Clinker content

The government s consultancy had identified significant potential for emission reduction in the cement sector by means of reducing the clinker content of finished cement. 

Fig. 6.11 Unhydrated clinker content in the interfacial transition zone. (According to [35])...

If used above ground, proper curing of concrete made from supersulfated cement is essential. The surface must be kept damp, as otherwise a friable surface layer, which tends to dusting, may develop. The tendency to dusting may be reduced by increasing the Portland clinker content in the cement. 

The total mass of solids does not stay constant during cement hydration free water is bound into hydration products (Figure 4.16) and the initial porosity is filled. Rietveld results normalised on a total solids base for dried samples will need to be corrected. Therefore, the final step in the data analysis is to recalculate the QPA to a common basis. This base of comparison may be the initial paste (free water + anhydrous binder) content, the initial binder (SCM + portland cement) or the initial portland cement or clinker content. The recalculation depends on whether free water is removed to stop the hydration reactions. If the sample is assumed to be undried and... 

In the relatively small Pordand cement 2one almost all modem cements fall in the high lime portion (about 65% CaO). Cements of lower lime content tend to be slow in hardening and may show trouble from dusting of the clinker by transformation of to especially if clinker cooling is... 

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) ... 

The potential hquid-phase content at clinkering temperatures range from 18 to 25% and can be estimated from the oxide analysis of the raw mix. 

Po22olans iaclude natural materials such as diatomaceous earths (see Diatomite), opaline cherts, and shales, tuffs, and volcanic ashes or pumicites, and calciaed materials such as some clays and shales. By-products such as fly ashes and siUca fume are also employed. In the United States the proportion of po22olan iaterground with clinker has varied from 15 to over 30%, whereas ia Italy, cements with a 30—40% po22olan content are produced. 

Cement kilns can handle quite a lot of different materials. In most cases the input material should be chipped or shredded. Licenses often limit the PVC and chlorine input to l%-2% chlorine in waste. It is said that chlorine also has a negative impact on the quality of the clinker if it is available in too high quantities. The content in clinker seems to be limited to some 0.1% at maximum, and hence the average chlorine content of all fuels used combined may have to be somewhat lower. This implies that waste with a high chlorine... 

Once the thermal runaway had become established, the high temperature could allow a smelting reaction (reduction of lead oxides by carbon to metallic lead) to occur, and the low m.p. and high density (327°C, 10.6, respectively) would cause the molten lead to concentrate at the base of the reactor, decreasing the lead content and raising the manganese content of the bulk of the clinker residue, as was observed [2],... 

Both fossil fuels and hazardous waste fuels used in Southdown cement kilns contain metals. The raw materials (limestone, clay, sand) used to make cement clinker also contain metals. In fact, certain metals, such as iron and aluminum, are essential components of the final product. While metals cannot be destroyed, the Southdown cement kiln process effectively manages them in the following ways (a) cement kiln operators limit emissions by carefully restricting the metals content in wastes accepted for recycling (b) dust particles containing metals are returned to the kUn through closed-loop mechanisms, where metals are chemically bonded into the cement clinker (c) particles not returned to the kiln are captured in state-of-the-art pollution control devices and (d) small amounts are emitted from the stack in quantities strictly hmited by USEPA s BIF mle. 

Bauxitic Kaolins andMullites. Deposits of bauxitic kaolins, kaolins having aluminous minerals, have been discovered that have alumina contents between 50 and 70%. These materials are made into refractory aggregates called calcines, grog, clinker, or grain. In addition to sdectivdy mined deposits, synthetic compositions can be prepared from kaolin and alumina and other minerals to produce compositions of desired alumina and mineralogical content. These synthetic mullites are readily available in the form of sintered and fused aggregates. 

Conversely, coarsely ground clinkers with lower alite content are preferred for situations where cement emplacement is slow or temperatures can be high, as in the lining of oil wells. In such circumstances, organic... 

Rapid cooling of the clinker is preferred for many reasons, notably to prevent the reversion of alite to belite and lime in the 1100 1250 °C regime and also the crystallization of periclase (MgO) at temperatures just below 1450 °C. The magnesium content of the cement should not exceed about 5% MgO equivalent because most of the Mg will be in the form of periclase, which has the NaCl structure, and this hydrates slowly to Mg(OH)2 (brucite), which has the Cdl2 layer structure (Section 4.6). Incorporation of further water between the OH- layers in the Mg(OH)2 causes an expansion that can break up the cement. Accordingly, only limestone of low Mg content can be used in cement making dolomite, for example, cannot be used. Excessive amounts of alkali metal ions, sulfates (whether from components of the cement or from percolating solutions), and indeed of free lime itself should also be avoided for similar reasons. 

Calculate the overall Ca and Si contents (expressed as CaO and Si02) of a Portland cement clinker that has 55% alite, 30% belite, 5% alumi-nate phase, and 10% ferrite (assume ideal compositions for the latter two). Would you expect this to behave as a fast or a slow setting cement ... 

The dampened material is mixed with K nitrate (previously finely ground) and the moisture content adjusted to ca 4%. About 300 lbs of this mixt are placed in a Wheel Mill(such as described in Ref 11,p 46 Ref 18,p 69 or Ref 28,p 87) where the mass is processed during 3-6hrs. This operation is called Incorporation or Milling. The resulting material is called "mill cake , "clinker or "wheel cake . It... 

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