Calcined clays represent a promising material because of worldwide deposits of suitable clays and low CO2 emissions during calcination process for facing the increasing demand for sustainable supplementary cementitious materials (SCM). One side effect of calcined clays is their high water demand as compared to cements. The application of superplasticizers is inevitable to ensure the workability of concretes with calcined clays as SCM. Early hydration kinetics, namely silicate and aluminate reaction of clinker phases, can be significantly modified by superplasticizers. Until now, their compatibility was barely investigated although it depends mainly on type of superplasticizer and on mineralogy of calcined clays. Main objective of this study is to evaluate the influence of selected superplasticizers on reaction kinetics of blended cementitious systems containing different types of calcined clay by investigating their hydration behavior. Four calcined clays are investigated: one calcined mixed layer clay which contains in its natural form approximately 25 w{%} kaolinite and 45 w{%} 2:1 clay minerals. The interaction with superplasticizers and those individual phyllosilicates is investigated on an industrially-used flash-calcined metakaolin, a calcined illitic clay and a calcined muscovite. Two different types of superplasticizers are used. One ordinary Portland cement and one Portland limestone cement are used as cement components. The hydration kinetics of blended cement pastes is measured by isothermal calorimetry in combination with in-situ X-ray diffraction during first 48 hours of hydration at a temperature of 25 °C. The findings are completed by investigations with scanning electron microscopy at different timings during early hydration.    «

Calcined clays represent a promising material because of worldwide deposits of suitable clays and low CO2 emissions during calcination process for facing the increasing demand for sustainable supplementary cementitious materials (SCM). One side effect of calcined clays is their high water demand as compared to cements. The application of superplasticizers is inevitable to ensure the workability of concretes with calcined clays as SCM. Early hydration kinetics, namely silicate and aluminate react...    »