Interaction of water vapour with anhydrous cement minerals: Fid-Bau Portal

Interaction of water vapour with anhydrous cement minerals

Dubina, E. / Black, L. / Sieber, R. / Plank, J.

In the present work, the influence of water vapour on the anhydrous cement minerals and different cements has been investigated. Based on the results presented in this paper, the following conclusions can be drawn. Prehydration leads to the retardation of cement clinker hydration reactions, as observed by isothermal calorimetry. Both RH and duration of prehydration play an important role in determining the extent of the effect. A combination of different analytical methods was used effectively to study the changes occurring on the surface of the clinker grains upon prehydration. Both environmental SEM and XRD revealed the formation of well defined hydration products on the surfaces of clinker grains after exposure for 1 week or greater. X-ray photoelectron spectroscopy was used successfully to follow prehydration from as short as 1 h. Exposure of C3S to water vapour led to the formation of a thin layer of C-S-H, which acts as a barrier upon mixing with water, retarding hydration. Exposure of both pure and doped C3A meanwhile led to the formation of a calcium aluminate hydrate. X-ray diffraction indicated that katoite (C3AH6) was formed, while XPS potentially revealed the formation of C4AH13 followed by katoite. However, slight differences in the exposure conditions of the samples for XPS analysis led to subsequent formation of calcium monocarboaluminate. The rate of C4AF prehydration was less than that for the other clinker phases, as expected. As a consequence, a higher C4AF content in cement can lead to a stronger protection of this cement to the water vapour during storage in moist air. Conversely, the high content of C3A in cement results in a higher sensitivity towards moisture. It was shown that cements with different compositions behave extremely different upon prehydration.