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

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.

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.

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

Reflection Cracking Mechanisms 1 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.

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

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

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.

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.

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

Data Sources for Analyses 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 X Site Visits Previous Rehab Projects Data from Literature; airfields only X

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

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.

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.

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).

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.