Download - Warm Mix Asphalt & Recycled Asphalt Pavements

AAPA 2010 Study Tour – WMA RAP

Warm Mix Asphalt&

Recycled Asphalt Pavements

Cassandra Simpson | Greg Stephenson Robert Patience | Rick Hennig


Background to US Mixes

• Virgin Source Aggregateso “Combined” Grading (eg passing ½” retained ¼”)oMore Variability in US Virgin Mixes

• Fractionated RAP (Single Size)o Reduces Variability in Final MixoMore Important at High Percentages of RAPo Helps in Design of High RAP Mixes


Background to US Mixes

Who owns the RAPand

What are they doingwith it????

AAPA 2010 Study Tour – WMA RAP4

Green Highway Partnership Major Partners: EPA, FHWA, and MD SHA

• Integrates transportation functionality and ecological sustainability

• Green Highways are:o Built with permeable materialso Constructed with recycled materialso Designed using cutting edge technologies to

protect habitats & ecosystems

www.greenhighways.orgwww.greenhighways.org


Advantages of Recycling

• Stabilise Cost• More Consistent Material (Fractionated RAP)• Environmentally Responsible• High Quality Material

o RAP is Old Material?!• Rocks in S. California ~14 million years• Bitumen ~10 to 200 million years

o Still high quality aggregate.o Bitumen is still coating the aggregate.


Advantages of Warm Mix Asphalt

• Improved working conditions• Less fumes and emissions• Less energy consumption• Decreased binder ageing during production

o 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


WMA + RAP - BenefitsWMA + RAP - Benefits

• Production (temperature)• Product (aggregate and binder)

o Aged binder in RAP• Works as an anti-stripping agent• Improves TSR values

• Environmental (recycle, landfill, etc)

www.aapa.asn.au


States That Have Tried WMA & Higher RAP


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


Specified Binder 58-2825% RAP


RAP and WMA

• Will RAP and New Binders Mix at WMA Process Temperatures?o Co-mingled binder properties?

• Interfacial Mixing Studyo Atomic Force Microscope

• Lab Mixing Studieso Dynamic Modulus Evaluation


NCHRP 9-43 - Sasobit

10

100

1000

10000

39.2

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39.2

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68 F

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68 F

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95 F

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Testing Condition

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Measured Estimated for Complete Mixing


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


Superpave Guidelines

• Guidelines for hotmix and potential guidelines for WMA + RAP

• Tier 1: Up to 15% RAP (25% for WMA)o use specified binder grade

• Tier 2: 15%-25% RAP (25% - 35% for WMA)o use one full binder grade lower

• Tier 3: Over 25% RAP (>35% for WMA)o use blending charts to determine required binder

grade


Determining Blended Binder Grade


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.


• 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 …??

Future National Research?


1818

High RAP Mix DesignHigh 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.


Questions?