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Crushed and naturally rounded aggregates come in all shapes and sizes. Since aggregates comprise the bulk of the volume in concrete, whether the matrix is asphalt or portland cement paste, the aggregate shape will play a crucial role in determining the properties of the composite material in which they are embedded [1, 2]. Two-dimensional (2-D) information, as obtained from microscopy or other imaging systems, is often biased, especially in the case of aggregates with low sphericity, and is not sufficient to properly characterize the three-dimensional shape. True three-dimensional (3-D) information is needed.
In this paper, we show how this kind of detailed 3-D information can be acquired via x-ray computed tomography (CT). Mathematical "burning" algorithms can be applied to a multi-aggregate image to extract individual particles of various sizes. A mathematical analysis based on spherical harmonics can then be used to completely characterize the three-dimensional shape of each extracted aggregate. This real shape information can be incorporated into algorithms for simulating the rheology of suspensions (fresh concrete or other materials) and into algorithms for simulating the structure of hardened portland cement concrete and other composites.
The following sections briefly describe the process of acquiring, analyzing, and using the 3-D aggregate information in a process mixing real images and computational techniques. This research is part of a larger effort, which unites the computational and experimental materials science of building materials to develop standards and tools useful to industry and to predict material performance. This process is exemplified by the Virtual Cement and Concrete Testing Laboratory [3], which unites the experimental capabilities of leading industries with the experimental and computational expertise of the National Institute of Standards and Technology (NIST) to develop a software tool for concrete that will make possible the engineered design of new concretes in a similar spirit to how the pharmaceutical industry now designs new drugs.