NIST has pioneered the use of SEM/X-ray imaging for the quantitative characterization of cement powders (Bentz and others, 1999). This analysis produces a 2-D image of the cement powder in which each pixel is identified as one of the major phases of portland cement as shown in Figure 10.3.6. The resultant image can then be further analyzed to determine phase area fractions, phase surface area (perimeter) fractions, and phase(s) correlation functions. These measures give an idea of how the particles are arranged next to each other, and how phases are arranged internally within a particle. These characteristics are duplicated in the computer generated three-dimensional microstructure of cement particles in water. This kind of individual particle characterization allows the model to make accurate predictions, since the accuracy of real results depends on this level of detail, given that this level of detail affects real cement performance.
Figure 10.3.6. Processed 2-D image of CCRL Cement 141: brown is C3S, blue is C2S, gray is C3A, white is C4AF, yellow is calcium sulfate, red is potassium sulfate, pink is periclase, and green is free lime. Image width is 256 µm x 200 µm.