Solubility reactions of cement components with NaCl solutions: I. Ca(OH)(2) and C-S-H

Synthetic calcium silicate hydrogels, of Ca/Si mole ratios 0.85, 1.10, 1.40 and 1.80, were prepared and homogenised at 25 degrees C Solubilities of Ca(OH)(2) and of C-S-H were measured in initially pure water at 25, 55 and 85'C. Equilibration times ranged from a few days up to 9 months: data are presented for the longer reaction times, 4.5 to 9 months. These solids were also equilibrated with NaCl solutions, approximately 0.5, 1.0 and 1.5 mol/l, at 25, 55 and 85 degrees C. The expected solubility trends emerge in initially pure water: C-S-H dissolved incongruently and Ca solubilities decreased with either rising temperature or at lower Ca : Si molar ratios. The presence of NaCl enhanced Ca solubilities, especially in the range 0-0.5mol/l NaCl. However pH remained almost unaffected, 0.1 unit, as a function of NaCl concentration, other factors remaining constant. The C-S-H gel partially crystallised in the course of solubility determinations made at 85 degrees C. Sorption of NaCl on C-S-H was negligible. Comments on the experimental procedures and quality of data are made. The long-term durability of cement exposed to dissolution in NaCl solutions is discussed.