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Kestutis Baltakys Anatolijus Eisinas Jolanta Doneliene Tadas Dambrauskas Gabriele Sarapajevaite 《Ceramics International》2019,45(2):2881-2886
In this work the impact of Al2O3 amount on the synthesis (200?°C; 4–8?h) of calcium aluminium silicate hydrates (CSAH) samples and their influence on the early stage hydration of calcium aluminate cement (CAC) was examined. It was found that the amount of Al2O3 plays an important role in the formation of calcium aluminate hydrates (CAH) because in the mixtures with 2.7% Al2O3 only calcium silicate hydrates (CSH) intercalated with Al3+ ions were formed. While in the mixtures with a higher amount of Al2O3 (5.3–15.4%), calcium aluminate hydrate – C3AH6, is formed under all experimental conditions. It is worth noting that the largest quantity of mentioned compound was obtained after 4?h of hydrothermal treatment, in the mixtures with 15.4% of Al2O3. It was proved that synthesized C3AH6 remain stable up to 300?°C and at higher temperature (945?°C) recrystallized to mayenite (Ca12Al14O33), which reacted with the rest part of CaO and amorphous structure compound, resulting in the formation of gehlenite (Ca2Al2SiO7). Moreover, the synthesized C3AH6 addition induced the early stage of CAC hydration. Besides, in the samples with an addition, the induction period was effectively shortened: in a case of pure CAC (G70) paste, hydration takes about 6–6.5?h, while with addition – only 2–2.5?h. The synthesized and calcinated compounds was characterized by using XRD and STA analysis. 相似文献
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The influence of gyrolite additive on the hydration properties of ordinary Portland cement was examined. It was found that the additive of synthetic gyrolite accelerates the early stage of hydration of OPC. This compound binds alkaline ions and serves as a nucleation site for the formation of hydration products (stage I). Later on, the crystal lattice of gyrolite becomes unstable and turns into C–S–H, with higher basicity (C/S ~ 0.8). This recrystallization process is associated with the consumption of energy (the heat of reaction) and with a decrease in the rate of heat evolution of the second exothermic reaction (stage II). The experimental data and theoretical hypothesis were also confirmed by thermodynamic and the apparent kinetic parameters of the reaction rate of C3S hydration calculations. The changes occur in the early stage of hydration of OPC samples and do not have a significant effect on the properties of cement stone. 相似文献
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K. Baltakys A. Eisinas T. Dizhbite L. Jasina R. Siauciunas S. Kitrys 《Materials and Structures》2011,44(9):1687-1701
Influence of hydrothermal synthesis conditions on the gyrolite specific surface area, dominant pore size and their differential distribution by the radius were determined. The synthesis of gyrolite has been carried out in unstirred suspensions within 32, 48, 72, 120, 168 h at 200°C temperature from a stoichiometric composition (the molar ratio of CaO/SiO2 was equal to 0.66 where water/solid ratio of the suspension was equal to 10.0) of the initial CaO and SiO2·nH2O mixture. It was found that the structure of gyrolite and the shape of dominated pores (from pores between parallel plates to cylindrical pores) changes prolonging the duration of hydrothermal synthesis. The stable gyrolite crystal lattice was formed only after 120 h of isothermal curing. Its specific surface area S BET = 38.28 m2/g, the radius of dominant plate pores r p = 30–40 Å, the cumulative pore volume ΣV p = 0.08 cm3/g. It was determined that the pores with 4.0–5.0 nm radius were dominated in gyrolite structure after 168 h of synthesis. It was estimated that the ion exchange between gyrolite with less orderly structure in Zn(NO3)2 + NH4OH alkaline solution ( ${c_{{{\text{Zn}}^{2+}}}}$ —0.3 g/dm3) proceeds more faster and effectively. 相似文献
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