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 1

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

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 3

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 Super. Pave system 4

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 5

Binder Grade • Super. Pave 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 6

100% RAP HMA Extracted Binder Grade • Two mixtures evaluated • Testing at NCAT • Binder extracted (centrifuge) and recovered (Roto-VAP) • Binder tested – AASHTO M 320 7

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 Mixture Performance Grade True Grade Intermediate Stiffness @ 25 C Target 64 – 22 <5000 k. Pa Stiffness Limit 40% RAP 82 – 16 82 – 21 6323 k. Pa Brittle 8 100% RAP 70 – 16 75 – 21 1690 k. Pa Very Flexible

Low Temperature Performance • Low temperature properties critical in northern climates • Binder properties alone not enough to determine mixture resistance to low temperature cracking • AASHTO T 322 to assess strength and flexibility of mix at low temperatures 9

Low Temperature Performance • 100% RAP mix placed on 26 th Street in New York City • AASHTO T 322 to determine critical low temperature – Critical NYC temp: -22°C – Extracted binder: -21°C – Mixture: -29. 44°C 10

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 11

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

Texas Overlay Tester - Crack Propagation 10000 Overlay Cycles 1000 10 20 30 40 50 Percent RAP 60 70 80 90 100 NYSDOT 12. 5 mm NHDOT 12. 5 mm VTDOT 9. 5 mm Green Asphalt 6 F CORES NYCDOT 6 F LAB SAMPLES 13

Rutting Performance • Rutting is a mixture stability problem • Hamburg Wheel Tracking Test is gaining popularity in assessing rutting resistance • AASHTO T 324 • Temperature: 50°C – Influenced by intermediate stiffness 14

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Moisture Susceptibiity • AASHTO T 283 • 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 16

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 17

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 18