CaO content

Mvailable lime, the total free lime (ie, CaO) content in a quicklime or hydrate, is the active constituent of a lime. It provides a means of evaluating the concentration of lime. 

Raw Material Proportions. The three main considerations in proportioning raw materials for cement clinker are the potential compound composition the percentage of Hquid phase at clinkering temperatures and the bumabiUty of the raw mix, ie, the relative ease, in terms of temperature, time, and fuel requirements, of combining the oxides into good quaUty clinker. The ratios of the oxides are related to clinker composition and bumabiUty. For example, as the CaO content of the mix is increased, more C S can be formed, but certain limits cannot be exceeded under normal burning conditions. The lime saturation factor (LSF) is a measure of the amount of CaO that can be combined (20) ... 

A blending system provides the kiln with a homogeneous raw feed. In the wet process the mill slurry is blended in a series of continuously agitated tanks in which the composition, usually the CaO content, is adjusted as required. These tanks may also serve as kiln feed tanks, or the slurry after agitation is pumped to large kiln feed basins. Dry-process blending is usually accompHshed in a silo with compressed air. 

The CaO content of commercially available quicklime can vary quite widely over an approximate range of 70 percent to 96 percent. Content below 88 percent is generally considered below standard in the municipal use field. Purchase contracts are often based on 90 percent CaO content with provisions for payment of a bonus for each 1 percent over and a penalty for each 1 percent under the standard. A CaO content less than 75 percent probably should be rejected because of excessive grit and difficulties in slaking. 

Figure 1.137. The variations of major element contents in andesite (drilling core. 8-MAHAK-4 and underground samples) away from the vein system (Shikazano et al., 2002), Diamond Hishikari Lower Andesitic tuff (underground samples) square Hishikari Lower Andesitic tuff (drilling core samples) triangle Hishikari Lower Andesitic lava (drilling core samples) x relatively fresh Hishikari Lower Andesitic lava (drilling core samples). (A) SiO content variation. (B) K2O content variation. (C) CaO content variation.

Figure 1.139. The relationship between K2O content and (Na20 + CaO) content in andesite (Shikazono et al., 2002).

The variations in K2O, Na20 and CaO contents could be interpreted by thermodynamic consideration. 

The Mg content of hydrothermally altered volcanic rocks is reflected by the extent of seawater-volcanic rock interaction at elevated temperatures, because it has been experimentally and thermodynamically determined that nearly all of the Mg in seawater transfer to volcanic rocks, owing to the reaction of the cycled seawater with volcanic rocks at elevated temperatures (Bischoff and Dickson, 1975 Mottl and Holland, 1978 Wolery, 1979 Hajash and Chandler, 1981 Reed, 1983 Seyfried, 1987). It has been shown that the CaO content of hydrothermally altered midoceanic ridge basalt is inversely correlated with the MgO content with a slope of approximately — 1 on a molar basis (Mottl, 1983). This indicates that Ca of basalt is removed to seawater and Mg is taken up from seawater by the formation of chlorite and smectite during the seawater-basalt interaction. This type of reaction is simply written as ... 

Fig. 3.2. (a) The relationship between MgO and CaO contents of basaltic rocks and of (b) dacitic rocks from the Green tuff region in Japan (Shikazono, 1994). 

Sample number Carbon by potentiometry/mg Mean/mg CaO content if all carbon is in CaC03, % CaO content by X-ray fluorescence spectrometry, %... 

Thomas et al. (1999) proposed that ash be classified according to CaO content as follows Class F, <8wt% CaO Class Cl, 8-20 wt% CaO and Class CH, >20 wt% CaO. These CaO ranges have a bearing on their behaviour in concrete, and these subdivisions are used in this review, where appropriate, along with the general term Class C ash defined by ASTM. Class F ash has pozzolanic properties Class Cl ash is similar to Class F ash but is also cementitious. Class CH is more aggressively cementitious and readily forms Ca(OH)2. It is more likely to contribute to the heat of hydration of the cement. 

Table 9 again demonstrates the high CaO content in the fine fraction (30-90 pm) of the combustion ash, due to the high carbonate content associated with the oil shale feedstock. In the very finest fraction (<30 pm), however, Si and Al contents are relatively elevated, at the expense of CaO, presumably due to the presence of clays in this fraction. 

Comparing metal concentrations in the BA with the amount of the different types of waste (household, industrial, etc.) only one poor correlation (R = 0.6) was observed a higher amount of waste coming from the construction sector caused higher CaO contents in the BA. It is likely that in this case Ca-rich CSH phases (calcium-silicate-hydrate) and gypsum account for a higher CaO content in the BA. 

Natural zeolite was enriched with potassium ions and dealuminized. Enrichment of exchangeable ions of L zeolites and of clinoptilolite was done by multiple treatment with 0.52V solutions of the corresponding nitrates. Decationization and dealuminization were done by treating the natural zeolite with solutions of hydrochloric acid 0.25-12.02V. The Si02/Al203 ratio increased from 8.0 to 69.5, and the CaO content decreased from 6.30 to 1.00 wt % (Table II). 

Recently, basalt materials, with MgO + CaO-contents typically of the order of 20wt% or less, but widely available, have been considered for C02 mineralization [74, 75] (see also the Hellisheidi project on Iceland [62]). 

The Ca(OH)2 suspension is prepared just before each run with commercial lime, with CaO content > 95%, and water, and the concentration of Ca in the form of Ca(OH)2 in the prepared suspension for each run is chemically analyzed. 

The Taylor-Howison hypothesis gives an almost identical structure for the three-layer tobermorite with the one shown in Figure 8 the pseudocell surface contains one molecule of Si02 and 0.75 molecule of CaO, and the CaO content of the layers between the pseudocells is 1.50 molecules. The two-layer structure, however, shows greater differences. The surface is not very different it contains... 

Deduct from the CaO content the amounts attributable to C AF, CjA and free lime, and solve two simultaneous equations to obtain the contents of CjS and CjS. 

As with LSF, the approach is applicable to cements if CaO is further corrected by deducting O.7SO3. Because minor oxide components are ignored, the total for the four main phases plus free lime will not add up to 100%. It is implicit in the approach that all the MgO is assumed to occur as periclase. The phase composition calculated by Bogue s method is related to the LSF in that a ratio of 38 to CjA 0.546, calculated without correcting the CaO content for free lime, corresponds to an LSF > 1.0 (D2). 

From the CaO content, deduct free lime and any CaO present as sulphate or CaCOj. In the absence of more detailed data, assume that 67% of the insoluble residue is Si02 and that 33% is AI2O3, and deduct accordingly. This gives AI2O3, 5.6% Si02, 21.5% CaO, 65.3%. 

The calculation of phase composition from bulk analysis for cements presents no special difficulties if the content and composition of the gypsum and any other admixture are known, as the analysis can then readily be corrected to give the composition of the clinker. If they are not known, an assumption must be made as to the amount of SOj in the clinker, so that the contribution of the gypsum to the CaO content of the cement may be estimated. Further assumptions and corrections may have to be made to allow for impurities in the gypsum or other additives (e.g. calcite). 

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