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Warm Mix Asphalt & Recycled Asphalt Pavements

Warm Mix Asphalt & Recycled Asphalt Pavements. Cassandra Simpson | Greg Stephenson Robert Patience | Rick Hennig. Background to US Mixes. Virgin Source Aggregates “Combined” Grading (eg passing ½” retained ¼”) More Variability in US Virgin Mixes Fractionated RAP (Single Size)

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Warm Mix Asphalt & Recycled Asphalt Pavements

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  1. Warm Mix Asphalt&Recycled Asphalt Pavements Cassandra Simpson | Greg Stephenson Robert Patience | Rick Hennig

  2. Background to US Mixes • Virgin Source Aggregates • “Combined” Grading (eg passing ½” retained ¼”) • More Variability in US Virgin Mixes • Fractionated RAP (Single Size) • Reduces Variability in Final Mix • More Important at High Percentages of RAP • Helps in Design of High RAP Mixes

  3. Background to US Mixes Who owns the RAPandWhat are they doingwith it????

  4. Green Highway Partnership Major Partners: EPA, FHWA, and MD SHA • Integrates transportation functionality and ecological sustainability • Green Highways are: • Built with permeable materials • Constructed with recycled materials • Designed using cutting edge technologies to protect habitats & ecosystems • www.greenhighways.org 4

  5. Stabilise Cost More Consistent Material (Fractionated RAP) Environmentally Responsible High Quality Material RAP is Old Material?! Rocks in S. California ~14 million years Bitumen ~10 to 200 million years Still high quality aggregate. Bitumen is still coating the aggregate. Advantages of Recycling

  6. Improved working conditions Less fumes and emissions Less energy consumption Decreased binder ageing during production Reduced temperature allows more RAP? Is Warm Mix the Future for Asphalt? 100% of production could be WMA in the future with up to 50% WMA within 5 years Advantages of Warm Mix Asphalt

  7. WMA + RAP - Benefits • Production (temperature) • Product (aggregate and binder) • Aged binder in RAP • Works as an anti-stripping agent • Improves TSR values • Environmental (recycle, landfill, etc) www.aapa.asn.au

  8. States That Have Tried WMA & Higher RAP

  9. RAP and WMA Lower mixing temperature resulted in less oxidation & light oil remaining in virgin bitumen Steam produced from drying RAP creates inert atmosphere Recovered binder from WMA with 25% RAP has same rheological properties as recovered binder from HMA with virgin bitumen

  10. Specified Binder 58-28 25% RAP

  11. RAP and WMA Will RAP and New Binders Mix at WMA Process Temperatures? Co-mingled binder properties? Interfacial Mixing Study Atomic Force Microscope Lab Mixing Studies Dynamic Modulus Evaluation

  12. NCHRP 9-43 - Sasobit

  13. WMA + RAP - US Practices Texas DoT – 33%-50% of all WMA work contain RAP North Carolina (Boggs) – only use WMA with RAP (15-20%) South Carolina (Banks) – view RAP inclusion as insurance California (Granite) – a means of achieving a similar binder to that of hotmix

  14. Superpave Guidelines Guidelines for hotmix and potential guidelines for WMA + RAP Tier 1: Up to 15% RAP (25% for WMA) use specified binder grade Tier 2: 15%-25% RAP (25% - 35% for WMA) use one full binder grade lower Tier 3: Over 25% RAP (>35% for WMA) use blending charts to determine required binder grade

  15. Determining Blended Binder Grade

  16. Production and Paving Notes Work to minimize aggregate moisture. Make sure the burner is tuned for the temperature. Keep bag-house temperature above condensation point - higher % RAP in WMA helped increase temperature of bag house. Consider superheating aggregate ahead of RAP. Follow normal placement practices.

  17. Future National Research? • Short Term Ageing of WMA Binders During Production (laboratory ageing protocols)* • Differences Between Field Produced WMA and HMA Volumetric Properties • Increased RAP Usage with WMA* • Shingle Use with WMA* • Rubber Use with WMA* • More to come …??

  18. High RAP Mix Design • NCHRP 9-46 Mix Design and Evaluation Procedure for High Reclaimed Asphalt Pavement Content in Hot Mix Asphalt • Objective: Develop mix design method and specification for HMA containing up to 50% RAP. 18 18

  19. Questions?

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