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Calcium hydroxide is modestly soluble in water, as seen for many dihydroxides. Its solubility increases from 0.66 g/L at 100 °C to 1.89 g/L at 0 °C. [8] Its solubility product K sp of 5.02 × 10 −6 at 25 °C, [1] its dissociation in water is large enough that its solutions are basic according to the following dissolution reaction:
Hydration is the mechanism by which hydraulic binders such as Portland cement develop strength. A hydraulic binder is a material that can set and harden submerged in water by forming insoluble products in a hydration reaction. The term hydraulicity or hydraulic activity is indicative of the chemical affinity of the hydration reaction. [2]
Calcium silicate hydrate (also shown as C-S-H) is a result of the reaction between the silicate phases of Portland cement and water. This reaction typically is expressed as: 2 Ca 3 SiO 5 + 7 H 2 O → 3 CaO · 2 SiO 2 · 4 H 2 O + 3 Ca(OH) 2 + 173.6 kJ
Each mole of CO 2 (44 g) reacts with one mole of calcium hydroxide (74 g) and produces one mole of water (18 g). The reaction can be considered as a strong-base-catalysed, water-facilitated reaction. [5] The reaction mechanism of carbon dioxide with soda lime can be decomposed in three elementary steps: 1) () (CO 2 dissolves in water – slow ...
Upon hydration, the main reaction products are calcium silicate hydrates (C-S-H) and calcium hydroxide Ca(OH) 2, written as CH in the cement chemist notation. C-S-H is the phase playing the role of the glue in the cement hardened paste and responsible of its cohesion.
When pH slowly drops due to the progress of the silica dissolution reaction, the solubility of calcium hydroxide increases, and the alkali gel reacts with Ca 2+ ions. Its viscosity increases due to gelation process and its mobility (fluidity) strongly decreases when C-S-H phases start to precipitate after reaction with calcium hydroxide ...
Pozzolanic reaction is a long term reaction, which involves dissolved silicic acid, water and CaO or Ca(OH) 2 or other pozzolans to form a strong cementation matrix. This process is often irreversible. Sufficient amount of free calcium ion and a high pH of 12 and above is needed to initiate and maintain the pozzolanic reaction. [2]
This action causes calcium carbonate to precipitate due to exceeding the solubility product. Additionally, magnesium can be precipitated as magnesium hydroxide in a double displacement reaction. [3] In the process both the calcium (and to an extent magnesium) in the raw water as well as the calcium added with the lime are precipitated.