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RAS Research Update

RAS Research Update. Dr. Richard Willis National Center for Asphalt Technology at Auburn University March 11, 2014. Background. Mix design considerations Binder Quantity and quality Aggregate Quantity and quality Volumetrics Air voids Voids in mineral aggregate

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RAS 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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