Journal
THERMOCHIMICA ACTA
Volume 672, Issue -, Pages 142-149Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.tca.2018.09.003
Keywords
Calcium silicate hydrate; Nano-silica; Silica fume; Heat of hydration; Calorimetry; Raman spectra
Funding
- UK Engineering and Physical Sciences Research Council (EPSRC) [EP/L014041/1]
- EPSRC [EP/L014041/1] Funding Source: UKRI
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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.
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