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| Titel |
Multi proxy approach for the formation of calcium carbonates in alkaline man-made environments |
| VerfasserIn |
T. Rinder, M. Dietzel, A. Leis |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250030899
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| Zusammenfassung |
| The formation of calcium carbonates, e.g. in drainage systems of tunnels, may be induced by
degassing of CO2-rich groundwater which enters the building. However, the dissolution of
portlandite (Ca(OH)2) from cements or the shotcrete of the tunnel wall bears an additional
and immense potential for the formation of carbonates from alkaline solutions. Variations in
trace element incorporation and distribution of the stable isotopes of carbon and oxygen in
the precipitated calcium carbonates may represent powerful tools to identify individual
mechanisms for carbonate formation.
As portlandite dissolves, highly alkaline solutions are obtained. In this case, precipitation
of calcium carbonate can be related to the absorption of CO2 from the atmosphere. Isotopic
analyses of the calcite show that fixation of CO2 from the Earth‘s atmosphere leads to
significantly lighter δ13Ccalcite values (down to -25 o/oo, VPDB) as expected for the
fixation of groundwater carbonate (typical δ13Ccalcite values between -10 and -16o/oo,
VPDB).
The evolution of Sr/Ca ratios in the alkaline drainage solutions and in the corresponding
calcium carbonate precipitation provides insight into the dissolution process at the concrete
with respect to the amount of primarily dissolved portlandite from the cement. Moreover,
an inverse relationship between Mg/Ca and Sr/Ca ratios is observed due to the
liberation of aqueous strontium by the dissolution of portlandite and the formation of
brucite (Mg(OH)2) at alkaline conditions. Less incorporation of magnesium in the
calcite structure is a strong indicator for carbonate precipitation from highly alkaline
environments.
Applications of such multi proxy approaches are discussed with case studies. Main tasks
are the reconstruction of the environmental conditions during primary CaCO3 formation and
monitoring of ongoing precipitation of calcium carbonates and cement-water interaction in
alkaline man-made environments. |
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