Alkaline Hydration of Tricalcium Aluminate

This study explored the behavior of laboratory‐synthesized tricalcium aluminate ( C 3 A ) in alkaline media. In all the trials, the C 3 A was hydrated with water containing a certain percentage of alkali activators (4% Na 2 CO 3 , 4% Na 2 SO 4, or 8% Na 2 SO 4 by weight of C 3 A ). Two‐ and 28‐day mechanical strength values were determined and the products were characterized with XRD , DTA , and NMR . The compressive strength of the C 3 A pastes rose in the presence of the alkaline activators used in this study. The alkalis induced the formation of calcium monocarboaluminate ( C 4 AČH 11 ) as the main hydration product in all cases. In addition, when Na 2 SO 4 was added, a sodium calcium sulfoaluminate, phase U ( C 4 AŠNH 16 ), formed. The presence of this mineral, whose formation is associated with high pH values, furnished indirect information on the alkalinity in the medium.