The construction industry faces significant environmental challenges due to its reliance on Portland cement, which accounts for up to 7% of global CO2 emissions (Benhelal, Zahedi, Shamsaei, & Bahadori, 2013). In the Netherlands, initiatives like the ”Betonakkoord” aim to
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The construction industry faces significant environmental challenges due to its reliance on Portland cement, which accounts for up to 7% of global CO2 emissions (Benhelal, Zahedi, Shamsaei, & Bahadori, 2013). In the Netherlands, initiatives like the ”Betonakkoord” aim to mitigate these emissions. Geopolymer concrete, which utilizes alkali-activated binders derived from industrial byproducts, presents a promising alternative. However, the carbon footprint associated with conventional activators remains a concern. This research investigates the
viability of using waste aluminium etching solutions as a sustainable source of alkali activators, with the goal of minimizing the environmental impact of geopolymer concrete and providing a practical recycling pathway for waste aluminium etching solutions.
The research begins with the characterization of the aluminium etching solution received from APT Extrusions B.V., which serves as the basis for thermodynamic modelling to assess the influence of activator composition on reaction products. This modelling informs the development of six distinct mixture designs based on a BFS precursor, each varying in activator composition. The experimental study is organized into three sections: the first investigates the reaction process through dissolution tests, isothermal calorimetry, and pore solution chemistry; the second examines the fresh and hardened properties, including setting time and strength; and the third presents an analysis of the reaction products using techniques such as TGA, XRD, FTIR, and SEM-EDS.
The results indicate that aluminium-containing activators significantly influence reaction kinetics, initially delaying strength development. However, mixtures with higher aluminium content exhibit enhanced long-term strength due to increased geopolymerization and the formation of more cross-linked C-(N-)A-S-H gel phases. The delayed reaction kinetics are attributed to the passivation of Si sites and the formation of metastable phases,
which temporarily impede the dissolution of slag particles. Although aluminium etching solutions can improve the mechanical performance of the mixtures, optimizing aluminium concentration is critical to avoid shrinkageinduced cracking. To validate this optimization, a new mixture was developed to prevent crack formation while enhancing strength development using the aluminium etching solution.
This study underscores the potential of aluminium etching solutions as eco-friendly activators in the production of sustainable cement alternatives. Given the promise of this byproduct, future research should focus on the dissolution behavior of the precursor in the new activator, detailed investigations of the reaction kinetics within the early age, and an in-depth exploration of metastable phases. Additionally, a comprehensive understanding of fresh and hardened properties, with a particular emphasis on autogenous shrinkage, will be essential for practical applications.
