Waste from hydrogen generation with recycled aluminum: characterization and potential application in Portland cement

The transition to a sustainable energy matrix requires strategies that integrate hydrogen generation with waste valorization. In this study, hydrogen is produced from the reaction of recycled aluminum in an alkaline medium and the resulting solid residues were evaluated as partial substitutes for Portland cement. The residues were characterized by SEM-EDS, ICP-OES, and XRD, which revealed metallic impurities (Cu, Mg, Fe), confirmed crystalline phases, and indicated alkaline characteristics from the NaOH medium. Mechanical tests were performed on cement pastes with 1% and 3% residue substitution and compared to a control sample. The control sample exhibited the highest compressive strength values, while the 1% substitution maintained equivalent performance without compromising mechanical integrity. In contrast, the 3% substitution showed strength reduction after 90 days, evidencing a saturation limit in the matrix. Microstructural analyses indicated that the residues did not hinder cement hydration, supporting the formation of C-S-H and C-A-S-H phases, while preserving porosity and the interfacial transition zone. Moreover, replacing 1% of cement by residue corresponded to a mitigation of ≈ 2.4 kgCO2 per m³ of concrete, highlighting its environmental benefit. These results demonstrate that residues from hydrogen generation can be incorporated into cement formulations, combining waste reduction, performance retention, and carbon footprint mitigation.