The Environmental Impact of Asphalt: Recycling and Sustainability

Asphalt: America's Most Recycled Material

Asphalt pavement covers roughly 94% of paved roads in the United States. It is also the country's most recycled material by weight — more than paper, plastic, glass, and aluminum combined. The National Asphalt Pavement Association reports that over 99% of reclaimed asphalt pavement is recycled back into new pavement or put to beneficial use.

This matters for Oregon, where hundreds of miles of roads, thousands of parking lots, and countless driveways are paved with asphalt. Understanding how asphalt recycling works, what it means for the environment, and how sustainability practices are evolving helps property owners and municipalities make informed decisions about their paving projects.

How Asphalt Recycling Works

The Milling Process

When an asphalt road or parking lot is resurfaced, the old surface is not hauled to a landfill. A milling machine grinds off the top 1.5 to 3 inches of pavement, breaking it into small pieces called millings or reclaimed asphalt pavement (RAP).

The milling process is precise. Modern cold milling machines can remove a specified depth across the full lane width, creating a consistent surface for the new pavement layer. The millings are loaded directly into trucks and transported to the asphalt plant.

Processing at the Plant

At the asphalt plant, RAP goes through several steps:

1. Crushing: Oversized pieces are broken down to specified maximum sizes
2. Screening: Material is separated by size using vibrating screens
3. Stockpiling: Processed RAP is stored in designated stockpiles, often separated by source and grade
4. Testing: RAP is tested for binder content, aggregate gradation, and binder properties
5. Blending: RAP is metered into the new asphalt mix at the specified percentage

The Chemistry of Recycling

Asphalt binder — the black, sticky material that holds aggregate together — ages through oxidation over time. It becomes stiffer and more brittle. But it does not lose its adhesive properties entirely.

When RAP is heated in the drum mixer at the asphalt plant, the aged binder in the RAP blends with the new (virgin) binder. The new, softer binder restores some of the flexibility lost to aging. For higher RAP percentages (above 25%), rejuvenator additives may be added to further restore binder properties.

The aggregate in RAP — the rock, sand, and gravel — is essentially permanent. It does not degrade through recycling. This makes RAP aggregate as good as or better than new aggregate for most applications, since it has already been coated with binder and proven in service.

Environmental Impact of Asphalt Production

Carbon Footprint

Asphalt production generates greenhouse gas emissions primarily from:

• Heating aggregate and binder to production temperatures (300-350 degrees F for hot mix)
• Drying aggregate to remove moisture before mixing
• Transporting materials to and from the plant and job site
• Extracting and refining crude oil into asphalt binder

A typical hot mix asphalt plant produces approximately 55 to 75 kg of CO2 equivalent per metric ton of mix. For context, paving a standard two-lane road for one mile consumes roughly 3,000 to 4,000 tons of mix, generating about 200 to 300 metric tons of CO2.

How Recycling Reduces Impact

Using RAP in new asphalt reduces environmental impact in several ways:

| Environmental Factor | Impact of 25% RAP | Impact of 40% RAP | |---|---|---| | Virgin aggregate needed | 25% reduction | 40% reduction | | New asphalt binder | 15-20% reduction | 25-35% reduction | | Energy for production | 10-15% reduction | 15-25% reduction | | CO2 emissions | 8-12% reduction | 12-20% reduction | | Landfill diversion | 25% of material | 40% of material | | Mining/quarrying impact | 25% reduction | 40% reduction |

For a deeper look at how asphalt is manufactured, see our guide on how asphalt is made.

Beyond RAP: Other Recycled Materials in Asphalt

The paving industry is incorporating other recycled materials into asphalt mixes:

Recycled asphalt shingles (RAS): Post-consumer roof shingles contain asphalt binder and fine aggregate. They can be processed and added to asphalt mixes at 3% to 5%, reducing the need for virgin binder. Oregon allows RAS in some mix designs.

Ground tire rubber (GTR): Recycled tires are ground into crumb rubber and used as an asphalt binder modifier. Rubberized asphalt is quieter, more flexible, and more resistant to cracking. It diverts tires from landfills and improves pavement performance.

Recycled glass: Crushed glass can replace a portion of fine aggregate in asphalt mixes. While not widely used in Oregon, it has been successfully tested in other states.

Steel slag: A byproduct of steel manufacturing, slag aggregate provides excellent friction and durability in asphalt surfaces. Oregon DOT has approved slag aggregate for some applications.

Warm Mix Asphalt: Reducing Emissions at Production

One of the most impactful sustainability advances in paving is warm mix asphalt (WMA). By reducing production temperatures 50 to 100 degrees F below conventional hot mix, WMA delivers:

• 15% to 30% reduction in fuel consumption at the plant
• Reduced fumes and emissions at the plant and job site
• Longer haul distances because the mix cools slower
• Extended paving season — WMA can be placed at lower ambient temperatures
• Better compaction — the mix remains workable longer

Oregon DOT has approved WMA for state highway projects, and most Willamette Valley asphalt plants can produce it. The cost premium over conventional hot mix is minimal (1% to 3%), and for many projects, the longer workability and better compaction actually reduce placement costs.

Cold In-Place Recycling (CIR)

For rural roads and lower-traffic streets, cold in-place recycling offers a way to rehabilitate pavement without hauling material to a plant at all:

How CIR Works

1. A milling machine grinds the existing pavement surface
2. The millings are mixed with an emulsion or foamed asphalt binder on site
3. The recycled mix is placed and compacted
4. A new surface layer (chip seal or thin overlay) is placed on top

Advantages

• 100% of existing pavement is recycled in place — no hauling, no plant energy
• 50% to 70% lower carbon footprint compared to mill and overlay
• Cost savings of 30% to 50% compared to conventional reconstruction
• Minimal material waste — nothing leaves the site

Oregon Applications

CIR is well-suited to Oregon's county roads and rural state highways. ODOT has used CIR on numerous projects across the state. For municipal streets with moderate traffic, CIR followed by a thin overlay provides a cost-effective rehabilitation option with strong sustainability credentials.

Permeable Pavement and Stormwater

Sustainability in paving extends beyond materials to how pavement interacts with water. Oregon's stormwater regulations make this particularly relevant.

Conventional pavement creates impervious surface that generates stormwater runoff. Runoff carries pollutants — oils, heavy metals, sediment — into streams and rivers. Managing this runoff requires expensive infrastructure: catch basins, pipes, detention ponds, and treatment facilities.

Permeable pavement addresses this at the source by allowing water to infiltrate through the surface. In Oregon's frequent-rain climate, permeable pavement can eliminate or dramatically reduce the need for separate stormwater infrastructure.

For property owners, this translates to lower stormwater utility fees in cities like Portland, Eugene, and Salem that offer credits for on-site stormwater management. For more details, see our guide to sustainable paving solutions.

The Circular Economy of Asphalt

Asphalt pavement operates closer to a true circular economy than almost any other construction material:

Production: Virgin aggregate and binder are combined with recycled materials at the plant.

Service: The pavement serves its purpose for 15 to 25 years.

Removal: At end of life, the pavement is milled off the surface.

Recycling: Millings are processed and returned to the plant.

Reuse: Recycled material becomes part of the next generation of pavement.

This cycle can repeat indefinitely. The aggregate is permanent. The binder can be rejuvenated. Nothing needs to go to a landfill.

Compare this to other construction materials:

| Material | Recycling Rate | Typical Fate at End of Life | |---|---|---| | Asphalt pavement | 99%+ | Recycled into new pavement | | Concrete | 70-80% | Crushed for road base or fill | | Steel | 90%+ | Recycled into new steel | | Wood | 10-30% | Landfill or incineration | | Brick/masonry | 5-15% | Landfill | | Roofing shingles | 10-20% | Landfill (increasing recycling) |

What This Means for Your Project

When you plan an asphalt paving project in Oregon, you can make choices that reduce environmental impact without sacrificing performance or increasing costs:

Request RAP content. Ask your contractor about incorporating recycled asphalt pavement into your mix. Standard RAP percentages (15-25%) are routinely available and may actually cost less than all-virgin mixes.

Consider warm mix. For larger projects, warm mix asphalt reduces emissions with minimal cost impact. Most Oregon asphalt plants can produce WMA.

Reclaim your old pavement. When your parking lot or driveway is resurfaced, the old material has value. Make sure your contractor recycles the millings rather than landfilling them (most already do, but it is worth confirming).

Explore permeable options. For parking lots, driveways, and pedestrian areas, permeable pavement manages stormwater at the source and may reduce your stormwater utility fees.

Cojo Excavation's Approach to Sustainability

At Cojo Excavation, we work with Oregon asphalt plants that incorporate recycled materials and produce warm mix asphalt. We ensure that material milled from your existing pavement is recycled, and we can advise on sustainable paving options that fit your project's performance requirements and budget.

Our services include excavation, grading, and paving for residential, commercial, and municipal projects throughout the Willamette Valley. We believe that building quality infrastructure and reducing environmental impact are not competing goals — they go together.

For more resources on making informed paving decisions, explore our blog or contact us to discuss your project.