Early hydration of C2S doped with combination of S and Li

Abstract

Production of low-energy cements would result in energy saving and lower CO2 emissions related to reduced consumption of fuel and high-grade limestone as a raw material. Belite rich clinker, made more reactive by doping with combination of S and Li, could possibly be one of the low-energy alternatives for Portland cement clinker. Paper describes the preparation of doped belite and deals with its early hydration and reactivity. Belite rich clinkers were prepared in laboratory in high-temperature solid state synthesis. Pure substances were used for the preparation of raw meal and clinker. Early hydration heat flow development of cement pastes was monitored by isothermal calorimetry, changes in phase composition by “in situ” X-ray diffraction and TGA/DTA and microstructure by SEM-SE. Heat flow exotherms were correlated with quantified phase composition at given time. Intensity and position of main exothermic peak related to hydration of C3S is changing with increasing Li content. Doping of the C2S by the S or the combination of S and Li significantly increases the reactivity of the C2S-rich cement. The formation of C–S–H products is a continuous process that depends mainly on C3S during first 6 h and then is supported by slow reaction of β-C2S. The reactivity of C2S is affected by the timing of the hydration of other clinker phases. Two generations of portlandite formation detectable as a double endotherm on TGA/DTA can be attributed to hydration of C3S and β-C2S.