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Enhancing Asphalt Mix Design with Recycled Materials: Research Update

Explore mix design considerations, RAP, RAS, and binder qualities in asphalt mixtures for better performance. Learn about deleterious materials and design limitations.

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Enhancing Asphalt Mix Design with Recycled Materials: Research Update

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  1. RAS Research Update Dr. Richard Willis National Center for Asphalt Technology at Auburn University March 11, 2014

  2. Background • Mix design considerations • Binder • Quantity and quality • Aggregate • Quantity and quality • Volumetrics • Air voids • Voids in mineral aggregate • Voids filled with asphalt • Dust

  3. Things to Consider RAP RAS 19 – 36% asphalt 2 – 15% fibers 20 – 38% mineral aggregate 8 – 40% mineral filler • 3 – 6 % asphalt binder • 94 – 97% stone

  4. What Affects Mix Design and Mixture Quality? • Shingle type • Shingle gradation • Shingle quantity • Deleterious materials

  5. Shingle Type Manufacturer’s Waste Post-Consumer Commonly 20-40 years old Oxidized asphalt Nails and other deleterious materials Might contain asbestos Must conform to EPA’s NESHAP and other local requirements • New shingles with less oxidation • No contaminants • No asbestos

  6. Shingle Gradation • Oversized shingles affect • Asphalt mobilized • Mixture consistency

  7. Shingle Aggregate Gradation • RAS Aggregate must be accounted for in new mix design • AASHTO – Assumes gradation • Does it matter if your RAS has a different gradation?

  8. RAS Quantity • Most states use between 3 – 5 percent RAS • AASHTO Recommendations • If greater than 30 percent is shingle binder, must evaluate the blended binder to ensure performance grade (MP 15-09) • Possibly effected by grind size

  9. Deleterious Materials • Material retained on #4 sieve • AASHTO • Total deleterious < 3% • Lightweight < 1.5% • Some states < 0.5% • Cleaner stockpiles = better mixtures

  10. Deleterious Materials • Example specification (TEX-217-F Part III) • Oven dry sample • Sample 1000 g = WT • Weigh Pan and pour sample over pan • Magnet on pan catches metal pieces in shingle • Weigh metal pieces = M

  11. Deleterious Materials • Sieves Used: 3/8”, No. 4, No. 8, No. 30 • Shake sample for 10 minutes • Discard – No. 30 material • Test material retained on each sieve for deleterious materials (wood, paper, plastic, felt paper) • Manual separation • Weigh material removed from RAS for each sieve • Deleterious materials on 3/8” sieve =N3/8

  12. Deleterious Materials • P = percent of deleterious matter by weight • M = weight of material retained by magnet, g • N# = weight of deleterious substance on sieve, g

  13. Design Considerations • How do I determine the specific gravity of the RAS? • How much binder is in the RAS? • How much of that binder am I actually getting?

  14. Shingle Specific Gravity Peregrine et al., 2011

  15. How Much Binder is in the RAS? • Chemical extraction vs. Ignition Oven • Chemical Extraction: • Do I get all of the RAS? • Ignition oven: • Do I burn off other organic matter? • AASHTO – Must use chemical extraction • Virginia – Developed ignition oven correction factor

  16. Shingle Binder Contribution What’s the truth?

  17. What Can Affect Binder Availability? • Size of RAS • Where is the RAS introduced • Aggregate temperature • Binder temperature • Mixing time • Moisture content! Schroer 2009

  18. AASHTO Methodology • Perform volumetric mix design on a mix which contains all components but RAS • Perform a second mix design on a RAS mixture • RAS added at ambient temperature to aggregate • Should I heat the RAS overnight at 140F and then preheat for two hours at mix temp? • Determine the difference between the optimum asphalt content of virgin and RAS mixtures, Δ

  19. AASHTO Methodology • If Δ is positive, RAS is contributing binder • Multiply the percentage of shingle binder in the RAS by the percent RAS in the mix = total available binder • Divide Δ by total binder available • Correct shingle asphalt binder availability factor

  20. Limitations of Methodology • Assumes • Differences in virgin and RAS mix is only due to shingle binder and not • Fibers • Aggregate Townsend et al., 2007

  21. Performance Grade • When using high amounts of reclaimed binder, do I need to use a softer virgin binder? • Blending charts

  22. Performance Grade • Challenge: • How do I determine the Performance Grade? • Too stiff for water controlled DSRs • BBRs can be difficult to make

  23. Are Volumetrics Enough? • Rutting • Flow number • Hamburg • Asphalt Pavement Analyzer • Cracking • Energy ratio • Semi-circular bend (low and intermediate) • TSRST or IDT Creep Compliance • Overlay Tester • Beam fatigue or S-VECD

  24. Research Plan Outline • Phase I • Volumetrics of 5% RAS Mixture & Temperature Study • Phase II • Volumetrics of Alternate RAS Breakdown Mixtures • Investigation of results and additional testing • Phase III • Performance testing of all mixtures

  25. Phase I • Lab mixed lab compacted 5% RAS Mixture • Based on Lee County Road Section 24 • Volumetric samples mixed at: • 350°F, 325°F, 300°F, 275°F, 250°F, & 225°F • Aged and conditioned at 25 °F below mixing temperature

  26. Phase I - Results

  27. Phase II • Volumetrics of Alternate RAS Breakdown Mixtures • 5% RAS equivalent recovered shingle aggregate • 5% RAS equivalent recovered shingle binder • Control mixture matched to Lee County Road 159 Section 19 (L-19)

  28. Phase II – 5% RAS Aggregate • Mix design equivalent to original 5% RAS design BUT uses recovered shingle aggregate and fibers instead of whole shingles

  29. Phase II – 5% RAS Binder • Mix design similar to original 5% RAS design BUT no shingle aggregate or fibers were used • Other blend percentages were divided by 95% to maintain aggregate structure • Recovered RAS binder was added equivalent to the amount of binder from 5% RAS • 100% binder activation and blending assumed

  30. Phase II – Control • 0% RAS in Mix Design • Matched to Lee County Road 159 Section 19 • Same aggregates and similar gradation to the other mixtures

  31. Further Investigations • Dry Mixing 5% RAS Samples • Three mixed for one minute • One washed and graded • One aged for two hours • One mixed for two minutes • Large Shingles still visible loosely coated with fines • Color change between un-aged and aged sample

  32. Further Investigations • Shingles still visible and intact • +#4 +#16

  33. Further Investigations • Fine aggregate color change • Un-aged Aged

  34. Conclusions • Temperature Study • Temperature has a significant impact on volumetrics • The 5% RAS mixture has high variability due to either the aggregate stockpiles, the inclusion of RAS, or both • Alternate Mixtures • RAS aggregate and fibers had a slightly lower binder content (6.2%) • Control mix, 5% RAS and RAS binder mixtures all had approximately 6.4% optimum binder content

  35. Conclusions • Further investigations • Dry mixing experiment indicated that during mixing little to no blending occurs • The color change may indicate that activation may be more prevalent during the aging of the mixture

  36. Thank you!NCAT report 13-07: RAS Characterization: Best Practiceswww.ncat.us J. Richard Willis (334) 844-7301 willi59@auburn.edu

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