Hydration Kinetics of Calcium Aluminate Cement with Calcium Sulfate Hemihydrate in Presence of Li+ and Tartaric Acid

摘要

Explained in the present paper are the reaction mechanisms responsible for the acceleration or retardation of the hydration of CA - the principal phase in calcium aluminate cement - in mix with CSH0.5 (calcium sulfate ˉ hemihydrate) in presence of Li or tartaric acid. Ettringite is the major + phase forming during hydration. Normalized quantitative phase analysis of aqueous pastes by XRD methods in combination with heat flow calorimetry has provided new evidence about the hydration processes. The time-dependent heat flow can be correlated clearly with the dissolving process of the CA and CSH_(0.5). When Li+ is added Li2Al4(OH)6[(OH)2nH2O] ˉ . is formed as a reactive intermediate compound that is consumed and then formed again. Li+ acts here as a catalyst for ettringite formation. On addition of tartaric acid a sparingly soluble calcium tartrate is formed which tends to retard hydration. This effect of tartaric acid ceases as soon as equilibrium is established between calcium tartrate in the solid phase and in the solution.^