Physical and mineralogical properties of calcined common clays as SCM and their impact on flow resistance and demand for superplasticizer

Physical properties of calcined clays differ significantly and depend to a large extent on the mineralogy of the raw clays. In this study, four common clays and one kaolinite-rich mine tailing are calcined at 800 degrees C. Their impact on flow properties of blended cement paste is measured via rotational viscometer and analyzed by (modified) Bingham and Herschel-Bulkley model, combined with the calculation of flow resistance. The demand for superplasticizers rises significantly due to the special characteristics of calcined clays, namely particle size, a high water demand and negative zeta potential. Muscovite present in raw clay is critical as it increases the water demand, yield stress and viscosity. In general, the addition of three industrial polycarboxylate-based super plasticizers (PCEs) reveals good dispersion. Calcined kaolinite-rich clays require more PCE compared to calcined clays rich in 2:1 phyllosilicates. The studied PCEs interact well with all types of metaphyllosilicates besides metamuscovite.

Automated summary

This study investigates the impact of calcined clays on the flow properties of blended cement paste. The demand for superplasticizers increases significantly due to the particle size, water demand, and negative zeta potential of calcined clays. The presence of muscovite in raw clay is critical as it increases water demand, yield stress, and viscosity. The addition of industrial polycarboxylate-based superplasticizers shows good dispersion except for metamuscovite.