1. FAA Airport Pavement Working Group Meeting, April 2012 1 1 Concrete Overlay Research Shelley Stoffels, D.E., P.E. Lin Yeh, PhD FAA Airport Pavement Working Group Meeting, April 2012 Measured Responses Gears Layer Interactions Performance SCI

2. FAA Airport Pavement Working Group Meeting, April 2012 2 2 6 inch OL 10 inch SL 7.5 inch OL 7.5 inch UL High-strength SubgradeLow-strength Subgrade 9 inch OL 6 inch UL Medium-strength Subgrade Baseline Experiment—2006 9 inch OL 6 inch OL 10 inch SL 7.5 inch OL 7.5 inch SL High-strength SubgradeLow-strength Subgrade 6 inch SL Medium-strength Subgrade SCI Validation Study—2007/2008 CC4 conducted through IPRF consisted of two overlapping experiments (QES)

3. FAA Airport Pavement Working Group Meeting, April 2012 3 3 NORTHSOUTH 55 12.5 10 12.5 6-inch P-154 Aggregate Base Experimental design included thickness variations, matched and mismatched joints

4. FAA Airport Pavement Working Group Meeting, April 2012 4 4 North test items were loaded with triple dual tandem and South test items with dual tandem 10.25 in. Test Item Structural Section Overlay Slab Thickness, mm Underlay Slab Thickness, mm Loading Gear N11229152 Triple Dual Tandem N22190 Dual Tandem N33152254 Triple Dual Tandem S11229152Dual Tandem S22190 Triple Dual Tandem S33152254Dual Tandem

5. Date Passes SCI 08/01/062046 80 4 4 6 6 88 10 08/03/062574 73 08/10/062772 68 08/11/063234 63 08/24/063234 57 08/28/063234 46 09/13/063234 39 09/14/063744 31 09/19/064552 24 09/22/065146 19 08/04/062574 73 09/29/065146 16 10/02/065146 14 10/03/065146 12 Triple Dual Tandem 57 in 54 in 50,000 lbs/wheel 230 psi tire pressure Test Item N1 0 -12.5-25 Final Passes OL SCI 5146 14 32 UL SCI 8.6-in PCC OL 6.3-in PCC UL 5.6-in Aggregate Base Subgrade k=135 pci -5-17.5 -30 1 2 3 4 5 6 7 8 9 10 11 12 UL SCI = 100

6. 4 4 6 6 88 10 0 12.5 25 Dual Tandem 57 in 54 in 50,000 lbs/wheel 230 psi tire pressure 5 17.5 30 7 8 9 10 11 12 1 2 3 4 5 6 Test Item S1 08/04/063168 93 08/08/063432 85 08/10/064356 76 08/09/063894 78 08/11/064818 67 09/13/065016 54 09/22/068116 46 09/26/06 9370 32 10/02/0611614 16 10/03/0612142 7 09/14/065526 51 09/29/0611020 22 10/31/0612142 7 09/19/068116 50 Date Passes SCI 8.7-in PCC OL 6.3-in PCC UL 5.8-in Aggregate Base Subgrade k=135 pci Final Passes OL SCI 12142 7 39 UL SCI UL SCI = 100

7. FAA Airport Pavement Working Group Meeting, April 2012 7 7

8. FAA Airport Pavement Working Group Meeting, April 2012 8 8

9. 12/18/06 Structural Section 1 02/20/07 Transition 1N-7U 1N-8U 1N-9U 1N-10U 1N-11U 1N-12U 1N-1U 1N-2U 1N-3U 1N-4U 1N-5U 1N-6U 1S-7U 1S-8U 1S-9U 1S-10U 1S-11U 1S-12U 1S-1U 1S-2U 1S-3U 1S-4U 1S-5U 1S-6U

10. 4 4 6 6 88 10 0 -12.5-25 -5-17.5 -30 1 2 3 4 5 6 7 8 9 10 11 12 Test Item N1 Triple Dual Tandem 57 in 54 in 42.5k lbs/wheel 230 psi tire pressure 9.3-in PCC OL 6.3-in PCC UL 5.6-in Aggregate Base Subgrade k=135 pci 11/14/07 3696 88 11/19/07 4422 83 11/21/07 4950 77 12/03/07 7194 68 12/05/07 7986 55 12/07/07 8712 51 12/10/07 9108 48 12/11/07 9504 42 12/19/07 11286 27 01/11/08 13398 26 01/16/08 14850 24 01/18/08 15510 12 Date Passes SCI Final3 UnderlaySCI Beginning25

11. 4 4 6 6 88 10 0 12.5 25 Dual Tandem 57 in 54 in 42.5k lbs/wheel 230 psi tire pressure 5 17.5 30 7 8 9 10 11 12 1 2 3 4 5 6 Test Item S1 9.3-in PCC OL 6.3-in PCC UL 5.8-in Aggregate Base Subgrade k=135 pci 04/02/08 33264 18 Date Passes SCI 01/16/08 14850 80 01/23/08 16316 80 02/01/08 19008 70 02/25/08 20328 58 03/24/08 31350 23 12/13/07 9966 88 03/05/08 24684 52 03/20/08 30096 31 03/21/08 30756 29 03/26/08 32604 20 02/04/08 19602 63 03/11/08 27126 46 UnderlaySCI Beginning23 Final8

12. FAA Airport Pavement Working Group Meeting, April 2012 12 12 Test Item Baseline Passes, k Baseline SCI SCI Val. Passes, k SCI Val. SCI North 15,100515,50012 North 25,1002435,30029 North 35,1002135,30027 South 112,100533,30018 South 216,4001142,80066 South 312,1002335,30039 Final Loading Status 50,000-lb wheel load42,500-lb wheel load

13. FAA Airport Pavement Working Group Meeting, April 2012 13 13 SCI Validation Study: Approximate Passes to SCI Values SCI Passes N1 9”/6” S1 9”/6” N2 7.5”/7.5” S2 7.5”/7.5” N3 6”/10” S3 6”/10” 8050001500010000230001250024000 6075002000015000>420001600030000 40100003000021000???2500035000

14. FAA Airport Pavement Working Group Meeting, April 2012 14 14 Preliminary Findings from CC4 Observations from Distress Surveys For unbonded overlay over intact slabs, the initial cracks were longitudinal, and longitudinal cracking, both top- down and bottom-up, predominated throughout testing. For unbonded overlay over damaged slabs, the initial cracks were longitudinal, but a variety of cracking progressed. Greatest distress concentrations in overlay over greatest distress in underlying.

15. FAA Airport Pavement Working Group Meeting, April 2012 15 15 Preliminary Findings from CC4 Observations from HWD Continued deterioration of the underlay slabs, in place throughout both experiments, could be seen in the progressive decrease of backcalculated moduli. After placement of the new overlay, the backcalculated stiffness for the upper layer was fully recovered. However, some of the underlying layers also exhibited an apparent (temporary) stiffened effect. The load transfer efficiency at mismatched joints deteriorated less than at matched joints in the same test item.

16. FAA Airport Pavement Working Group Meeting, April 2012 16 16 Preliminary Findings from CC4 Observations from Instrumentation The soil pressure cells during loading of the second overlay experienced significantly greater (normalized) responses than those in the initial testing. The ratio in magnitude of peak strain produced by the triple dual tandem and twin dual tandem gears is not inversely proportional to the number of passes to failure. The ratio of passes to achieve a given SCI is greater than can be explained only by the peak magnitude of the measured strains. For all ratios of overlay to underlay thickness, the peak strains from instrumentation were larger in the overlay than in the underlay. This corresponds to the observed relative distress progression.

17. FAA Airport Pavement Working Group Meeting, April 2012 17 17 Preliminary Findings from CC4 Comparisons to Design Models The test items loaded with the twin dual tandem consistently required more passes to achieve a given SCI level than the test items loaded with the triple dual tandem at the same wheel load. This reinforces that gross aircraft weight is an important factor. The thin overlay over thick overlay cross section performed better than anticipated. While the overlay deteriorated at a rate similar to that of the other test items, the underlay slabs had only minor distress at the end of the testing. The unbonded overlay data, consolidated from both experiments, did not follow the pattern of slowing deterioration shown by the Rollings relationship between Cn and SCI, instead following an almost linear trend. A likely explanation is the corresponding deterioration of the underlying slabs, resulting in decreasing support with increased cumulative passes.

18. FAA Airport Pavement Working Group Meeting, April 2012 18 18 Preliminary Findings from CC4 Relative Comparison to FAARFIELD The thick-over-thin test items did not perform as well as predicted. The effects of underlying cracking, in terms of reducing relative passes to an SCI of 80, were not as significant as expected. The relative differences in passes to an SCI of 80 for the twin dual tandem as compared to the triple dual tandem were greater. Stress estimations from FAARFIELD, in terms of relative values, corresponded to the relative degree of damage to the underlay versus overlay that was observed in the Baseline Experiment.

19. Damaged slab material characterization for stress computation Failure model for traffic prediction for concrete overlays FAARField

20. FAA Airport Pavement Working Group Meeting, April 2012 20 20 Based on data of six individual slab-on-subgrade structures (WES) Assumed 50% of a test item would have that distress to compute SCI FAARFIELD Cracked Slab Model (Rollings) E-Ratio = 0.02 + 0.0064 X SCI + (0.00584 X SCI) 2 E-Ratio: Damaged Modulus / Intact Modulus SCI: A rating based upon the observed structural distress (ASTM D5320) A. Structure and Materials Relationship between pavement condition and materials characterization

21. FAA Airport Pavement Working Group Meeting, April 2012 21 21 Model Assessment Backcalculation (BAKFAA) As-built thickness from level surveys supplemented with core data Seed modulus = design modulus Average modulus of 12 slabs = modulus of a test item

22. FAA Airport Pavement Working Group Meeting, April 2012 22 22 Underlay Modulus vs SCI

23. FAA Airport Pavement Working Group Meeting, April 2012 23 23 Underlay Modulus vs SCI

24. FAA Airport Pavement Working Group Meeting, April 2012 24 24 Relationship between SCI and elastic modulus based upon backcalculation results and distress surveys. Should relationships from backcalculations with elastic layer analysis be valid for use in finite element forward calculations? Rollings used only the maximum deflection due to the crack discontinuities. It is suggested that additional sensors be used for unbonded overlays. Relationship was developed for single slab, assuming half would be deteriorated. Field SCIs based upon sample units. Is SCI the only parameter having a significant effect on variation of elastic modulus? A key area of investigation is the re-examination of the SCI and modulus relationship and the possible development of a modified cracked slab model.

25. FAA Airport Pavement Working Group Meeting, April 2012 25 25 The Modulus “Side of the Equation” Backcalculation Approaches Layered elastic Plate theory 3D finite element Backcalculation Considerations Interlayer effects Interface conditions (bonded, unbonded) Overlay cracking Sources of Data Slab test data (WES) Full-scale rigid pavement data (CC2) Full-scale UBOL data (CC4)

26. FAA Airport Pavement Working Group Meeting, April 2012 26 26 The Distress “Side of the Equation” Exploratory Statistical Analysis Predictive Variables Selection Overlay Data Independent VariablesP-value Intercept0.00 Overlay Thickness, HOL0.79 LTE0.48 NP0.97 CD0.01 Test Item SCI0.18 CD^20.04 NP^20.89 SCI^20.86 ISM0.88 Independent VariablesP-value Intercept0.14 NP0.93 CD0.02 NP^20.11 CD^20.01 SCI0.83 SCI^20.46 SCI*HUL0.31 Underlay Thickness, HUL0.58 HBASE0.21 Underlay Data

27. FAA Airport Pavement Working Group Meeting, April 2012 27 27

28. FAA Airport Pavement Working Group Meeting, April 2012 28 28 Model Development Distress Type Effect (Failure Index)

29. FAA Airport Pavement Working Group Meeting, April 2012 29 29 D. Failure Model SCI = 80 is defined as failure (i.e. 50% low severity longitudinal crack) Current failure model has been developed based on rigid pavement. Can the same failure model be applied to unbonded concrete overlay design? The damage accumulation and failure model for unbonded concrete overlays is being reassessed. Given the two concrete pavement layers and the interaction of relative deterioration, another model may be more effective than that used for original pavements.

30. FAA Airport Pavement Working Group Meeting, April 2012 30 30 Traffic Prediction Model DF: Ratio between flexural strength and 75% of maximum tensile stress at bottom of a free slab under edge loading

31. FAA Airport Pavement Working Group Meeting, April 2012 31 31 (Rollings, 1988)

32. FAA Airport Pavement Working Group Meeting, April 2012 32 32

33. FAA Airport Pavement Working Group Meeting, April 2012 33 33

34. FAA Airport Pavement Working Group Meeting, April 2012 34 34 Traffic Prediction Model Development Explorations Proposed Design Factor for UBOL

35. FAA Airport Pavement Working Group Meeting, April 2012 35 35 Traffic Prediction Model Explorations

36. FAA Airport Pavement Working Group Meeting, April 2012 36 36 Traffic Prediction Model Explorations THANK YOU!