Samples of bauxite based low- and ultra-low cement castables have been investigated. Main ingredients were Chinese bauxite aggregates, calcium aluminate cement, microsilica and bauxite/alumina fines. Two types of 75 urn fines, bauxite and white fused alumina were tested. The overall starting compositions were 82wt% aggregates and 18wt% fine matrix phase. Cement level was successively adjusted from 0.5 to 6wt% with 8 or 9wt% microsilica. The self-flow of castables decreases with the replacement of fused alumina fines with bauxite fines, as well as with increase in the cement content. The bauxite fines seem to prolong the wet-out process and to lead to lower high-temperature strength in comparison with fused alumina fines. In the sample with 0.5% cement, a hot-MOR of ~12MPa was achieved at 1400°C with white fused alumina fines, whereas the one with bauxite fines showed significantly lower strength, ~5MPa. Similarly with increased cement content, from 0.5% to 6%, the hot-MOR at 1400°C decreased from ~12MPa to ~4MPa. By either replacing bauxite fines with purer alumina fines or reducing cement content, workability and properties of bauxite castables can be dramatically improved. Additionally, the mullite formation and the effect it has on hot properties is discussed using white fused alumina based castables as reference.
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