In Maine, engineers turn about 1 million scrap tires a year into lightweight highway fill; the shredded rubber stabilizes embankments built on weak marine clay

In Maine, shredded tyres have been repurposed as construction material. Tyres that have been shredded to produce tyre-derived aggregate (TDA), also referred to as tyre chips, have been used as a fill material in highway embankments in areas with weak foundations, according to U.S. Federal Highway Administration guidance on civil engineering applications of scrap tyres. The largest use of tyres was in the construction of the Portland Jetport Interchange. Approximately 1.2 million passenger‑tyre equivalents from an abandoned stockpile were converted into tyre‑derived aggregate used as lightweight fill in highway approach embankments. The tyre aggregate was used in weak marine clay to reduce the load from the embankment on the foundation. This project shows how used tyres can be applied in civil engineering. Used tyres have a low unit weight, making it possible to build embankments without the loads created by conventional soil fills. The Maine Turnpike Authority saved approximately $250,000.

Shredded tyres reduce the load imposed on weak foundations

The primary engineering benefit of TDA is its low unit weight compared with natural soil. In the case of an embankment on weak and compressible soil, the weight of the filling becomes a direct stress to which the foundation is subjected. Reducing this stress helps stabilize the embankment and limit problems caused by weak foundation soil. Lightweight material is especially useful when removing or reinforcing the foundation soil is difficult. The investigation Design of Highway Embankments Using Tyre Chips analyzed the feasibility of using tyre chips as lightweight fill for highway construction through laboratory model tests, numerical analyses and field investigations.


The Portland Jetport interchange was built over about 12.2 metres of marine clay

The interchange's approach roads were built on the 12.2 m of weak marine clay described above, which had low undrained shear strength and was unsuitable for supporting conventional heavy embankments. Traditional soil fill would have placed a heavy load on the weak clay foundation and raised stability concerns. Other foundation-improvement options were evaluated, but their higher cost made lightweight fill the more economical choice. Using tyre shreds saved roughly $250,000 compared with alternative lightweight fills. Tyre-derived aggregate was used in the approach-road embankment to reduce the load on the weak foundation.

About 1.2 million passenger tyres supplied the tyre-derived aggregate

Other Maine highway projects consumed on the order of one million additional passenger-tyre equivalents of tyre-derived aggregate, drawn from the same statewide stockpile-cleanup effort. Instead of treating the tyres as waste, the project used their properties to solve a geotechnical challenge. The embankments were built with tyres incorporated into the fill.

The tyre fill was about $250,000 cheaper than alternative lightweight materials

Cost was also a factor in selecting tyre-derived aggregate for the project. The Portland Jetport project documented savings of about $250,000 compared with other lightweight-fill options. To save money and reduce the load on the marine clay, they chose to use waste tyres from an existing stockpile.

Tyre-derived aggregate must be placed as an engineered fill

Using shredded tyres under a road is different from burying whole tyres under an embankment. Processing and placing TDA must meet engineering requirements. Federal guidance on highways suggests using tyre shreds and chips as materials for embankments and other civil engineering structures. Designers must account for settlement, drainage, containment and proper soil cover. The study also considered tyre chips as engineered fill rather than unprocessed waste. Their performance depends on how they are integrated into the embankment.

Maine turned large tyre stockpiles into construction material

The construction of the highway is part of a wider scheme to address the issue of stockpiling of abandoned tyres in Maine. State records show that Maine had hundreds of illegal tire stockpiles in the early 1990s, including some with thousands of dumped tyres. Maine has cleared millions of tyres from stockpiles, and a substantial share, including the more than 2 million passenger-tyre equivalents cited above, has been recycled into civil engineering projects such as highways.

Other Maine highway projects also used tyre-derived aggregate

The example of the Portland Jetport interchange is not unique as regards the use of shredded tyres. Other projects by the Maine Department of Transportation and the Maine Turnpike Authority also used shredded tyres in civil engineering. For embankments over weak soils, the light weight of tyre-derived aggregate may matter more than its origin as waste. The Maine Department of Environmental Protection reports that scrap-tire cleanup efforts across the state have fed more than 60,000 tons of tyre-derived products into construction projects, including three Maine Turnpike Authority interchange projects beyond the Jetport.

However, the tyres do not replace all elements of the highway structure. The tyres are used in an engineered embankment built for specific geotechnical conditions.