When considering computational models of microstructure, a classification can be made into continuum models and discrete or digital-image-based models [1]. Continuum models consider the microstructure as a set of particles, typically spheres, and simulate microstructural development by modifying the particle attributes such as radius [17]. Digital-image-based models consider these materials at the sub-particle level and operate on all of the pixels comprising the microstructure using a series of cellular automaton (CA) rules. A cellular automaton is basically a computer algorithm that is discrete in space and time and operates on a lattice of sites (in our case, pixels) [18,19]. Examples of physical processes that can be simulated using CA-like rules include dissolution, precipitation, nucleation, and diffusion [7]. For example, to simulate random diffusion (Brownian motion), a diffusing species pixel may interchange its location with a neighboring porosity pixel chosen at random from all neighboring pixels. To simulate microstructural development over time, the CA rules are applied iteratively to all of the pixels comprising the microstructure. Thus, each cycle of the CA model corresponds to some unit of aging (curing) time in the physical material. After execution of each cycle of the model, digital image processing techniques may be employed to determine the new phase volume fractions, etc. In addition to the present model for cement hydration [7, 20], CA-type models have been developed for sintering [21], dendritic growth [22], and the carbonation of cement [23].