As calls for tougher environmental regulations intensify, so does the accumulation of reclaimed asphalt pavement (RAP). To enable higher RAP content in public infrastructure projects, updates to state and federal policies are essential.
As Demand for Sustainability Grows, So Do RAP Stockpiles
As environmental regulations tighten and sustainability expectations rise, so too does the accumulation of Reclaimed Asphalt Pavement (RAP). Despite advancements in asphalt recycling technology, regulatory policies still hinder the use of higher RAP percentages in many government-funded projects. Until state and federal specifications evolve, contractors remain restricted in how much recycled content they can incorporate into public infrastructure.
The asphalt and road construction industries continue to face mounting pressure to reduce environmental impact. There’s a growing push to lower carbon emissions, improve production efficiency, increase surface durability, and adopt cleaner paving practices. Yet, massive RAP reserves continue to grow unused, even though current technology demonstrates that mixes with significantly higher RAP content can still meet performance and durability standards.
NAPA president Audrey Copeland highlights this issue in a published paper, noting that asphalt recycling surged during the 1970s oil crisis, prompting rapid innovation in construction practices. For years, federal highway specifications included modest RAP content—usually below 15%—to avoid additional testing. However, as environmental priorities shift again, there’s renewed momentum behind maximizing RAP usage.
“Elevating RAP content is once again a major focus for the HMA industry,” Copeland wrote. Today’s market pressures—rising material costs, environmental regulations, and the adoption of sustainable technologies like warm-mix asphalt—are forcing stakeholders to reconsider the benefits of using higher levels of RAP without compromising pavement quality.
Although Copeland’s observations reference historical practices, her insights remain relevant. Many believe it’s time for national guidelines that encourage widespread use of high-RAP mixes. The tools to make this a reality—including the ability to theoretically use 100% RAP—are already available.
What Makes Higher RAP Possible: Understanding Softeners and Rejuvenators
One key enabler of increased RAP usage is the use of asphalt rejuvenators—specialized additives designed to restore aged binder properties. These have existed in various forms since the 1950s. One early was introduced and Richard White as a surface treatment. Unlike traditional surface sealers, which mainly functioned as adhesives, Reclamite addressed binder degradation at the molecular level—a concept that laid the groundwork for today’s advanced rejuvenation technologies.
In earlier times, asphalt producers leaned on “bump grading” to incorporate more RAP. As Austin Hohmann of Colorbiotics explains, this involved selecting a softer binder—like a 52-34 grade—to offset the stiffness of aged RAP and blend back up to a 58-28 spec. While cost-effective, this method acted more as a viscosity adjustment than a true rejuvenation.
“These softer grades are often synthetically produced today,” said Hohmann, “and while they reduce stiffness, they don’t reverse the chemical aging that’s already occurred in the binder.” Think of it like adding oil to peanut butter—it softens it, but doesn’t restore its original chemical composition.
This approach works only up to about 30% RAP content. Beyond that, it becomes unstable, as Hassan , Global R&D Leader at Cargill, explained: “At higher levels of RAP, the mix can lose structural integrity unless more advanced recycling agents are introduced to restore and stabilize the chemistry of the binder.”
How Rejuvenators Differ
So, what sets rejuvenators apart from softeners? The difference lies in their chemistry. While softeners dilute stiffness, rejuvenators chemically interact with aged binders, reversing oxidation and restoring elasticity. They’re designed to address the underlying molecular damage caused by long-term exposure and aging.
“As asphalt oxidizes, it forms rigid molecular clusters,” Tabatabaee noted. “Rejuvenators break up these clusters and restore balance by reintroducing missing fractions like resins, which are essential for flexibility.” He compares this to rehydrating overcooked oatmeal—add the right component, and the mixture becomes pliable again.
These rejuvenators go beyond merely softening—they reverse damage on a microscopic scale. For instance, Colorbiotics’ rejuvenators use oxirane compounds that react with oxidized binder components, preventing asphaltenes from clumping and improving dispersion throughout the mix.
Limits and Application Considerations
Despite their promise, rejuvenators raise questions: How many times can a binder be rejuvenated? Are there environmental conditions that limit their effectiveness?
According to both Hohmann and Tabatabaee, there’s no known cap on how often rejuvenation can occur. The technology is viable in both hot mix and warm mix asphalt, offering the added benefit of improving compaction—a crucial factor for quality and longevity.
Rejuvenators are versatile and can be used across various applications, from base layers to surface courses and even in SMA and open-graded mixes.
However, producers need to evaluate their operation size and mixing protocols before integrating rejuvenators. Hohmann outlines three common methods:
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Terminal addition – Incorporate rejuvenator before transporting binder to the plant.
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In-line blending – Mix rejuvenator directly into the asphalt stream prior to mixing.
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Tank dosing – Add rejuvenator into storage tanks during refills—ideal for plants without in-line blending infrastructure.
How Much RAP Is Achievable?
One of the biggest takeaways from current trends is that private industry is already pushing RAP usage far beyond traditional thresholds. In some U.S. states—like New York, New Jersey, and Virginia—mix designs with 45-55% RAP content are becoming increasingly common, proving that high-RAP pavements can meet quality standards.
Tabatabaee emphasized that while private firms have embraced high RAP and rejuvenation practices, government projects remain behind. “The public sector could benefit greatly from the private sector’s experience in this area,” he said.
Data tracking for RAP usage remains inconsistent nationwide, but that may soon change. As Environmental Product Declarations (EPDs) gain traction, we can expect more standardized data and transparency. With it, states may be encouraged to adopt higher RAP thresholds, helping shift the industry toward a more sustainable and circular approach to road construction.
