Simulations of tricalciumsilicate (C3S) hydration using a kinetic cellular automaton program, HydratiCA, indicate
that the net rate depends both on C3S dissolution and on hydration product growth. Neither process can be considered
the sole rate-controlling step because the solution remains significantly undersaturated with respect to
C3S yet significantly supersaturated with respect to calcium silicate hydrate (C–S–H). The reaction rate peak is
attributed to increasing coverage of C3S by C–S–H, which reduces both the dissolution rate and the supersaturation
of C–S–H. This supersaturation dependence is included in a generalized boundary nucleation and growth
model to describe the kineticswithout requiring significant impingement of products on separate cement grains.
The latter point explains the observation that paste hydration rates are insensitive to water/cement ratio. The
simulations indicate that the product layer on C3S remains permeable; no transition to diffusion control is
indicated, even long after the rate peak