Paste and Mortar Hydration

Observation of the hydration process indicated the following. In the first few minutes of the dissolution of free lime, the hydration of anhydrite and hemihydrate and the formation of calcium aluminate hydrate and monosulfate hydrate occur. Ettringite is formed within one hour, monosulfate hydrate within 2-6 hours and C-S-H gel within 1-16 hours, with the maximum heat ofhydration of C3S at about 10 hours. Measurements of the non-evaporable water indicate that the amount of combined water is 60-80% of the theoretically determined total amount of combined water at complete hydration. (The total amount of combined water was estimated to be 36%.) The amount of ettringite in the paste is estimated to be about 18-25% for the period one hourto seven days. The monosulfate content increases from about 10% at six hours to about 15-25%inone day. The alite in Reg Set cement paste is approximately 65-70% hydrated in one day and 8 0-95% hydrated in seven days. It is suggested that fluoride is tied up as A1(0H)2F. The possibility of fluoride-substituted ettringite and the formation of halo-aluminate hydrates of the form ( A CaXj wHjO is conceivable. 

Addition of calcium suliate anhydrate has little effect in the intial stage ofhydration. Calcium aliuninate monosulfate hydrate, cubic hydrate, and ettringite form and coexist for a long period. Hexagonal hydrate is depleted with the formation of monosulfate hydrate and ettringite. 

The addition of carboxylic acid lowers the solubility of the calcium ion in the liquid phase and severely retards the hydration of CuA7 CaF2. Hydration proceeds gradually if calcium ion is supplied from calcium hydroxide and carboxylic acid is sufficiently depleted. Surface active agents, e g., j8-naphthalene sulfonic acid, influence the morphology of the hydrates, but do not appear to significantly affect the hydration process. 

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Mixing, casting and curing of pastes and mortars Hydration stoppage... 

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