Analysis of Setting Mechanism of Low-Cement Castable (III): The Acceleration of the Setting Time by Addition of Ca~(2+) Ions

摘要

The author investigated effective accelerators for the setting of low-cement castables by applying the setting mechanism of the castables reported in a previous paper. By the proposed mechanism, the addition of Ca~(2+) ions to the castables in excess of those provided by the alumina cement is considered to be an effective accelerator. Ca(OH)_2 was found to be a superior accelerator. The necessary amount that reduced the setting time by one half while maintaining the flow characteristic for the castables ranged from 0.02 to 0.1 mass% depending on the castable system. The influence on the characteristics of the castables was negligible. From the analysis of the concentration of ions in the capillary water, the setting mechanism was discussed in more detail. While the essence of the present setting mechanism and the one reported before is the same, the details of the mechanism are more complicated because many chemical reactions occur, the thresholds of the coagulation change and the stability of the colloid alters.