Influence of silica micropowder on the hydration of calcium aluminate cement

In most cases, silica powder is used together with cement and other binders. Silica powder has a higher surface area, which can provide more nucleation sites for the hydration products of calcium aluminate cement, which is beneficial to the crystallization of the hydration products, and improves the cementation between the castable particles, thereby increasing the castable Strength of Silica powder can change the hydration product composition of calcium aluminate cement.

Studies have shown that adding silica powder to the clay clinker castable combined with calcium aluminate cement and curing at 40°C can affect the production and conversion of calcium aluminate cement hydration products. Pure calcium aluminate cement is hydrated for 24 hours, and the production of β-C2AH8 and α-C2AH8 of its hydration products increases with the extension of curing time, but the production of α-C2AH8 gradually decreases after 24h. After adding silica powder to calcium aluminate cement, the production of α-C2AH8 and β-C2AH8 can reach the maximum after curing for 24 hours. After 24h, α-C2AH8 and β-C2AH8 were converted into calcein hydrate C2ASH8. Silica micropowder is collected by vapor precipitation in industrial production, and it contains a variety of alkali metal impurity elements inside, which makes it exhibit different chemical properties in aqueous solution, such as zeta potential and pH value. Some studies have shown that silica micropowders with different pH values in aqueous solutions have a greater impact on the hydration process of calcium aluminate cement (CAC).

With the increase of pH value (2.77, 6.91 and 7.66), silica powder can increase the hydration rate of calcium aluminate cement and promote the generation of hydration products. This may be because the higher the pH value of silica micropowder, the more OH- is ionized in the aqueous solution, which accelerates the "hydroxylation" process in cement hydration, thereby accelerating the hydration reaction of calcium aluminate cement and promoting the hydration products of cement are formed; When the pH value of the silica powder is low enough, the aqueous solution will dissociate more H+, and part of it will neutralize the OH- and hinder the "hydroxylation" process of calcium aluminate cement, thus Delayed the hydration rate of cement.

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