Abstract :
[en] The increasing demand for sustainable construction materials and the urgent need to reduce greenhouse gas emissions have driven research toward innovative solutions that promote both resource efficiency and carbon mitigation. Municipal solid waste incineration bottom ash (MSWI-BA), a by-product generated by waste-to-energy facilities, represents a promising alternative to natural aggregates in concrete and other construction applications. However, its direct utilization is often limited by high alkalinity, the presence of reactive mineral phases, volumetric instability, and concerns regarding the release of contaminants.
This PhD thesis investigates accelerated carbonation as a treatment strategy for MSWI-BA and evaluates the feasibility of incorporating the treated material as a secondary aggregate in concrete. The work examines the characteristics of MSWI-BA, the mechanisms governing carbonation, and the key operational parameters influencing carbonation efficiency, while assessing the technical, environmental, and practical implications of its valorisation in construction materials.
The research was conducted through a multi-scale experimental approach. First, the physical, chemical, and environmental characteristics of MSWI-BA were investigated to identify the factors governing its suitability for concrete production. Accelerated carbonation was subsequently studied under controlled conditions to evaluate the effects of particle size, moisture content, CO₂ concentration, treatment duration, and gas flow rate. Static carbonation experiments identified moisture availability as a critical parameter controlling carbonation efficiency, with the highest CO₂ uptake achieved under wet carbonation conditions. Dynamic carbonation tests performed in a percolation column further examined the influence of gas flow rate and ash-bed thickness and provided insights into the potential scale-up of the carbonation process.
The carbonated MSWI-BA was then evaluated as a partial replacement of natural aggregates in concrete. Different replacement levels and particle size fractions were investigated to assess their effects on fresh-state properties, mechanical performance, durability, and environmental behaviour. The results were compared with those obtained using conventionally matured bottom ash. Particular attention was given to the influence of replacement rate, aggregate fraction, and bottom ash quality on concrete performance. In addition, the potential for higher substitution rates was explored using the coarse 6/20 mm fraction. The findings identified key material quality requirements and application conditions necessary for the reliable use of carbonated MSWI-BA in concrete production.
Finally, a life cycle assessment demonstrated that accelerated carbonation requires limited energy input while simultaneously enabling permanent CO₂ sequestration. Increasing the replacement of natural aggregates with carbonated MSWI-BA progressively reduced the environmental impacts of concrete, particularly with respect to climate change, particulate matter formation, acidification, and photochemical ozone formation. These benefits were primarily attributed to the substitution of virgin aggregates, the valorisation of a waste-derived material, and the uptake of CO₂ during carbonation. Overall, the results demonstrate that accelerated carbonation is an effective strategy for transforming MSWI-BA into a valuable secondary resource for concrete production, contributing to both circular economy objectives and the decarbonisation of the construction sector
