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D.P. Bentz, E.J. Garboczi, and P.E. Stutzman
National Institute of Standards and Technology
Building Materials Division, 226/B350
Gaithersburg, MD 20899 USA
A digital-image-based microstructure model is applied to simulating cement paste-aggregate interfacial transition zone microstructure development in a variety of concretes. A starting model system consists of a single square, flat plate, or cubic aggregate surrounded by circular or spherical cement and mineral admixture particles. A cement hydration model based on a cyclic process of dissolution, diffusion, and reaction is used to hydrate starting microstructures. In addition to supporting the well-known concept of the "wall effect," the model has suggested that a "one-sided growth" effect also contributes to the microstructural features developed in interfacial transition zones. The effects of mineral admixture particle size and reactivity and those of aggregate reactivity and water absorptivity on interfacial transition zone microstructure are explored via simulation. In many cases, it appears that improvements in the uniformity and density of the interfacial transition zone (ITZ) microstructure can be achieved by controlling these properties. Quantitative validation of the model is obtained by comparing model systems to ones prepared in the laboratory for concretes containing 0, 10, and 20% silica fume content. Good agreement between model and experiment is observed.