Synthesis, characterization and hydration analysis of Ba²⁺-, Cu²⁺- or Bi³⁺-doped CaO–Al₂O₃–ZrO₂-based cements

This paper deals with the design, synthesis, hydration mechanism and hydration products of novel Ba²⁺-, Cu²⁺- or Bi³⁺-doped CaO–Al₂O₃–ZrO₂-based cementitious materials used for heavyweight concrete mixes. The results of the heating microscopy thermal analysis indicated that both Cu and Bi in a Ca₇ZrAl₆O₁₈-based cement clinker can effectively reduce the sintering temperature by 150–200 °C. Incorporation of barium for the synthesis of calcium zirconium aluminate-based hydraulic binder increased its thermal resistance since Ba²⁺-doped Ca₇ZrAl₆O₁₈ along with accessory (Ca,Ba)ZrO₃ with a perovskite‐type structure and BaAl₂O₄ phases having high melting points were formed. The presence of metal ions, i.e., Cu²⁺ or Bi³⁺, created conditions which were favorable for the formation of hexagonal calcium aluminate hydrates rather than the cubic one, as confirmed by coupled DSC–TG/EGA–MS thermal analysis techniques and X-ray diffraction. For the Ba²⁺ doping ions, this effect was the least noticeable. The effect of metal ions including Ba²⁺, Cu²⁺ and Bi³⁺ on microstructural features of cement pastes was investigated by SEM–EDS. These doping ions strongly affected the morphologies of Ca–Al hydrates.