Los Angeles recycled old street asphalt with microwaves instead of buying virgin paving material; over 800,000 tons were avoided over 5 years, saving approximately $8 million

When an old city road is scraped up for resurfacing, most people probably do not think about where the chunks of asphalt end up. The material can look like little more than a pile of black rubble waiting to be hauled away. In Los Angeles, however, much of that old pavement was given another life. A U.S. Environmental Protection Agency case study on recycling enterprises documented how Cyclean used microwave technology to turn reclaimed asphalt pavement into new hot-mix asphalt for the city's streets.

The EPA's Manufacturing from Recyclables: 24 Case Studies of Successful Enterprises reported that, over five years, Los Angeles had reduced its use of virgin paving material by more than 800,000 tons, while saving approximately $8 million in materials and disposal costs. The case study described the Cyclean operation as an example of how an existing waste material could become a useful feedstock for a new product.

How the microwave process worked


Old asphalt removed during road maintenance does not necessarily have to become waste. Once it is recovered and processed, it is known as reclaimed asphalt pavement, or RAP. The material contains the aggregate and asphalt binder used in the original road, meaning much of what is needed to make new pavement is already present.

At the Los Angeles plant, city crews brought old pavement to the facility, where Cyclean screened it to remove oversized pieces and unwanted fines. The larger pieces were crushed and sent back through the screening process. The material was then sized according to the requirements of the particular pavement mix.

From there, the RAP passed through a warm-air drum dryer that heated it to more than 220°F and removed moisture. It then entered a large microwave oven, where the material was heated to about 300°F. The EPA case study describes the system as using seven microwave generators to achieve that temperature without burning the asphalt. Rejuvenating and anti-stripping agents were then added before the mixture was moved to a heated storage silo.

The finished material was transported hot to paving sites and applied in much the same way as conventional asphalt concrete. The EPA case study said Cyclean's process could produce hot-mix asphalt made from 100% recovered pavement. It also reported that the previous generation of conventional asphalt-recycling technology generally allowed about 25% reclaimed asphalt in new pavement, with concerns about air pollution and safety limiting the amount that could be incorporated. The report attributed the claim that Cyclean produced minimal emissions to the technology's manufacturers, rather than presenting it as an independent finding.

The broader federal literature provides useful context. An EPA report on recycled paving materials said conventional hot-mix technology at the time commonly used around 10% to 22% RAP, while state-of-the-practice conventional technology could achieve substantially higher percentages. It also noted that microwave technology had demonstrated the ability to produce hot recycled asphalt with 80% or more RAP while meeting emissions standards.

A Los Angeles Times article similarly described the Cyclean plant as using microwave equipment to heat ground-up asphalt to roughly 300°F and said the city had been using the resulting material on its streets. The article reported that the process used six microwave transmitters, illustrating why equipment counts can differ between descriptions of the plant.

Where the savings came from

The economic case was not based simply on avoiding the purchase of new asphalt. The EPA case study said Cyclean's technology saved Los Angeles roughly $2 million per year through a combination of disposal savings, reduced virgin-material purchases, and transportation savings. Over five years, the city had reduced its use of virgin paving material by more than 800,000 tons and saved approximately $8 million in materials and disposal costs.

The figures need some context. Cyclean's early commercial arrangement was based on a $4.1 million contract to produce 320,000 tons of recycled hot mix for Los Angeles over a two-year period. That was an early production contract, not a competing figure for the later five-year savings reported by the EPA case study. The technology continued to be used after its initial production period, so the two figures describe different stages of the programme.

By the time of the EPA case study, Los Angeles was using more than 200,000 tons of reprocessed RAP each year in approximately 80% of its maintenance projects. That figure refers to the share of the city's maintenance projects using reprocessed RAP, not to the percentage of recycled material in each asphalt mixture. The distinction matters because the two numbers describe completely different aspects of the programme.

There was also a broader resource benefit. Every tonne of recovered pavement put back into a road reduced the immediate need for virgin paving material. RAP contains valuable aggregate and asphalt binder, and modern highway guidance continues to recognise it as a useful substitute for virgin materials in asphalt mixtures and other road-building applications.

The Los Angeles experiment therefore rested on a relatively simple idea: the material being removed from a road was not necessarily finished with its useful life. Instead of treating the old pavement solely as something to transport away, the city could process it, restore the properties needed for paving, and put it back into another road.

The approach did not eliminate the need for new materials. The Cyclean process used rejuvenating and anti-stripping agents, and the broader recycling literature makes clear that the appropriate RAP percentage depends on the technology, material properties, and mix design. But for Los Angeles, the documented result was significant: hundreds of thousands of tons of virgin paving material were no longer needed, while the city reduced disposal and material costs.

The story is ultimately less about microwaves than about changing how a city views something it has already paid for. An old road may look like waste once it has been milled and removed, but much of its aggregate and asphalt binder can still have value. In Los Angeles, engineers found a way to process that material and send it back onto the streets, turning part of the road being replaced into material for the road that came next.