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The service life and durability of concrete depends on a wide variety of factors [1]. Possible degradation mechanisms include environmental exposure to deleterious compounds of sulfates or chlorides, damage due to frost attack, and spalling as a result of exposure to the high temperature of a fire. The rate of damage can strongly depend on a concrete's transport properties which in turn depend on its microstructure. With knowledge of the three-dimensional concrete microstructure it is possible to determine transport properties that are then used to predict service life. To do this, representative models of the concrete or mortar microstructure are needed.
Two current approaches to representing the microstructure of concrete are 1) constructing ideal models of concrete (e.g., sphere packings modeling the placement of sand in a mortar) and 2) using real two-dimensional images to carry out a variety of studies. For instance, reasonably high resolution two-dimensional images can be made of a mortar or concrete via scanning electron microscopy. Clearly, these two approaches are not mutually exclusive in that data from real images can be used to help guide model building.
In the last decade significant improvements [2] have been made in the development of experimental methods to create three-dimensional images of real microstructures such as sandstone, coal, and biological materials. In particular, it is possible to nondestructively generate maps of X-ray attenuation with about 1 % accuracy and a resolution of about 1 micrometer [2]. In this paper, we present results of a study concerning the generation of a three-dimensional image of cement mortar using X-ray microtomography. The image processing techniques are discussed. We find that realistic images of the mortar can be made that preserve the volume fractions of cement paste and sand grains.