Reference: Reprinted from Innovations in Portland Cement Manufacturing, Chapter 10.3, J.I. Bhatty, F.M. Miller and S.H. Kosmatka, eds., Portland Cement Association, 5420 Old Orchard Road, Skokie, IL 60077, pp. 1311-1331 (2004).

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Virtual Cement

by
Jeffrey W. Bullard, Clarissa Ferraris, Edward J. Garboczi, Nicos Martys, and Paul Stutzman Building and Fire Research Laboratory National Institute of Standards and Technology Gaithersburg, MD 20899 USA

Cementitious materials, including cement paste, mortar, and concrete, possess great chemical and structural complexity. Chemically, cement pastes contain many chemical components and mineral phases. Many of these phases can be amorphous or poorly crystalline, with metastable solid solution compositions varying over a fairly wide range. Dozens of chemical hydration reactions may occur simultaneously at rates that vary from region to region within the material. Structurally, a cementitious material is a random composite structure on length scales from nanometers to millimeters, and the contrast in various physical properties among the different composite phases is often quite large. One would be hard pressed to find a system that even approaches this range of complexity from among other classes of engineering materials such as ceramics and metals.

Figure 10.3.1. Pictorial representation of the current VCCTL software modules, showing the range of input specifications and predicted properties.

One consequence of this complexity is that the hydration, properties, and long-term field performance of cement and concrete are difficult to predict; simple empirical relations cannot be universally applied with confidence. As a result, mix design and optimization for tailored applications is a long, arduous, and expensive proposition.

A promising alternative is to use scientifically based models to guide testing and development efforts. To be accurate and reliable, such models must account for all the relevant chemistry and physics that influence cementitious systems. Because of the complexity of these materials, these models must take the form of computer simulations. Computer hardware has advanced to the point that sufficient computational power for most relevant simulations can be obtained on a standard personal desktop computer. Therefore, computer modeling potentially could supplant much of the current empirical design and testing procedures with relatively inexpensive and quick simulations. Computer modeling applied to materials is usually called "computational materials science," which is a term that will be used extensively throughout this chapter. What is meant by "computational materials science of concrete" is this: computer-based models of microstructure at the relevant length scale, operated on by algorithms that give accurate measures of physical properties.

• The Computational Materials Science of Cement and Concrete: A Brief History
• The Virtual Cement and Concrete Testing Laboratory
• Cement Hydration
• Current Research
• Future Hydration Research
• Elastic Properties
• Current Research
• Future Research
• Rheological Properties
• Materials Characterization
• Particle Size Distribution
• SEM/X-Ray Imaging
• Visualization
• Current Research
• VCCTL Case Studies
• Case I. Replacement of "Coarse" Cement Particles by Limestone Fillers - Hydration and Strength Development
• Case II. Multi-Scale Modeling of the Influence of Condensed Silica Fume Additions on the Diffusivities of Cement Pastes
• Case III. Influence of Cement Particle Size Distribution on Properties
• Conclusion
• Appendix: The NIST/Industry VCCTL Consortium - 2003
• References