Asphalt is the most recycled material in the United States according to the National Asphalt Pavement Association (NAPA), amounting to nearly 97 million tons of reclaimed asphalt pavement (RAP). As a result, over 90% of new roadway surfaces in the U.S. are built using RAP. This trend is spreading globally as more contractors and transportation agencies explore the environmental and economic benefits of working with RAP such as reduced reliance on virgin materials, project costs, and carbon footprint implications. 

 

While the advantages of RAP use are clear, traditional standards for RAP usage in surface mixes infrequently exceeds 30% of a mix. This is partially because RAP contains aged, stiff binder that, when used in large quantities, can compromise the long-term durability of a mix. Without intervention, higher RAP use can lead to premature cracking, poor workability, and failure to meet performance specifications. 

 

Asphalt rejuvenators were developed to address the need for high-performance in high-RAP mixes (those with over 30% RAP). A rejuvenator or recycling agent works to restore the functional characteristics of RAP materials. An ideal asphalt rejuvenator can make mix designs with 40%, 50%, or even higher RAP content a reality while maintaining integrity during the lifespan of the roadway.  

 

The Challenge of High RAP Usage 

RAP contains valuable aggregate and aged asphalt binder that, when used effectively, can reduce the amount of virgin materials needed to produce a high-performing asphalt mix. Sourced from worn and failing roadway surfaces, RAP requires the work of an asphalt rejuvenator to make the material viable as a material used in a new pavement project. This is because the binder in RAP has experienced oxidation through prolonged use and exposure, leaving the material hard and brittle and causing the roadway to lose its flexibility and durability.  

 

With the aged RAP binder also come limitations in how much can be used in a new mix without addressing the functional characteristics of the binder itself. Too much RAP without an asphalt rejuvenator can result in a stiff mix that, in turn:  

  • Reduces workability during placement and compaction 
  • Increases likelihood of thermal or fatigue cracking 
  • Fails to meet modern performance specifications and increasing traffic loads 

 

These concerns are why many departments of transportation restrict RAP in asphalt mixes to a maximum of 20-30%. In the U.S., the average percentage of RAP used is 21.9%, while in Europe, average RAP use lingers around 22%. Understandably, without an asphalt rejuvenator, high-performing, high-RAP roadways are not viable for the long term.  

 

How Asphalt Rejuvenators Work 

Asphalt rejuvenators are specialty additives designed to restore the functional properties of aged asphalt binder contained within RAP material. More than just softening agent, asphalt rejuvenators penetrate aggregate particles and rejuvenate the aged bitumen contained in the RAP. The result is the return of functional balance such as improved workability and flexibility, manageable viscosity, and sustained durability to resist cracking and fatigue.  

 

Working with an ideal rejuvenator can enable mix engineers to use RAP as more than just aggregate (black rock). RAP becomes a critical component of the functional binder as well, helping to reduce costs and environmental impacts along the way. 

 

How to Achieve a High-RAP Mix with an Asphalt Rejuvenator 

Incorporating an asphalt rejuvenator into a mix design requires careful consideration of material selection, anticipated roadway conditions, performance requirements, and testing outcomes. To do this, engineers and producers can evaluate the following:  

  • Material Characteristics: Evaluate RAP source and composition variability to ensure a consistent outcome. Proper stockpile management, fractionation, and homogenization can help with this process.  
  • Rejuvenator Selection: Look for a recycling agent compatible with existing RAP and binder materials as well as proven performance. Note that while asphalt rejuvenators can support sustainability through recycled material use, not all rejuvenators are environmentally friendly products.  
  • Performance Testing: Simulate long-term aging while also validating performance outcomes with mechanical tests.  

 

Examples of High-RAP Mixes with High Performance Results 

Asphalt rejuvenators vary in composition, manufacture, and performance. From petroleum-based products to those incorporating used cooking oils or REOBs, these recycling agents take different paths to address the challenge of using reclaimed asphalt pavement effectively in new asphalt mixes. The most effective asphalt rejuvenator is one that softens bitumen, adjusts grade, aids compaction, and enhances durability all while restoring functional balance through rapid penetration.  

 

ReLIXER®, a specially formulated elixir of bio-based oils, has been tested and proven worldwide for over 10 years. Field trials and laboratory testing have been conducted by third-party, independent researchers, producers, and departments of transportation. In most cases, these tests are performed with locally sourced materials and subjected to rigorous regional performance specifications.  

 

AfPA Uses 40% RAP with ReLIXER for Heavy Traffic Roadway 

A major field trial led by the Australian Flexible Pavement Association in Queensland showcased the effectiveness of ReLIXER in real-world conditions. The project involved a 40% RAP mix containing PMB applied to a high-traffic quarry road. Designed to reflect local climate and performance standards, the trial was followed by extended monitoring and performance evaluations. The findings showed that ReLIXER not only restored binder properties within regional viscosity targets but also supported long-term pavement durability. 

 

New York City Trial Successfully Paves with 100% RAP Mix  

A test project in New York City highlighted the performance of a 100% RAP mix enhanced with just 0.55% ReLIXER—without any virgin binder. Despite the absence of new binder, the mix achieved excellent compaction, rutting resistance, and cracking performance. Laboratory evaluations confirmed it met or exceeded key specifications, including results from the Marshall compaction test, Hamburg Wheel Tracking Test, and Semi-Circular Bending Test. Notably, the mix delivered an average of 4.1% air voids and maintained rut depths well within acceptable limits (14.6 mm at 10,000 cycles and 10.9 mm at 20,000 cycles) demonstrating its viability as a high-performance, fully recycled pavement solution. 

 

Advancing Sustainable Pavement Design Through Rejuvenation and High-RAP Use 

The continued use of high-RAP asphalt mixtures represents a critical opportunity to advance performance and sustainability goals. However, the widespread adoption of high-RAP mix designs has traditionally been limited by the challenges posed by aged binder stiffness and resulting durability concerns. 

 

Asphalt rejuvenators like ReLIXER offer a proven, technically sound solution. By restoring functional properties to aged binder, they enable the production of asphalt mixtures with 25% or more RAP content that meet modern performance specifications for cracking, fatigue, and rutting resistance. With proper material characterization, product selection, dosage optimization, and performance validation, these technologies can be confidently implemented at scale. 

 

 

For more information about reclaimed asphalt pavement, asphalt rejuvenation, and ReLIXER, contact info@sripath.com.  

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