The development of carbon-neutral construction materials has stimulated interest in alkali-activated systems for the valorization of industrial non-hazardous waste. This study proposes an original quantitative approach to assess the reactivity of several wastes, including black and white fly ash, bottom ash, fine glass dust, and float glass polishing sludge, through their use as partial replacements for metakaolin (MK). For-mulations containing 5-50 wt% of fine waste powders (< 45 μm) were prepared and mechanically compared with a reference MK-based geopolymer. Formulations con-taining waste additions to the reference geopolymeric paste were also evaluated to in-vestigate their role as aggregates. Mechanical testing identified black fly ash as the most reactive precursor, achieving a compressive strength of 30 MPa at 50% substitu-tion, compared with 18 MPa for the reference material. Float glass polishing sludge and white fly ash reached approximately 22 MPa at 25% replacement. Conversely, bottom ash and fine glass dust at substitution levels above 5% reduced mechanical performance owing to their high crystallinity and unfavorable Si/Al molar ratios. Mi-crostructural characterization by XRD, FT-IR, density measurements, and SEM was correlated with reactivity. The results provide a basis for performance-based design criteria aimed at the sustainable valorization of locally available industrial by-products in alkali-activated materials.

The development of carbon-neutral construction materials has stimulated interest in alkali-activated systems for the valorization of industrial non-hazardous waste. This study proposes an original comparative approach to assess the cementing reactivity of several wastes, including black and white fly ash, bottom ash, fine glass dust, and float-glass polishing sludge, through their use as partial replacements for metakaolin (MK). Formulations containing 5–50 wt% of fine waste powders (<45 μm) were prepared and mechanically compared with a reference MK-based geopolymer. Formulations containing waste additions to the reference geopolymeric paste were also evaluated to investigate their role as aggregates/fillers. Mechanical testing identified float-glass polishing sludge as the most reactive precursor, achieving a compressive strength of 25 MPa at 10 w% addition, compared with 16 MPa for the reference material. Bottom ash and black and white fly ash reached approximately 19–21 MPa at 5–10% replacement or addition. Conversely, bottom ash at substitution levels above 5% reduced mechanical performance owing to its high crystallinity and unfavorable Si/Al molar ratio. Microstructural characterization by XRD, FT-IR, density measurements, and SEM was correlated with the observed cementing activity. These results provide a basis for performance-based design criteria aimed at the sustainable valorization of locally available industrial by-products in alkali-activated materials.