MORE-CASH: Effects of minor and heavy metal oxides on the structure and reactivity of CAS glasses as novel SCMs and the resulting C-A-S-H phase composition and the environmental compatibility

• Applicant: Professorin Dr. Alisa Machner
• Subject Area: Construction Material Sciences, Chemistry, Building Physics
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 584513610

The phase-out of coal combustion and the increasing shift in the steel industry away from blast furnaces pose a significant challenge for the construction industry. Until now, the by-products from these extensive industrial processes, fly ash and granulated blast furnace slag, were the most popular supplementary cementitious materials for replacing clinker in cement and thus reducing CO2 emissions. Therefore, the search for new additives is focused on filling the gap left by these materials. A basic prerequisite for this is that the supplementary cementitious materials used have a sufficiently high reactivity. This reactivity is affected by many factors, particularly its chemical composition. Possible future supplementary cementitious materials, such as steel slag, introduce some metal and heavy metal oxides into the cementitious system, which can affect reactivity and negatively impact the environment. Our research project, therefore, examines the effects of various metal and heavy metal oxides on the structure of the amorphous part of the supplementary cementitious materials, their reactivity, and environmental compatibility. For this purpose, a calcium aluminosilicate glass with a composition similar to granulated blast furnace slag will be synthesized. In addition, variations of this glass will be produced by replacing one of the main oxides with a quarter of a metal oxide. In addition to analyzing the structure of the supplementary cementitious materials, their reactivity will be investigated using the R3 test and dissolution tests. By using the glasses in cementitious systems, it will be examined whether the previously identified trends can be transferred to cement systems. For this purpose, in addition to analyzing the resulting phases, the composition of the strength-imparting C-S-H phases in particular will be investigated. Finally, the cement samples will be used to determine the form in which the metal ions are bound in the cementitious matrix and how easily they can be leached out, depending on the pH, to be able to assess the environmental compatibility of supplementary cementitious materials containing the corresponding metal oxides. Based on the results obtained, supplementary cementitious materials with certain compositions can be specifically sought in the future.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Harald Hilbig