A thermodynamic model of dissolution and precipitation of calcium silicate hydrates

Abstract A thermodynamic incongruent dissolution/precipitation model of calcium silicate hydrate (C-S-H) is proposed, assuming a binary nonideal solid solution of Ca(OH)2 and SiO2. Using this model, both dissolution and precipitation of the C-S-H phase, with a continuous change in the Ca / Si ratio of the solid phase, can be predicted. The notable features of the model are its good continuity and simplicity so that calculation can be easily compiled in a calculation code. A series of experiments were carried out. C-S-H precipitates were prepared using two techniques: precipitation by contacting Ca(OH)2 solution with C-S-H gel and hydrolysis in a mixture of Ca and Si solutions. The equilibria in these experiments were predicted well by the proposed model. A calculation using the model also predicted well the dissolution of ordinary Portland cement hydrate with water exchange.

[1]  Donald E. Macphee,et al.  Solubility and Aging of Calcium Silicate Hydrates in Alkaline Solutions at 25°C , 1989 .

[2]  Dissolution Phenomena of Ca0-Si02-H20 Gel at Ca/Si>l Coexisting with Ettringite System , 2000 .

[3]  P. Glynn MBSSAS: a code for the computation of Margules parameters and equilibrium relations in binary solid-solution aqueous-solution systems , 1991 .

[4]  Shinya Nagasaki,et al.  A model for dissolution of CaO-SiO2-H2O gel at Ca/Si > 1 , 1999 .

[5]  Wakichi Kondo,et al.  Heterogeneous equilibrium of calcium silicate hydrate in water at 30 °C , 1981 .

[6]  F. Adenot,et al.  Study of the structural properties of the CSH(I) BY molecular dynamics simulation , 1997 .

[7]  Christian Ekberg,et al.  A thermodynamic model for the calcium silicate hydrate gel, modelled as a non-ideal binary solid solution , 1997 .

[8]  E. Reardon Problems and approaches to the prediction of the chemical composition in cement/water systems , 1992 .

[9]  D. Macphee,et al.  Modelling approach to the prediction of Equilibrium Phase Distribution in Slag-Cement Blends and their Solubility Properties. , 1987 .

[10]  T. N. Chang,et al.  Investigation of the Colloidal Hydrated Calcium Silicates. II. Solubility Relationships in the Calcium Oxide-Silica-Water System at 25° , 1965 .

[11]  U. R. Berner,et al.  Evolution of pore water chemistry during degradation of cement in a radioactive waste repository environment , 1992 .

[12]  Shinya Nagasaki,et al.  A model for dissolution of CaO-SiO{sub 2}-H{sub 2}O gel at Ca/Si<1 by considering disordered structure , 1999 .

[13]  W. Kondo,et al.  Communications of the American Ceramic Society Estimation of Thermochemical Data for Calcium Silicate Hydrate (C‐S‐H) , 1983 .

[14]  Dmitrii A. Kulik,et al.  Aqueous Solubility Diagrams for Cementitious Waste Stabilization Systems: II, End‐Member Stoichiometries of Ideal Calcium Silicate Hydrate Solid Solutions , 2001 .