Effects of slag and temperature on the reaction kinetics of alkali-activated fly ash/slag

Knowledge gaps on the reaction kinetics of alkali-activated slag/fly ash (FA) binders need to be clarified to optimise the formulation design and gain approval for practical field application. The effects of slag substitution and reaction temperature on the heat release during alkali activation were investigated using isothermal conduction calorimetry. The results showed that a higher reaction temperature accelerated the reaction kinetics, while a higher slag content improved the reaction degree. The reactivity of slag surpassed that of FA. As the slag content was increased from 0% to 80%, the apparent activation energy (AAE) increased from 23.00 kJ/mol to 42.03 kJ/mol. However, further slag addition up to 100% reduced the AAE to 40.90 kJ/mol. Kinetic equations for alkali activation were formulated using the Johnson–Mehl–Avrami–Kolmogorov model and the Arrhenius equation. The calculated reaction degree, based on the heat release and selective dissolution test, fitted well with the empirical equations.