As the fifth largest metro in the United States with a population exceeding 4.8 million and more than 1,400 miles of paved roads, the City of Phoenix, Arizona, conducted its first ever recycled asphalt pavement (RAP) overlay pilot project on a laned road in October 2020. For a city of this magnitude, the absence of RAP on municipal roadways was a noticeable gap in sustainable pavement management. That hesitancy was rooted in long-held misconceptions about RAP performance and a lack of firsthand data. But when Solterra Materials, a Phoenix-based asphalt mix company, presented compelling lab evidence, city officials reconsidered their position. This article examines how Phoenix broke through institutional skepticism to pilot RAP with Cargill Anova Rejuvenator, the technical results that followed, and what the city new specification means for the future of asphalt recycling in municipal paving programs. For a deeper look at handling asphalt materials safely on site, refer to Asphalt Safety Comprehensive Guide to Hazard Management in.
The Case for RAP in a Historically Skeptical Market
Phoenix had long restricted RAP use to low-risk applications such as dust suppression in alleys and road shoulders. The city street transportation department, like many municipal agencies, operated under the assumption that recycled binders could not match the durability of virgin asphalt in high-traffic environments. That assumption went untested for years because no contractor had brought forward the laboratory data necessary to challenge it.
Why Municipalities Hesitate on RAP
The barriers to municipal RAP adoption fall into several categories. Understanding these helps explain why a city like Phoenix moved cautiously before committing to its first laned-road pilot.
- Lack of local performance data – Most published RAP studies focus on state highway or interstate applications, not urban arterial streets with unique traffic patterns and climate conditions.
- Binder variability concerns – Aged RAP binder is stiffer and more brittle than virgin binder, raising fears of premature cracking under Phoenix extreme heat and diurnal temperature swings.
- Specification inertia – Municipal specifications often lack provisions for RAP content above low percentages, requiring formal amendments before contractors can propose recycled mixes.
- Perceived risk of failure – A failed pilot on a heavily trafficked arterial road would attract public scrutiny and could set back recycling efforts by years.
Solterra Materials Builds the Evidence Base
Solterra Materials took a methodical approach. Rather than asking the city to approve a RAP mix based on general industry claims, the company conducted extensive lab evaluations at 10 percent, 15 percent, and 25 percent RAP content levels. Each blend was tested for flexibility, rutting resistance, and low-temperature cracking performance. The data gave Phoenix street transportation officials a defensible foundation for moving forward.
The lab results confirmed what Solterra team suspected: Arizona naturally aged and highly oxidized asphalt binder required a rejuvenator to restore its rheological properties. Without restoration, high RAP content would produce a mix too brittle for Phoenix demanding traffic loads. This finding set the stage for the rejuvenator selection process. For more information on how asphalt materials are produced and handled at the plant level, see Asphalt Plants and Pavement Construction Equipment a Complete.
Selecting the Right Rejuvenator for Arizona Binder
Not all rejuvenators perform equally. The chemistry of the rejuvenator must match the oxidation profile of the reclaimed binder. In Arizona, where asphalt binder ages under intense solar radiation and high ambient temperatures, Solterra evaluated multiple rejuvenator families before settling on a solution.
Rejuvenator Categories Evaluated
| Rejuvenator Type | Source | Performance with Aged Arizona Binder |
|---|---|---|
| Fatty acids | Animal fats, tall oil | Moderate softening, limited durability |
| Vegetable oils | Soybean, canola, rapeseed | Good softening, variable long-term aging |
| Petroleum-based oils | Refined crude oil fractions | Consistent performance, environmental concerns |
| Engineered vegetable oil blends | Modified plant oils (Cargill Anova) | Best overall rheology restoration and durability |
Why Cargill Anova Rejuvenator Won Out
After side-by-side comparisons, Solterra selected Cargill Anova Rejuvenator, an engineered vegetable oil-based product. The decision came down to three measurable advantages:
- Superior binder restoration – The Anova chemistry restored the aged RAP binder rheological and mechanical damaged properties more completely than the alternatives.
- Reduced compaction temperatures – The mix compacted at temperatures up to 45 degrees Fahrenheit lower than conventional hot mix, reducing energy consumption and emissions at the plant.
- Enhanced low-temperature cracking resistance – The flexibility index increased significantly, addressing the primary concern that had kept RAP off Phoenix laned roads for years.
Pat Weaver, president of Solterra Materials, noted that todays bio-based chemistries actually restore the RAP binder properties rather than simply softening the mix. This distinction is critical because simple softening agents can fail over time as the rejuvenated binder re-oxidizes.
The Buckeye Road Pilot: Design, Execution, and Measured Results
With the rejuvenator selected and lab validation complete, Solterra and the City of Phoenix identified a test section on Buckeye Road, a heavily trafficked arterial corridor just west of downtown Phoenix. The pilot covered nearly one mile and used 2,300 tons of hot mix asphalt containing 20 percent RAP with Anova Rejuvenator at a precisely calibrated dosage rate.
Mix Design Parameters
The mix design process involved several coordinated steps between Solterra, Cargill, and the city street transportation department. Key parameters included:
- 20 percent RAP content in the surface course (intermediate layer used a different specification)
- Slight binder grade bump to compensate for the aged RAP binder stiffness
- Anova Rejuvenator dosage tailored to the specific oxidation level of the stockpiled RAP
- Warm mix asphalt production temperatures enabled by the rejuvenator lubricating effect
Performance Results After Several Months in Service
Post-construction monitoring produced data that exceeded expectations. The table below summarizes the key performance indicators measured during the first several months of service.
| Performance Metric | Virgin Mix Baseline | 20% RAP + Anova Mix | Improvement |
|---|---|---|---|
| Flexibility Index (I-FIT) | 12.0 | 18.5 | +54% |
| Compaction temperature | Standard HMA | Up to 45F lower | Energy savings |
| Surface cracking (visual) | None expected | None observed | Equivalent |
| Rutting (visual) | None expected | None observed | Equivalent |
| Material cost vs. virgin | Baseline | 10% lower | Cost savings |
| VOC emissions | Standard | Reduced | Environmental benefit |
Contractor Feedback During Placement
The laydown contractor on the project reported that the RAP mix with Anova Rejuvenator handled well and was very easy to place and compact. The mix behaved like any standard warm mix asphalt, which meant crews did not need special training or modified procedures. This ease of placement reduced the risk of construction defects that could compromise long-term pavement performance.
Weaver added that after driving on the test section personally several times, the pavement was performing excellently with no cracking or rutting visible. He noted that the section sits in a heavy industrial zone with significant truck traffic, making the early results especially encouraging for future residential applications. For insights on how the broader construction industry is approaching workforce and market challenges, read New England Home Builders Associations Drive Workforce Innovation.
How Phoenix Rewrote Its Specification and Expanded RAP Use
The most consequential outcome of the Buckeye Road pilot was not the performance data itself, but what the city did with it. Phoenix officials moved quickly to revise their pavement specification to include RAP as an approved option for future paving projects. This shift from skeptical observer to active adopter represents a template for other municipalities considering recycled materials.
Specification Changes and Future Plans
The city adjusted its specification to accommodate higher RAP content and planned expanded testing in April 2021 with additional road sections around the city. The rationale for the rapid expansion rested on three pillars:
- Cost savings to taxpayers – The 20 percent RAP mix delivered a 10 percent cost reduction compared to virgin mix, a meaningful saving when applied across an annual paving program of hundreds of thousands of tons.
- Environmental benefits – Reduced need for virgin aggregate and binder, lower energy use at the asphalt plant, minimized landfill space consumption, and decreased greenhouse gas emissions.
- Demonstrated performance equivalence – The RAP mix matched or exceeded virgin mix performance on flexibility, cracking resistance, and rutting resistance, removing the technical objection that had delayed adoption for years.
Lessons for Municipalities Considering RAP
Phoenix experience offers practical guidance for other municipal agencies evaluating recycled asphalt programs. The path from skepticism to adoption required coordinated effort across multiple stakeholders.
- Start with lab data – Municipal decision-makers need localized test results, not generic industry claims. Solterra investment in lab testing at multiple RAP percentages gave the city confidence to proceed.
- Select the right rejuvenator chemistry – Not all rejuvenators work equally well with all binders. Testing multiple products against the specific RAP source is essential.
- Engage the state DOT early – Solterra worked with the Arizona Department of Transportation throughout the process, ensuring the pilot aligned with state-level technical guidance.
- Start with a visible test section – A heavily trafficked arterial road like Buckeye Road made the demonstration credible. A low-visibility test would not have carried the same persuasive weight with city leadership.
- Share results transparently – By being proactive in sharing industry best practices and transparent with its mix development and testing, Solterra shifted perceptions and built trust with a once skeptical audience.
The city is now sold on RAP and is looking forward to longer-term performance data to determine a comprehensive strategy for incorporating recycled materials into standard paving operations. Six-month and twelve-month evaluations will help refine rejuvenator dosage rates and RAP content targets for different road classifications. For lessons on how paving contractors build lasting customer relationships through quality and transparency, see Building Customer Loyalty in Asphalt and Paving Lessons.
Conclusion
The City of Phoenix first RAP overlay on a laned road marks a turning point for asphalt recycling in large municipal markets. What began as a single pilot project on Buckeye Road has already led to specification changes, cost savings, and a measurable reduction in environmental impact. The combination of rigorous lab testing, appropriate rejuvenator chemistry, and transparent collaboration between contractor and agency created a replicable model that other cities can follow.
For contractors and materials suppliers working to introduce RAP into conservative municipal markets, the Phoenix case study demonstrates that skepticism can be overcome with data. The key is not to ask for approval based on what has worked elsewhere, but to generate local evidence that addresses local concerns. When paired with the right rejuvenator technology, RAP delivers performance that matches virgin materials while reducing costs and environmental footprint. That is a combination that more cities are likely to adopt as the pavement recycling movement continues to gain momentum.