Strength of kaolinite-based ceramics: Comparison between limestone- and quartz-tempered bodies

The addition of temperwas a common practice in the fabrication of traditional ceramics. The presentwork shows the effects of limestone or quartz added as temper to a kaolinitic clay, on the strength of the ceramic body. With this purpose ceramic tests were prepared adding the 5, 15 and 25% of each temper to a kaolinitic clay. Unimodal skewed grain size distributions (GSDs) for temperwere used instead on single grain sizes used in previous experimental works. Furthermore, samples were fired at 500, 750 and 1000 °C in order to analyse the effect of firing temperature on ceramic strength. A correlation between the strength and the porosity, the mineralogy and the microstructure of the samples is presented. Results shows that while temper improves the strength of 500 °Cand 750 °C-fired bodies, it worsens that of samples fired at 1000 °C. Moreover, while at 500 and 1000 °C limestone-tempered materials are less strong than quartz-tempered ones, at 750 °C the opposite occurs. For quartz-tempered bodies fired up to 750 °C, no difference in strength changing the temper GSD is observed, while in other cases the coarser the temper, the less strong the ceramic.