Yes, asphalt pavement is consistently recognized as the most recycled material in the United States when measured by tonnage. Asphalt pavement is a composite material, primarily made up of aggregate—such as stone, sand, and gravel—bound together by asphalt cement, a black, sticky substance derived from crude oil. Because of its inherent makeup, the material maintains its structural integrity and can be reused repeatedly without significant degradation. This circular life cycle makes it an ideal candidate for reuse within the massive infrastructure system of roadways across the country.
Quantifying the Claim: Why Asphalt Ranks Highest
The scale of asphalt recycling is immense, dwarfing that of more commonly perceived materials like paper or aluminum. In the United States, asphalt pavement recycling consistently exceeds a volume of 90 million tons annually, with over 94 million tons of Reclaimed Asphalt Pavement (RAP) used in 2021 alone.
The high recycling rate, which often exceeds 99%, is a direct result of the continuous demand for road rehabilitation. Aluminum cans, for example, have a much lower recycling rate, typically around 55%. Unlike consumer-driven recycling programs, asphalt recycling is an industrial process embedded within the road construction industry itself. The material’s ability to be easily collected, reprocessed, and immediately reintroduced into new pavement mixtures ensures that virtually all reclaimed material is put back into service, conserving billions of dollars annually in avoided raw material costs.
The Reclaiming Process: Turning Pavement into RAP
The process begins with the removal of the existing road surface, typically through cold milling. Specialized milling machines mechanically grind off the worn asphalt layer to a specific depth, which can range from a shallow two inches for surface repairs to eight or more inches for full-depth reclamation. This collected material, now referred to as Reclaimed Asphalt Pavement (RAP), is transported to a processing facility for further refinement.
The raw RAP undergoes a series of steps to prepare it for integration into new mixes. Large chunks are first broken down using crushing equipment, such as jaw or impact crushers, to create a more manageable particle size. This is followed by a crucial screening and fractionating stage, where the material is sorted by size and checked for contaminants to ensure a consistent and uniform product. This quality control is particularly important because the aged asphalt binder within the RAP has become stiffer and harder over time.
Once processed, the RAP is ready to be incorporated into new pavement mixtures using one of two primary methods. Hot Mix Asphalt (HMA) recycling involves introducing the RAP into a heated drum or batch plant, where it is blended with virgin aggregate and new asphalt binder. Alternatively, cold mix recycling, often used for lower-volume roads, skips the high-heat process and combines the RAP with an emulsified or foamed asphalt and a recycling agent without the application of heat. In both cases, the material is tested for its gradation and residual binder content before a rejuvenating agent may be added to restore the aged properties of the asphalt cement, ensuring the new road will perform as well as one made entirely from virgin materials.
New Life for Old Roads: Applications of Recycled Asphalt
The vast majority of the reclaimed material finds its way back into new Hot Mix Asphalt (HMA) for high-traffic roadways, accounting for over 94% of all RAP use. On average, new asphalt mixtures in the United States contain around 21% RAP, but this percentage can be much higher in certain specialized mixes.
While major roadways are the main destination, RAP also has several other practical applications in civil engineering projects. The material is commonly used in the foundational layers of road construction, such as the unbound aggregate base or subbase layers, where its structural stability is highly valued. Additionally, it can be repurposed as fill material for embankments and road shoulders. By using RAP in these varied ways, the industry significantly reduces the demand for newly quarried stone and sand, simultaneously conserving natural resources and minimizing the environmental impact of transportation and mining operations.