Ceramics-Silikáty 56, (3) 198 - 203 (2012)

The hot moduli of rupture (HMOR) measurements have been performed for the low-cement castable (LCC), the ultra-low cement castable (ULCC), and the no-cement castable (NCC). All castables contained SiO₂-Al₂O₃ based aggregates (burned fireclay and kaolin). The experimental data points have been described using the model based on the Varshni approach within the temperature region 1000-1200^oC and by the model based on the Adam-Gibbs theory above 1400^oC. A smooth but distinct transition between both temperature regions has been observed. The limits and applicability of the models have been analyzed. At lower temperature the loss of strength of castables was attributed to weakening of bonds most probably in the frontal process zone of cracking. At higher temperature, the liquid phase causes slowing down of the crack propagation by formation of the viscous bridging in the following wake region. And finally, at very high temperatures, the castable behaves as very viscous suspension which can be described using models originally developed for molten glasses.