Cubic C 3 A was synthesized according to a recently developed protocol . Briefly, C 3 A was prepared by sintering cylindrical green bodies composed of CaCO 3 , Al 2 O 3 , calcium aluminate cement and water (water-to-solid ratio w/s = 0.5) in stoichiometric amounts (Ca/Al ratio = 1.5) twice at 1400 • C. The detailed synthesis procedure and characterization can be found elsewhere .