Tire-Derived Aggregate as Embankment Fill
This project is located in Milpitas, California, at the intersection of Interstate 880 (I-880) and Dixon Landing Road. The site is underlain by about 30 feet of San Francisco Bay mud.
Due to the poor strength of the bay mud, lightweight fill was specified for most fill sections to reduce total settlement. The project owner is the California Department of Transportation (Caltrans). Two sources of lightweight fill were considered: tire-derived aggregate (TDA) and lightweight aggregate
TDA was chosen because it had a lower unit weight (in-place unit weight of 50 pounds per cubic foot) than the lightweight aggregate (unit weight of about 60 pounds per cubic foot) and because it was less expensive.
TDA was supplied through an interagency agreement between the California Integrated Waste Management Board (CIWMB) (now the Department of Resources Recycling and Recovery, or CalRecycle)--and the California Department of Transportation (Caltrans). Under the agreement, CIWMB was responsible for procuring the TDA and having it delivered to the site. Some of the TDA was delivered in advance and stockpiled at a nearby landfill to facilitate delivery in this traffic-congested area. In total, 6,627 tons or 662,700 passenger tire equivalents (PTE) of TDA was used for this project.
Project design. TDA was placed with conventional construction equipment in two layers up to 10 feet thick. The layers were separated by 3 feet of low-permeability soil. The embankment applied a vertical stress of 2,250 pounds per square foot (psf) to the foundation soil compared to 3,750 psf for an embankment constructed with conventional earth fills. This is a 40 percent reduction in vertical stress.
Cost savings. This project used approximately 660,000 waste tires and saved Caltrans $477,000 compared to using lightweight aggregate for the project. This shows that TDA can be a cost-effective alternative to lightweight aggregate.