Retention of Cobalt, Cesium, and Strontium in the Hydrates of C3S, C3A, and Gypsum

The retention of cobalt, cesium, and strontium as trace elements in the hydrates of simple ordinary portland cement components has been investigated. The combined characterization of the solid by SEM, electron microprobe, XRD, and SIMS, as well as the chemical analysis of the solutions, allowed us to identify the likely localization of these trace elements in the solid. In particular, cobalt is dramatically incorporated into the solid during the hydration of C3S; we show that this is due to the formation of a cobalt oxychloride, a compound which is unstable at temperatures ≥60°C. Cesium is retained in small amounts in the C‐S‐H and CH mixture. The formation of hydrated aluminates notably increases its retention. Finally, small quantities of strontium are also retained in silicates and, in the presence of gypsum, its retention is markedly higher. This is likely due to the formation of sulfoaluminates.