Studies on the Hydration of Calcium Aluminoferrite Phase and its Glass in Portland Cement Clinker

Abstract

Interstitial phases in portland cement clinker, consisting of calcium aluminate, calcium aluminoferrite and its glasses, are so complicated that have not yet been well investigated, especially on the hydration of these minerals.The authors attempted to clarify the reaction mechanism in the initial stage of the hydration of these minerals (in ten hours) by a adiabatic calorimeter which had been already reported in a previous paper.The results obtained are as follows;(1) Hydration in the water without gypsum and alite.In general, calcium aluminoferrite (crystalline) showed the increase in the rate of heat liberation with increasing Al2O3 content. The rate of heat liberation of quenched materials was smaller than that of crystallized materials. It was suggested that in the hydration of portland cement, the finest hydration products precipitate near the cement grain and the rate of hydration depends on the diffusion of water through the products layer on surface of the grain. From the above reason, considering that the nature of the film varies with time, parabollic equation seemed to represent the hydraton process well. In the other hand, as the hydration rate obeyed logarithmic equation well, the occurrence of the flaw path or the loosed structure zone in the hydration product layer, which were caused by the transformation of the hydration product, was assumed in the same hydration prosess. Moreover the approximte activation energy of diffusion through the hydration product layer was calculated.(2) The amount of Fe2O3 which 3CaO⋅Al2O3⋅6H2O can take in solid solution became smaller with the increase in hydration temperature.(3) Hydration in the water with gypsum and alite.In this case, the rate of heat liberation of quenched materials was greater than that of crystallized materials. It was suggested that the rate determining step is the liquid-solid interaction, because the relationship between heat liberation and time was expressed as straight line. When gypsum was depleted, hydration proceeded the same as in the water without gypsum and alite, and then logarithmic equation was applied. In addition, activation energy in solid-liquid interaction was calculated for C4AF (E=11.0kcal/mole).