Thermal analysis of hydrated calcium aluminates
01 Sep 1996-Journal of Thermal Analysis and Calorimetry (Kluwer Academic Publishers)-Vol. 47, Iss: 3, pp 765-774
TL;DR: Differential scanning calorimeter has been used to study the dehydration characteristics of hydrated calcium aluminates such as CA, CA2 and C12A7 where C and A stand for CaO and Al2O3 respectively.
Abstract: Differential scanning calorimeter (DSC) has been used to study the dehydration characteristics of hydrated calcium aluminates such as CA, CA2 and C12A7 where C and A stand for CaO and Al2O3 respectively. Dehydration of CAH10 and C2AH8 (whereH=H2O) occur ∼ at 160–180°C and 200–280°C respectively. These two phases are unstable and ultimately get transformed to AH3 and C3AH6. Dehydration of AH3 and C3AH6 occur between 290 and 350°C and overlap at lower scanning rate. The activation energy for dehydration of the stable AH3 and C2AH6 phases has been found to be 107.16 and 35.58 kJ mol−1 respectively. The compressive strength of the hydrated calcium aluminates has been determined. The result shows that in the case of CA, almost 90% of ultimate strength has been attained in 1 day whereas in CA2, ultimate strength has been attained in 14 days and in C12A7 in 1 day. DSC results have been correlated with the rate of strength developments.
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TL;DR: In this article, the spinel containing high alumina cement prepared from high titania blast furnace slag via smelting reduction method is studied and the hydration behavior of spinel and splat cooling cement is analyzed.
Abstract: Hydration behavior of the spinel containing high alumina cement prepared from high titania blast furnace slag via smelting reduction method is studied. Cooling condition has considerable effect on the phase compositions and hydration behavior of the prepared cements. Hydraulic CA, CA 2 , inert spinel and gehlenite are the main mineral phases of the naturally cooling cement. Glassy phase, CA and some spinel are the main phases of the splat cooling cement. Both of the prepared cements have controllable setting time, water requirements. Strength of splat cooling cement develops slowly than naturally cooling cement. The naturally cooling cement has satisfactory compressive strength, which is higher than splat cooling cement, but lower than commercial CA80 and Secar71. XRD and SEM observation confirms that CAH 10 is the main hydrate of splat cooling cement. Metastable CAH 10 , C 2 AH 8 , are the main hydrates of naturally cooling cement, which will convert to stable C 3 AH 6 with continuing hydration.
15 citations
TL;DR: In this article, the reactivities of binary and ternary mixtures of reactive magnesia (MgO≡M), hydratable alumina (Al2O3≡A) and microsilica (SiO2≡S) micropowders were investigated by calorimetric method and other analytical techniques (X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), differential thermal/thermogravimetric (DTA-TG) analysis and scanning electron microscope (SEM) observations
Abstract: The reactivities of the binary and ternary mixtures of reactive magnesia (MgO≡M), hydratable alumina (Al2O3≡A) and microsilica (SiO2≡S) micropowders were investigated by calorimetric method and other analytical techniques (X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), differential thermal/thermogravimetric (DTA-TG) analysis and scanning electron microscope (SEM) observations). Effect of water/solid mass ratio and temperature on the hydration behavior of the M–A, M–A–S, M–S, A–M–S and A–S hydratable binders were established. The methodological considerations on both in situ and ex situ mixing techniques have also been taken. The initial mixing peak was due to wetting of the binder particles and initial dissolution reactions. A second, extensive heat peak was associated with the formation of crystalline and noncrystalline hydration products, i.e., brucite Mg(OH)2, magnesium aluminate hydrate (MAH; H≡H2O)-like phase, magnesium silicate hydrate (MSH)-like phase and magnesium aluminum silicate hydrate gels (MASH). Negligible heat was evolved during the hydration reaction of A–S mixture, and the second reaction peak was not observed. Nevertheless, the presence of Al2O3 and SiO2 in other combinations contributes to the consumption of Mg(OH)2 which was formed during the initial stages of hydration and leads to the formation of cementitious products, like M–A–H, M–S–H and M–A–S–H.
14 citations
TL;DR: Predications are in good agreement with experimental findings that C12A7 can be used as a functional component to adjust the consumption rate of suphates in OPC, and also components of carbonate phases can be modified in hydrate assemblage.
Abstract: Influence of C12A₇ (12CaO·7Al₂O₃) as a functional component on hydration properties of Ordinary Portland Cement is studied using isothermal microcalorimetric technique, X-ray diffraction analysis, and thermodynamic calculation. Meanwhile, hydrate assemblages are simulated by hydrothermal software. C₂AH₈ (2CaO·Al₂O₃·8H₂O) is generated as a transition phase during the hydration of pure C12A₇, while formation of CAH10 (CaO·Al₂O₃·10H₂O) is uncertain. Heat-releasing behavior of Ordinary Portland Cement (OPC) could be noticeably affected by C12A₇, especially for the duration of interaction at boundary stage reduces with C12A₇ replacement. Correspondingly, all hydration kinetic parameters first increase and then diminish with C12A₇ replacement. Simulation results manifest in the main hydration products of OPC being ettringite, C-S-H (Calcium-Silicate-Hydrate) gel, portlandite and brucite. Increasing C12A₇ replacement accelerates the consumption rates of gypsum and calcite that are typically included in OPC, and thus the ettringite content is changed and carbonate phases will be produced. Therefore, the microstructure properties of hydrated products of OPC are affected and the compressive strength is influenced. These predications are in good agreement with experimental findings. C12A₇ can be used as a functional component to adjust the consumption rate of suphates in OPC, and also components of carbonate phases can be modified in hydrate assemblage.
13 citations
Cites background from "Thermal analysis of hydrated calciu..."
...[29] claimed that CAH10 would be produced as the only transition phase according to Equation (6), and the conversion process followed reaction (9)....
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TL;DR: In this paper, different formulations of calcium aluminate cement pastes (CACP) with 51wt% (wt% -percentage by weight) of Al2O3 were made at 0.4 water to cement ratio with additions.
Abstract: In this study different formulations of calcium aluminate cement pastes (CACP) with 51 wt% (wt% -percentage by weight) of Al2O3 (CACP 51) were made at 0.4 water to cement ratio (W/C) with additions...
11 citations
TL;DR: In this article, 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 were discussed.
Abstract: 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.
11 citations
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10,842 citations
TL;DR: The chemistry of hydration of monocalcium aluminate, CA, has been studied at several temperatures using conduction calorimetry, X-ray diffraction and other techniques as discussed by the authors.
Abstract: The chemistry of hydration of monocalcium aluminate, CA, has been studied at several temperatures using conduction calorimetry, X-ray diffraction and other techniques. At 4 °C, hydration to the decahydrate CAH 10 occurs about 15 hours after mixing; this hydration time increases with increasing temperature up to 30 °C, and C 2 AH 8 appears as a hydration product. At 40 °C rapid hydration to C 2 AH 8 is followed over a period of weeks by the ‘conversion’ reaction producing C 3 AH 6 . The reaction of CA to form crystalline hydrates was monitored by X-ray diffraction analysis; the results indicate that hydration also produces significant amounts of noncrystalline material. The enthalpies of the reactions involved in hydration and ‘conversion’ were measured by conduction calorimetry.
63 citations
TL;DR: In this article, the authors studied the hydration behavior of Secar 71 refractory aluminous cement using conduction calorimetry, X-ray diffraction and thermal analysis techniques.
Abstract: The hydration behaviour of Secar 71 refractory aluminous cement has been studied over a range of temperature using conduction calorimetry, X-ray diffraction and thermal analysis techniques. The first reaction is the hydration of monocalcium aluminate, CA, producing a sharp calorimeter peak within 12 hours of mixing. Following this reaction the other major component, calcium dialuminate (CA 2 ), undergoes slow hydration over a period of weeks. The enthalpies of these two reactions have been measured. The initial hydration products of both components are CAH 10 , or C 2 AH 8 with alumina gel. These can subsequently convert to C 3 AH 6 ; after one month significant conversion is observed even at room temperature. A method of estimating the degree of conversion based on X-ray measurement of C 3 AH 6 is proposed.
46 citations
TL;DR: Differential scanning calorimetry (dsc) was used to investigate the freezing behaviour of hardened cement paste (hcp) subjected to nacl and cacl2 solutions containing up to 5.4 mol cl/l as mentioned in this paper.
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31 citations
TL;DR: In this paper, the hydration process of a high alumina cement was investigated through ultrasonic wave propagation techniques, and a correlation between wave amplitude and velocity and breaking strength of the cement was demonstrated.
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6 citations