作者：CHRISTOPHER PARR;BENOIT VALDELIEVRE;A. NAMBA;

作者单位：ost.tau.ac.il;ost.tau.ac.il;ost.tau.ac.il

刊名：Taikabutsu Overseas

ISSN：0285-0028

出版年：2001-01-05

卷：21

期：3

起页：148

止页：154

分类号：TQ175

语种：英文

关键词：

内容简介

In order to understand the effect of ambient temperature on castable placing properties it is necessary to first consider the hydration process of Calcium Aluminate Cement (CAC). The hydration mechanism of Calcium Aluminate is via solution, where an anhydrous phase dissolves and is followed by the precipitation of the hydrates from solution~(1)). Three distinct reactions can be identified within the hydration reaction: dissolution, nucleation and precipitation.When the anhydrous cement grain is exposed to water, the hydration process~(2)) is initiated by the hydroxylation of the cement surface. This is followed by the dissolution of the cement into water, which liberates calcium and aluminum ions. A small amount of hydrates will form at this point if the solution concentration rises over the super saturation limit level of the hydrates C_2AH_8 (Cement terminology is used to describe the various anhydous and hydrated phases, where C=CaO, A=A1_2O_3, R=H_2O) and AH_3 (usually in a localized area). The dissolution will continue with a consequent increase in the concentration of Calcium and Aluminum ions until a saturation point is reached, which is the equilibrium solubility of the anhydrous phases with the hydroxylated surface layers. After the dissolution reaction, there follows an induction period during which nuclei are formed and grow to a critical size and quantity. When this critical size and quantity is achieved, a rapid precipitation of the hydrates occurs. This causes a drop in solution concentration where as more anhydrous cement can now be dissolved. This is a dynamic process, which continues to consume anhydrous cement. In a physical sense it is the growth of these hydrates, which interlock and bind together to provide mechanical resistance. The ambient temperature significantly modifies the hydrates~(1)) that result, due to the fact that their solubility changes with temperature~(3)). This change in solubility will change the precipitation kinetics as a function of temperature and result in differing setting times according to temperature.