Influence of fireclay granules on calcium aluminate cement hydration and properties after firing

This study investigates the effect of granules produced from dispersive fireclay using liquid glass as a binder on the hydration of calcium aluminate cement (CAC). The peculiarities of the hydration process were evaluated from the results of calorimetry, thermal analysis, X-ray diffractometry (XRD), scanning electron microscopy (SEM), and mechanical property tests, as well as the relative viscosity of the cement pastes. It was determined that the granules were capable of entrapping water and releasing it later, shortening the incubation period and increasing the maximal heat release rate during the CAC crystallisation stage and total cumulative heat as compared with the control samples with the same active cement part and containing dispersive fireclay particles, which are cement inert. The redistribution of water owing to the addition of granules also resulted in more C 2 AH 8 and AH 3 in CAC pastes containing granules than in those containing dispersive fireclay. Because of the reaction between the water solution containing dissolved cement minerals and sodium silicate film (dried liquid glass), the hydrogel-like phases form inside the granules during the hydration, which fill the gaps between the fireclay particles, and after firing at 1100 °C, form a glassy phase enveloping the fireclay particles and binding them to each other, providing the granules with integrity and contributing to their strength. The specific structure formed by the addition of fireclay granules did not change the density of the composite dramatically, resulting in 7.4%–18.5 % higher strength after drying with 7.5%–15 % granule addition and ∼11 % higher strength after sintering at 1100 °C with 5 % granule addition (compared with compositions containing dispersive fireclay). Granule addition of 30 % was excessive, causing significant strength loss.