The hydration kinetics of slag is generally divided into three stages: (1) a nucleation period during which product growth is accelerating, (2) a phase boundary controlled stage, and (3) a diffusion controlled stage.
The reaction degree of slag in blended cement is influenced by many factors. The main factors affecting the reaction of slag in blended system include the reactivity of slag that could be defined as (C+A+M)/S, the fineness of grinding (specific surface area), the vitreous fraction of slag, the replacement level of slag in blended system, the hydration temperature and the water/solids ratio.
Precisely, the rate of reaction of slag decreases with the decreasing water/solids ratio and with increasing proportion of slag in the blend. Higher hydration temperatures increase the reactivity of slag. However, the composition of cement and the incorporation of additional gypsum in slag blended cement have no influence on the extent of reaction of slag at ages of 28 days to 1 year, though variations in Portland cement can affect early strength. The following figure is a representation of the effect of hydration conditions and slag characteristics on the reactivity of slag.
Representation of the effect of hydration conditions and slag characteristics on the reactivity of slag.