A new hydration kinetic model based on boundary nucleation and growth mechanism with time-dependent growth rate: Application to quantitively characterize the influence of alkali on the early hydration of cement

In this study, a boundary nucleation and growth model with a time-dependent growth rate was proposed to quantitively characterize the precipitation of CSH. The newly constructed model was typically applied to quantitively analyse the influence of alkali content on the growth of CSH, and the value-taking equations of the time-dependent growth rate of CSH in various alkali content systems were proposed and verified. The experimental and simulation results proved that a high soluble alkali content stimulated early hydration (within the initial several hours) and inhibited the late growth of CSH (>20 h) in cement paste. The time-varying ion concentrations in cement solutions were the main driving force for the change in the growth rate of CSH with time. Likewise, the variation in the aqueous phase properties of cement pastes also explains the influence of alkali content on the growth rate of CSH, i.e., the high initial pH of the solution with high soluble alkali led to the high supersaturation degree and high growth rate of CSH, consuming large amounts of calcium ions and in turn reducing the later supersaturation degree and growth rate. The newly constructed model is also expected to precisely characterize the factors that have a significant influence on the precipitation of cement hydrates.