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Title: Feasibility Study on PCE Based Superplasticizers in Calcined Clay Blended Cements with Focus on the Type of Phyllosilicate

Author(s): Ricarda Sposito, Matthias Maier, Nancy Beuntner and Karl-Christian Thienel

Publication: Symposium Paper

Volume: 354


Appears on pages(s): 233-246

Keywords: calcined clays, flow resistance, hydration kinetics, superplasticizers, workability

DOI: 10.14359/51736077

Date: 7/1/2022

The use of calcined clays as clinker replacement requires the addition of effective superplasticizers. Phyllosilicates in clays are known for their contribution to the pozzolanic reactivity after calcination. Previous investigations on single components of clays identified metaphases of phyllosilicates as the challenging minerals, whereas quartz can promote a proper workability and effectiveness of superplasticizers. It is still under discussion which type of calcined phyllosilicate (1:1 or 2:1), namely metakaolin or metamuscovite/metaillite is more challenging regarding their interaction with superplasticizers. A comparison of these single phyllosilicates among each other and with calcined clays relevant to the cement industry is limited due to physical properties differing too significantly. The study focuses on the question of whether calcined clays with 1:1 or 2:1 phyllosilicates interact better with polycarboxylate ether-based superplasticizers (PCEs) in cementitious systems under the consideration of their physical properties. Five calcined common clays originating from German clay pits are used. The clays differ significantly in their mineralogical composition before calcination, especially regarding their amount of kaolinite, muscovite, and quartz. A Portland limestone cement is replaced by 30% by weight of calcined clay. Two PCEs are used that exhibited good compatibilities with calcined clays in investigations beforehand. Measurements with a rotational viscometer determine the flow resistance each 5, 30, 50, and 105 minutes after water addition. In combination with the adsorption behavior analyzed via zeta potential measurements, the results give fundamental knowledge about the efficiency of superplasticizers depending on the type of calcined clay.