AWWA WQTC63967

The most important ingredients of cement powder are dicalcium and tricalciumsilicate. When the cement powder is mixed with water, these ingredientshydrolyze to form a calcium silicate hydrate (C-S-H) and calcium hydroxide. Anexample of such a reaction is the formation of 1.4 nm tobermorite through thehydrolysis of dicalcium silicate. As cement paste hydrates and hardens, it forms a heterogeneous structure ofamorphous C-S-H with saturated calcium hydroxide in its pores. The C-S-H inthe hydrated cement can be viewed as a metastable form of calcium silicatehydrate. Although more than 30 crystalline C-S-H phases are known, adequatethermodynamic data are not available on these. In this discussion simple calciumsilicate, or Wollastonite (CaSiO₃), is proposed as a model for which data areavailable and which might be used to develop a saturation index. The thermodynamic properties of Wollastonite are known and can be found incompilations like those in Stumm and Morgan (1996). From these it is possibleto determine the solubility product of Wollastonite as a function of temperature(see the appendix of this discussion for a summary of this derivation). At 25ºCthe solubility product, Kso, is 1013.05.Using that solubility product, a saturation index is proposed for judging thesolubility of cement-based surfaces exposed to water. Includes 13 references, tables, figures, appendix.

Product Details

Edition:

Vol. - No.

Published:

11/01/2006

Number of Pages:

17

File Size:

1 file , 1.6 MB