A thermodynamic and experimental study of the conditions of thaumasite formation

Journal Article · Sat Mar 15 04:00:00 EDT 2008 · Cement and Concrete Research

DOI:https://doi.org/10.1016/j.cemconres.2007.11.003· OSTI ID:21033070

Schmidt, Thomas ^[1]; Lothenbach, Barbara ^[1]; Romer, Michael ^[1]; Scrivener, Karen ^[2]; Rentsch, Daniel; Figi, Renato ^[1]

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1. Empa, Swiss Federal Institute for Material Testing and Research, 8600 Duebendorf (Switzerland)
2. EPFL, Swiss Federal Institute of Technology, Laboratory of Construction Materials, 1015 Lausanne (Switzerland)

The formation of thaumasite was investigated with the progressive equilibrium approach (PEA). This approach experimentally simulates the conditions of various levels of sulfate addition in hardened cement pastes. The influence of limestone, time, C{sub 3}A content, temperature and leaching on thaumasite formation was investigated. The results show that thaumasite formation is favoured at lower temperatures (8 deg. C) independently of the type of cement clinker (high or low C{sub 3}A content) used. Thaumasite was found to form only in systems where limestone was present and where sufficient sulfate had been added. Thaumasite precipitated only in systems where the Al present has already been consumed to form ettringite and the molar SO{sub 3}/Al{sub 2}O{sub 3} ratio exceeded 3. In leached samples (reduction of portlandite and alkalis) slightly less thaumasite was formed whereas gypsum and ettringite are favoured under these conditions. The PEA, used to investigate the chemical aspects of sulfate attack was found to be a good tool for simulating external sulfate attack. Generally, thaumasite was detected were it was modelled to be stable in significant amounts. However, in this study equilibrium conditions were not reached after 9 months.

• OSTI ID: 21033070
• Journal Information: Cement and Concrete Research, Journal Name: Cement and Concrete Research Journal Issue: 3 Vol. 38; ISSN 0008-8846; ISSN CCNRAI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM OXIDES
CEMENTS
EQUILIBRIUM
GYPSUM
LEACHING
LIMESTONE
SIMULATION
SULFATES
SULFITES