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. 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 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

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: °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

14. 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

16. 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

17. 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

18. 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