Two synthesis pathways (one- and two-part) in alkali-activated binders were compared using ground granulated blast furnace slag (GGBFS), mineral wool (MW) activated using dry and liquid alkali activators with similar Na₂O/SiO₂ modulus. The effect of activator type on reaction kinetics, strength development, setting times, and durability shows that one-part synthesis does not only improve early strength, but also provide better durability properties. While the highest compressive strength (56 MPa, 90 days) was achieved for the one-part mix (DM), the reaction products (presence of Mg–Al layered double hydroxide and C–S–H-like phases) observed for both mortar mixes were similar. The DM mortars showed better resistance to sulfate attack than two-part mix (WM) mortars and sets faster. The results highlight the significance of the one-part pathways in the synthesis of alkali-activated materials.

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The pursuit of low-carbon binders as alternatives to Portland cement has sparked interest in developing alkali-activated materials (AAM).¹ Using municipal solid waste incineration (MSWI) bottom ash as precursor for AAM has attracted increasing attention as it offers a sustainable, resource-efficient solution to mitigate the environmental impacts associated with the landfill of MSWI bottom ash. However, the varying properties of MSWI bottom ash present challenges in its wide application as AAM precursor. This review provides a comprehensive overview of advances in MSWI bottom ash-based AAM,² with a particular focus on the relationship between the physicochemical properties of MSWI bottom ash and the engineering properties of MSWI bottom ash-based AAM. This work consolidates the most up-to-date understanding of the reaction mechanism and reaction products of MSWI bottom ash, along with the existing knowledge about mix design and microstructure formation of MSWI bottom ash-based AAM. The factors influencing the engineering properties of MSWI bottom ash-based AAM are detailed, and the environmental impacts of MSWI bottom ash-based AAM are reviewed. Ultimately, this review provides recommendations for the standardized and effective use of MSWI bottom ash as AAM precursor.@en

In recent years, the widespread application of waste incineration technology has led to an increased generation of municipal solid waste incineration (MSWI) bottom ash. There is growing interest in the use of MSWI bottom ash as a mineral resource to produce construction materials. The utilization potential of MSWI bottom ash is determined by its chemical and mineralogical compositions, which can vary from incineration plant to incineration plant, and even from batch to batch within a single incineration plant. The quality of MSWI bottom ash often needs to be improved before it can be used as supplementary cementitious material (SCM) and precursor for alkali-activated materials (AAM). This review summarizes the composition of MSWI bottom ash sourced from different regions and the proposed treatments for quality upgrades of MSWI bottom ash. The reactivity of MSWI bottom ash as SCM and AAM precursor is discussed. Finally, the challenges regarding the use of MSWI bottom ash as a mineral resource for the production of construction materials are examined and possible solutions are provided.

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Abstract: The increasing amount of fluidized bed combustion (FBC) ash is putting pressure on researchers to invent novel methods for utilizing the ash. The low reactivity and heavy metal content constrict the use of FBC ash in the same way as coal ash from pulverized combustion. Four FBC fly ashes from different power plants were granulated with sodium silicate solution in order to produce artificial aggregates. All aggregates matched the definition for lightweight aggregate according to the EN 13055-1 standard. The strongest aggregates were produced from fly ashes that had the highest X-ray amorphous material content and the highest amount of selectively soluble SiO₂ and Al₂O₃. However, the same leaching problem (leaching of the anionic species) as with coal fly ashes was observed with the FBC fly ashes. The simultaneous high shear granulation and alkali activation of FBC ashes showed that artificial aggregates with satisfactory physical properties, such as density and strength, can be obtained even from low-reactive fly ashes that contain heavy metals. Graphical Abstract: [Figure not available: see fulltext.]

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