The detection of the carboaluminate phase in hydrated high alumina cements by differential thermal analysis

2017

This paper studies hydration stages and phase transformation mechanism of the Sr 2? -doped calcium zirconium aluminate cement at room temperature. Features of different hydration stages of this cement paste are identified by X-ray diffraction, scanning electron microscopy, differential thermal analysis, thermogravimetric analysis, evolved gas analysis and heat evolution test. It was found that the partial isovalent substitution of Ca 2? for Sr 2? such as Ca 7-x Sr x ZrAl 6 O 18 , with x = 0.3, 0.6, 1.0, reduced the hydraulic reactivity of Ca 7 ZrAl 6 O 18 phase. The course of hydration of mixed oxides of the type 6CaOÁSrOÁ3Al 2 O 3 Á ZrO 2 documented using microcalorimetry was supported by investigations of the solid hydration products. Research showed that the hexagonal hydrates were stable at early and middle curing ages, an indication that including Sr in solid solution could effectively inhibit the conversion from both C 4 AH 13-19 and C 2 AH 8 to C 3 AH 6 and AH 3 . Calcium monocarboaluminate C 4 A CH 11 phases were also found in this system due to the carbonation process of C 4 AH 13 phase. Substitution of Ca 2? ions by Sr 2? ions in hexagonal calcium aluminate hydrates causes structural disorder and then contributes to the broadening of lines in the powder X-ray diffraction patterns of layered structures of metastable hydrates. At later curing ages, the formation of two hydrogarnet phases, one Sr-rich (C,Sr) 3 AH 6 and the other Ca-rich (C,Sr) 3 AH 6 , was proved.

Section: Microstructural Investigations Of the Sr 21 -Doped Calcium Zmentioning

confidence: 99%

Section: Experimental Synthesismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Hydration, carbonation and thermal stability of hydrates in Ca7−xSrxZrAl6O18 cement

2017

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

Boris

2019

This paper deals with the design, synthesis, hydration mechanism and hydration products of novel Ba 2? -, Cu 2? -or Bi 3?doped CaO-Al 2 O 3 -ZrO 2 -based cementitious materials used for heavyweight concrete mixes. The results of the heating microscopy thermal analysis indicated that both Cu and Bi in a Ca 7 ZrAl 6 O 18 -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 Ba 2? -doped Ca 7 ZrAl 6 O 18 along with accessory (Ca,Ba)ZrO 3 with a perovskite-type structure and BaAl 2 O 4 phases having high melting points were formed. The presence of metal ions, i.e., Cu 2? or Bi 3? , 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 Ba 2? doping ions, this effect was the least noticeable. The effect of metal ions including Ba 2? , Cu 2? and Bi 3? on microstructural features of cement pastes was investigated by SEM-EDS. These doping ions strongly affected the morphologies of Ca-Al hydrates.

Structure, microstructure and thermal stability characterizations of C3AH6 synthesized from different precursors through hydration

Litwinek

2019

In this paper, the influence of precursors (CA, C 7 A 3 Z, C 12 A 7 , C 6 SrA 3 Z, C 7 A 2 FZ and commercial calcium aluminate cement 'Gorkal 70') on the structure, microstructure and thermal stability characterizations of C 3 AH 6 through hydration was investigated. The materials were characterized by X-ray diffraction, differential thermal analysis-thermogravimetric analysis-evolved gas analysis and scanning electron microscopy combined with energy-dispersive spectroscopy 24 h and 72 h after starting the hydration process. Results of investigation confirmed the influence of precursor on shape and grain size of C 3 AH 6 . The CaO/Al 2 O 3 mass ratio of precursors before the hydration process affects the size of C 3 AH 6 crystals: the higher the CaO/Al 2 O 3 value, the larger the size of the crystals of C 3 AH 6 . Moreover, the presence of Sr and Fe affects the formation of stable C 3 AH 6 crystals.