Effect of particle size distribution and calcium aluminate cement on the rheological behaviour of all-alumina refractory castables

Previous works based on statistical design of experiments (DoE) defined a model all-alumina self-flow refractory castable (SFRC) with optimized particle size distribution for simultaneous high flowability index (FI) and superior post-sintering performance.This work compares the SFRC rheological behaviour and setting time with those of alternative all-alumina castables with different Andreasen aggregate particle size distribution modulus, and of the equivalent castables containing calcium aluminate cement. The model castable showed Bingham behaviour with low yield stress, viscosity and thixotropy, guaranteeing easier casting and less wear in the casting and/or projection equipment. However, as the coarse particle fraction increases, the castable flow tends to be non-linear and changes from Bingham to Herschel–Bulkley. The cement containing castables quickly loose flowability despite the applied shear.This work confirmed previous conclusions based on FI measurements and demonstrates the adequacy of the use of FI values in the calculation of FI response surface by DoE.

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► Castable flowability index tests are interpreted through rheology tests.
► Castables with optimized particle size composition show better workability.
► All-alumina fresh pastes retain flowability as long as there is an applied shear.
► Equivalent castables with cement quickly loose flowability even with applied shear.
► Self-flow all-alumina castables result in easier casting and less equipment wear.