Calcium hydroxide content

Calcium hydroxide content, thermal analysis and indirect determination of the Ca/Si ratio of the C-S-H... 

Fig. 9.3 Calcium hydroxide contents of pastes of Portland- pfa cements containing 0, 20, 40 and 60% of low-CaO pfa. Taylor et al. (T44).

Blast-furnace slag cements with high slag contents have lower heats of hydration than pure Portland cement, which is advantageous for large scale concrete structures (e.g. dams). The lower calcium hydroxide content results in their being somewhat more chemically stable than Portland cement. Blast-furnace slag cements are used in similar applications to Portland cement. 

Pozzolanic materials can be either natural, like pozzolana, or artificial, like fly ash and silica fame [2]. They are mainly glassy siliceous materials that may contain aluminous compounds but have a low lime (calcium hydroxide) content. In them-... 

With regard to protection against sulfate attack, the quality of the concrete is a crucial factor a low permeability is the best defence against this type of attack, since it reduces sulfate penetration. This can be obtained by decreasing the w/c ratio and using blended cement (i. e. pozzolanic or blast furnace slag cement that reduce the calcium hydroxide content and refine the pore stracture of the matrix). Finally, the severity of the attack depends on the content of CjA and, to a lesser extent, of C4AF in the cement. Standards in different countries provide for sulfate resistant cements with a C3A content below 3-5 %. 

Quite another conditions occur in the case of concrete with porous aggregate, particularly a dry one, which will significantly absorb water. However, the construction of interfacial transition zone has not been studied in such a concrete as yet [10]. One can even suppose, based upon the model studies, that the growth of calcium hydroxide content around the aggregate grains will not be formed. There are some premises indicating the emichment in ettringite [10]. Incase of diy, porous... 

Determination of the calcium hydroxide content of mixed filler for bituminous mixtures is conducted in accordance with CEN EN 459-2 (2011). 

The main difference in the composition of cement pastes made from cements with increased belite and reduced alite contents is their lower calcium hydroxide content. This may affect positively the resistance of such hardened pastes to chemical corrosion. At the same time the depth of carbonation increases with declining C3S content in cement (Kelham and Moir, 1992). 

At low fly ash additions— that is, below 15%—the extent of carbonation in mature fly ash concrete tends to be equal to or lower than that in similar concrete mixes with no ash, in spite of the lower calcium hydroxide content of the formed hydrated cement paste (Buttler et al., 1983 Hobbs, 1988 Goni et al, 1997). This is due mainly to the reduced permeability of the paste to CO2. However, at higher fly ash contents the resistance to carbonation is significantly reduced (Goni et al, 1997). 

One of the methods of following the degree of hydration as a function of time is by the determination of the calcium hydroxide content. Figure 15 compares the relative amounts of calcium hydroxide formed at different times of hydration, using DTA and chemical methods. Although the general trend of the curves is similar, the values derived from the chemical analysis are somewhat higher than those from the thermal method. This may be due to attack of the C-S-H phase by the solvents used in the extraction of lime that is adopted in the chemical method. 

Figure 21. Relationship between strength and calcium hydroxide content in cement paste hydrated at -5°C...

Table 3. Calcium Hydroxide Content in C3S Pastes in the Presence of Si02...

Figure 9. Effect of time of hydration on calcium hydroxide contents in cement pastes.

Figure 33. Calcium hydroxide contents of different pozzolan-cement mixtures.

Weise, C. H., "Determination of the Free Calcium Hydroxide Contents of Hydrated Portland Cements and Calcium Silicates," Analytical Chemistry, 1961,33,7,877-882. 

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