The ambivalent role of aluminum in concrete: Inhibition of silicate dissolution vs. ASR prevention

• Applicant: Dr. Elisabeth John
• Subject Area: Construction Material Sciences, Chemistry, Building Physics
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 574103344

Ranking as the third biggest contributor to global CO₂ emissions, the cement industry is a significant factor in climate change. Given the persistent growth of the construction sector, finding sustainable solutions to reduce these emissions has become imperative. Innovations such as low-CO₂ binders, carbon capture and utilization technologies, and energetically optimized production processes are indispensable for mitigating these emissions. Nevertheless, the most straightforward and efficient strategy to reduce the carbon footprint of cement is to partially replace clinker with supplementary cementitious materials (SCMs). However, the introduction of SCMs not only reduces the strength development of composite cements but also further complicates the already intricate cement reaction system. Additional aluminum introduced by SCMs presents a particularly interesting and ambivalent influence. It proves advantageous in mitigating alkali-silica reaction (ASR)-induced damage, while simultaneously adversely affecting the hydration kinetics of the original cement, thereby diminishing its reactivity. For both reactions, changes to the dissolving surfaces or the product formation have been discussed in the literature. The influence of aluminum over the lifetime of concrete is not yet fully understood; however, several studies point to a significant role of surface interactions and the influence of foreign ions such as sulfate and calcium. Seeding with C-S-H crystals has been shown to be a valuable method for probing hypotheses regarding the mechanisms of cement hydration. C-S-H seeds provide alternative nucleation pathways and might locally alter the pore solution of hydrating cement. Thus, they may be able to counteract aluminum’s negative early effect while preserving its advantageous long-term impact. In this project, we aim to investigate the interaction of aluminum with silicate surfaces in depth using dedicated surface analytical methods under various relevant conditions. We will evaluate the extent to which C-S-H seeds can intervene in this reaction system. By intentionally triggering changes in nucleation pathways, we will test hypotheses regarding changes in product formation. Ultimately, we aim to determine whether it is possible to diminish the initial disadvantage and preserve the long-term advantage of aluminum ions in blended cements.

• DFG Programme: Research Grants