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

Abstract

Synthetic calcium silicate hydrogels, of Ca/Si mole ratios 0·85, 1·10, 1·40 and 1·80, were prepared and homogenised at 25°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°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°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.

Carbonation of hardened cement pastes: Influence of temperature

“…This difference was thought to result from the differences in their mineralogical composition and properties (Table 5): less portlandite and more C-(A)-S-H for the CEM V paste with regards to CEM I. The reduced C/S ratio of the C-(A)-S-H in the CEM V paste [106][107][108][109] may also have played a prominent role, as the calcium concentration at equilibrium is known to be lower (whatever the temperature between 25°C and 85°C) [16].…”

“…The effect of temperature is difficult to estimate because different contradictory mechanisms are at work. First, temperature modifies the solubility of the reactants: the higher the temperature, the lower the calcium [15,16] and CO 2 contents in solution [17,18]. This effect is expected to lessen the probability of reaction and thus inhibit carbonation.…”

Gypsum-Dependent Effect of NaCl on Strength Enhancement of CaO-Activated Slag Binders

“…In addition, when comparing the weight losses of Ca(OH) 2 for Ca-N0-G0 and Ca-N1-G0 at around 430 • C, the use of NaCl clearly reduced the weight loss of Ca(OH) 2 at all days. Note that the presence of NaCl in the pore solution generally increases the solubility of Ca(OH) 2 [57]. Thus, Ca(OH) 2 in Ca-N1-G0 tended to exist in an ionic state and was used to form Ca-bearing reaction products; for instance, in Figure 4a, Ca-N1-G0 showed more dehydration of C-S-H than Ca-N0-G0; although, this difference nearly disappeared at 28 days.…”

Role of Processing Temperature and Time on the Hydrothermal Alteration of K-Feldspar Rock in Autoclave

“…The actual pH of the leaching solution at 24 h (Figure 5), is likely determined by the elusive soluble component (either KOH or K 2 CO 3 species) that is present in the hydrothermal material although not detected by XRD [2]. However, C-A-S-H phases also play a role, as evidenced by comparison of XRD results (Figure 1) with pH data (Figure 5 leached [22][23][24]. For the batch processed at T=200 °C and t=0.5 h, the actual leaching pH is ~12.6 due to the presence of portlandite (Figure 1).…”

“…This behavior is confirmed in batches processed at higher T, which show again the same pH of ~12.3 as long as α-C 2 S is present in the hydrothermal material. If processing is carried out for a sufficiently long time to allow the transformation of α-C 2 S into tobermorite, then the leaching pH decreases to a value of ~12 [22][23][24].…”