# Presentation: 799317

## 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

- February 1, 2005

## 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.

- February 1, 2005

## CC2 Test Item Layout

- February 1, 2005

## Construction Cycle 2 – Trafficking MRC

- 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.

- North

- South

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## Construction Cycle 2:Trafficking Test Item MRG

*Construction Cycle 2:**Trafficking Test Item MRG*

- MRG After 31,020 Passes

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## MRG After 31,020 Passes

- MRG After 31,020 Passes

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## Construction Cycle 2:Trafficking Test Item MRS

- MRS After 30,996 Passes

*Construction Cycle 2:**Trafficking Test Item MRS*

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## MRS After 30,996 Passes

- MRS After 30,996 Passes

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## 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.

- February 1, 2005

## 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.

- February 1, 2005

## 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.

- February 1, 2005

## 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.

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## CC2 Test Item Distresses

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## 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 *C**O* (cov. to 1st crack).
- Intercept with SCI=0 line yields *C**F* (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.

- February 1, 2005

## Test Item MRC - SCI versus Coverages (All Distresses)

- PRELIMINARY DATA

*Test Item MRC - SCI versus Coverages (All Distresses)*

- February 1, 2005

## Test Item MRC - SCI versus Coverages (Center Traffic Lane Distresses Only)

*Test Item MRC - SCI versus Coverages (Center Traffic Lane Distresses Only)*

- PRELIMINARY DATA

- February 1, 2005

## Test Item MRS - SCI versus Coverage(Center Traffic Lane Distresses Only)

*Test Item MRS - SCI versus Coverage**(Center Traffic Lane Distresses Only)*

- PRELIMINARY DATA

- February 1, 2005

## Test Item MRG - SCI versus Coverage(Center Traffic Lane Distresses Only)

*Test Item MRG - SCI versus Coverage**(Center Traffic Lane Distresses Only)*

- PRELIMINARY DATA

- SCI = -246.96 log(C) + 935.11R2 = 0.9647

- SCI = -247.03 log(C) + 941.57R2 = 0.9636

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## CC2 Test Strip - SCI versus Coverage(S Slab Distresses Only)

- S SLABS

- C SLABS

- PRELIMINARY DATA

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## Summary of SCI vs. Coverage

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

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## 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 (*C**O*)  *coverages to onset of cracking*
- DF = 0.2967 + 0.3881 log (*C**F*)  *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.

- February 1, 2005

## Recalculate Design Factors(Historic Full-Scale Test Data)

- Original Regression

- Recalculated Using FEDFAA Edge Stress

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## Design Factor vs. Coverages (Coverages to Complete Failure, SCI=0)

- PRELIMINARY DATA

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

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

- PRELIMINARY DATA

- February 1, 2005

## 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.

- February 1, 2005

## Questions?

- February 1, 2005