Influence of water-to-cement ratio on hydration kinetics: Simple models based on spatial considerations

Based on simple spatial considerations, models to describe the hydration kinetics of portland cement are developed and compared to existing experimental data, particularly in terms of the influence of the starting water-to-cement ratio (w/c) on hydration rates. The conceptual basis for the models is to relate the instantaneous hydration rate to local probabilities for the dissolution and precipitation of the cement phases. In the simplest model, hydration kinetics are strictly a function of the volume fraction of local (global) water-filled porosity, as computed based on Power's model for cement hydration. While this simplest model is inadequate to quantitatively describe the observed hydration behavior in real cement pastes with various w/c, a more complicated version of the model that considers both the water-filled porosity and the unhydrated cement volume fractions appears to provide an adequate description. Finally, the models are extended to consider the influence of the replacement of a portion of the cement by an inert filler on the resulting hydration kinetics.