A Model for Particle Size and Phase Distributions in Ground Cement Clinker
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A MODEL FOR PARTICLE SIZE AND PHASE DISTRIBUTIONS IN GROUND CEMENT CLINKER
P.W. BROWN AND K.G. GALUK Building Materials Division, National Bureau of Standards, 20899
Gaithersburg,
MD
ABSTRACT A model has been developed to describe a granule of unground clinker, to simulate the grinding process by the removal of particles according to a user-defined particle size distribution, and to characterize the exposed surface areas and volumes of each clinker phase present. The composition of the clinker granule and the distribution of phases within the granule are also user defined.
INTRODUCTION A variety of mathematical models have been developed to describe the kinetics of hydration of pure cement phases. In general, modeling the kinetics of hydration is complicated by several factors. First, the rate controlling process may change depending on the degree of hydration. Second, elucidation of the kinetics may be complicated by the polydisperse size distributions of the individual cement phases. However, in spite of these difficulties, it is still possible to develop kinetic models for these systems because each particle in the system is monomineralic. This is not true with portland cement in which a significant fraction of the particles in the system are polymineralic. In addition, the average compositions of cement particles vary depending on their size. As a consequence, the exposed surface areas of the various clinker phases are also likely to vary with particle size. However, the relationships between the phase distributions in
clinker and the phase and particle
size distributions
in
the ground
clinker are not well understood. In addition, little experimental work to characterize the distribution of phases in ground clinker seems to have been done. As a result of these factors it is difficult to develop physically significant, predictive mathematical models for cement hydration. Because the distributions of cement phases in ground clinker are poorly understood, it is the objective of this paper to describe a computer model that relates the phase and particle size distributions that may be representative of the ground cement clinker to the chemical composition and phase distributions in unground clinker.
MODEL INPUTS
Inputs to the model include the composition of the unground cement clinker and the particle size distribution of the ground clinker. Userdefined composition and particle size dependent parameters are selected to simulate the unground clinker. Volume ratios for alite, belite and interstitial phase are calculated from the clinker composition. Once the volume ratios are calculated, the dimensions of the clinker matrix components are calculated. Figure 1, which is intended to simulate a granule of unground clinker, shows an example of this. In the present case, the alite and belite grains are assumed to be identical in size and have square cross2 sections, a . This clinker phase distribution was selected in an attempt to represent a typical clinker microstructure [1,2]. The locations of the alite and
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