Reaction Kinetics and Thermodynamic Modeling of Sodium Hydroxide Activated Slag Paste

Abstract

The technology of alkaline activation of calcium aluminosilicate materials, as an alternative to Portland cement to produce a clinker-free material, can address the energy and environmental concerns associated with Portland cement production. As this technology attracts more and more attention in recent years, there are increasing researches carried out on the thermodynamics of alkali-activated slag cement. However, none of the thermodynamic modeling studies were carried out in combination with the reaction kinetics of alkali-activated slag. As a result, the modeling results were expressed in term of reaction extent instead of time, which makes it difficult and inconvenient to compare with the experimental results that are usually indicated as a function of time. In order to deal with this issue in this study, the reaction kinetics of sodium hydroxide activated slag (SHAS) was studied through the measurement of heat evolution rate and quantified as a function of time using the modified Jander equation. The quantification of reaction kinetics enables the correlation between the reaction extent and time, by which the hydration of SHAS can be thermodynamically simulated in a time scale. The simulated elemental concentrations in the aqueous solution show a good agreement with the experimental results in the altering trend, and match the experimentally measured solubility data to be within ±1 order of magnitude. The phase assemblages of SHAS simulated as a function of time using thermodynamic modeling, shows no obvious dependence on the Na2O content in the range of 4% to 8%. Based on the modeled phase assemblages, some properties can be calculated as a function of time, such as chemical shrinkage, capillary porosity, etc.