The recycling use of MSWI bottom ash as road construction material for carbon emissions reduction based on life cycle Assessment—A case study in China

This study evaluates the potential of municipal solid waste incineration-bottom ash (MSWI-BA) as a partial substitute for natural aggregates (NAs) in asphalt pavement, focusing on carbon emissions reduction. A comparative life cycle assessment (LCA) was conducted for a 5.142-km municipal road (Guangying Avenue, Sichuan, China) under two scenarios: a conventional pavement with NAs and a pavement incorporating MSWI-BA aggregates (MAs) at optimised (Alternative A) and maximised (Alternative B) substitution rates. The LCA covered raw-material production, transportation, and construction phases, using carbon emission factors (CEFs) and a Data Quality Indicator-Monte Carlo uncertainty analysis for robust quantification. Results indicate that high substitution of Mas yields significant carbon savings. Under Alternative B (70 % MA in the base layer and 100 % in the subbase/capping layers), the pavement saved approximately 2.78 × 10⁴ tonnes of NAs and reduced life-cycle emissions by about 31 %. The greatest reductions occurred in lower layers, with base, subbase, and capping courses achieving 51 %-78 % CE reductions, compared to only 5 % in the surface layer. Transportation emissions partially offset benefits, as MAs were transported 156 km compared to 8 km for NAs. Local processing (Alternative B within 50 km) is recommended to maximise net gains. Despite a modest 7 % increase in construction-phase energy use for MA paving, the overall carbon benefit remains clear. These findings highlight the scalability of MSWI-BA for low-carbon road construction and provide practical insights for engineers and policymakers pursuing sustainable infrastructure solutions.