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Model Execution

The microstructural model was in all cases executed at a constant w/s ratio of 0.45, and hydrated to either a constant degree of hydration, = 0.77, or to a degree of hydration ( greater than 0.77) in agreement with that achieved in the various experimental mixes that were used for comparison in this study. After the appropriate degree of hydration is reached, the final microstructure is quantitatively analyzed by measuring the volume fractions of all cementitious phases present as a function of distance from the aggregate surface. Knowing these volumetric phase fractions, the molar ratio of CaO to SiO2 is given by

where the values of 71, 33, 124, and 27 represent the molar volumes (cc/mole) of C3S, CH, C-S-H and silica fume respectively [14].

For more easily visualized qualitative assessments, images of two-dimensional slices through the microstructure are obtained. Images of slices taken just in front of the aggregate surface (surface slices) were created and photographed to enable a qualitative evaluation of microstructure to be made. These images were produced for both the starting model microstructures and the microstructures formed after the requisite hydration.