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
Fractionating RAP and non-fractionated raw materials

3. Who owns the RAP and What are they doing with it????
Background to US Mixes
Who owns the RAP and What are they doing with 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
Environmental issues are increasingly impacting on highway construction. The use of RAP and WMA are just some of the ways that these issues can be addressed.
Main driver for using RAP is economics & sustainability has become the new driver. 4

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

6. Advantages of Warm Mix Asphalt
Improved working conditions
Less fumes and emissions
Less energy consumption
Decreased binder ageing during production
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

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)
The main production benefit is the ability to run higher temperatures so that the exhaust gasses are at temperatures above their dew point (bag house).
Product benefits of WMA+RAP (which lead to improved performance) include:
Addressing the potential issue of the less aged WMA binder,
Increases the TSR of the resultant WMA+RAP blend
Ensures virgin aggregates are dry (due to super heating) prior to mixing with the virgin binder (and RAP)
Environmental benefits include:
Recycling reduces the dependence on natural resources (aggregates and crude oil)
Reduce “waste” to landfill

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
Co-mixing (or interfacial mixing) of binders (virgin with RAP binder) is being investigated using an atomic force microscope. Additional work is also being undertaken to assess the resultant dynamic modulus of the WMA/RAP blend
Expanded RAP mixing study utilizing dynamic modulus E* evaluation criteria developed by Advanced Asphalt Technologies: Bonaquist & Christensen
E* from specified mixing and compaction temperatures compared to fully blended condition E* determined through the Hirsch model (assuming 100% blending of RAP and virgin binders)

10. Specified Binder 58-28 25% RAP
DSR = Dynamic Shear Rheometer; G*/sin delta = Rutting Parameter of Superpave bitumen specification.
Original binder is PG58-28
Original binder (RTFOT Aged) is equivalent to the binder of hotmix after manufacture and placement
WMA (Post Plant) is the binder recovered from a WMA with 25% RAP
HMA (Post Plant) is the binder recovered from hotmix with 25% RAP
This basically indicates that the WMA (Post Plant) binder (containing 25% RAP) and the original binder (RTFOT Aged) are equivalent i.e. the addition of RAP stiffens the (WMA) binder to a level equivalent of the virgin binder in hotmix – addressing concerns that may exist with the tenderness of WMA.

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
Co-mixing (or interfacial mixing) of binders (virgin with RAP binder) is being investigated using an atomic force microscope. Additional work is also being undertaken to assess the resultant dynamic modulus of the WMA/RAP blend
Expanded RAP mixing study utilizing dynamic modulus E* evaluation criteria developed by Advanced Asphalt Technologies: Bonaquist & Christensen
E* from specified mixing and compaction temperatures compared to fully blended condition E* determined through the Hirsch model (assuming 100% blending of RAP and virgin binders)

12. NCHRP 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
Texas limits the amount of RAP in their specifications to 20% in wearing courses, 30% in the binder/intermediate courses and 40% in lower layers (greater than 100mm from the pavement surface). Also, if the RAP is not processed and fractionated, these maximum allowable limits are reduced by 10% i.e. 10%, 20% and 30% respectively.
North Carolina allows WMA only on secondary roads.
South Carolina limits the amount of RAP in their specifications to 10-20% in wearing courses, 10-25% in the binder/intermediate courses and 30% in base layers and is dependent on the mix type. Banks indicated that RAP eliminates stripping concerns and stiffens the binder to address tenderness/rutting concerns. RAP is also used to bump a PG grade rather than using an expensive intermediate grade (PG76 = PG70+RAP)

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
Superpave guidelines exist for RAP% in hotmix but not currently for WMA. The values in red are currently being proposed by various industry personnel.

15. 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.

16. 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 …??

17. WMA Validation Project

18. AAPA/Austroads WMA Field Validation Project