1. AAPTP 05-04— TECHNIQUES FOR MITIGATION OF REFLECTIVE CRACKING OF HMA AIRFIELD PAVEMENTS
Harold L. Von Quintus, P.E., ARA
Jagannath Mallela, ARA
Robert L. Lytton, P.E., Consultant
April 21, 2010

2. Products focused towards the practionioner.
Presentation Focus
Reflective Cracking Overview & Study Products
Data Sources to Assess Mitigation Strategies
Findings/Summary Comments
Products focused towards the practionioner.

3. Project Objective
Develop technical guidance on the selection of strategies (materials & procedures) to resist, control, or delay reflective cracking of HMA overlays for airfield pavements.

4. Reflective Cracks
Overlay cracks initiate in the weakest area of pavement (existing cracks) & propagate along the path of least resistance and greatest stress concentrations.

5. Reflection Cracking Mechanisms1
Thermal expansion & contraction of joints.
Thermal Induced
Crack initiates & propagates in tension. 2
Curling of PCC slabs
Thermal Induced
Crack initiates & propagates in tension. 3
Differential vertical deflections.
Traffic Induced
Crack initiates & propagates in shear.

6. Mitigation Methods Modify Existing Surface:
PCC – Rubblization, crack & seat
HMA – Full-depth reclamation, mill-inlay, hot in place recycling, heater scarification
Cushion Layer: Open-graded HMA or crack relief layer, unbound aggregate layer.
Stress/Strain Absorbing Membrane Interlayer: Chip seal, DBST, fabrics, bond breaker
Reinforcement of HMA Overlay: Steel mesh, geogrids, fabrics
HMA Mix Modification: PMA, SMA
Crack Control: Saw and seal

7. Products; Practicing Engineer
Research Report
Technical Guide
Decision Trees
1. Assess Condition of Existing Pavement
2. Identify Mitigation Methods
3. Conduct LCCA to Select Strategy

8. Products: Technical Guide
Assess Condition of Existing Pavement
Level 1
+Level 2
+Level 3
Condition surveys, PCI.
Destructive sampling; cores & borings.
DCP testing of support layers.
Deflection basin testing.
Differential vertical deflections; load transfer.
GPR – Thickness, voids, & other defects.
Horizontal movements at joints & cracks.
Laboratory testing of materials.
Italic items were generally unavailable from data sources.

9. Products: Technical Guide
Provides engineer/airport manager guidance in selecting appropriate mitigation methods based on condition of existing pavement.
Identifies key items for each method: advantages, design and construction issues/features.
Suggests inputs (design features & properties) to M-E based methods to determine overlay thickness based on mitigation strategy, climate, and traffic.

10. Data Sources for Analyses
Literature & other documents (airfields & roadways).
Contacts & historical data from airfields; construction projects.
Previous rehabilitation projects for airfields.
Site visits.

11. Data Sources for AnalysesX X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X
Site Visits
Previous Rehab Projects
Data from Literature; airfields only X

12. Assess Mitigation Methods
Evaluating/comparing mitigation methods using:
Mechanistic-empirical methods & pavement responses.
Empirical methods to define effective overlay thickness.
Insufficient material properties & data.

13. Assess Mitigation Methods
Sufficient data unavailable to complete & define key factors limiting performance; project specific.
Technical Guide/Decision Trees prepared based on ratings of mitigation methods.
Probability of Success – Number (%) of projects not exhibiting premature or accelerated reflective cracks.
Confidence or Risk – Number of projects where mitigation strategy has been used.

14. Common Reasons for Poor Performance
Thin overlay and/or inappropriate rehab strategy for existing pavement condition & traffic.
Inadequate HMA overlay mixture properties to reduce crack deterioration (moisture damage, brittle, aging, etc.).
Inappropriate method selected for joint/crack condition.

15. Summary Findings
No method always prevented reflective cracks, with exception of rubblization for PCC pavements and full depth reclamation for HMA pavements; if properly done.
Cost effective rehabilitation design to mitigate reflective cracks usually includes a combination of methods for rehab/mitigation strategy.
Complete an adequate pavement evaluation to determine rehab/mitigation strategy.
Four critical factors: (1) condition of existing pavement, (2) climate, (3) HMA overlay properties, and (4) design traffic (HMA overlay thickness).

16. Acknowledgements Monte Symons –AAPTP Project Manager.
AAPTP Technical Panel – Darrell Bryan, Rodney Joel, John Harvey, & Stan Herrin.
Jim Hall, ARA – Identification of airfield projects, historical data, etc.
Bill Weiss, ARA – Field surveys & site visits.
Other ARA personnel.