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Title: On the Occurrence of CAH10 in Hydrated Calcium Sulfoaluminate Cements

Author(s): Frank Winnefeld and Barbara Lothenbach

Publication: Symposium Paper

Volume: 349


Appears on pages(s): 125-142

Keywords: Aluminum hydroxide, CAH10, Calcium sulfoaluminate cement, hydration, thermodynamic modelling

DOI: 10.14359/51732744

Date: 4/22/2021

The occurrence of CAH10 in a calcium sulfoaluminate (CSA) clinker and in the CSA clinker blended with anhydrite was assessed by experimental data and thermodynamic modelling. For the CSA clinker it was found that CAH10 forms as an intermediate phase directly from the hydration of ye’elimite together with ettringite and aluminium hydroxide, which is an alternative reaction path to the formation of monosulfate and aluminium hydroxide. The occurrence of CAH10 is linked to the solubility of the aluminum hydroxide formed, which decreases with time due to an increase of its crystallinity. In case of a highly soluble aluminum hydroxide, which occurs at early hydration times, the formation of CAH10 and ettringite is thermodynamically more favoured than the formation of monosulfate. At later ages, when the solubility of aluminum hydroxide decreases, CAH10 and a part of the ettringite convert to monosulfate. This conversion is associated with an increase of porosity, which leads to a significant loss of compressive strength beyond a sample age of 28 days. In the CSA clinker blended with anhydrite the formation of CAH10 could not be evidenced. No loss of compressive strength was observed for this sample.