Composition of Portland Cement Clinkers

Table 4 Potential phase composition of Portland cement clinker...

For the composition of Portland cement clinkers also see Fig. 5.3-1 and Table 5.3-8. 

TABLE 2.4 Average Overall Composition of Portland Cement Clinker ... 

Parallel with cement production development the significant progress in cement chemistry was achieved. The real revolution we owe to French scientist Le Chat-eher. This great chemist determined the phase composition of Portland cement clinker and the hypothesis of hydration process. Le Chatelier stated that, similarly as in the case of gypsum, the anhydrite cement components dissolve, the solution became oversaturated in relation to hydrates, which causes their crystallization [3],... 

Cement heat of hardening is affected primarily by the phase composition of the clinker. This heat is an additive value and therefore it can be evaluated based on the known composition of Portland cement clinker and the heat of hardening for particular phases, given in Table 3.4. 

Chromy, S., "Relation Between the Chemical and the Mineralogical Composition of Portland Cement Clinkers and the Prediction of Cement Strengths," Zement-Kalk-Gips, Vol. 36, No. 8,1983, pp. 458-463. 

Figure 5.2 Phase composition of Portland cement clinker as a function of temperature and distance from discharge point, respectively. Alite CasSiOj, belite p Ca2Si04, ferrite (celite) Ca4Al2Fe20io, spurrite Ca5[C03/(Si04)2].

A knowledge of the relevant high-temperature phase equilibria is necessary for understanding the factors that govern acceptable bulk compositions for Portland cement clinker, the conditions under which the latter can be manufactured, and the phase composition and microstructure of the resulting material. This chapter deals with these equilibria and with the phases to which they relate, with the exception of the major clinker phases, which were described in Chapter I. Some anhydrous phases primarily of interest in relation to other types of cement are also considered here. Principles underlying the preparation of anhydrous silicate, aluminate and other high-temperature phases are outlined. 

The chemical composition of clinker is complex, however, it is easy to notice that the sum of four components, CaO, Si02, AI2O3 and Fe203 is as a rule higher than 95 %. The processes of Portland cement clinker phases ciystallization in the four components system can thus be presented. It is especially justified that MgO is not forming own compounds in the rich in calcium part of five-components system, but solid solutions with remaining clinker phases, or is present as periclase. However, the four-components system is seldom used, because the use of ternary systems is much more convenient. They are usually presented as the horizontal projection. 

Insley, H. and others, "Relation of Compositions and Heats of Solution of Portland Cement Clinker," Journal of Research of the National Bureau of Standards, Vol. 21, Research Paper RP1135, Washington, D.C., September 1938, pp. 355-365. 

Kolenova, K.G., "Factors Determining Composition of Aluminoferrife and Aluminate Phases of Portland Cement Clinker and Their Effect on Coating Formation and Clinker Granulation Processes," Sixth International Congress on Chemistry of Cement, Supplementary Paper 1-3, Moscow, 1974,11 pp. 

The composition of Portland cement raw meals and Portland clinkers can be characterized by the mutual ratio of the main oxides present. The following ratios are those most widely employed (all amounts of oxides are given in wt%) ... 

The average chemical composition of Portland cement is given in Table 15.1. A typical cement factory produces annually about 1,500,000 tonnes of cement type I and II and one tonne of clinker is used to make approximately 1.1 tonnes of Portland cement. 

The average phase composition of Portland cement (ASTM Type I, CSA 10) is -50% alite, C3S -25% belite, P-C2S -12% tricalcium aluminate, C3A -8% ferrite, C4AF > and -3.5% gypsum (Mindness, 1983). The structural order and crystallinity of the cement phases-and hence their hydraulic reactivities-are heavily dependent on the rate of cooling of the clinker ... 

The first formation of liquid (melt), marking the start of what is known as "sintering" or "clinkering", occurs at a temperature of between about 1260° and 1310° C. With further rise in temperature the proportion of liquid phase increases to around 20-30% (by weight) at 1450° C, the actual proportion being dependent on the chemical composition of the material. (Thus, the proportion of liquid formed is less according as the silica modulus is higher see Fig. 6.) At these temperatures the main component of portland cement clinker is formed, namely, tricalcium silicate (C3S), known also as alite. 

Portland cement is manufactured by burning until partial melting of an intimate mixture of substances that mainly contain calcium Ca, silicon Si, aluminium A1 and iron Fe. During burning, so-called clinkers are formed. When ground, these clinkers are able to react with water - to hydrate - and to deposit hydrates with binder properties. A typical clinker mineral composition of Portland cement is ... 

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 ... 

There are three fundamental stages in the process of manufacture of Portland cement, namely. (I) preparation of the raw mixture. (2) production of the clinker. (3) preparation of Ihe cement. Whether the process used is wet or dry. the raw materials are selected, analyzed, and mixed so dial, alter ireatmeni, Ihe product, or clinker, has a desired, narrowly specified composition A factory analysis of slurry, where the wet process is in use. is as follows calcium oxide 44%. aluminum oxide 3.5%. silicon oxide... 

Portland cement clinker potential phase composition is presented in Table 4. It could be seen that the C3A content in the clinker was 9.46% which is important for the cement hydration rate and cement sulfate resistance. Common Portland cement is not resistant to the sulfate influence because of the significant C3A content, whose hydrates react with sulfate ions resulting in expansive compounds. Portland cement with the higher resistance to sulfates must have low C3A content. Moderate to high content of mineral alite - C3S (54.72%) is usual for the Serbian cement plants and enables the addition of higher quantities of mineral admixtures without influencing the quality of final cement. 

Alite is the most important constituent of all normal Portland cement clinkers, of which it constitutes 50-70%. It is tricalcium silicate (CajSiOj) modified in composition and crystal structure by incorporation of foreign ions, especially Mg ", AP and Fe. It reacts relatively quickly with water, and in normal Portland cements is the most important of the constituent phases for strength development at ages up to 28 days, it is by far the most important. 

The ferrite phase makes up 5 15% of normal Portland cement clinkers. It is tetracalcium aluminoferrile (CajAIFeOj) substantially modified in composition by variation in Al/Fe ratio and incorporation of foreign ions. The rale at which it reacts with water appears to be somewhat variable, perhaps due to differences in composition or other characteristics, but in general is high initially and intermediate between those of alite and belite at later ages. 

Table 1.2 Typical compositions of phases in Portland cement clinkers (weight per cent)... 

In many clinkers, the ferrite phase is closely mixed with aluminate due to a similarity in cell parameters, oriented intergrowth can occur (MIS). The close admixture often renders X-ray microanalysis difficult or unreliable. For ordinary Portland cement clinkers, the compositions found in dilferent laboratories are nevertheless remarkably consistent. Table 1.2 includes an average value based on the results of investigations using X-ray microanalysis (H8,K1,B2,U1,H3,B4) or chemical analysis of separated material (Yl). Table 1.3 includes suggested site occupancies corresponding to these data. 

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