Abstract
Geopolymer composite has been synthesized at room temperature by mixing metakaolin, potassium silica solution and ceramic grog based on sintered schistous clay. Ceramic aggregate has been added in an amount from 250 to 325% of metakaolin weight. In this study, standard sieve analysis, particle size analyzer and electron microscopy were applied for a detailed investigation of the ceramic filler. The effect of aggregate gradation according to Fuller's model on mechanical strength and thermomechanical behavior during and after thermal exposure at 1000°C was investigated. The thermal properties of geopolymer matrix formulated by main molar ratios of SiO2/Al2O3=2.6 and H2O/K2O=18.50 were studied by TGA-DSC analyzers. A significant weight decrease was observed up to 250°C, which is attributed to the loss of free and tightly absorbed water. According to DSC, the temperature range from 800°C to 1000°C represents a stable region without additional crystallization. XRD revealed that after thermal exposure at 1000°C, the kaolinite phase disintegrated completely and quartz content was significantly reduced. No substantial differences in the content of illite, mullite and titanium dioxides anatase and rutile were observed. It is evident that the addition of the investigated ceramic granular reinforcement resulted in a reduced thermal shrinkage with respect to non-reinforced geopolymer. The aggregate-to-metakaolin weight proportion of 250% and the gradation design according to Fuller's model reduced thermal shrinkage of geopolymer composite from 2.243% to 1.212% at 1000°C. The results have shown that a higher content of fine ceramic particles under 90µm and gradual distribution of other fractions from 150 to 710µm leads to an improved dimensional stability after thermal exposure. Potassium-based geopolymer reinforced with fine ceramic particles revealed a constant flexural strength of ∼12MPa and a compressive strength of ∼90MPa, both in initial state and after exposure at 1000°C.
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