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Dale P. Bentz
Building and Fire Research Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
A three-dimensional computer model for the simulation of portland cement hydration and microstructure development has been developed. Starting with a measured particle-size distribution and a set of scanning electron microscopy images, a three-dimensional representation of a cement of interest is reconstructed, matching the phase volume fractions and surface-area fractions of the two-dimensional images. A set of cellular-automata rules is then applied to the starting microstructure to model the chemical reactions for all of the major phases during the evolving hydration process. The dissolution cycles used in the model have been calibrated to real time using single set of parameters for two cements at three different water-to-cement ratios. Based on this calibration, there is excellent agreement between the model predictions and experimental measurements for degree of hydration, heat release, and chemical shrinkage. The degree-of-hydration predictions have been successfully applied to predicting the compressive strength development of mortar cubes for the two cements. The effects of temperature have been examined by performing hydration experiments at 15º 25º and 35º and applying a maturity-type relationship to determine a single degree of hydration-equivalent time curve that can be compared to the model predictions. Finally, the computer model has been further extended to simulate hydration under sealed conditions, where self-desiccation limits the achievable hydration.
Note: Conventional cement chemistry notation is used throughout this paper: C is CaO, S is SiO2, A is Al 2O3, F is Fe2O3, H is H2O, and is SO3.