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Hydration of calcium sulfoaluminate cements — Experimental findings and thermodynamic modelling

Hydration of calcium sulfoaluminate cements — Experimental findings and thermodynamic modelling,10.1016/j.cemconres.2009.08.014,Cement and Concrete Re

Hydration of calcium sulfoaluminate cements — Experimental findings and thermodynamic modelling   (Citations: 10)
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Calcium sulfoaluminate cements (CSA) are a promising low-CO2 alternative to ordinary Portland cements and are as well of interest concerning their use as binder for waste encapsulation. In this study, the hydration of two CSA cements has been investigated experimentally and by thermodynamic modelling between 1 h and 28 days at w/c ratios of 0.72 and 0.80, respectively.The main hydration product of CSA is ettringite, which precipitates together with amorphous Al(OH)3 until the calcium sulfate is consumed after around 1–2 days of hydration. Afterwards, monosulfate is formed. In the presence of belite, strätlingite occurs as an additional hydration product. The pore solution analysis reveals that strätlingite can bind a part of the potassium ions, which are released by the clinker minerals. The microstructure of both cements is quite dense even after 16 h of hydration, with not much pore space available at a sample age of 28 days.The pore solution of both cements is dominated during the first hours of hydration by potassium, sodium, calcium, aluminium and sulfate; the pH is around 10–11. When the calcium sulfate is depleted, the sulfate concentration drops by a factor of 10. This increases pH to around 12.5–12.8.Based on the experimental data, a thermodynamic hydration model for CSA cements based on cement composition, hydration kinetics of clinker phases and calculations of thermodynamic equilibria by geochemical speciation has been established. The modelled phase development with ongoing hydration agrees well with the experimental findings.
Journal: Cement and Concrete Research - CEM CONCR RES , vol. 40, no. 8, pp. 1239-1247, 2010
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    • ...28 days [16], whereas an ordinary Portland cement reaches about 4–5 cm 3 /g. Chemical shrinkage of a CSA cement...
    • ...Recent examples of the application of thermodynamic modelling to cement hydration using the GEMS-PSI code are given in [16, 26, 27]...
    • ...This behaviour of anhydrite is confirmed by a study on the pore solution chemistry of two technical CSA cements [16]...

    Frank Winnefeldet al. Calorimetric and thermogravimetric study on the influence of calcium s...

    • ...Unlike OPC, the hydration of such a mixture is mainly based on the reaction of the ye’elimite phase (calcium aluminum sulfate, C4A3s) with calcium sulfate to ettringite and, when the calcium sulfate is depleted, to monosulfate [17, 18]...
    • ...The sealed sample in the CSA mixture shows a dormant period after the initial heat event, until the heat flow starts to increase again after about 4 h. The maximum heat flow is reached after 7 h. An additional maximum at a lower heat flow is reached after a hydration time of 36 h, which can be associated to the depletion of the added anhydrite [14, 17, 18]...
    • ...This is in good agreement with theoretical calculations of chemical shrinkage of CSA cements derived from a thermodynamic hydration model [17]...
    • ...By applying thermodynamic modelling [17], it is calculated that the CSA/anhydrite mixture needs a water/binder ratio of 0.58 for complete hydration...
    • ...A fast selfdesiccation might also be connected to the very rapid development of a dense microstructure in CSA cements [17], which causes also the development of higher early strengths compared to Portland cements [18]...

    Pietro Luraet al. Simultaneous measurements of heat of hydration and chemical shrinkage ...

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