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NISTIR 5756

A Three-Dimensional Cement Hydration and Microstructure Program. I. Hydration Rate, Heat of Hydration, and Chemical Shrinkage

Dale P. Bentz
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, Maryland 20899

U.S. Department of Commerce
William M. Daley, Secretary

 

Technology Administration
Dr. Cheryl L. ShaversUnder Secretary of Commerce for Technology
National Institute of Standards and Technology
Raymond G. Kammer, Director

ABSTRACT

A computer program that implements a three-dimensional model for the microstructural development occurring during the hydration of portland cement has been developed. The model includes reactions for the four major cement phases: tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium aluminoferrite, and the gypsum which is added to avoid flash setting. The basis for the computer model is a set of cellular automata-like rules for dissolution, diffusion, and reaction. The model operates on three-dimensional images of multi-phase cement particles generated to match specific characteristics of two-dimensional images of real cements. To calibrate the kinetics of the model, experimental studies have been conducted at room temperature on two cements issued by the Cement and Concrete Reference Laboratory at NIST. Measurements of non-evaporable water content, heat of hydration, and chemical shrinkage over periods of up to 90 days have been performed for comparison with model predictions. The measurement of chemical shrinkage is particularly critical, as it allows an estimation of the density of the calcium silicate hydrate gel formed during the hydration to be made. The dispersion models of Knudsen have been applied in fitting both the model and experimental data. For the two cements investigated, it appears that a single function can be used to convert between model cycles and experimental time for the three water-to-cement ratios investigated in this study. This suggests that accurately capturing the particle size distribution, phase fractions, and phase distributions of a given cement allows for an accurate estimation of its hydration characteristics. Finally, the calibrated kinetic models for the two cements have been used to successfully predict 7 and 28-day compressive strengths of ASTM C109 50 mm mortar cubes from 3-day compressive strength data, illustrating one engineering application for such a three-dimensional cement hydration and microstructure model.

Keywords: Building technology, cement hydration, chemical shrinkage, compressive strength, computer modelling, heat of hydration, microstructure, non-evaporable water, simulation.


 
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