Climate impacts of using mineral incineration bottom ash in Swedish road construction: Assessing the influence of...

Sweden has begun using mineral incineration bottom ash (MIBA) as a subbase material in road construction. Two regulatory-compliant projects feature contrasting transport distances between MIBA handling options, such as landfills and road construction sites, providing valuable case studies for exploring the climate impacts of different project settings for MIBA utilization. This study evaluates the climate impacts of MIBA utilization in road subbase construction, exploring on key factors influencing these impacts in Sweden. These factors include: (i) transport fuels from fossil- to bio-based, (ii) aggregate materials from primary to secondary sources, (iii) MIBA handling from use as landfill cover to landfilling, and (iv) MIBA processing from no treatment to high-intensity treatment. The two cases are assessed using scenario-based life cycle assessment (LCA), with 1 km of road as the functional unit and limited to climate change impact category. Using the basket-of-products approach, the reference cases are assessed followed by the sensitivity analysis conducted by defining three alternatives for each factor, generating 81 exploratory scenarios (3⁴) per case. Results show that MIBA utilization is generally climate-beneficial, although the magnitude of benefits varies substantially, ranging from -675 to -29 t CO₂ eq. in Case 1 and from -454 to +72 t CO₂ eq. in Case 2. The analysis identifies critical project settings required to ensure climate benefits and synthesizes findings into guiding principles for future project development. Further research demands material characterization including geotechnical and leaching tests, to better account for functional comparability and enable a comprehensive LCA that extends beyond climate impacts.