Ecological and energetic optimization of concretes: Challenges in the processing of calcined illitic and smectitic clays - solution approaches using tailor-made superplasticizer structures

• Applicants: Professor Dr. Johann Plank; Professor Dr.-Ing. Karl-Christian Thienel
• Subject Area: Construction Material Sciences, Chemistry, Building Physics
• Term: since 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 314833927

In the preceding project, it was found that while metamuscovite and metakaoline can be fluidized well, it was however impossible to disperse metaillite with conventional polycarboxylate superplasticizers.For this reason, in the present submission the focus is on the behavior of calcined illite with respect to its chemical-mineralogical properties and its surface structure after calcination. Apart from a physical characterization, comprehensive mineralogical investigations (particle size & morphology, water sorption capacity, cation exchange capacity, zeta potential) are planned to capture its surface properties (layer charge). Utmost attention will be given to the development of the surface charge in the cementitious system. For this purpose, zeta potential measurements will be carried out especially in a pore solution in which ions taken up by the calcined clay will be replenished immediately. This way, the actual surface charge existing in cement can be assessed under equilibrium conditions (saturated adsorption). Based on these data, the spatial distance between Ca2+ ions adsorbed on the surface of the calcined clay can be calculated. Relative to this subject, a cooperation with the institute for “Applied mineralogy/Clay science” at KIT (Dr. Emmerich) is planned to incorporate the well-known expertise of this research group on illitic clays into this project.Because illite often occurs as mineral interstratified with smectite clay it is planned to study such mixed layer clay and pure smectite as well. This series from metaillite → metaillite-smectite → metasmectite should allow to develop a model describing the specific mineralogical changes within this sequence.The second part of the project addresses the rheological properties of the calcined clays as well as their interaction with superplasticizers. Based on the findings on the surface structure and charge, tailor-made superplasticizers shall be synthesized which according to a steric analysis of the molecular geometry of their functional groups can form a complex with Ca2+ ions sorbed on the surface of the calcined clay. For this purpose, MPEG-, APEG- and HPEG-based polycarboxylates with varied spatial distance between the carboxylate groups, an amphoteric as well as sulfonated and phosphated comb polymers will be synthesized and tested. To achieve certain structures, entirely new synthesis routes incl. RAFT/ATR polymerization may need to be developed. This way, a profound understanding of why conventional superplasticizers cannot fluidize metaillite, and which specific molecular parameters are required to achieve such fluidizing effects shall be achieved.The fluidizing effect of the optimized superplasticizers shall be evaluated further via rotational viscosimetry. Finally, for an in-depth understanding of the interaction superplasticizer-cement-calcined clay it will be investigated via pressure filtration whether the polymers adsorb preferentially on cement or on the calcined clay.

• DFG Programme: Research Grants