Report of TC 238-SCM: hydration stoppage methods for phase assemblage studies of blended cements—results of a round robin test
For many microstructural studies it is necessary to “stop” cement hydration—to remove free water. This paper describes the results of a round robin test on the impact of hydration stoppage methods on the composition of hydrated cements. A regular and a fly ash blended Portland cement hydrated for 90 days were selected. Ten laboratories participated in the round robin test. Four common hydration stoppage methods were studied: (1) oven drying at 105 °C, (2) solvent exchange by isopropanol, (3) vacuum drying and (4) freeze drying. After the stoppage of hydration powder samples were studied by thermogravimetry (TG) and X-ray diffraction (XRD). Bound water and Ca(OH)2 content were determined based on the TG data. Portlandite and ettringite content were quantified by Rietveld analysis of the XRD data. The goal was to establish interlaboratory reproducibility and to identify the best available protocols for research and standardization purposes. Based on the results of the round robin test three recommendations are made. (1) Oven drying at 105 °C is not recommended. This dehydrates, alters and decomposes calcium aluminate hydrates significantly more than other methods and often produced carbonation artefacts. (2) Isopropanol exchange is the most appropriate hydration stoppage method for the study of the complete hydrate assemblage of cements, including calcium aluminate hydrates such as ettringite and AFm phases. (3) For quantification of portlandite (Ca(OH)2) all tested hydration stoppage protocols are satisfactory, with the exception of oven drying.
KeywordsSupplementary cementitious materials Hydration stoppage Round robin test Protocol Blended cement Hydration products
This work was carried out as part of the activities of RILEM Technical Committee 238-SCM on Supplementary Cementitious Materials. Maria Juenger is gratefully acknowledged for the detailed review that considerably improved the paper. As Postdoctoral Research Assistant of the Research Foundation-Flanders (FWO-Vlaanderen), Didier Snoeck wants to thank the foundation for its financial support.
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Conflict of interest
The authors declare that they have no conflict of interest.
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