Recycle & Reuse High Levels of RAP

Impact of Using Higher Levels of RAP​

Roadway deteriorate over time, resulting in raveling, cracking, and fatigue damage. Globally, over 750 million tons of RAP are generated annually. On an average, only less than 20 %, of RAP is recycled, the rest ships to landfills.​

To accommodate growing needs, there is an need to expand the global network of roadways.  This results in the increased depletion of natural resources, such as virgin bitumen and aggregates.​

The industry is attempting to maximize RAP usage.  It has been demonstrated that there is a reduction in Green House Gases (GHG) with increasing RAP usage.  Increasing RAP from 0% to 60%, the total GHG emissions decreases from 72 to 51 Kg of CO2 [Courtesy: N Michel, AfPA Tech Talk, Nov 23, 2021].

The Economic Case for Greater RAP Usage​

  • Using RAP can Lower Cost of Hot Mix​
         Reduced need for aggregates​
         Reduced need for virgin bitumen

  • Bitumen from RAP can Replace More Expensive Virgin Bitumen

  • More RAP = Lower Material Costs

[Courtesy: FHWA-HRT-11-021]

Environmental Impact vs. Economic Viability vs. Roadway Performance​

Balanced Mix Design Approach to Optimize High-RAP Mixes​

For Greater than 25 % to 30 % RAP​ a REJUVENATOR is Needed

  • Seek a balance between Rutting and​
    Fracture Toughness properties​
  • Rutting: Hamburg, APA, Cooper, French Wheel, Cantabro, etc.​
  • Fracture Toughness:  Overlay, SCB, SENB,​
    I-FIT, DCT, Ideal CT, etc.
  • Costs
  • Potential Cracking
  • Potential Rutting
  • Potential Fatigue

ReLIXER®: Impact on Resistance to Rutting & Cracking​

The concept of balanced mix design was employed to design an idea for a wear layer application in the USA.​

Two high-RAP Mixes, 25 % RAP and 50 % RAP were evaluated.  The 25 % RAP Mix contained 0.5 Kg per ton of ReLIXER and 3.4 % virgin bitumen, PG 64-22.  The 50 % RAP Mix contained 1 Kg per ton of ReLIXER and 2.4 % virgin bitumen.  The total amount of liquids was targeted around 5.6 %.  ​

Both the Mixes resulted in an excellent balance between rutting resistance and fracture toughness properties

Deeper Insight