Question

I would like to ask about the possibility of the partial dissolution, over curing time, of portlandite, CaCo3 and C-S-H phases due to high pH (12.5 - 13) of the lime-clay-water systems (lime-stabilized clay). These phases were already newly formed phases in the lime-stabilized bentonite formed in the short term (1 day). I noticed a decrease in their amounts over curing time.

Answer 1

The solubility dynamics within a high-pH lime-stabilized clay system could lead to dissolution of newly formed phases over time due to complex chemical equilibria between different species like CaCO3, Ca(OH)2, and others.

Step-by-step explanation:

The question pertains to the solubility dynamics of various compounds in a lime-stabilized clay system with a high pH. Over time, the dissolution of portlandite (calcium hydroxide), calcium carbonate (CaCO3), and calcium-silicate-hydrates (C-S-H) can be affected by the pH of the system.

Calcium carbonate (CaCO3) is slightly soluble in water, having a molar solubility of 7.1x10-5 M, but this solubility increases when the pH decreases, that is, under more acidic conditions. The presence of CO2 can further increase the dissolution rate of CaCO3 due to the formation of carbonic acid (H2CO3), which reacts with CaCO3 to release calcium ions (Ca2+) and bicarbonate ions (HCO3-).

On the other hand, the reaction of quicklime, CaO, with water produces slaked lime, Ca(OH)2, which is important in construction for making mortar and plaster. The dissolution and precipitation reactions within the lime-clay-water system are quite complex and could lead to the observed decreases in the amounts of freshly formed phases over time.