Life cycle assessment of urban pavements: Environmental impact analysis of integrating waste silt in hot mix asphalt

Over the past decade, numerous studies have explored the incorporation of recycled aggregates into asphalt concrete to reduce the environmental impacts associated with the production of hot mix asphalt (HMA). Nonetheless, only a limited number of these studies have specifically investigated the substitution of waste silt for limestone fillers. This study seeks to enhance understanding of the environmental implications of using waste silt in asphalt concrete pavement, applying the life cycle assessment (LCA) methodology. The analysis includes both ‘cradle-to-gate’ and ‘cradle-to-grave’ approaches to compare the environmental impacts of four different asphalt mixtures: 1) a control mixture with virgin aggregates, 2) a mixture incorporating silt, 3) a mixture with calcinated waste silt, and 4) a mixture with flash calcinated waste silt. The environmental assessment employs the non-renewable cumulative energy demand (nr-CED) and global warming potential (GWP) as primary indicators, spanning a projected lifecycle of 30 years. Furthermore, the ReCiPe midpoint method is utilized to focus on the most critical environmental indicators, including terrestrial, marine, and freshwater ecotoxicity, human carcinogenic and non-carcinogenic toxicity, and land use impacts. Preliminary results indicate that while the recycled mixtures show increased environmental benefits per kilogram of asphalt concrete produced compared to the control mixture during the production phase, the longevity of the control mixture surpasses that of the recycled alternatives over the complete 30-year lifecycle, resulting in lower overall environmental burdens. • From a ‘cradle-to-gate' analysis, the use of the untreated waste silt, increasing the environmental benefits of the mixture and decrease the energy demand associated with its production; • The process of calcination has a greater impact in terms of energy demand and emission of CO2; • In the cradle-to-grave approach, the control mixture performed better in terms of environmental properties, due to its higher lifespan and mechanical properties; • HMA NS turns out to be the least beneficial in a long-term perspective from an environmental point of view.