Blacklidge Emulsions’ ReGen Rejuvenates RAP
BY Asphalt Testing Solutions & Engineering LLC
A technical report on ReGen® rejuvenating additive
Using recycled asphalt pavement (RAP) is one way to help drive down mixture costs. Too much RAP has been known to make some asphalt mixtures stiff and brittle, which in turn will result in poor performance of the pavement. Creating a design that balances and optimizes the cracking and rutting performance of a mix is one way to allow an asphalt producer to find innovative ways to add more RAP while maintaining performance.
During design, if the performance test results are low, a typical fix would be to decrease the RAP content or increase the asphalt binder content; the latter being more expensive. An innovative alternative is to add a rejuvenator to the mix that reactivates the RAP binder and enhances the overall performance.
Blacklidge Emulsions looked at volumetrics and performance of plant-produced mixes with increasing RAP content and its rejuvenating product, ReGen®. ReGen was developed to restore reclaimed asphalt binder to a highly durable and age-resistant state allowing the use of more RAP in road construction projects while improving pavement performance.
Three mixes were produced at Duval Asphalt’s Philips Highway asphalt plant with components outlined in Table 1. Each mix used a PG52-28 asphalt binder with 35 percent, then 45 percent and then 60 percent RAP. The 35 percent RAP mix was used as the control and did not contain ReGen. The 45 percent and 60 percent RAP mixes were properly dosed with ReGen based on Blacklidge’s recommendation.
ReGen was introduced from a tote connected to the asphalt binder line and a custom in-line injection system. Duval Asphalt’s custom system ensured a thorough blending of the rejuvenator into the binder prior to introduction into the mix.
Performance Testing Evaluation Completed by Asphalt Testing Solutions & Engineering (ATS)
Rutting: The rutting for all mixes per AASHTO T 324 was minimal and well below the industry standard maximum of 12.5 millimeters (See Figure 1). None of the mixes displayed signs of stripping through visual inspection or a stripping inflection point (SIP). The high RAP and ReGen mixes performed just as well as the 35 percent RAP control mix.
Cracking: The Illinois Flexibility Test (I-FIT), AASHTO TP 124, for each mix resulted in Flexibility Indexes (FI) above 4.00. Increasing the RAP content from 35 percent to 60 percent would normally result in lower FI due to the high recycled binder replacement and the stiffness of the binder. The addition of ReGen to the 45 percent and 60 percent RAP mixes resulted in comparable performance to the control mix; for not only the FI, but also strength and fracture energy.
Durability: Each mix was conditioned with short-term oven aging (STOA) and long-term oven aging (LTOA) per AASHTO R 30 for Cantabro Testing. STOA of the plant-produced mix consisted of two hours at compaction temperature prior to compacting triplicate specimens. The target air void content was 7.0 ± 0.5 percent in lieu of 4.0 percent as prescribed by AASHTO TP 108. Using the higher air void content is more representative of a new pavement, giving an indication of the durability of the mix in the beginning of its life.
For LTOA, the compacted specimens were placed in an 85oC force-draft oven for five days. These specimens were also compacted to 7.0 ± 0.5 percent air voids for comparison purposes. There was no statistical difference between the three mixes and in terms of mass loss for both the STOA and LTOA specimens.
The average mass loss of each mix, even after LTOA, was under 10 percent with the exception of the 45 percent RAP mix, which was 10.9 percent. The maximum mass loss for a dense graded mix is typically around 10.0 percent with specimens compacted to 4.0 percent air voids. Since these specimens were compacted at 7.0 ± 0.5 percent air voids, they would be expected to have a slightly higher mass loss result.
Overall, the higher RAP mixes (45 percent and 60 percent with ReGen) showed little to no difference in performance compared to the 35 percent RAP control mix in terms of Hamburg Wheel Tracking, Illinois Flexibility Test and Cantabro Durability Test. All mixes performed well; showing that the addition of ReGen is an innovative way of increasing the mix RAP content, creating a cost-effective solution to an expensive product, while maintaining performance.