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 Level 3 – Mixes are optimized for performance while maintaining volumetric criteria

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

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

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

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

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

Intermediate Stiffness @ 25C 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 @ 25C Target   64 – 22 <5000 kPa Stiffness Limit 40% RAP 82 – 16 82 – 21 6323 kPa Brittle 100% RAP 70 – 16 75 – 21 1690 kPa 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 T322 to assess strength and flexibility of mix at low temperatures

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

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

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

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

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

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

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