Götz-Neunhoeffer F (2007)
Publication Language: English
Publication Type: Journal article
Publication year: 2007
Publisher: Bauverlag BV Gmbh
Book Volume: Vol. 5
Pages Range: 90-101
X-ray diffraction patterns of hydrating pastes made of calcium aluminate cement with α-calcium sulfate hemihydrate were evaluated to clarify the phase development and its effect on workability. Binder mixtures of this type are used in filler compounds and plasters. The behaviour pattern of the phase formation at 23 °C can be documented in situ with XRD analysis. The results of the normalized quantitative phase analysis of the pastes with a water/solids ratio W/S = 0.5 in combination with the time-dependent data from the heat flow calorimetry have made it possible to develop models for the hydration of calcium aluminate cement in the presence of calcium sulfate, Li2CO3 and tartaric acid. The quantitative phase analysis of the hydration of calcium aluminate cement with calcium sulfate hemihydrate showed that monocalcium aluminate (CA) and calcium sulfate hemihydrate are dissolved and that ettringite and also gypsum can be detected as new formations. The behaviour pattern of the hydration of calcium aluminate cement-calcium sulfate hemihydrate-mixtures is altered by the addition of Li2CO3 solutions as CA accelerators. The rate of reaction of ettringite formation is significantly dependent on the concentration of the Li+. As with pure calcium aluminate cement the formation of an impermeable Al hydroxohydrate layer around the particles of CA in calcium aluminate cement-calcium sulfate hemihydrate-mixtures is also hindered by the effect of Li+ and the availability of aluminium is increased via the lithium aluminium hydrate intermediate compound (LA2H10 where L = Li2O). LA2H10 is a compound of the hydrotalcite type and consists of a main layer [Li2Al4(OH) 12]2+ and an intermediate layer
[(OH) 2•3H2O] 2- but anions, such as CO32-, 2Cl- or 2(NO3-), can also be incorporated in the intermediate layer in place of the hydroxide. The function of the Li2CO3 is confined to the dissolving of the CA and has no influence on the dissolving of the calcium sulfate hemihydrate. The tartaric acid can lead to precipitation of Ca tartrate, which affects the Ca2+ from the dissolving of the CA and of the calcium sulfate hemihydrate and it can also coat the reactive surfaces of the CA and calcium sulfate hemihydrate.
APA:
Götz-Neunhoeffer, F. (2007). The function of Li carbonate and tartaric acid in the hydration of mixtures of calcium aluminate cement (CAC) with calcium sulfate hemihydrate. Cement International, Vol. 5, 90-101.
MLA:
Götz-Neunhoeffer, Friedlinde. "The function of Li carbonate and tartaric acid in the hydration of mixtures of calcium aluminate cement (CAC) with calcium sulfate hemihydrate." Cement International Vol. 5 (2007): 90-101.
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