Influence of K2HPO4 or CaSO4E2H2O on the Hydration of Alite

Etsuo SAKAI, Akinori NAKAMURA*†, Toyohiko YANO*††, Yasuichi JOH† and Masaki DAIMON

Department of Inorganic Materials, Tokyo Institute of Technology; 2-12-1, Ookayama, Meguro-ku, Tokyo 152-8552 Japan
† Tokuyama Research Laboratory, Tokuyama Corp.; 1-1, Mikage-cho, Tokuyama-shi 745-8648 Japan
†† Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology; 2-12-1, Ookayama, Meguro-ku, Tokyo 152-8552 Japan

This study discusses the influence of K2HPO4 or CaSO4·2H2O on the hydration of alite, a main composition of ordinary Portland cement. The early stages of hydration were measured by a conduction calorimeter. The added amounts of K2HPO4 or CaSO4·2H2O were from 0 to 3% (counted as P2O5) or from 0 to 10% (counted as SO3), respectively. The rate of heat liberation of alite was retarded by the addition of K2HPO4 and accelerated by the addition of CaSO4·2H2O. At 1.5% K2HPO4 addition, the retardation effect of K2HPO4 showed a maximum. On CaSO4·2H2O addition, as the amount of CaSO4·2H2O increased, the acceleration effect of CaSO4·2H2O increased.
The reaction ratio of alite was measured by XRD at late stage of the hydration.
Calcium silicate hydrates produced by hydration of alite with 1.5% K2HPO4 or 4% CaSO4·2H2O included P2O5 or SO3, respectively. These CaO/SiO2 ratios of calcium silicate hydrates were higher than that of alite without additives. Calcium silicate hydrates could contain P2O5 or SO3 with CaO, and P2O5 and SO3 influenced the morphology of produced calcium silicate hydrates.


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