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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.

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Presentation on theme: "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."— Presentation transcript:

1 FAA Airport Pavement Working Group Meeting, April 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 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— 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 NORTHSOUTH inch P-154 Aggregate Base Experimental design included thickness variations, matched and mismatched joints

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

5 Date Passes SCI 08/01/ /03/ /10/ /11/ /24/ /28/ /13/ /14/ /19/ /22/ /04/ /29/ /02/ /03/ Triple Dual Tandem 57 in 54 in 50,000 lbs/wheel 230 psi tire pressure Test Item N Final Passes OL SCI UL SCI 8.6-in PCC OL 6.3-in PCC UL 5.6-in Aggregate Base Subgrade k=135 pci UL SCI = 100

6 Dual Tandem 57 in 54 in 50,000 lbs/wheel 230 psi tire pressure Test Item S1 08/04/ /08/ /10/ /09/ /11/ /13/ /22/ /26/ /02/ /03/ /14/ /29/ /31/ /19/ 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 UL SCI UL SCI = 100

7 FAA Airport Pavement Working Group Meeting, April

8 FAA Airport Pavement Working Group Meeting, April

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 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/ /19/ /21/ /03/ /05/ /07/ /10/ /11/ /19/ /11/ /16/ /18/ Date Passes SCI Final3 UnderlaySCI Beginning25

11 Dual Tandem 57 in 54 in 42.5k lbs/wheel 230 psi tire pressure Test Item S1 9.3-in PCC OL 6.3-in PCC UL 5.8-in Aggregate Base Subgrade k=135 pci 04/02/ Date Passes SCI 01/16/ /23/ /01/ /25/ /24/ /13/ /05/ /20/ /21/ /26/ /04/ /11/ UnderlaySCI Beginning23 Final8

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

13 FAA Airport Pavement Working Group Meeting, April 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” > ???

14 FAA Airport Pavement Working Group Meeting, April 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 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 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 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 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 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 = X SCI + ( 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 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 Underlay Modulus vs SCI

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

24 FAA Airport Pavement Working Group Meeting, April 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 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 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

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

29 FAA Airport Pavement Working Group Meeting, April 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 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 (Rollings, 1988)

32 FAA Airport Pavement Working Group Meeting, April

33 FAA Airport Pavement Working Group Meeting, April

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

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

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


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