Effect of silica fume additions on the hydration behaviour of calcium aluminates

In the recent refractory castables technology, the calcium aluminate cement is being replaced in increasing proportion by very fine matrix components, such as silica fume and colloidal alumina. More efficient particle packing and the resulting lower water requirements have been the proposed explanation for the improved green density and strength, without sacrificing the castable workability. However, the aluminates are still responsible for the hydraulic setting of the castable. The hydration mechanisms of single calcium aluminates, and mixtures thereof, synthesised by combustion reaction of the appropriate nitrate-urea mixtures, were recently investigated. The present work describes the effect of silica time additions on the hydration behaviour of pure single calcium aluminates, also produced by combustion reaction. Results on the hydration mechanisms, the microstructure development and the resulting physical and/or mechanical properties of the hydrated samples, as a tiction of the water/cement ratio and the silica content, me presented and discussed.JNICT-Portugal - PALOP/24