Use of industrial by-products in urban transportation infrastructure: Argument for increased industrial symbiosis

The incorporation of roadways into a region's industrial ecology is an ideal method of managing some of the industrial by-products (IBPs) that may be generated. Current management of these industrial by-products is through beneficial use (for certain types of materials), but also stockpiling or landfilling, which have economic and environmental implications. IBPs (coal ash, foundry sand and slag) are compared here to virgin aggregate for use in the sub-base of roadway construction and/or repair in an optimization analysis to minimize the transportation impacts in the greater Pittsburgh urban region. The life cycle impacts associated with the choice of material (virgin or IBP) are also evaluated in this paper, and it is shown that IBP usage results in lower life cycle impacts in all categories. Additionally the transportation costs are 25% less for the IBP usage than for the use of virgin aggregates due to the closer proximity to the IBP source materials. The combination of reduced economic and environmental costs provide a strong argument for state transportation departments to develop symbiotic relationships with large IBP producers in their regions to minimize impacts associated with roadway construction and maintenance with the additional benefit of improved management of these materials.