Studies on the interaction of starch-based superplasticizers with alkali-activated 2:1 metaclays

• Applicants: Professor Dr.-Ing. Frank Dehn; Dr.-Ing. Stephan Partschefeld
• Subject Area: Construction Material Sciences, Chemistry, Building Physics ; Architecture, Building and Construction History, Construction Research, Sustainable Building Technology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 571427145

The aim of the research project is to synthesize alternative superplasticizer structures based on chemically modified starch for alkali-activated 2:1 metaclays and to elucidate the mechanism of action with regard to particle-polymer interactions. The synthesis of alternative superplasticizer structures is based on a low molecular mass cassava starch. By chemical modification, anionic starch-based superplasticizers are first synthesized by varying the anionic groups (carboxyl, sulfonic acid and phosphate groups) and the molecular parameters (amount of charge and molecular mass) are determined. Subsequently, the solubility and stability in alkaline activators (NaOH, KOH) are determined by varying the molarity. Furthermore, cationic starch-based superplasticizer structures are synthesized by implementing ammonium groups while varying the amount of charge and are also recorded with regard to solubility and stability in the alkaline activators typical for geopolymers. An illite-dominated raw clay and a smectite-dominated raw clay are used as starting components for the production of 2:1 metaclays. The raw clays are first characterized in terms of their chemical and mineralogical composition and particle size and then thermally activated. The aim is to determine the optimum calcination temperature first for the individual raw clays and then for mixtures of the two raw clays with regard to their reactivity. The reactivity of the 2:1 metaclays and metaclay mixtures (mixture of meta clays in a ratio of 70:30, 50:50 and 30:70) is determined by the R³ test, IR spectroscopy and by solubility experiments with variation of the alkaline activators (NaOH, KOH) and their molarity. In addition, AAB mortar formulations are developed. Rheological experiments are used to characterize the flow behaviour of alkaline activated binder glues (AAB) consisting of 2:1 metaclays and alkalis with the addition of the synthesized superplasticizers and classified according to rheological models (Herschel-Bulkley, Bingham). The first aim is to identify which superplasticizer structures achieve the highest dispersing performance depending on the molecular parameters and concentration determined and whether differences in dispersing performance occur with the illite-dominated metaclay and smectite-dominated metaclay and their mixtures. Investigations into the influence of effective starch-based superplasticizers on the reaction behaviour, mechanical properties, porosity, durability and microstructure of AAB glues are to be carried out. The results are summarized in an empirical interaction model and dependencies between molecular parameters of the superplasticizers, type of calcined clays and the solid mortar properties of the geopolymers are defined.

• DFG Programme: Research Grants