This thesis debutes a systematic study of the rheological behavior of cements blended with both metaphyllosilicates and calcined common clays. With their addition, the flow resistance, yield stress and viscosity of blended cement pastes increase in parts significantly as shown via rotational viscometer tests. The analysis of single-phase materials reveals the influence of mineralogical composition of raw clays, especially their concentration of kaolinite, different types of 2:1 phyllosilicates, and quartz. The correlation of rheological behavior with physical characteristics of metaphyllosilicates and calcined common clays, such as particle size, zeta potential, water demand, and surface area is evaluated critically. The dispersion performance of a broad variety of superplasticizer (lignosulfonates, NSF polycondensate, polycarboxylate-based co-polymers (PCEs)) is determined via mini slump tests and rotational viscometer tests. The demand for superplasticizer is directly linked to the flow resistance of the respective reference mixture. It increases to different extents depending on the calcined clay added, its water demand, particle fineness, and negative zeta potential; the latter mainly resulting from kaolinite content. Regardless of their increased demand, the performance of superplasticizers in calcined clay blended cements is as efficient as it is in plain cements. In case of PCEs, a higher anionic charge density enables a better initial dispersion. All conventional macromonomers exhibit an overall good to excellent dispersion performance. Metamuscovite is the only phase that perturbs the performance of superplasticizers and is sensitive towards the type of superplasticizer. The use of calcined clays can lead to rapid slump loss, which is stronger with the addition of conventional PCEs than with NSF polycondensate as time related mini slump tests and rheological tests show. The addition of lignosulfonates may limit this phenomenon, but often goes along with significant retardation effects. This thesis investigates one possible solution to prevent rapid slump loss, namely the introduction of hydroxyethyl methacrylate into the PCE polymer. Its decomposition into ethylene glycol and carboxyl groups in alkaline media leads to a later adsorption of the latter and can enable a subsequent dispersion. The study reveals the total phyllosilicate content in clay as well as the specific surface area of the calcined clay as decisive parameters for the functionality of this special type of polymer. Complementing tests study the early hydration of calcined clay blended cements in the presence of superplasticizers via isothermal calorimetry, as well as in situ XRD and ultrasound method on selected samples. The early hydration kinetics depend mainly on the characteristics of the calcined clay as well as on the superplasticizer dosage. Overall, the retardation is minor in calcined clay blended cements. This is related to the increased surface area which favors the formation of early hydration products - despite the adsorption of superplasticizers onto binder particle surfaces. An enhanced ettringite formation of calcined clay blended cements enables an unhindered silicate hydration and transformation of ettringite to hemicarboaluminate, even in the presence of most superplasticizers. This thesis reveals the suitability of a wide array of calcined common clays and their limitations as future SCM regarding their impact on rheological behavior in combination with the correct choice of superplasticizer. A fair assessment and a careful selection provided, their use can meet the high demand for sustainable cementitious materials and help improving the ecological footprint of modern concrete.    «

This thesis debutes a systematic study of the rheological behavior of cements blended with both metaphyllosilicates and calcined common clays. With their addition, the flow resistance, yield stress and viscosity of blended cement pastes increase in parts significantly as shown via rotational viscometer tests. The analysis of single-phase materials reveals the influence of mineralogical composition of raw clays, especially their concentration of kaolinite, different types of 2:1 phyllosilicates,...    »