Effect of silica particle size on the formation of calcium silicate hydrate [C-S-H] using thermal analysis

Maddalena, Riccardo and Hall, Christopher and Hamilton, Andrea (2019) Effect of silica particle size on the formation of calcium silicate hydrate [C-S-H] using thermal analysis. Thermochimica acta, 672. pp. 142-149. ISSN 0040-6031

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    Abstract

    Calcium silicate hydrate (C-S-H) is made by mixing calcium hydroxide (portlandite), silica and water at two calcium oxide to silica (C/S) ratios, using nano-silica and silica fume. We investigate how silica particle size influences the rate and extent of formation of C-S-H at room temperature by isothermal calorimetry, thermal analysis, Raman spectroscopy and X-ray diffraction. Rate of reaction increases as silica particle size decreases, and is five times greater with nano-silica than with silica fume. Final composition depends only on initial C/S ratio. Compositions at 28 days are estimated from thermogravimetric and X-ray diffraction data. There is a weak maximum in the reaction rate of nanosilica pastes about 20–30 h after mixing. The overall kinetics is well described by a simple exponential (first-order) reaction model. The early-time reaction rate around the rate maximum is described by an Avrami model.