In 1998, The King County Roads Division tested a process in which deteriorated concrete roadways are rehabilitated by crushing this concrete surface into rubble and using this as a base for a new asphalt road surface. This process is about one-fourth the cost of other techniques, because it avoids the expense of landfill disposal and of new aggregate for the roadbed. These applications have resulted in cost-savings, but are still considered trial uses, since the availability and quality of recycled glass aggregate is highly variable. Antifreeze manufactured with re-refined ethylene glycol has been available under a contract maintained by Procurement Services Division since 1991. This contract also requires that the material be re-refined in a manner that meets all regulatory requirements, thereby avoiding the discharge of a toxic material into local waterways and ensuring compliance with State and Federal regulations.
Asphalt can be economically and effectively recycled and used for many applications.
Documentation of King County's past use of recycled asphalt is available for a road project and as road base at the Regional Justice Center . Asphalt made with recycled rubber was used in an overlay project by Roads Division in 1998. No significant differences in noise-levels were found between the asphalt surfaces, though all were quieter than the deteriorated concrete surface, with noise reduced from between 2.6 to 4.8 decibels. Compost-amended topsoil is specified by the Roads Maintenance Section and by Roads Engineering Section in construction projects. The contractor has indicated that it plans to be able to furnish this material for future contracts.