How Does Asphalt Recycling Work?

August 14, 2023

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asphalt recycling

Asphalt is one of the most widely used construction materials in the world. The black, sticky substance we know as asphalt is used to pave roads, driveways, parking lots, airports, and more. Given how ubiquitous asphalt is in our infrastructure, you'd think it has an unlimited lifespan. But while asphalt is sturdy stuff, it doesn't last forever. Exposure to weather and wear-and-tear from vehicles slowly degrades and deteriorates asphalt over time.

This is where asphalt recycling comes in - reusing old asphalt to create new pavement can save money and resources. So, how does it work? Used asphalt is broken up and crushed into aggregate pieces and fine particles called reclaimed asphalt pavement (RAP). The RAP is then combined with new asphalt binder and virgin aggregates at high heat to produce fresh hot mix asphalt.

As they say, one man's trash is another man's treasure! Here's a look at how asphalt recycling works and why it's become a common practice.

Grinding Up the Old Blacktop

When asphalt needs to be repaired or replaced, the old deteriorated pavement is removed from the ground. This broken-up asphalt is then transported to a recycling facility. Here, the material is fed into a crushing and screening operation to break it down. The asphalt chunks are ground down into smaller aggregate pieces and fine particles.

This resulting material is known as reclaimed asphalt pavement (RAP). The percentage of reclaimed asphalt can vary based on the characteristics of the original asphalt. High-quality aggregates that can be reused will make up a larger percentage of the RAP.

old damaged asphalt blacktop

Mixing in New Asphalt and Aggregates

Once the old asphalt has been processed into RAP, it’s then combined with new liquid asphalt binder and virgin aggregates to create fresh hot mix asphalt. The RAP usually makes up 20-80% of the total content, mixed with 10-40% new asphalt cement and 20-50% virgin aggregates.

The specific composition will depend on the quality of the reclaimed asphalt pavement and the performance specifications required for the new pavement. The percentage of RAP used can potentially go up to 100% for some low-traffic applications. However, most asphalt mixes incorporate at least some virgin materials to achieve suitable engineering properties.

Introducing new asphalt binder helps rejuvenate the old binder attached to the RAP and provides improved adhesion. Virgin aggregates are generally angular crushed rocks that provide stability to the new pavement layer. RAP particles tend to be more rounded from their previous use. The shape and texture of the aggregates impact how well the materials compact and bond.

Lab testing is performed to design an optimal asphalt mix meeting gradation and volumetric targets. The goal is to use the highest amount of recycled materials while still achieving durability and performance. Quality control continues as the hot mix is produced to ensure it meets specifications. Proper blending and heating are critical for recycled asphalt incorporation.

asphalt recycling

Heating It Up!

The key to reusing RAP is heating it up and blending it with the right proportions of new materials. This all happens in an asphalt plant. The RAP chunks have surface areas already coated with asphalt binder, so they don't require as much new liquid asphalt to be added compared to using all virgin materials.

The reclaimed asphalt pieces are first heated and dried to improve workability and adhesion with the new binder and aggregates. Hot new asphalt cement is added to recoat the RAP pieces and bind everything together. Virgin aggregates might be incorporated to improve the quality and performance characteristics of the final product.

hot asphalt mix

Paving the New Asphalt Mix

Once the old asphalt has been recycled into a fresh hot mix, it can be hauled to the paving site for installation. Paving contractors receive the hot mixture in dump trucks, which keep it at a high temperature. The hot mix asphalt is then spread and compacted with rollers to form the new smooth pavement surface.

The heat helps compact and densify the recycled asphalt mix as it cools. The end result is a durable new asphalt road, driveway, or parking lot constructed partially from recycled materials. No one even knows the difference!

asphalt paving crew

Why Recycle Asphalt?

Asphalt recycling provides both environmental and economic benefits. Reusing old asphalt reduces the amount of virgin natural resources needed for paving. It also saves on disposal costs to landfill old asphalt, which takes up valuable space.

Incorporating recycled asphalt pavement into new hot mix asphalt can lower material expenses by 20-50%. The cost savings add up when you consider the vast amounts of asphalt used for roads. Recycling also saves on the energy and emissions associated with trucking virgin aggregates.

Some estimates show that recycling can cut CO2 emissions from pavement construction by over 20%. With concerns about climate change and sustainability growing, asphalt recycling provides a greener solution.

recycle sign

The Future of Asphalt Recycling

Asphalt recycling methods will continue advancing to maximize reuse and achieve energy, cost, and emissions reductions. For example, research is looking into ways to increase the percentage of RAP used. Producing warm mix asphalt at lower temperatures could also boost energy efficiency compared to traditional hot mix production.

While asphalt recycling may not seem glamorous, it provides a practical way to reuse one of the most abundant wasted materials on the planet. Next time you drive on a smooth asphalt road, there's a good chance it contains recycled materials!

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What is the difference between asphalt and recycled asphalt?

Asphalt is a mixture of bitumen and aggregate that is used to pave roads, driveways, and parking lots. Recycled asphalt, also called reclaimed asphalt pavement (RAP), is made by crushing and processing old asphalt that is removed from the ground. The RAP is then combined with new asphalt binder and virgin aggregates to create fresh hot mix asphalt. While recycled asphalt contains reused old asphalt, traditional asphalt is made entirely from new materials.

What is recycled asphalt used for?

Recycled asphalt can be used to construct new roads, highways, driveways, parking lots, runways, and other pavement surfaces. The reclaimed asphalt pavement (RAP) is incorporated into new hot mix asphalt at asphalt plants. Typically 20-80% of the content of new asphalt mixes comes from recycled RAP. Using recycled asphalt reduces the need for virgin aggregates and provides significant cost savings on materials for paving projects.

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