Slag and Activator Chemistry Control the Reaction Kinetics of Sodium Metasilicate-Activated Slag Cements

The reaction kinetics of four commercial ground granulated blast furnace slags with varying percentages of MgO (6 to 14 wt.%), activated with four different doses of sodium metasilicate, were evaluated using isothermal calorimetry. The reaction kinetics were strongly dependent on the dose of the alkaline activator used, and the chemical and physical properties of the slag. When using low concentrations of sodium metasilicate as an activator, the MgO content in the slag influences the kinetics of the reaction, while the CaO content plays a more significant role when the concentration of metasilicate is increased. This study elucidated a close relationship between the dose of the alkali-activator and the chemistry of the slag used, although it was not possible to identify a clear correlation between any of the published chemically-based “slag quality moduli” and the calorimetry results, highlighting the complexity of blast furnace slag glass chemistry, and the importance of the physical properties of the slag in defining its reactivity.