Use of industrial by-products in urban roadway infrastructure: Argument for increased industrial ecology

Incorporating the beneficial use of industrial by-products into the industrial ecology of an urban region as a substitute or supplement for natural aggregate can potentially reduce life cycle impacts. This article specifically looks at the utilization of industrial by-products (IBPs) (coal ash, foundry sand, and foundry slag) as aggregate for roadway sub-base construction for the Pittsburgh, Pennsylvania, urban region. The scenarios compare the use of virgin aggregate with the use of a combination of both virgin and IBP aggregate, where the aggregate material is selected based on proximity to the construction site and allows for minimization of transportation impacts. The results indicate that the use of IBPs to supplement virgin aggregate on a regional level has the potential of reducing impacts related to energy use, global warming potential, and emissions of nitrogen oxides (NO_x), sulfur dioxide (SO₂), carbon monoxide (CO), PM₁₀ (particulate matter-10 microns), mercury (Hg), and lead (Pb). Regional management of industrial by-products would allow for the incorporation of these materials into the industrial ecology of a region and reduce impacts from the disposal of the IBP materials and the extraction of virgin materials and minimize the impacts from transportation. The combination of reduced economic and environmental costs provides a strong argument for state transportation agencies 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.