With increased emphasis on sustainability efforts and achieving net-zero emissions goals, transportation authorities in Canada are exploring ways to use higher amounts of reclaimed asphalt pavement (RAP) in their mixes. To achieve these goals, researchers are evaluating the impact of using aged binder on roadway performance and the impact different additives can have on performance outcomes.
A technical paper on the topic was recently co-authored by Natalie Lee, B.Sc.E, from the New Brunswick Department of Transportation and Infrastructure, and Xiomara Sanchez-Castillio, Ph.D., P.Eng., assistant professor at the University of New Brunswick, and published during the Canadian Technical Asphalt Association (CTAA) 69th annual conference. Titled “Exploring the Laboratory Performance of High RAP Mixes for New Brunswick,” the paper focused on how varying amounts of softer binders and rejuvenating agents impacted sample performance to encourage use of high-RAP mixes while meeting functional requirements.
While current standards may restrict RAP usage in an asphalt mix out of concern for performance and existing plant capabilities, the researchers proposed that using higher amounts of RAP may not only be achievable with the use of effective additives but may also contribute to reduced carbon emissions. The study explored the performance of mixes incorporating 28% RAP based on estimates of current, effective plant management thresholds. Samples were created using three primary mixes: a virgin mix with PG 58S-28 binder, a 28% RAP mix with PG 52S-34 binder, and a 50% RAP mix with PG 58S-28 binder dosed with a recycling agent.
The technical paper details an in-depth review of the materials and methods used for the study including RAP sourcing, aggregates, and binder used. For the recycling agent / asphalt rejuvenator, the researchers selected ReLIXER®, a rejuvenator formulated from bio-based oils engineered by Sripath Technologies®.
Performance testing included the use of IDEAL-CT for cracking, IDEAL-RT and Hamburg Double Wheel Tracking Test for rutting, and ITSR for tensile strength. The results demonstrated high performance for the high-RAP mix sample dosed with a recycling agent. In terms of cracking, this sample exceeded the minimum value required, which was attributed to ReLIXER’s ability to restore functional properties for flexibility and elasticity. The IDEAL-RT test revealed that only the sample dosed with ReLIXER met requirements with a result of RT Index 67, exceeding the minimum value of 60. The researchers also attributed the high-RAP sample’s superior performance in the Hamburg Wheel Tracking Test to the mix’s ability to incorporate increased amounts of RAP through the use of a recycling agent, as larger amounts of RAP tend to result in improved rutting resistance.
As a result of this research, team recommended additional field trials using 50% RAP along with a recycling agent, explaining that high-RAP mixes performed similarly or better than virgin mixes when dosed with a rejuvenator. Further testing could help the New Brunswick Department of Transportation and Infrastructure develop new RAP guidelines that could incorporate higher amounts, allowing for greater confidence in performance and improved outcomes for sustainability goals.
Read the full technical paper for more information about the high-RAP laboratory testing.
Learn more about using high levels of RAP and ReLIXER, an asphalt rejuvenator / recycling agent from Sripath.
