Speaker
Description
The study is focused on how the hydration of a refractory binder system consisting of commercial white CAC and tabular alumina is changed by the addition of different silica fumes. Four silica fumes, two each of identical quality grade, but obtained from different batches, were selected and characterized by their physical and chemical properties (XRF, laser granulometry, BET). Then they were added to the system with a SF/CAC ratio of 1 and w/c of 1.4 at 23 °C. Even though no clear differences could be observed between the fumes of the same grade with regard to chemical bulk analysis and specific surface area, they exhibited different rheological behavior after paste preparation. To examine this, the hydration was followed via heat flow calorimetry, in-situ XRD and pore solution analysis. Additionally, hardness development within the first hours of hydration was measured with a Gillmore-needle device (IMETER).
It was found that the mixes with lower viscosity show an additional heat flow event located between the initial heat flow after mixing and the main reaction. This intermediate event is likely correlated to an initial dissolution of CA, which occurs directly after water addition in the mixes without this event. Also, an increased rate of hardness development was observed during the intermediate event. A potential link to the amount of dissolved silicon provided by the silica fumes shown in the pore solution data was examined by adding solutions containing low amounts of sodium silicate to the mixes. By this, the event could be induced in the two systems previously not showing this reaction. Higher concentrated solutions retard the hydration until a critical point, where the main reaction is eventually suppressed for at least 48 h.
Affiliations
Friedrich-Alexander-Universität Erlangen-Nürnberg, GeoZentrum Nordbayern, Mineralogy, Schlossgarten 5a, 91054 Erlangen, Germany, tillmann.schramm@fau.de
| Title | Hydration of CAC-alumina systems in the presence of silica fume |
|---|---|
| Keywords | Hydration, Silica Fume, Refractories |