Mitigation_of_Reflective_Cracks-Von_Quintus.ppt
- 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. Expanding the Realm of Possibility Presentation Focus 1. Reflective Cracking Overview & Study Products 2. Data Sources to Assess Mitigation Strategies 3. Findings/Summary Comments Products focused towards the practionioner.
- 3. Expanding the Realm of Possibility 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. Expanding the Realm of Possibility 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. Expanding the Realm of Possibility Reflection Cracking Mechanisms 1 Thermal expansion & contraction of joints. Thermal Induced Crack initiates & propagates in tension. 3 Differential vertical deflections. Traffic Induced Crack initiates & propagates in shear. 2 Curling of PCC slabs Thermal Induced Crack initiates & propagates in tension.
- 6. Expanding the Realm of Possibility Mitigation Methods 1. Modify Existing Surface: PCC – Rubblization, crack & seat HMA – Full-depth reclamation, mill-inlay, hot in place recycling, heater scarification 2. Cushion Layer: Open-graded HMA or crack relief layer, unbound aggregate layer. 3. Stress/Strain Absorbing Membrane Interlayer: Chip seal, DBST, fabrics, bond breaker 4. Reinforcement of HMA Overlay: Steel mesh, geogrids, fabrics 5. HMA Mix Modification: PMA, SMA 6. Crack Control: Saw and seal
- 7. Expanding the Realm of Possibility Products; Practicing Engineer 1. Research Report 2. Technical Guide 3. Decision Trees Existing Pavement—Rigid Pavement JPCP & JRCP Use Nondestructive Testing; AC 150/5370-11: Measure deflections across the joints & cracks with the FWD, ASTM D 4670 Use GPR for subsurface characterization, ASTM D 4748 Use differential vertical deflections across discontinuities to estimate load transfer. Moderate Load Transfer (0.01 to 0.05 in.) Poor Load Transfer (> 0.05 in.); LTE < 0.70 Good Load Transfer (< 0.01 in.); LTE > 0.80 Pavement Condition Assessment (FAA AC 150/5320-6, Chapters 4 & 6): Use Condition Survey to Define Cracking Extent & Severity;ASTM D 5340 Minor to Moderate Faulting (< 0.05 in.) Severe Faulting (> 0.15 in.) Extensive & Severe Mid-Slab Cracking Minor Mid-Slab Cracking Large Voids Exist Under PCC Minor to No Voids Under PCC 1. Rubbilize PCC, plus leveling course 2. Thick Cushion Layer 1. Stress/Strain Absorbing Interlayer 2. Asphalt-Rubber Modified Mixes 3. Reinforce HMA Overlay 4. Saw & Seal Joints in HMA Overlay 1. Fracture PCC, plus leveling course 2. Cushion Layer Subseal & fill voids under PCC Leave voids; no subsealing or filling voids Are Voids Present? Long Joint Spacing; >30 ft. Short Joint Spacing; <25 ft. 1. Fracture PCC, plus leveling course 2. Cushion Layer 3. Asphalt-Rubber Modified Mixes 4. Reinforce HMA Overlay 1. Rubbilize JPCP, plus level course 2. Rubbilize JRCP & Thick Cushion Layer 2. Rubblize PCC, plus leveling course 3. Cushion Layer 1. Assess Condition of Existing Pavement 2. Identify Mitigation Methods 3. Conduct LCCA to Select Strategy
- 8. Expanding the Realm of Possibility Products: Technical Guide Level 1 +Level 2 +Level 3 1. Condition surveys, PCI. 2. Destructive sampling; cores & borings. 3. DCP testing of support layers. 4. Deflection basin testing. 5. Differential vertical deflections; load transfer. 6. GPR – Thickness, voids, & other defects. 7. Horizontal movements at joints & cracks. 8. Laboratory testing of materials. Italic items were generally unavailable from data sources. Assess Condition of Existing Pavement
- 9. Expanding the Realm of Possibility Products: Technical Guide 1. Provides engineer/airport manager guidance in selecting appropriate mitigation methods based on condition of existing pavement. 2. Identifies key items for each method: advantages, design and construction issues/features. 3. Suggests inputs (design features & properties) to M-E based methods to determine overlay thickness based on mitigation strategy, climate, and traffic.
- 10. Expanding the Realm of Possibility Data Sources for Analyses 1. Literature & other documents (airfields & roadways). 2. Contacts & historical data from airfields; construction projects. 3. Previous rehabilitation projects for airfields. 4. Site visits.
- 11. Expanding the Realm of Possibility Data Sources for Analyses X X X X X X X X X X X X X X X XX X X X X X X X X X X X X X X XX XX X X Site Visits Previous Rehab Projects Data from Literature; airfields only X
- 12. Expanding the Realm of Possibility Assess Mitigation Methods bt a e RC 1 100 ■ Evaluating/comparing mitigation methods using: 1. Mechanistic-empirical methods & pavement responses. 2. Empirical methods to define effective overlay thickness. eff H a 75 . 0 5 . 3 915 . 0 37 . 3 689 . 0 eff H b Thickness Overlay Effective H years Age t eff ,
- 13. Expanding the Realm of Possibility Assess Mitigation Methods o Probability of Success – Number (%) of projects not exhibiting premature or accelerated reflective cracks. o Confidence or Risk – Number of projects where mitigation strategy has been used. Risk ob Rating s * Pr ■ Sufficient data unavailable to complete & define key factors limiting performance; project specific. ■ Technical Guide/Decision Trees prepared based on ratings of mitigation methods.
- 14. Expanding the Realm of Possibility Common Reasons for Poor Performance 1. Thin overlay and/or inappropriate rehab strategy for existing pavement condition & traffic. 2. Inadequate HMA overlay mixture properties to reduce crack deterioration (moisture damage, brittle, aging, etc.). 3. Inappropriate method selected for joint/crack condition.
- 15. Expanding the Realm of Possibility Summary Findings 1. No method always prevented reflective cracks, with exception of rubblization for PCC pavements and full depth reclamation for HMA pavements; if properly done. 2. Cost effective rehabilitation design to mitigate reflective cracks usually includes a combination of methods for rehab/mitigation strategy. 3. Complete an adequate pavement evaluation to determine rehab/mitigation strategy. 4. Four critical factors: (1) condition of existing pavement, (2) climate, (3) HMA overlay properties, and (4) design traffic (HMA overlay thickness).
- 16. Expanding the Realm of Possibility 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.