1. Nondestructive Testing and Data Analysis Module 2-3

2. Learning Objectives  Describe pavement responses to load  List non-destructive testing (NDT) devices and characteristics  List factors that influence pavement deflection  Describe procedures for conducting NDT  Describe the uses of NDT data

3.  NDT - Valuable engineering tool for assessing: –Variability –Structural adequacy (in situ material properties)  Fast and produces repeatable results  Used by most states for project and some network level evaluation Introduction

4. Subgrade Soil Base/Subbase Surface SUR  SUB  SUR Axle Load  Pavement Responses Under Load

5. NDT Load “Strong” Pavement “Weak” Pavement  Strong vs. Weak Pavements

6. NDT Sensors NDT Load  Measurement of Surface Deflection r

7. Types of NDT Equipment  Static  Vibratory  Impulse  Surface wave propagation

8. “Static” Load Devices  Benkelman  California Traveling Deflectometer  La Croix Deflectograph Beam

9. Vibratory Equipment (steady state dynamic) Dynaflect Road Rater

10. m h k Impulse Equipment: Falling Weight Deflectometer

11. Typical FWD Equipment KUABDynatest JILSOther: Phonix

12. Rolling Wheel Deflectometer

13. Measures speed, amplitude, and wavelength Sensors Amplitude Spectral Analysis of Surface Waves (SASW)

14. Factors for Consideration in Selecting NDT Equipment  Operational characteristics  Data quality  Versatility  Cost

15. Factors That Influence Pavement Deflections  Load factors  Pavement factors  Climatic factors

16. Projected deflection:  40-kN = 0.25 mm Measured deflection:  40-kN = 0.35 mm 0 10 20 30 40 50 0.028 0.10 0.20 Measured 40-kN deflection Load (kN) Deflection (mm) 0.40 0.30 0.35 Load Factors (Stress Sensitivity) 0.25

17. Pavement Factors  Distress  Subsurface variations  Random variability

18. Climatic Factors  Temperature  Moisture  Frost penetration

19. Time DecJanFebMarAprMayJunJulAugSepOctNov Deflection Period of Deep Frost Period of Slow Strength Recovery Period of Rapid Strength Recovery Period of Strength Loss Seasonal Variation in Pavement Deflection

20.  NDT must be used in conjunction with information from distress survey  Accurate layer thickness information is essential  Time of testing –Time that best represents effective year-round condition is also good –Seasonal (year-round) testing is desirable Conducting NDT Surveys

21. Testing Locations and Frequency  Typically outer lane only – in the outer wheel path  Both directions - staggered  30 to 150 m (100 to 500 ft) intervals –More intensive testing may be used to investigate cause of distress –Excessive deflection in one area may indicate the need for intensive testing

22. Temperature Measurement  Needed for correction of deflections and backcalculated HMA modulus values  Develop deflection vs. temperature relationships using data from select sites –Drill hole to mid-depth and add oil –Measure deflection and air, surface and mid- depth temperature (hourly, if possible)  For every deflection point, measure air and pavement surface temperature

23. Uses of Deflection Testing Data  Uniformity of project –Design sections for rehabilitation –Locations for sampling / testing  Backcalculate layer moduli –Pavement layers –Subgrade soil resilient modulus

24. 0 1000 2000 3000 0.75 0.50 0.25 0 Distance Along Roadway (m) Maximum Deflection  (mm) Project Variability

25. Backcalculation… What is the origin? OUTPUT INPUT MODEL

26. L P L / 2 b h PL 3 48EI bh 3 12 I = δ  δ Simple Backcalculation Case

27. Layer Characteristics Surface NDT Load r Backcalculation Typical Pavement Case E11D1E11D1 E22D2E22D2 E33E33  Base / Subbase Subgrade Soil

28. Backcalculation Programs for HMA Pavements  Most are based on multi-layer elastic theory  Approaches: –Iterative solution –Deflection basin matching

29. Backcalculation - Rules of Thumb -  Deflections away from the load – mostly a function of E subgrade  Underlying “rigid” layers – do affect deflections and analysis results  Multiple bound layers – may not be a unique solution  Modulus of “thin” layers - may be difficult to determine

30. Typical Modulus Values Material General Range (MPa) Typical Value (MPa) HMA1,500 - 3,5003,000 PCC20,000 - 55,00030,000 ATB700 - 6,0001,500 CTB3,500 - 7,0005,000 LCB7,000 - 20,00010,000 Granular base100 - 350200 Granular soil50 - 150100 Fine-grained soil20 - 5030

31. Review  Why are we concerned about a pavement’s response to load?  What is the primary NDT device?  What are three factors that influence pavement deflection?  What is the typical NDT test spacing?  What are two primary uses for NDT data?

32. Key References  AASHTO. 1993. AASHTO Guide for Design of Pavement Structures.  AASHTO T256-77. “Standard Recommended Practice for Pavement Deflection Measurements.” Standard Specifications for Transportation Materials and Methods of Sampling and Testing, Part II.  NHI. 1994. Pavement Deflection Analysis. NHI Course No. 13127. Report No. FHWA-HI-94-021. Federal Highway Administration, Washington, DC.

33. Key References (cont.)  ASTM. 1999. “Nondestructive Testing of Pavements and Backcalculation of Moduli,” STP 1375, American Society for Testing and Materials, West Conshohoken, PA