Beside the coarse and medium grain size distribution, the matrix components play a pivotal role in the performance of refractory castables. Based on practical experience, it is evident that the PSD and the resulting specific surface area of the ceramic matrix exert a significant influence on the processing, setting and sintering properties of refractory castables, which in turn influence each other. However, there is a paucity of knowledge regarding the extent to which the properties of refractory castables are influenced by changes in PSD or specific surface area of the raw materials in the matrix. The objective is to gain a general understanding of this.
To shed more light on this issue, the ceramic matrices were varied, resulting in model castables with gradations in the specific surface area of the matrix. The refractory castables were dispersed using two disparate dispersing agents with different mechanisms of action (electrosteric and steric) at graded concentrations.
This contribution demonstrates that matrices with lower specific surface areas require less mixing energy than coarser ones. A higher specific surface area leads to a lower slump-flow. A shear-thinning behaviour was observed for matrix compositions with higher specific surface areas and a dilatant behaviour for matrix compositions with lower specific surface areas. Higher specific surface areas of the matrix result in an earlier first rise of the US signal, while the addition of more dispersing agent leads to a delayed first stiffening. However, there are clear differences in the setting behaviour of the various dispersing agents.