Abstract

The behaviour of refractory castables with regard to wet mixing, flow over time, and setting and strength development depends on the composition of the mix and external factors such as ambient temperature, water quality, intensity of mixing, etc. Variation of the castable behaviour in those properties mentioned above can challenge the whole installation and trigger countermeasures on site. Sometimes these countermeasures are detrimental for the performance of the installation, e.g. through increased water demand and higher porosity as consequence. In general, conventional castables can be considered more robust due to their higher cement content when compared to low and ultra-low cement mixes. The latter ones provide higher performance in use but are more sensitive for changes in installation conditions. Their formulation is also more complex with various fine matrix components and additives for dispersion and setting control. The raw materials especially in the matrix fines can have a significant influence on the robustness of low and ultra-low cement castables. Trace contaminations and homogeneity in raw materials, under- or over-dosage of small additive amounts, aging behaviour in the ready dry-mix, and different wet-out times depending on the mixing intensity are just examples here. In order to overcome problems with too low or too high ambient temperatures during the installation, sometimes heated or cooled water is used, even if the effect might be questionable. Trials in the laboratory were performed under defined conditions for systematic investigation of dry mix and mixing water temperature influence. They also provide information on the robustness of additive systems at these different ambient temperatures. In addition, experiences and results with matrix compounds including cements are reported, which can contribute to higher robustness in installation of more sophisticated low and ultra-low cement castables.