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) 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

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????

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. www.greenhighways.org 4

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.

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

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 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 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)

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.

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)

NCHRP 9-43 - Sasobit

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)

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.

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.

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 …??

WMA Validation Project

AAPA/Austroads WMA Field Validation Project