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Performance Assessment of 100% Recycled Hot Mix Asphalt

Performance Assessment of 100% Recycled Hot Mix Asphalt. Dr. J. Richard Willis National Center for Asphalt Technology. Background. Strategic Highway Research Program (SuperPave) mix design Level 1 – Purely volumetric Level 2 – Volumetrics and some performance testing

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Performance Assessment of 100% Recycled Hot Mix Asphalt

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  1. Performance Assessment of 100% Recycled Hot Mix Asphalt Dr. J. Richard Willis National Center for Asphalt Technology

  2. Background • Strategic Highway Research Program (SuperPave) mix design • Level 1 – Purely volumetric • Level 2 – Volumetrics and some performance testing • Level 3 – Mixes are optimized for performance while maintaining volumetric criteria

  3. Background • Most agencies use Level 1 or basic Level 2 • Transition to Level 3 and performance tests to • Assure long term performance • Enable higher recycled contents • Design high performing materials • Volumetrics aren’t enough

  4. 100% Recycled HMA • 100% of fine and coarse aggregate from RAP • 90% of asphalt binder from RAP • 10% of binder from recycling agent (RA) • Softens and rejuvenates aged RAP binder • Low viscosity oil • Requires new understanding of mix design within SuperPave system

  5. Objective • Summarize performance tests conducted on 100% RAP mixtures • Produced by Green Asphalt, LLC • New York City • 2011 – 2014 • Compare to established acceptance criteria • Evaluate suitability of 100% RAP mixtures for mainline projects

  6. Binder Grade • SuperPave performance graded binders • Ensure binder is not too stiff at low and intermediate temperatures • – premature cracking • Ensure binder is not too soft at high temperatures • – rutting susceptibility • RAP binders are stiffer due to aging • Oxidation and loss of oils • Rutting is not concern with conventional mixes

  7. 100% RAP HMA Extracted Binder Grade • Two mixtures evaluated • Testing at NCAT • Binder extracted (centrifuge) and recovered (Roto-VAP) • Binder tested – AASHTO M320

  8. 100% RAP HMA Binder Grade • RA improved performance of 100% RAP mixtures at all temperatures • Binder stiffness at intermediate temperature • critical to mixture cracking resistance

  9. Low Temperature Performance • Low temperature properties critical in northern climates • Binder properties alone not enough to determine mixture resistance to low temperature cracking • AASHTO T322 to assess strength and flexibility of mix at low temperatures

  10. Low Temperature Performance • 100% RAP mix placed on 26th Street in New York City • AASHTO T322 to determine critical low temperature • Critical NYC temp: -22°C • Extracted binder: -21°C • Mixture: -29.44°C

  11. Reflective Cracking Performance • Overlays are common maintenance technique • Reflective cracking is common distress • Previous cracks moving through new pavement • Overlay tester • Assess reflective cracking resistance of asphalt over concrete

  12. Reflective Cracking Resistance • Repeated loading at a singular temperature one strain level • 0.025 inches • 25°C • Analysis: Crack propagation • Output: Cycles to failure, Nf

  13. Rutting Performance • Rutting is a mixture stability problem • Hamburg Wheel Tracking Test is gaining popularity in assessing rutting resistance • AASHTO T324 • Temperature: 50°C • Influenced by intermediate stiffness

  14. Moisture Susceptibiity • AASHTO T283 • Tensile strength ratio calculated on cores, field mix, and lab mix • Ratio of conditioned to unconditioned mix was greater than 0.99 for all mixtures

  15. Summary • 100% RAP mixtures were able to either outperform and/or pass standard requirements for • Low temperature binder performance • Low temperature mixture performance • Reflective cracking • Rutting • And moisture susceptibility

  16. Recommendations • Choose recycling agent dose to balance cracking resistance with rutting susceptibility • Conduct field trials and evaluate actual pavement performance • Develop test program that ensures all mixes will perform satisfactorily without limiting recycled content in standard specifications

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