Comparative life cycle assessment of beneficial applications for scrap tires

Life cycle assessment is used to determine the most environmentally beneficial alternatives for reuse of scrap tires, based on the concept of industrial ecology. Unutilized scrap tires can be a major source of pollution, and in the past decade Federal and state governments in the United States have encouraged the recycling and reuse of scrap tires in a number of applications, ranging from energy recovery to civil engineering materials to utilization of ground rubber in manufacturing. Life cycle inventory data are collected from primary industry sources as well as published literature, and life cycle impact analysis is performed using the TRACI tool. The results indicate that beneficial reuse of scrap tires, particularly in cement plants and artificial turf, provides reductions in greenhouse gas (GHG) emissions, air toxics, and water consumption. For example, every metric ton of tire-derived fuel substituted for coal in cement kilns avoids an estimated 543 kg (CO2 equivalent) of direct and indirect GHG emissions. Taking into account the deductible CO2 from natural rubber, the avoided GHG emissions would be 613 CO2 kg eq. per metric ton. The use of scrap tires for fuel in cement plants provides more reductions in most environmental impact categories compared to other scrap tire applications, excluding application in artificial turf. Although the use of ground rubber for artificial turf offers the greatest environmental emission reductions, it has limited potential for large-scale utilization due to the saturated market for artificial turf. Therefore, the use of fuel derived from scrap tires in cement production appears to be an attractive option in view of its large market capacity and significant potential for environmental impact reductions.