolation, and evaluation

22. Application of Video Imaging • Segregation measurement: • Identify texture variation related to HMA segregation • Use GLCM technique to identify segregation • Crack Detection/ Surface Distress • Individual crack information can be vectorizing • WiseCrax is used to automatically detect cracks, classify and generate crack map • Recent development uses processing algorithm for high-speed, real-time inspection of pavement cracking

23. Limitations of Imaging Technique • Video image can only detect surface distress • There is environmental requirement during data collection • The system is vulnerable to vehicle vibration • Video image can measure gradation segregation level; but not temperature segregation

24. Laser Technique • Pavement surface information can be determined by the movement of reflected beam spot on the detector • It can supply rapid, continuous, and high accurate measurement

25. Line scan and area scan laser systems (Xu et al. 2006) Equipment and Data Collection Two types of laser camera are available to digitally image pavement surface: area scan and line scan

26. Friction and Roughness Measurements • For friction use high-pass filter with 50mm wavelength cutoff • For roughness use low-pass filter with 0.5m wavelength cutoff

27. Applications • Detect segregation: • texture ratio of segregated to non-segregated area to measure segregation level • Rutting measurements: • Automatic, rapid and continuous • Crack measurements: • Valley detection of candidate cracks • Validation algorithm • Characterize crack types and pattern • 3D laser imaging has been introduced

28. Limitations • It provides pavement surface condition only • Difficult to distinguish between texture and crack • Transversal cracks are likely to be detected, while longitudinal cracks are easily missed • Narrow and shallow cracks may be filtered out during data processing

29. Infrared Thermography • Infrared thermography is standardized by ASTM D4788. It includes passive and active methods • Subsurface changes in pavements generate surface temperature variations

30. Infrared sensors bar Equipment and Data Collection

31. Defect Applications • QC/QA • Segregation measurement • Crack and defect measurement detection

32. Limitations • It is applied for near-surface surveys • It cannot distinguish between gradation and temperature segregation • For existing pavements, it depends on solar energy

33. Ground Penetrating Radar • Ground Penetrating Radar (GPR) is a special kind of RADAR • Purpose of using GPR: • Detect targets buried in a dielectric medium • Estimate their depths • GPR applications: geophysics, archeology, law enforcement, evaluation of civil structures (buildings, bridges, pavements)

34. Layer 1 Layer 2 Principle of GPR Transceiver Control Unit DMI Antenna

35. GPR Antennae • Ground-coupled antenna: in contact with ground surface • Air-coupled antenna: 1 to 2 ft above surface Ground Coupled Antenna Horn Antennae

36. HMA Base Subgrade Typical GPR Response (scan) A0 HMA t1 A1 Base t2 A2 Subgrade

37. GPR Data Collection HMA Base Subgrade HMA Base Subgrade

38. A0 HMA t1, d1 r,1 A1 Base t2, d2 r,2 A2 Subgrade r,3 Layer Thickness Estimation Thickness of i th layer:

39. New Pavements (QC/QA ) Classic GPR thickness estimation gives accurate results:

40. GPR Accuracy: New Pavements

41. x T T/R R t1 HMA er1 h t2 P Dielectric Constant Using CMP Common midpoint (CMP) technique (or common-depth point, CDP) is used as follows:  : EM velocity in the layer

42. x0 T R air er0=1 x1 qi h0 T/R t1 PCC er1 h1 qt t2 P Modified CMP Technique Modified common midpoint technique: Snell’s law of refraction: (1) Using the figure: (2) (3) (4)

43. Modified CMP Technique • Modified common midpoint algorithm: • Measure the reflection times t1 and t2 • Calculate the transmission angle t using: • Find the angle i by solving numerically • Solve for er1 using: • Compute HMA thickness using t1 and er1 Modified CMP Setup

44. Surface Reflection HMA/Base Reflection Base/Subgrade Reflection Reflection Overlap Surface Reflection WS/BM-25.0 Reflection OGDL/Base Reflection Base/Subgrade Reflection BM-25.0/OGDL Reflection Depth Resolution Enhancement WS BM-25.0 OGDL Base Measured Signal from: Thin layer interfaces not visible because of reflection overlap Synthesized Signal

45. Measured vs. Simulated Signal

46. Layer Thickness Estimation by Iteration Raw GPR Data Preprocessing Layer Thicknesses Layer Interface Detection Dielectric Properties Estimation

47. WS BM-25.0 OGDL Base Copper plates Detected Layer Interfaces Detection Results

48. Channel 1 Channel 2 Channel 1 Channel 2 GPR Data Analysis Software

49. Density Measurement with GPR • According to volumetric mixture theory, HMA dielectric constant depends on aggregate, binder and air volumes • Note: calibration coefficients (a and b) are determined • from field cores. • A drop in dielectric value may indicate a density change • 2GHz antenna is preferred • It has potential….it requires more investigation

50. Defects Detection with GPR • Segregation: locations of course-graded and dense-graded mixes has been reported • Stripping: additional reflections appear between surface and layer interface • Moisture content: relationship between dielectric constant and moisture content