The microstructural model allows for both the size and reactivity of mineral admixtures such as silica fume and fly ash to be varied [6]. Since in the model, a pixel is typically 1 µm on a side, well dispersed silica fume can be represented by small particles one pixel in size. Conversely, fly ash or agglomerated silica fume is "large," and is assigned the same size as cement particles. Pozzolanic activity is varied by specifying a pozzolanic reactivity factor, corresponding to how many units of CH each unit of mineral admixture may consume via the pozzolanic reaction. According to the reaction given earlier, pure silica would be able to consume 2.08 units of CH. Fly ash must be assigned a lower reactivity as it is typically only about 50% silica. Thus 1.04 might be a reasonable maximum activity to be expected for fly ash, while 0.47 appears to be a more likely value to be achieved in practice [7].