Influence of particle size on the early hydration of slag particle activated by Ca(OH)₂ solution

This paper investigates the influence of slag particle size on its hydration speed at particle level in the early age. Slags were separated with sieves into groups of different size fractions, considering a wide range of sizes. The chemical compositions of each group were analyzed by X-ray Fluorescence (XRF). Activated by 15% Ca(OH)₂ (by mass) at water/powder ratio 1:1, the hydration heat evolution was recorded by isothermal calorimetry up to 84 h and converted to hydration degree. Based on the hydration degrees and particle size distributions, the rate of increase of hydrating layer thickness of each single slag particle (k value) was calculated. Results reveal that k values of coarse particles are higher than that of fine particles. Coarse particles contain higher content of CaO but relatively lower content of MgO, Al₂O₃ and SiO₂, resulting in higher reactivity index of (CaO + Al₂O₃ + MgO)/SiO₂.