In a webinar hosted by the University of Oklahoma and the Southern Plains Transportation Center on May 20, 2025, Dr. Krishna Srinivasan, President of Sripath Technologies®, shared valuable insights into how high-RAP (Reclaimed Asphalt Pavement) mixes can innovate asphalt paving practices. With over 25 years of experience in the bitumen industry, Srinivasan offered a data-driven guide on best practices for integrating RAP into hot asphalt mixes using asphalt rejuvenators. 

The Importance of Reclaimed Asphalt Pavement 

As infrastructure development surges globally, so does the demand for sustainable and cost-efficient materials. RAP, derived from milled or excavated asphalt, is the most recycled material on Earth, surpassing steel, aluminum, and glass.  

According to the National Asphalt Pavement Association (NAPA), more than 750 million tons of RAP are generated annually. Reusing RAP can significantly reduce the need for virgin bitumen and fresh aggregates. When properly processed and homogenized, RAP can also help lower carbon emissions and conserve natural resources, aligning with both environmental and economic priorities. 

The Role of Asphalt Rejuvenators in High RAP Mixes 

What are Asphalt Rejuvenators? 

An asphalt rejuvenator is a specialized additive that restores the functional properties of the oxidized binder found in RAP. Over time, the asphalt binder hardens and becomes brittle due to environmental exposure. Rejuvenators, or recycling agents, reverse this aging process to help improve flexibility, compaction, and durability of the subsequent roadway surface. 

Srinivasan emphasized that not all rejuvenators are equal. Bio-based rejuvenators have become a preferred option due to their superior dosage efficiency, low VOC emissions, and better aging resistance compared to traditional petroleum-based alternatives. 

Optimizing Mix Design with Rejuvenators 

Effective use of rejuvenators enables higher RAP content in mixes (up to 60% or more) without compromising on road performance. Srinivasan outlined two main design strategies during the webinar: 

  • Binder-Level Testing: Adjusting binder properties to meet performance specification targets (PG, viscosity, penetration, etc.) using blends of RAP, virgin binder, and rejuvenator 
  • Balanced Mix Design (BMD): Evaluating crack resistance and rutting potential at the mix level to fine-tune rejuvenator dosage and RAP percentage 

These strategies can help ensure high-RAP mixes perform as well, or better, than virgin mixes both in the lab and on the road. 

What Makes an Asphalt Rejuvenator Effective 

The effectiveness of a rejuvenator depends on its ability to restore aged RAP binder properties without compromising long-term performance. Unlike petroleum-based or soft-grade binders, bio-based rejuvenators can offer better Delta Tc values, indicating enhanced durability and crack resistance over time.  

An asphalt rejuvenator’s compatibility with a wide range of binders and ease of use under ambient conditions makes them especially attractive for high-RAP applications. These properties not only ensure better field performance but also contribute to lower greenhouse gas emissions. 

Best Practices for RAP in Asphalt Plants 

The transition to high-RAP mixes also requires operational adjustments at the plant level. Key recommendations include: 

  • Fractionating RAP: Separating RAP into coarse, medium, and fine fractions to meet gradation specs 
  • Homogenizing RAP Stockpiles: Turning RAP piles multiple times to ensure consistency 
  • Rejuvenator Dosing Systems: Installing flexible systems that allow co-injection based on RAP percentages and mix types 

Srinivasan also emphasized the importance of moisture management, binder testing, and environmental safety in plant operations. 

The use of reclaimed asphalt pavement and effective asphalt rejuvenators is steadily improving practices in the paving industry. Offering cost efficiencies, environmental benefits, and reliable performance, high-RAP mixes present a practical solution for contractors, transportation agencies, and communities alike.  

ReLIXER®, a bio-based rejuvenator, has been proven across tens of thousands of lane miles since 2016, offering reliable performance, excellent low-temperature properties, and long-term aging resistance. Its efficiency at low dosing levels and ease of integration make it a practical tool for sustainable, high-RAP mix designs. 

For more information about ReLIXER, contact info@sripath.com.