New Insights Into the Effect of Calcium Hydroxide Precipitation on the Kinetics of Tricalcium Silicate Hydration

After decades of research, there still is no universal agreement on the basic mechanisms that are responsible for the induction period (Stage 2) in cement hydration at early times. This paper surveys several theories and critical experimental data on early‐age hydration kinetics of tricalcium silicate, the most abundant phase in Portland cement clinker. Using HydratiCA, a kinetic cellular automaton model of cement hydration and microstructure development, we investigate two of the leading hypotheses on the mechanism of slow hydration in Stage 2, and see for each one the implications of suppressing the growth of calcium hydroxide formation. Each hypothesized mechanism leads to quite different kinetic behavior when calcium hydroxide is suppressed, a result which indicates a line of future experimental inquiry that could decisively determine the Stage 2 mechanism. Furthermore, the simulations demonstrate how the early theory of calcium hydroxide triggering might be reconciled to the more modern theoretical models and to the experimental data.