Fine particles play a major role not only in the flowingcharacteristics of castables but also in the final properties of thecastable in application. To optimize the particle packing of thecastable, different kinds of fine aluminas can be used to form thematrix: calcined, semi-reactive, monomodal reactive ormultimodal reactive aluminas. A systematic approach has beenconducted to investigate different ways to optimize particle sizepacking in Low Cement Castable formulations thanks to the useof different kinds of aluminas. Typical average particle size forthese aluminas ranges from 0,3μm to 6μm. The potential of anew alumina product has been explored as a competitivealternative to reactive alumina. It has a median particle diameter(d50) around 3μm and has a monomodal granulometry withsome fines particles around 0.5 microns coming from its specificmilling technology. Dinger and Funk's packing model has beenused to optimize packing design of the castable with thisalumina. In many cases the sole use of this alumina in theformulation can be fully satisfying for the application. In othercases, the combination with a reactive alumina (d50=0,5μm) isuseful to further improve rheological properties. Bimodalaluminas are usually found to be very efficient to achieve goodrheological properties and high levels in applicative refractorytests. The effects of the particle size curve have beeninvestigated to understand the impact on castable properties.Flowability behavior and torque evolution during mixing havebeen followed to characterize rheology. It will be shown thatdifferences between various aluminas can be compensated byusage of specific additives.
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