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Analysis of Test Slab Failure Data

Analysis of Test Slab Failure Data. David R. Brill FAA Airport Technology R&D Branch, AAR-410 William J. Hughes Technical Center, Atlantic City, NJ Airport Pavement Working Group Meeting Sheraton Atlantic City Convention Center Hotel February 2, 2005. Objectives.

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Analysis of Test Slab Failure Data

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  1. Analysis of Test Slab Failure Data David R. BrillFAA Airport Technology R&D Branch, AAR-410William J. Hughes Technical Center, Atlantic City, NJ Airport Pavement Working Group MeetingSheraton Atlantic City Convention Center HotelFebruary 2, 2005 1

  2. Objectives • Quantify CC2 rigid test item performance and failure using the SCI concept. • Relate to historical rigid full-scale tests (Lockbourne, Sharonville, MWHGL etc.). • Compare with current failure model. • Analyze effects of test variables: • Support type (stabilized base vs. conventional). • 4-wheel vs. 6-wheel. • Traffic on outside lane. 2

  3. CC2 Test Item Layout 3

  4. Construction Cycle 2 – Trafficking MRC North South • MRC trafficking stopped on June 24, 2004 (north side after 12,675 passes and south side after 5,402 passes. • A total of 96 cracks were detected and 20 cores taken.

  5. MRG After 31,020 Passes Construction Cycle 2:Trafficking Test Item MRG 5

  6. MRG After 31,020 Passes 6

  7. MRS After 30,996 Passes Construction Cycle 2:Trafficking Test Item MRS 7

  8. MRS After 30,996 Passes 8

  9. CC2 Test Items - Results • Full-scale traffic testing began on 4/27/04. • Trafficking ended 12/10/04. • Passes completed: • Top-down cracking has not been eliminated, but bottom-up longitudinal cracks have occurred in the lane receiving loading from both lines of tires. 9

  10. Performance Monitoring • Visual Distress Surveys. • ASTM D 5340-93 and FAA AC 150/5380-6. • Daily up to 10,000 passes. Weekly after 10,000 passes. • Embedded Sensors. • Responses monitored for early indication of cracking. • Nondestructive Tests. • HWD every 15 wanders (990 passes) up to 10,000 passes. Every 30 wanders after 10,000 passes. • Destructive Testing. • Cores to investigate origin of cracks. 10

  11. Structural Condition Index (SCI) • Rollings (1988) • SCI is structural component of rigid PCI. • Only load related distress types are considered (e.g., L/T/D cracks, corner breaks, shattered slab). • SCI is always equal to or higher than PCI for the same pavement feature. • Joint and corner spalling was excluded from the SCI computation for CC2 test items. 11

  12. Micro PAVER Computations • Record structural distresses based on visual surveys. • Treat each test item (north side or south side) as a sample unit. • Follow ASTM procedures for counting distresses and assigning severity levels. 12

  13. MRS North - Shattered Slab MRG North - Corner Spall MRG South - Longitudinal Crack Intersecting Corner Break MRS North - Long. & Diag. Cracks CC2 Test Item Distresses 13

  14. SCI Versus Coverage Analysis • Plot SCI as a function of applied coverages. • P/C ratio is computed from wander pattern. • All slabs in sample unit versus inside traffic lane only. • Obtain linear regression of SCI versus log(C). • Intercept with SCI=100 line yields CO (cov. to 1st crack). • Intercept with SCI=0 line yields CF (cov. to full failure). • New rigid design concerned with coverages to SCI=80. • Lower portions of failure curve (below SCI = 80) are important for overlay designs. 14

  15. Test Item MRC - SCI versus Coverages (All Distresses) PRELIMINARY DATA 15

  16. Test Item MRC - SCI versus Coverages (Center Traffic Lane Distresses Only) PRELIMINARY DATA 16

  17. Test Item MRS - SCI versus Coverage(Center Traffic Lane Distresses Only) PRELIMINARY DATA 17

  18. Test Item MRG - SCI versus Coverage(Center Traffic Lane Distresses Only) SCI = -247.03 log(C) + 941.57R2 = 0.9636 SCI = -246.96 log(C) + 935.11R2 = 0.9647 PRELIMINARY DATA 18

  19. CC2 Test Strip - SCI versus Coverage(S Slab Distresses Only) PRELIMINARY DATA C SLABS S SLABS 19

  20. Summary of SCI vs. Coverage 20

  21. Regression Data for SCI vs. Log of Coverages (preliminary) 21

  22. Design Factor vs. Coverages • Design Factor (DF) = ratio of concrete flexural strength to maximum calculated bending stress. • LEDFAA model based on Rollings (1988) regression: • DF = 0.5234 + 0.3920 log (CO) coverages to onset of cracking • DF = 0.2967 + 0.3881 log (CF) coverages to full failure (SCI 0) • Recompute design factors for all test items using FEDFAA (3D-FEM) edge stress. • Evaluate parameters including 7 new NAPTF data points. • Preliminary analysis - design factors subject to change as we continue to characterize the material properties. 22

  23. Recalculate Design Factors(Historic Full-Scale Test Data) Original Regression Recalculated Using FEDFAA Edge Stress 23

  24. Design Factor vs. Coverages (Coverages to Complete Failure, SCI=0) PRELIMINARY DATA 24

  25. Design Factor vs. Coverages (Coverages to Onset of Failure, SCI=100 -) PRELIMINARY DATA 25

  26. Current Efforts • Finalize material characterization (e.g., concrete strength, subgrade properties) for design factor computation. • Finalize “best fit” parameters for FAARFIELD rigid failure model from full-scale test data. • Re-evaluate current base stiffness compensation model considering: • full-scale test results showing straight-line trend. • improved ability of 3D-FEM model to give accurate stresses for stabilized base structures. 26

  27. Questions? 27

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