Hydration of calcium sulfoaluminate cements - Experimental findings and thermodynamic modelling

Journal Article · Sun Aug 15 00:00:00 EDT 2010 · Cement and Concrete Research

DOI:https://doi.org/10.1016/j.cemconres.2009.08.014· OSTI ID:21483645

Winnefeld, Frank ^[1]; Lothenbach, Barbara ^[1]

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1. Empa, Swiss Federal Laboratories for Materials Testing and Research, Laboratory for Concrete and Construction Chemistry, Duebendorf (Switzerland)

Calcium sulfoaluminate cements (CSA) are a promising low-CO{sub 2} 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){sub 3} until the calcium sulfate is consumed after around 1-2 days of hydration. Afterwards, monosulfate is formed. In the presence of belite, straetlingite occurs as an additional hydration product. The pore solution analysis reveals that straetlingite 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.

• OSTI ID: 21483645
• Journal Information: Cement and Concrete Research, Journal Name: Cement and Concrete Research Journal Issue: 8 Vol. 40; ISSN 0008-8846; ISSN CCNRAI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALKALI METALS
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM
ALUMINIUM COMPOUNDS
ALUMINIUM HYDROXIDES
BINDERS
BUILDING MATERIALS
CALCIUM COMPOUNDS
CALCIUM SULFATES
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON OXIDES
CEMENTS
CHALCOGENIDES
CHARGED PARTICLES
DISPERSIONS
ELEMENTS
ENCAPSULATION
HOMOGENEOUS MIXTURES
HYDRATION
HYDROGEN COMPOUNDS
HYDROXIDES
IONS
KINETICS
MATERIALS
MATHEMATICAL MODELS
METALS
MICROSTRUCTURE
MIXTURES
OXIDES
OXYGEN COMPOUNDS
PARTICLE MODELS
PH VALUE
PORTLAND CEMENT
POTASSIUM
POTASSIUM IONS
PRECIPITATION
SEPARATION PROCESSES
SIMULATION
SODIUM
SOLUTIONS
SOLVATION
STATISTICAL MODELS
SULFATES
SULFUR COMPOUNDS
THERMODYNAMIC MODEL