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D.P. Bentz and E.J. Garboczi
Building 226, Rm. B-348
Building Materials Division
National Institute of Standards and Technology
Gaithersburg, MD 20899
In concrete, the interfacial zone between cement paste and aggregate plays a critical role in determining mechanical performance. In recent years, high performance concretes have been produced based on a low water-to-cement ratio cement paste containing a superplasticizer and silica fume. One of the key benefits of silica fume is its ability to improve the integrity of the interfacial zone in concrete. This paper presents a three- dimensional microstructural model for simulating the interfacial zone in concrete, including the incorporation of inert and pozzolanic mineral admixtures. The model is utilized to obtain the cementitious material phase distributions as a function of distance from the aggregate surface, in order to quantitatively characterize the interfacial zone. Pozzolanic admixtures, such as silica fume and fly ash, are found to increase the homogeneity of the interfacial region, with the most important enhancement proposed to be the improved homogeneity of the calcium silicate hydrate phase. The effects of mineral admixture particle size and reactivity are also computed via simulations. Simulation results are compared to conventional experimental measurements, such as compressive strength, and scanning electron micrographic investigations of the microstructure of real cement-based materials.